FreeBSD/Linux Kernel Cross Reference
sys/mm/memory.c

     /*
      *  linux/mm/memory.c
      *
      *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
      */
     
     /*
      * demand-loading started 01.12.91 - seems it is high on the list of
      * things wanted, and it should be easy to implement. - Linus
     */
    
    /*
     * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
     * pages started 02.12.91, seems to work. - Linus.
     *
     * Tested sharing by executing about 30 /bin/sh: under the old kernel it
     * would have taken more than the 6M I have free, but it worked well as
     * far as I could see.
     *
     * Also corrected some "invalidate()"s - I wasn't doing enough of them.
     */
    
    /*
     * Real VM (paging to/from disk) started 18.12.91. Much more work and
     * thought has to go into this. Oh, well..
     * 19.12.91  -  works, somewhat. Sometimes I get faults, don't know why.
     *              Found it. Everything seems to work now.
     * 20.12.91  -  Ok, making the swap-device changeable like the root.
     */
    
    /*
     * 05.04.94  -  Multi-page memory management added for v1.1.
     *              Idea by Alex Bligh (alex@cconcepts.co.uk)
     *
     * 16.07.99  -  Support of BIGMEM added by Gerhard Wichert, Siemens AG
     *              (Gerhard.Wichert@pdb.siemens.de)
     *
     * Aug/Sep 2004 Changed to four level page tables (Andi Kleen)
     */
    
    #include <linux/kernel_stat.h>
    #include <linux/mm.h>
    #include <linux/hugetlb.h>
    #include <linux/mman.h>
    #include <linux/swap.h>
    #include <linux/highmem.h>
    #include <linux/pagemap.h>
    #include <linux/ksm.h>
    #include <linux/rmap.h>
    #include <linux/export.h>
    #include <linux/delayacct.h>
    #include <linux/init.h>
    #include <linux/writeback.h>
    #include <linux/memcontrol.h>
    #include <linux/mmu_notifier.h>
    #include <linux/kallsyms.h>
    #include <linux/swapops.h>
    #include <linux/elf.h>
    #include <linux/gfp.h>
    #include <linux/migrate.h>
    #include <linux/string.h>
    
    #include <asm/io.h>
    #include <asm/pgalloc.h>
    #include <asm/uaccess.h>
    #include <asm/tlb.h>
    #include <asm/tlbflush.h>
    #include <asm/pgtable.h>
    
    #include "internal.h"
    
    #ifndef CONFIG_NEED_MULTIPLE_NODES
    /* use the per-pgdat data instead for discontigmem - mbligh */
    unsigned long max_mapnr;
    struct page *mem_map;
    
    EXPORT_SYMBOL(max_mapnr);
    EXPORT_SYMBOL(mem_map);
    #endif
    
    unsigned long num_physpages;
    /*
     * A number of key systems in x86 including ioremap() rely on the assumption
     * that high_memory defines the upper bound on direct map memory, then end
     * of ZONE_NORMAL.  Under CONFIG_DISCONTIG this means that max_low_pfn and
     * highstart_pfn must be the same; there must be no gap between ZONE_NORMAL
     * and ZONE_HIGHMEM.
     */
    void * high_memory;
    
    EXPORT_SYMBOL(num_physpages);
    EXPORT_SYMBOL(high_memory);
    
    /*
     * Randomize the address space (stacks, mmaps, brk, etc.).
     *
     * ( When CONFIG_COMPAT_BRK=y we exclude brk from randomization,
     *   as ancient (libc5 based) binaries can segfault. )
     */
   int randomize_va_space __read_mostly =
   #ifdef CONFIG_COMPAT_BRK
                                           1;
   #else
                                           2;
   #endif
   
   static int __init disable_randmaps(char *s)
   {
           randomize_va_space = 0;
           return 1;
   }
   __setup("norandmaps", disable_randmaps);
   
   unsigned long zero_pfn __read_mostly;
   unsigned long highest_memmap_pfn __read_mostly;
   
   /*
    * CONFIG_MMU architectures set up ZERO_PAGE in their paging_init()
    */
   static int __init init_zero_pfn(void)
   {
           zero_pfn = page_to_pfn(ZERO_PAGE(0));
           return 0;
   }
   core_initcall(init_zero_pfn);
   
   
   #if defined(SPLIT_RSS_COUNTING)
   
   void sync_mm_rss(struct mm_struct *mm)
   {
           int i;
   
           for (i = 0; i < NR_MM_COUNTERS; i++) {
                   if (current->rss_stat.count[i]) {
                           add_mm_counter(mm, i, current->rss_stat.count[i]);
                           current->rss_stat.count[i] = 0;
                   }
           }
           current->rss_stat.events = 0;
   }
   
   static void add_mm_counter_fast(struct mm_struct *mm, int member, int val)
   {
           struct task_struct *task = current;
   
           if (likely(task->mm == mm))
                   task->rss_stat.count[member] += val;
           else
                   add_mm_counter(mm, member, val);
   }
   #define inc_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, 1)
   #define dec_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, -1)
   
   /* sync counter once per 64 page faults */
   #define TASK_RSS_EVENTS_THRESH  (64)
   static void check_sync_rss_stat(struct task_struct *task)
   {
           if (unlikely(task != current))
                   return;
           if (unlikely(task->rss_stat.events++ > TASK_RSS_EVENTS_THRESH))
                   sync_mm_rss(task->mm);
   }
   #else /* SPLIT_RSS_COUNTING */
   
   #define inc_mm_counter_fast(mm, member) inc_mm_counter(mm, member)
   #define dec_mm_counter_fast(mm, member) dec_mm_counter(mm, member)
   
   static void check_sync_rss_stat(struct task_struct *task)
   {
   }
   
   #endif /* SPLIT_RSS_COUNTING */
   
   #ifdef HAVE_GENERIC_MMU_GATHER
   
   static int tlb_next_batch(struct mmu_gather *tlb)
   {
           struct mmu_gather_batch *batch;
   
           batch = tlb->active;
           if (batch->next) {
                   tlb->active = batch->next;
                   return 1;
           }
   
           if (tlb->batch_count == MAX_GATHER_BATCH_COUNT)
                   return 0;
   
           batch = (void *)__get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
           if (!batch)
                   return 0;
   
           tlb->batch_count++;
           batch->next = NULL;
           batch->nr   = 0;
           batch->max  = MAX_GATHER_BATCH;
   
           tlb->active->next = batch;
           tlb->active = batch;
   
           return 1;
   }
   
   /* tlb_gather_mmu
    *      Called to initialize an (on-stack) mmu_gather structure for page-table
    *      tear-down from @mm. The @fullmm argument is used when @mm is without
    *      users and we're going to destroy the full address space (exit/execve).
    */
   void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, bool fullmm)
   {
           tlb->mm = mm;
   
           tlb->fullmm     = fullmm;
           tlb->start      = -1UL;
           tlb->end        = 0;
           tlb->need_flush = 0;
           tlb->fast_mode  = (num_possible_cpus() == 1);
           tlb->local.next = NULL;
           tlb->local.nr   = 0;
           tlb->local.max  = ARRAY_SIZE(tlb->__pages);
           tlb->active     = &tlb->local;
           tlb->batch_count = 0;
   
   #ifdef CONFIG_HAVE_RCU_TABLE_FREE
           tlb->batch = NULL;
   #endif
   }
   
   void tlb_flush_mmu(struct mmu_gather *tlb)
   {
           struct mmu_gather_batch *batch;
   
           if (!tlb->need_flush)
                   return;
           tlb->need_flush = 0;
           tlb_flush(tlb);
   #ifdef CONFIG_HAVE_RCU_TABLE_FREE
           tlb_table_flush(tlb);
   #endif
   
           if (tlb_fast_mode(tlb))
                   return;
   
           for (batch = &tlb->local; batch; batch = batch->next) {
                   free_pages_and_swap_cache(batch->pages, batch->nr);
                   batch->nr = 0;
           }
           tlb->active = &tlb->local;
   }
   
   /* tlb_finish_mmu
    *      Called at the end of the shootdown operation to free up any resources
    *      that were required.
    */
   void tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
   {
           struct mmu_gather_batch *batch, *next;
   
           tlb->start = start;
           tlb->end   = end;
           tlb_flush_mmu(tlb);
   
           /* keep the page table cache within bounds */
           check_pgt_cache();
   
           for (batch = tlb->local.next; batch; batch = next) {
                   next = batch->next;
                   free_pages((unsigned long)batch, 0);
           }
           tlb->local.next = NULL;
   }
   
   /* __tlb_remove_page
    *      Must perform the equivalent to __free_pte(pte_get_and_clear(ptep)), while
    *      handling the additional races in SMP caused by other CPUs caching valid
    *      mappings in their TLBs. Returns the number of free page slots left.
    *      When out of page slots we must call tlb_flush_mmu().
    */
   int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
   {
           struct mmu_gather_batch *batch;
   
           VM_BUG_ON(!tlb->need_flush);
   
           if (tlb_fast_mode(tlb)) {
                   free_page_and_swap_cache(page);
                   return 1; /* avoid calling tlb_flush_mmu() */
           }
   
           batch = tlb->active;
           batch->pages[batch->nr++] = page;
           if (batch->nr == batch->max) {
                   if (!tlb_next_batch(tlb))
                           return 0;
                   batch = tlb->active;
           }
           VM_BUG_ON(batch->nr > batch->max);
   
           return batch->max - batch->nr;
   }
   
   #endif /* HAVE_GENERIC_MMU_GATHER */
   
   #ifdef CONFIG_HAVE_RCU_TABLE_FREE
   
   /*
    * See the comment near struct mmu_table_batch.
    */
   
   static void tlb_remove_table_smp_sync(void *arg)
   {
           /* Simply deliver the interrupt */
   }
   
   static void tlb_remove_table_one(void *table)
   {
           /*
            * This isn't an RCU grace period and hence the page-tables cannot be
            * assumed to be actually RCU-freed.
            *
            * It is however sufficient for software page-table walkers that rely on
            * IRQ disabling. See the comment near struct mmu_table_batch.
            */
           smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
           __tlb_remove_table(table);
   }
   
   static void tlb_remove_table_rcu(struct rcu_head *head)
   {
           struct mmu_table_batch *batch;
           int i;
   
           batch = container_of(head, struct mmu_table_batch, rcu);
   
           for (i = 0; i < batch->nr; i++)
                   __tlb_remove_table(batch->tables[i]);
   
           free_page((unsigned long)batch);
   }
   
   void tlb_table_flush(struct mmu_gather *tlb)
   {
           struct mmu_table_batch **batch = &tlb->batch;
   
           if (*batch) {
                   call_rcu_sched(&(*batch)->rcu, tlb_remove_table_rcu);
                   *batch = NULL;
           }
   }
   
   void tlb_remove_table(struct mmu_gather *tlb, void *table)
   {
           struct mmu_table_batch **batch = &tlb->batch;
   
           tlb->need_flush = 1;
   
           /*
            * When there's less then two users of this mm there cannot be a
            * concurrent page-table walk.
            */
           if (atomic_read(&tlb->mm->mm_users) < 2) {
                   __tlb_remove_table(table);
                   return;
           }
   
           if (*batch == NULL) {
                   *batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
                   if (*batch == NULL) {
                           tlb_remove_table_one(table);
                           return;
                   }
                   (*batch)->nr = 0;
           }
           (*batch)->tables[(*batch)->nr++] = table;
           if ((*batch)->nr == MAX_TABLE_BATCH)
                   tlb_table_flush(tlb);
   }
   
   #endif /* CONFIG_HAVE_RCU_TABLE_FREE */
   
   /*
    * If a p?d_bad entry is found while walking page tables, report
    * the error, before resetting entry to p?d_none.  Usually (but
    * very seldom) called out from the p?d_none_or_clear_bad macros.
    */
   
   void pgd_clear_bad(pgd_t *pgd)
   {
           pgd_ERROR(*pgd);
           pgd_clear(pgd);
   }
   
   void pud_clear_bad(pud_t *pud)
   {
           pud_ERROR(*pud);
           pud_clear(pud);
   }
   
   void pmd_clear_bad(pmd_t *pmd)
   {
           pmd_ERROR(*pmd);
           pmd_clear(pmd);
   }
   
   /*
    * Note: this doesn't free the actual pages themselves. That
    * has been handled earlier when unmapping all the memory regions.
    */
   static void free_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
                              unsigned long addr)
   {
           pgtable_t token = pmd_pgtable(*pmd);
           pmd_clear(pmd);
           pte_free_tlb(tlb, token, addr);
           tlb->mm->nr_ptes--;
   }
   
   static inline void free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
                                   unsigned long addr, unsigned long end,
                                   unsigned long floor, unsigned long ceiling)
   {
           pmd_t *pmd;
           unsigned long next;
           unsigned long start;
   
           start = addr;
           pmd = pmd_offset(pud, addr);
           do {
                   next = pmd_addr_end(addr, end);
                   if (pmd_none_or_clear_bad(pmd))
                           continue;
                   free_pte_range(tlb, pmd, addr);
           } while (pmd++, addr = next, addr != end);
   
           start &= PUD_MASK;
           if (start < floor)
                   return;
           if (ceiling) {
                   ceiling &= PUD_MASK;
                   if (!ceiling)
                           return;
           }
           if (end - 1 > ceiling - 1)
                   return;
   
           pmd = pmd_offset(pud, start);
           pud_clear(pud);
           pmd_free_tlb(tlb, pmd, start);
   }
   
   static inline void free_pud_range(struct mmu_gather *tlb, pgd_t *pgd,
                                   unsigned long addr, unsigned long end,
                                   unsigned long floor, unsigned long ceiling)
   {
           pud_t *pud;
           unsigned long next;
           unsigned long start;
   
           start = addr;
           pud = pud_offset(pgd, addr);
           do {
                   next = pud_addr_end(addr, end);
                   if (pud_none_or_clear_bad(pud))
                           continue;
                   free_pmd_range(tlb, pud, addr, next, floor, ceiling);
           } while (pud++, addr = next, addr != end);
   
           start &= PGDIR_MASK;
           if (start < floor)
                   return;
           if (ceiling) {
                   ceiling &= PGDIR_MASK;
                   if (!ceiling)
                           return;
           }
           if (end - 1 > ceiling - 1)
                   return;
   
           pud = pud_offset(pgd, start);
           pgd_clear(pgd);
           pud_free_tlb(tlb, pud, start);
   }
   
   /*
    * This function frees user-level page tables of a process.
    *
    * Must be called with pagetable lock held.
    */
   void free_pgd_range(struct mmu_gather *tlb,
                           unsigned long addr, unsigned long end,
                           unsigned long floor, unsigned long ceiling)
   {
           pgd_t *pgd;
           unsigned long next;
   
           /*
            * The next few lines have given us lots of grief...
            *
            * Why are we testing PMD* at this top level?  Because often
            * there will be no work to do at all, and we'd prefer not to
            * go all the way down to the bottom just to discover that.
            *
            * Why all these "- 1"s?  Because 0 represents both the bottom
            * of the address space and the top of it (using -1 for the
            * top wouldn't help much: the masks would do the wrong thing).
            * The rule is that addr 0 and floor 0 refer to the bottom of
            * the address space, but end 0 and ceiling 0 refer to the top
            * Comparisons need to use "end - 1" and "ceiling - 1" (though
            * that end 0 case should be mythical).
            *
            * Wherever addr is brought up or ceiling brought down, we must
            * be careful to reject "the opposite 0" before it confuses the
            * subsequent tests.  But what about where end is brought down
            * by PMD_SIZE below? no, end can't go down to 0 there.
            *
            * Whereas we round start (addr) and ceiling down, by different
            * masks at different levels, in order to test whether a table
            * now has no other vmas using it, so can be freed, we don't
            * bother to round floor or end up - the tests don't need that.
            */
   
           addr &= PMD_MASK;
           if (addr < floor) {
                   addr += PMD_SIZE;
                   if (!addr)
                           return;
           }
           if (ceiling) {
                   ceiling &= PMD_MASK;
                   if (!ceiling)
                           return;
           }
           if (end - 1 > ceiling - 1)
                   end -= PMD_SIZE;
           if (addr > end - 1)
                   return;
   
           pgd = pgd_offset(tlb->mm, addr);
           do {
                   next = pgd_addr_end(addr, end);
                   if (pgd_none_or_clear_bad(pgd))
                           continue;
                   free_pud_range(tlb, pgd, addr, next, floor, ceiling);
           } while (pgd++, addr = next, addr != end);
   }
   
   void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma,
                   unsigned long floor, unsigned long ceiling)
   {
           while (vma) {
                   struct vm_area_struct *next = vma->vm_next;
                   unsigned long addr = vma->vm_start;
   
                   /*
                    * Hide vma from rmap and truncate_pagecache before freeing
                    * pgtables
                    */
                   unlink_anon_vmas(vma);
                   unlink_file_vma(vma);
   
                   if (is_vm_hugetlb_page(vma)) {
                           hugetlb_free_pgd_range(tlb, addr, vma->vm_end,
                                   floor, next? next->vm_start: ceiling);
                   } else {
                           /*
                            * Optimization: gather nearby vmas into one call down
                            */
                           while (next && next->vm_start <= vma->vm_end + PMD_SIZE
                                  && !is_vm_hugetlb_page(next)) {
                                   vma = next;
                                   next = vma->vm_next;
                                   unlink_anon_vmas(vma);
                                   unlink_file_vma(vma);
                           }
                           free_pgd_range(tlb, addr, vma->vm_end,
                                   floor, next? next->vm_start: ceiling);
                   }
                   vma = next;
           }
   }
   
   int __pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
                   pmd_t *pmd, unsigned long address)
   {
           pgtable_t new = pte_alloc_one(mm, address);
           int wait_split_huge_page;
           if (!new)
                   return -ENOMEM;
   
           /*
            * Ensure all pte setup (eg. pte page lock and page clearing) are
            * visible before the pte is made visible to other CPUs by being
            * put into page tables.
            *
            * The other side of the story is the pointer chasing in the page
            * table walking code (when walking the page table without locking;
            * ie. most of the time). Fortunately, these data accesses consist
            * of a chain of data-dependent loads, meaning most CPUs (alpha
            * being the notable exception) will already guarantee loads are
            * seen in-order. See the alpha page table accessors for the
            * smp_read_barrier_depends() barriers in page table walking code.
            */
           smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */
   
           spin_lock(&mm->page_table_lock);
           wait_split_huge_page = 0;
           if (likely(pmd_none(*pmd))) {   /* Has another populated it ? */
                   mm->nr_ptes++;
                   pmd_populate(mm, pmd, new);
                   new = NULL;
           } else if (unlikely(pmd_trans_splitting(*pmd)))
                   wait_split_huge_page = 1;
           spin_unlock(&mm->page_table_lock);
           if (new)
                   pte_free(mm, new);
           if (wait_split_huge_page)
                   wait_split_huge_page(vma->anon_vma, pmd);
           return 0;
   }
   
   int __pte_alloc_kernel(pmd_t *pmd, unsigned long address)
   {
           pte_t *new = pte_alloc_one_kernel(&init_mm, address);
           if (!new)
                   return -ENOMEM;
   
           smp_wmb(); /* See comment in __pte_alloc */
   
           spin_lock(&init_mm.page_table_lock);
           if (likely(pmd_none(*pmd))) {   /* Has another populated it ? */
                   pmd_populate_kernel(&init_mm, pmd, new);
                   new = NULL;
           } else
                   VM_BUG_ON(pmd_trans_splitting(*pmd));
           spin_unlock(&init_mm.page_table_lock);
           if (new)
                   pte_free_kernel(&init_mm, new);
           return 0;
   }
   
   static inline void init_rss_vec(int *rss)
   {
           memset(rss, 0, sizeof(int) * NR_MM_COUNTERS);
   }
   
   static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
   {
           int i;
   
           if (current->mm == mm)
                   sync_mm_rss(mm);
           for (i = 0; i < NR_MM_COUNTERS; i++)
                   if (rss[i])
                           add_mm_counter(mm, i, rss[i]);
   }
   
   /*
    * This function is called to print an error when a bad pte
    * is found. For example, we might have a PFN-mapped pte in
    * a region that doesn't allow it.
    *
    * The calling function must still handle the error.
    */
   static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
                             pte_t pte, struct page *page)
   {
           pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
           pud_t *pud = pud_offset(pgd, addr);
           pmd_t *pmd = pmd_offset(pud, addr);
           struct address_space *mapping;
           pgoff_t index;
           static unsigned long resume;
           static unsigned long nr_shown;
           static unsigned long nr_unshown;
   
           /*
            * Allow a burst of 60 reports, then keep quiet for that minute;
            * or allow a steady drip of one report per second.
            */
           if (nr_shown == 60) {
                   if (time_before(jiffies, resume)) {
                           nr_unshown++;
                           return;
                   }
                   if (nr_unshown) {
                           printk(KERN_ALERT
                                   "BUG: Bad page map: %lu messages suppressed\n",
                                   nr_unshown);
                           nr_unshown = 0;
                   }
                   nr_shown = 0;
           }
           if (nr_shown++ == 0)
                   resume = jiffies + 60 * HZ;
   
           mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
           index = linear_page_index(vma, addr);
   
           printk(KERN_ALERT
                   "BUG: Bad page map in process %s  pte:%08llx pmd:%08llx\n",
                   current->comm,
                   (long long)pte_val(pte), (long long)pmd_val(*pmd));
           if (page)
                   dump_page(page);
           printk(KERN_ALERT
                   "addr:%p vm_flags:%08lx anon_vma:%p mapping:%p index:%lx\n",
                   (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
           /*
            * Choose text because data symbols depend on CONFIG_KALLSYMS_ALL=y
            */
           if (vma->vm_ops)
                   print_symbol(KERN_ALERT "vma->vm_ops->fault: %s\n",
                                   (unsigned long)vma->vm_ops->fault);
           if (vma->vm_file && vma->vm_file->f_op)
                   print_symbol(KERN_ALERT "vma->vm_file->f_op->mmap: %s\n",
                                   (unsigned long)vma->vm_file->f_op->mmap);
           dump_stack();
           add_taint(TAINT_BAD_PAGE);
   }
   
   static inline bool is_cow_mapping(vm_flags_t flags)
   {
           return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
   }
   
   /*
    * vm_normal_page -- This function gets the "struct page" associated with a pte.
    *
    * "Special" mappings do not wish to be associated with a "struct page" (either
    * it doesn't exist, or it exists but they don't want to touch it). In this
    * case, NULL is returned here. "Normal" mappings do have a struct page.
    *
    * There are 2 broad cases. Firstly, an architecture may define a pte_special()
    * pte bit, in which case this function is trivial. Secondly, an architecture
    * may not have a spare pte bit, which requires a more complicated scheme,
    * described below.
    *
    * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a
    * special mapping (even if there are underlying and valid "struct pages").
    * COWed pages of a VM_PFNMAP are always normal.
    *
    * The way we recognize COWed pages within VM_PFNMAP mappings is through the
    * rules set up by "remap_pfn_range()": the vma will have the VM_PFNMAP bit
    * set, and the vm_pgoff will point to the first PFN mapped: thus every special
    * mapping will always honor the rule
    *
    *      pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT)
    *
    * And for normal mappings this is false.
    *
    * This restricts such mappings to be a linear translation from virtual address
    * to pfn. To get around this restriction, we allow arbitrary mappings so long
    * as the vma is not a COW mapping; in that case, we know that all ptes are
    * special (because none can have been COWed).
    *
    *
    * In order to support COW of arbitrary special mappings, we have VM_MIXEDMAP.
    *
    * VM_MIXEDMAP mappings can likewise contain memory with or without "struct
    * page" backing, however the difference is that _all_ pages with a struct
    * page (that is, those where pfn_valid is true) are refcounted and considered
    * normal pages by the VM. The disadvantage is that pages are refcounted
    * (which can be slower and simply not an option for some PFNMAP users). The
    * advantage is that we don't have to follow the strict linearity rule of
    * PFNMAP mappings in order to support COWable mappings.
    *
    */
   #ifdef __HAVE_ARCH_PTE_SPECIAL
   # define HAVE_PTE_SPECIAL 1
   #else
   # define HAVE_PTE_SPECIAL 0
   #endif
   struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
                                   pte_t pte)
   {
           unsigned long pfn = pte_pfn(pte);
   
           if (HAVE_PTE_SPECIAL) {
                   if (likely(!pte_special(pte)))
                           goto check_pfn;
                   if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
                           return NULL;
                   if (!is_zero_pfn(pfn))
                           print_bad_pte(vma, addr, pte, NULL);
                   return NULL;
           }
   
           /* !HAVE_PTE_SPECIAL case follows: */
   
           if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
                   if (vma->vm_flags & VM_MIXEDMAP) {
                           if (!pfn_valid(pfn))
                                   return NULL;
                           goto out;
                   } else {
                           unsigned long off;
                           off = (addr - vma->vm_start) >> PAGE_SHIFT;
                           if (pfn == vma->vm_pgoff + off)
                                   return NULL;
                           if (!is_cow_mapping(vma->vm_flags))
                                   return NULL;
                   }
           }
   
           if (is_zero_pfn(pfn))
                   return NULL;
   check_pfn:
           if (unlikely(pfn > highest_memmap_pfn)) {
                   print_bad_pte(vma, addr, pte, NULL);
                   return NULL;
           }
   
           /*
            * NOTE! We still have PageReserved() pages in the page tables.
            * eg. VDSO mappings can cause them to exist.
            */
   out:
           return pfn_to_page(pfn);
   }
   
   /*
    * copy one vm_area from one task to the other. Assumes the page tables
    * already present in the new task to be cleared in the whole range
    * covered by this vma.
    */
   
   static inline unsigned long
   copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                   pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct *vma,
                   unsigned long addr, int *rss)
   {
           unsigned long vm_flags = vma->vm_flags;
           pte_t pte = *src_pte;
           struct page *page;
   
           /* pte contains position in swap or file, so copy. */
           if (unlikely(!pte_present(pte))) {
                   if (!pte_file(pte)) {
                           swp_entry_t entry = pte_to_swp_entry(pte);
   
                           if (swap_duplicate(entry) < 0)
                                   return entry.val;
   
                           /* make sure dst_mm is on swapoff's mmlist. */
                           if (unlikely(list_empty(&dst_mm->mmlist))) {
                                   spin_lock(&mmlist_lock);
                                   if (list_empty(&dst_mm->mmlist))
                                           list_add(&dst_mm->mmlist,
                                                    &src_mm->mmlist);
                                   spin_unlock(&mmlist_lock);
                           }
                           if (likely(!non_swap_entry(entry)))
                                   rss[MM_SWAPENTS]++;
                           else if (is_migration_entry(entry)) {
                                   page = migration_entry_to_page(entry);
   
                                   if (PageAnon(page))
                                           rss[MM_ANONPAGES]++;
                                   else
                                           rss[MM_FILEPAGES]++;
   
                                   if (is_write_migration_entry(entry) &&
                                       is_cow_mapping(vm_flags)) {
                                           /*
                                            * COW mappings require pages in both
                                            * parent and child to be set to read.
                                            */
                                           make_migration_entry_read(&entry);
                                           pte = swp_entry_to_pte(entry);
                                           set_pte_at(src_mm, addr, src_pte, pte);
                                   }
                           }
                   }
                   goto out_set_pte;
           }
   
           /*
            * If it's a COW mapping, write protect it both
            * in the parent and the child
            */
           if (is_cow_mapping(vm_flags)) {
                   ptep_set_wrprotect(src_mm, addr, src_pte);
                   pte = pte_wrprotect(pte);
           }
   
           /*
            * If it's a shared mapping, mark it clean in
            * the child
            */
           if (vm_flags & VM_SHARED)
                   pte = pte_mkclean(pte);
           pte = pte_mkold(pte);
   
           page = vm_normal_page(vma, addr, pte);
           if (page) {
                   get_page(page);
                   page_dup_rmap(page);
                   if (PageAnon(page))
                           rss[MM_ANONPAGES]++;
                   else
                           rss[MM_FILEPAGES]++;
           }
   
   out_set_pte:
           set_pte_at(dst_mm, addr, dst_pte, pte);
           return 0;
   }
   
   int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                      pmd_t *dst_pmd, pmd_t *src_pmd, struct vm_area_struct *vma,
                      unsigned long addr, unsigned long end)
   {
           pte_t *orig_src_pte, *orig_dst_pte;
           pte_t *src_pte, *dst_pte;
           spinlock_t *src_ptl, *dst_ptl;
           int progress = 0;
           int rss[NR_MM_COUNTERS];
           swp_entry_t entry = (swp_entry_t){0};
   
   again:
           init_rss_vec(rss);
   
           dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl);
           if (!dst_pte)
                   return -ENOMEM;
           src_pte = pte_offset_map(src_pmd, addr);
           src_ptl = pte_lockptr(src_mm, src_pmd);
           spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
           orig_src_pte = src_pte;
           orig_dst_pte = dst_pte;
           arch_enter_lazy_mmu_mode();
   
           do {
                   /*
                    * We are holding two locks at this point - either of them
                    * could generate latencies in another task on another CPU.
                    */
                   if (progress >= 32) {
                           progress = 0;
                           if (need_resched() ||
                               spin_needbreak(src_ptl) || spin_needbreak(dst_ptl))
                                   break;
                   }
                   if (pte_none(*src_pte)) {
                           progress++;
                           continue;
                   }
                   entry.val = copy_one_pte(dst_mm, src_mm, dst_pte, src_pte,
                                                           vma, addr, rss);
                   if (entry.val)
                           break;
                   progress += 8;
           } while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end);
   
           arch_leave_lazy_mmu_mode();
           spin_unlock(src_ptl);
           pte_unmap(orig_src_pte);
           add_mm_rss_vec(dst_mm, rss);
           pte_unmap_unlock(orig_dst_pte, dst_ptl);
           cond_resched();
   
           if (entry.val) {
                   if (add_swap_count_continuation(entry, GFP_KERNEL) < 0)
                           return -ENOMEM;
                   progress = 0;
           }
           if (addr != end)
                   goto again;
           return 0;
   }
   
   static inline int copy_pmd_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                   pud_t *dst_pud, pud_t *src_pud, struct vm_area_struct *vma,
                   unsigned long addr, unsigned long end)
   {
           pmd_t *src_pmd, *dst_pmd;
           unsigned long next;
   
           dst_pmd = pmd_alloc(dst_mm, dst_pud, addr);
           if (!dst_pmd)
                   return -ENOMEM;
           src_pmd = pmd_offset(src_pud, addr);
           do {
                   next = pmd_addr_end(addr, end);
                   if (pmd_trans_huge(*src_pmd)) {
                           int err;
                           VM_BUG_ON(next-addr != HPAGE_PMD_SIZE);
                           err = copy_huge_pmd(dst_mm, src_mm,
                                               dst_pmd, src_pmd, addr, vma);
                           if (err == -ENOMEM)
                                   return -ENOMEM;
                           if (!err)
                                   continue;
                           /* fall through */
                   }
                   if (pmd_none_or_clear_bad(src_pmd))
                           continue;
                   if (copy_pte_range(dst_mm, src_mm, dst_pmd, src_pmd,
                                                  vma, addr, next))
                          return -ENOMEM;
          } while (dst_pmd++, src_pmd++, addr = next, addr != end);
          return 0;
  }
  
  static inline int copy_pud_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                  pgd_t *dst_pgd, pgd_t *src_pgd, struct vm_area_struct *vma,
                  unsigned long addr, unsigned long end)
  {
          pud_t *src_pud, *dst_pud;
          unsigned long next;
  
          dst_pud = pud_alloc(dst_mm, dst_pgd, addr);
          if (!dst_pud)
                  return -ENOMEM;
          src_pud = pud_offset(src_pgd, addr);
          do {
                  next = pud_addr_end(addr, end);
                  if (pud_none_or_clear_bad(src_pud))
                          continue;
                  if (copy_pmd_range(dst_mm, src_mm, dst_pud, src_pud,
                                                  vma, addr, next))
                          return -ENOMEM;
          } while (dst_pud++, src_pud++, addr = next, addr != end);
          return 0;
  }
  
  int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                  struct vm_area_struct *vma)
  {
          pgd_t *src_pgd, *dst_pgd;
          unsigned long next;
          unsigned long addr = vma->vm_start;
          unsigned long end = vma->vm_end;
          unsigned long mmun_start;       /* For mmu_notifiers */
          unsigned long mmun_end;         /* For mmu_notifiers */
          bool is_cow;
          int ret;
  
          /*
           * Don't copy ptes where a page fault will fill them correctly.
           * Fork becomes much lighter when there are big shared or private
           * readonly mappings. The tradeoff is that copy_page_range is more
           * efficient than faulting.
           */
          if (!(vma->vm_flags & (VM_HUGETLB | VM_NONLINEAR |
                                 VM_PFNMAP | VM_MIXEDMAP))) {
                  if (!vma->anon_vma)
                          return 0;
          }
  
          if (is_vm_hugetlb_page(vma))
                  return copy_hugetlb_page_range(dst_mm, src_mm, vma);
  
          if (unlikely(vma->vm_flags & VM_PFNMAP)) {
                  /*
                   * We do not free on error cases below as remove_vma
                   * gets called on error from higher level routine
                   */
                  ret = track_pfn_copy(vma);
                  if (ret)
                          return ret;
          }
  
          /*
           * We need to invalidate the secondary MMU mappings only when
           * there could be a permission downgrade on the ptes of the
           * parent mm. And a permission downgrade will only happen if
           * is_cow_mapping() returns true.
           */
          is_cow = is_cow_mapping(vma->vm_flags);
          mmun_start = addr;
          mmun_end   = end;
          if (is_cow)
                  mmu_notifier_invalidate_range_start(src_mm, mmun_start,
                                                      mmun_end);
  
          ret = 0;
          dst_pgd = pgd_offset(dst_mm, addr);
          src_pgd = pgd_offset(src_mm, addr);
          do {
                  next = pgd_addr_end(addr, end);
                  if (pgd_none_or_clear_bad(src_pgd))
                          continue;
                  if (unlikely(copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
                                              vma, addr, next))) {
                          ret = -ENOMEM;
                          break;
                  }
          } while (dst_pgd++, src_pgd++, addr = next, addr != end);
  
          if (is_cow)
                  mmu_notifier_invalidate_range_end(src_mm, mmun_start, mmun_end);
          return ret;
  }
  
  static unsigned long zap_pte_range(struct mmu_gather *tlb,
                                  struct vm_area_struct *vma, pmd_t *pmd,
                                  unsigned long addr, unsigned long end,
                                  struct zap_details *details)
  {
          struct mm_struct *mm = tlb->mm;
          int force_flush = 0;
          int rss[NR_MM_COUNTERS];
          spinlock_t *ptl;
          pte_t *start_pte;
          pte_t *pte;
  
  again:
          init_rss_vec(rss);
          start_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
          pte = start_pte;
          arch_enter_lazy_mmu_mode();
          do {
                  pte_t ptent = *pte;
                  if (pte_none(ptent)) {
                          continue;
                  }
  
                  if (pte_present(ptent)) {
                          struct page *page;
  
                          page = vm_normal_page(vma, addr, ptent);
                          if (unlikely(details) && page) {
                                  /*
                                   * unmap_shared_mapping_pages() wants to
                                   * invalidate cache without truncating:
                                   * unmap shared but keep private pages.
                                   */
                                  if (details->check_mapping &&
                                      details->check_mapping != page->mapping)
                                          continue;
                                  /*
                                   * Each page->index must be checked when
                                   * invalidating or truncating nonlinear.
                                   */
                                  if (details->nonlinear_vma &&
                                      (page->index < details->first_index ||
                                       page->index > details->last_index))
                                          continue;
                          }
                          ptent = ptep_get_and_clear_full(mm, addr, pte,
                                                          tlb->fullmm);
                          tlb_remove_tlb_entry(tlb, pte, addr);
                          if (unlikely(!page))
                                  continue;
                          if (unlikely(details) && details->nonlinear_vma
                              && linear_page_index(details->nonlinear_vma,
                                                  addr) != page->index)
                                  set_pte_at(mm, addr, pte,
                                             pgoff_to_pte(page->index));
                          if (PageAnon(page))
                                  rss[MM_ANONPAGES]--;
                          else {
                                  if (pte_dirty(ptent))
                                          set_page_dirty(page);
                                  if (pte_young(ptent) &&
                                      likely(!VM_SequentialReadHint(vma)))
                                          mark_page_accessed(page);
                                  rss[MM_FILEPAGES]--;
                          }
                          page_remove_rmap(page);
                          if (unlikely(page_mapcount(page) < 0))
                                  print_bad_pte(vma, addr, ptent, page);
                          force_flush = !__tlb_remove_page(tlb, page);
                          if (force_flush)
                                  break;
                          continue;
                  }
                  /*
                   * If details->check_mapping, we leave swap entries;
                   * if details->nonlinear_vma, we leave file entries.
                   */
                  if (unlikely(details))
                          continue;
                  if (pte_file(ptent)) {
                          if (unlikely(!(vma->vm_flags & VM_NONLINEAR)))
                                  print_bad_pte(vma, addr, ptent, NULL);
                  } else {
                          swp_entry_t entry = pte_to_swp_entry(ptent);
  
                          if (!non_swap_entry(entry))
                                  rss[MM_SWAPENTS]--;
                          else if (is_migration_entry(entry)) {
                                  struct page *page;
  
                                  page = migration_entry_to_page(entry);
  
                                  if (PageAnon(page))
                                          rss[MM_ANONPAGES]--;
                                  else
                                          rss[MM_FILEPAGES]--;
                          }
                          if (unlikely(!free_swap_and_cache(entry)))
                                  print_bad_pte(vma, addr, ptent, NULL);
                  }
                  pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
          } while (pte++, addr += PAGE_SIZE, addr != end);
  
          add_mm_rss_vec(mm, rss);
          arch_leave_lazy_mmu_mode();
          pte_unmap_unlock(start_pte, ptl);
  
          /*
           * mmu_gather ran out of room to batch pages, we break out of
           * the PTE lock to avoid doing the potential expensive TLB invalidate
           * and page-free while holding it.
           */
          if (force_flush) {
                  force_flush = 0;
  
  #ifdef HAVE_GENERIC_MMU_GATHER
                  tlb->start = addr;
                  tlb->end = end;
  #endif
                  tlb_flush_mmu(tlb);
                  if (addr != end)
                          goto again;
          }
  
          return addr;
  }
  
  static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
                                  struct vm_area_struct *vma, pud_t *pud,
                                  unsigned long addr, unsigned long end,
                                  struct zap_details *details)
  {
          pmd_t *pmd;
          unsigned long next;
  
          pmd = pmd_offset(pud, addr);
          do {
                  next = pmd_addr_end(addr, end);
                  if (pmd_trans_huge(*pmd)) {
                          if (next - addr != HPAGE_PMD_SIZE) {
  #ifdef CONFIG_DEBUG_VM
                                  if (!rwsem_is_locked(&tlb->mm->mmap_sem)) {
                                          pr_err("%s: mmap_sem is unlocked! addr=0x%lx end=0x%lx vma->vm_start=0x%lx vma->vm_end=0x%lx\n",
                                                  __func__, addr, end,
                                                  vma->vm_start,
                                                  vma->vm_end);
                                          BUG();
                                  }
  #endif
                                  split_huge_page_pmd(vma, addr, pmd);
                          } else if (zap_huge_pmd(tlb, vma, pmd, addr))
                                  goto next;
                          /* fall through */
                  }
                  /*
                   * Here there can be other concurrent MADV_DONTNEED or
                   * trans huge page faults running, and if the pmd is
                   * none or trans huge it can change under us. This is
                   * because MADV_DONTNEED holds the mmap_sem in read
                   * mode.
                   */
                  if (pmd_none_or_trans_huge_or_clear_bad(pmd))
                          goto next;
                  next = zap_pte_range(tlb, vma, pmd, addr, next, details);
  next:
                  cond_resched();
          } while (pmd++, addr = next, addr != end);
  
          return addr;
  }
  
  static inline unsigned long zap_pud_range(struct mmu_gather *tlb,
                                  struct vm_area_struct *vma, pgd_t *pgd,
                                  unsigned long addr, unsigned long end,
                                  struct zap_details *details)
  {
          pud_t *pud;
          unsigned long next;
  
          pud = pud_offset(pgd, addr);
          do {
                  next = pud_addr_end(addr, end);
                  if (pud_none_or_clear_bad(pud))
                          continue;
                  next = zap_pmd_range(tlb, vma, pud, addr, next, details);
          } while (pud++, addr = next, addr != end);
  
          return addr;
  }
  
  static void unmap_page_range(struct mmu_gather *tlb,
                               struct vm_area_struct *vma,
                               unsigned long addr, unsigned long end,
                               struct zap_details *details)
  {
          pgd_t *pgd;
          unsigned long next;
  
          if (details && !details->check_mapping && !details->nonlinear_vma)
                  details = NULL;
  
          BUG_ON(addr >= end);
          mem_cgroup_uncharge_start();
          tlb_start_vma(tlb, vma);
          pgd = pgd_offset(vma->vm_mm, addr);
          do {
                  next = pgd_addr_end(addr, end);
                  if (pgd_none_or_clear_bad(pgd))
                          continue;
                  next = zap_pud_range(tlb, vma, pgd, addr, next, details);
          } while (pgd++, addr = next, addr != end);
          tlb_end_vma(tlb, vma);
          mem_cgroup_uncharge_end();
  }
  
  
  static void unmap_single_vma(struct mmu_gather *tlb,
                  struct vm_area_struct *vma, unsigned long start_addr,
                  unsigned long end_addr,
                  struct zap_details *details)
  {
          unsigned long start = max(vma->vm_start, start_addr);
          unsigned long end;
  
          if (start >= vma->vm_end)
                  return;
          end = min(vma->vm_end, end_addr);
          if (end <= vma->vm_start)
                  return;
  
          if (vma->vm_file)
                  uprobe_munmap(vma, start, end);
  
          if (unlikely(vma->vm_flags & VM_PFNMAP))
                  untrack_pfn(vma, 0, 0);
  
          if (start != end) {
                  if (unlikely(is_vm_hugetlb_page(vma))) {
                          /*
                           * It is undesirable to test vma->vm_file as it
                           * should be non-null for valid hugetlb area.
                           * However, vm_file will be NULL in the error
                           * cleanup path of do_mmap_pgoff. When
                           * hugetlbfs ->mmap method fails,
                           * do_mmap_pgoff() nullifies vma->vm_file
                           * before calling this function to clean up.
                           * Since no pte has actually been setup, it is
                           * safe to do nothing in this case.
                           */
                          if (vma->vm_file) {
                                  mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex);
                                  __unmap_hugepage_range_final(tlb, vma, start, end, NULL);
                                  mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex);
                          }
                  } else
                          unmap_page_range(tlb, vma, start, end, details);
          }
  }
  
  /**
   * unmap_vmas - unmap a range of memory covered by a list of vma's
   * @tlb: address of the caller's struct mmu_gather
   * @vma: the starting vma
   * @start_addr: virtual address at which to start unmapping
   * @end_addr: virtual address at which to end unmapping
   *
   * Unmap all pages in the vma list.
   *
   * Only addresses between `start' and `end' will be unmapped.
   *
   * The VMA list must be sorted in ascending virtual address order.
   *
   * unmap_vmas() assumes that the caller will flush the whole unmapped address
   * range after unmap_vmas() returns.  So the only responsibility here is to
   * ensure that any thus-far unmapped pages are flushed before unmap_vmas()
   * drops the lock and schedules.
   */
  void unmap_vmas(struct mmu_gather *tlb,
                  struct vm_area_struct *vma, unsigned long start_addr,
                  unsigned long end_addr)
  {
          struct mm_struct *mm = vma->vm_mm;
  
          mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
          for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next)
                  unmap_single_vma(tlb, vma, start_addr, end_addr, NULL);
          mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);
  }
  
  /**
   * zap_page_range - remove user pages in a given range
   * @vma: vm_area_struct holding the applicable pages
   * @start: starting address of pages to zap
   * @size: number of bytes to zap
   * @details: details of nonlinear truncation or shared cache invalidation
   *
   * Caller must protect the VMA list
   */
  void zap_page_range(struct vm_area_struct *vma, unsigned long start,
                  unsigned long size, struct zap_details *details)
  {
          struct mm_struct *mm = vma->vm_mm;
          struct mmu_gather tlb;
          unsigned long end = start + size;
  
          lru_add_drain();
          tlb_gather_mmu(&tlb, mm, 0);
          update_hiwater_rss(mm);
          mmu_notifier_invalidate_range_start(mm, start, end);
          for ( ; vma && vma->vm_start < end; vma = vma->vm_next)
                  unmap_single_vma(&tlb, vma, start, end, details);
          mmu_notifier_invalidate_range_end(mm, start, end);
          tlb_finish_mmu(&tlb, start, end);
  }
  
  /**
   * zap_page_range_single - remove user pages in a given range
   * @vma: vm_area_struct holding the applicable pages
   * @address: starting address of pages to zap
   * @size: number of bytes to zap
   * @details: details of nonlinear truncation or shared cache invalidation
   *
   * The range must fit into one VMA.
   */
  static void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
                  unsigned long size, struct zap_details *details)
  {
          struct mm_struct *mm = vma->vm_mm;
          struct mmu_gather tlb;
          unsigned long end = address + size;
  
          lru_add_drain();
          tlb_gather_mmu(&tlb, mm, 0);
          update_hiwater_rss(mm);
          mmu_notifier_invalidate_range_start(mm, address, end);
          unmap_single_vma(&tlb, vma, address, end, details);
          mmu_notifier_invalidate_range_end(mm, address, end);
          tlb_finish_mmu(&tlb, address, end);
  }
  
  /**
   * zap_vma_ptes - remove ptes mapping the vma
   * @vma: vm_area_struct holding ptes to be zapped
   * @address: starting address of pages to zap
   * @size: number of bytes to zap
   *
   * This function only unmaps ptes assigned to VM_PFNMAP vmas.
   *
   * The entire address range must be fully contained within the vma.
   *
   * Returns 0 if successful.
   */
  int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
                  unsigned long size)
  {
          if (address < vma->vm_start || address + size > vma->vm_end ||
                          !(vma->vm_flags & VM_PFNMAP))
                  return -1;
          zap_page_range_single(vma, address, size, NULL);
          return 0;
  }
  EXPORT_SYMBOL_GPL(zap_vma_ptes);
  
  /**
   * follow_page - look up a page descriptor from a user-virtual address
   * @vma: vm_area_struct mapping @address
   * @address: virtual address to look up
   * @flags: flags modifying lookup behaviour
   *
   * @flags can have FOLL_ flags set, defined in <linux/mm.h>
   *
   * Returns the mapped (struct page *), %NULL if no mapping exists, or
   * an error pointer if there is a mapping to something not represented
   * by a page descriptor (see also vm_normal_page()).
   */
  struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
                          unsigned int flags)
  {
          pgd_t *pgd;
          pud_t *pud;
          pmd_t *pmd;
          pte_t *ptep, pte;
          spinlock_t *ptl;
          struct page *page;
          struct mm_struct *mm = vma->vm_mm;
  
          page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
          if (!IS_ERR(page)) {
                  BUG_ON(flags & FOLL_GET);
                  goto out;
          }
  
          page = NULL;
          pgd = pgd_offset(mm, address);
          if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
                  goto no_page_table;
  
          pud = pud_offset(pgd, address);
          if (pud_none(*pud))
                  goto no_page_table;
          if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
                  BUG_ON(flags & FOLL_GET);
                  page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
                  goto out;
          }
          if (unlikely(pud_bad(*pud)))
                  goto no_page_table;
  
          pmd = pmd_offset(pud, address);
          if (pmd_none(*pmd))
                  goto no_page_table;
          if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
                  BUG_ON(flags & FOLL_GET);
                  page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
                  goto out;
          }
          if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
                  goto no_page_table;
          if (pmd_trans_huge(*pmd)) {
                  if (flags & FOLL_SPLIT) {
                          split_huge_page_pmd(vma, address, pmd);
                          goto split_fallthrough;
                  }
                  spin_lock(&mm->page_table_lock);
                  if (likely(pmd_trans_huge(*pmd))) {
                          if (unlikely(pmd_trans_splitting(*pmd))) {
                                  spin_unlock(&mm->page_table_lock);
                                  wait_split_huge_page(vma->anon_vma, pmd);
                          } else {
                                  page = follow_trans_huge_pmd(vma, address,
                                                               pmd, flags);
                                  spin_unlock(&mm->page_table_lock);
                                  goto out;
                          }
                  } else
                          spin_unlock(&mm->page_table_lock);
                  /* fall through */
          }
  split_fallthrough:
          if (unlikely(pmd_bad(*pmd)))
                  goto no_page_table;
  
          ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
  
          pte = *ptep;
          if (!pte_present(pte))
                  goto no_page;
          if ((flags & FOLL_NUMA) && pte_numa(pte))
                  goto no_page;
          if ((flags & FOLL_WRITE) && !pte_write(pte))
                  goto unlock;
  
          page = vm_normal_page(vma, address, pte);
          if (unlikely(!page)) {
                  if ((flags & FOLL_DUMP) ||
                      !is_zero_pfn(pte_pfn(pte)))
                          goto bad_page;
                  page = pte_page(pte);
          }
  
          if (flags & FOLL_GET)
                  get_page_foll(page);
          if (flags & FOLL_TOUCH) {
                  if ((flags & FOLL_WRITE) &&
                      !pte_dirty(pte) && !PageDirty(page))
                          set_page_dirty(page);
                  /*
                   * pte_mkyoung() would be more correct here, but atomic care
                   * is needed to avoid losing the dirty bit: it is easier to use
                   * mark_page_accessed().
                   */
                  mark_page_accessed(page);
          }
          if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
                  /*
                   * The preliminary mapping check is mainly to avoid the
                   * pointless overhead of lock_page on the ZERO_PAGE
                   * which might bounce very badly if there is contention.
                   *
                   * If the page is already locked, we don't need to
                   * handle it now - vmscan will handle it later if and
                   * when it attempts to reclaim the page.
                   */
                  if (page->mapping && trylock_page(page)) {
                          lru_add_drain();  /* push cached pages to LRU */
                          /*
                           * Because we lock page here, and migration is
                           * blocked by the pte's page reference, and we
                           * know the page is still mapped, we don't even
                           * need to check for file-cache page truncation.
                           */
                          mlock_vma_page(page);
                          unlock_page(page);
                  }
          }
  unlock:
          pte_unmap_unlock(ptep, ptl);
  out:
          return page;
  
  bad_page:
          pte_unmap_unlock(ptep, ptl);
          return ERR_PTR(-EFAULT);
  
  no_page:
          pte_unmap_unlock(ptep, ptl);
          if (!pte_none(pte))
                  return page;
  
  no_page_table:
          /*
           * When core dumping an enormous anonymous area that nobody
           * has touched so far, we don't want to allocate unnecessary pages or
           * page tables.  Return error instead of NULL to skip handle_mm_fault,
           * then get_dump_page() will return NULL to leave a hole in the dump.
           * But we can only make this optimization where a hole would surely
           * be zero-filled if handle_mm_fault() actually did handle it.
           */
          if ((flags & FOLL_DUMP) &&
              (!vma->vm_ops || !vma->vm_ops->fault))
                  return ERR_PTR(-EFAULT);
          return page;
  }
  
  static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr)
  {
          return stack_guard_page_start(vma, addr) ||
                 stack_guard_page_end(vma, addr+PAGE_SIZE);
  }
  
  /**
   * __get_user_pages() - pin user pages in memory
   * @tsk:        task_struct of target task
   * @mm:         mm_struct of target mm
   * @start:      starting user address
   * @nr_pages:   number of pages from start to pin
   * @gup_flags:  flags modifying pin behaviour
   * @pages:      array that receives pointers to the pages pinned.
   *              Should be at least nr_pages long. Or NULL, if caller
   *              only intends to ensure the pages are faulted in.
   * @vmas:       array of pointers to vmas corresponding to each page.
   *              Or NULL if the caller does not require them.
   * @nonblocking: whether waiting for disk IO or mmap_sem contention
   *
   * Returns number of pages pinned. This may be fewer than the number
   * requested. If nr_pages is 0 or negative, returns 0. If no pages
   * were pinned, returns -errno. Each page returned must be released
   * with a put_page() call when it is finished with. vmas will only
   * remain valid while mmap_sem is held.
   *
   * Must be called with mmap_sem held for read or write.
   *
   * __get_user_pages walks a process's page tables and takes a reference to
   * each struct page that each user address corresponds to at a given
   * instant. That is, it takes the page that would be accessed if a user
   * thread accesses the given user virtual address at that instant.
   *
   * This does not guarantee that the page exists in the user mappings when
   * __get_user_pages returns, and there may even be a completely different
   * page there in some cases (eg. if mmapped pagecache has been invalidated
   * and subsequently re faulted). However it does guarantee that the page
   * won't be freed completely. And mostly callers simply care that the page
   * contains data that was valid *at some point in time*. Typically, an IO
   * or similar operation cannot guarantee anything stronger anyway because
   * locks can't be held over the syscall boundary.
   *
   * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
   * the page is written to, set_page_dirty (or set_page_dirty_lock, as
   * appropriate) must be called after the page is finished with, and
   * before put_page is called.
   *
   * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
   * or mmap_sem contention, and if waiting is needed to pin all pages,
   * *@nonblocking will be set to 0.
   *
   * In most cases, get_user_pages or get_user_pages_fast should be used
   * instead of __get_user_pages. __get_user_pages should be used only if
   * you need some special @gup_flags.
   */
  int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                       unsigned long start, int nr_pages, unsigned int gup_flags,
                       struct page **pages, struct vm_area_struct **vmas,
                       int *nonblocking)
  {
          int i;
          unsigned long vm_flags;
  
          if (nr_pages <= 0)
                  return 0;
  
          VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
  
          /* 
           * Require read or write permissions.
           * If FOLL_FORCE is set, we only require the "MAY" flags.
           */
          vm_flags  = (gup_flags & FOLL_WRITE) ?
                          (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
          vm_flags &= (gup_flags & FOLL_FORCE) ?
                          (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
  
          /*
           * If FOLL_FORCE and FOLL_NUMA are both set, handle_mm_fault
           * would be called on PROT_NONE ranges. We must never invoke
           * handle_mm_fault on PROT_NONE ranges or the NUMA hinting
           * page faults would unprotect the PROT_NONE ranges if
           * _PAGE_NUMA and _PAGE_PROTNONE are sharing the same pte/pmd
           * bitflag. So to avoid that, don't set FOLL_NUMA if
           * FOLL_FORCE is set.
           */
          if (!(gup_flags & FOLL_FORCE))
                  gup_flags |= FOLL_NUMA;
  
          i = 0;
  
          do {
                  struct vm_area_struct *vma;
  
                  vma = find_extend_vma(mm, start);
                  if (!vma && in_gate_area(mm, start)) {
                          unsigned long pg = start & PAGE_MASK;
                          pgd_t *pgd;
                          pud_t *pud;
                          pmd_t *pmd;
                          pte_t *pte;
  
                          /* user gate pages are read-only */
                          if (gup_flags & FOLL_WRITE)
                                  return i ? : -EFAULT;
                          if (pg > TASK_SIZE)
                                  pgd = pgd_offset_k(pg);
                          else
                                  pgd = pgd_offset_gate(mm, pg);
                          BUG_ON(pgd_none(*pgd));
                          pud = pud_offset(pgd, pg);
                          BUG_ON(pud_none(*pud));
                          pmd = pmd_offset(pud, pg);
                          if (pmd_none(*pmd))
                                  return i ? : -EFAULT;
                          VM_BUG_ON(pmd_trans_huge(*pmd));
                          pte = pte_offset_map(pmd, pg);
                          if (pte_none(*pte)) {
                                  pte_unmap(pte);
                                  return i ? : -EFAULT;
                          }
                          vma = get_gate_vma(mm);
                          if (pages) {
                                  struct page *page;
  
                                  page = vm_normal_page(vma, start, *pte);
                                  if (!page) {
                                          if (!(gup_flags & FOLL_DUMP) &&
                                               is_zero_pfn(pte_pfn(*pte)))
                                                  page = pte_page(*pte);
                                          else {
                                                  pte_unmap(pte);
                                                  return i ? : -EFAULT;
                                          }
                                  }
                                  pages[i] = page;
                                  get_page(page);
                          }
                          pte_unmap(pte);
                          goto next_page;
                  }
  
                  if (!vma ||
                      (vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
                      !(vm_flags & vma->vm_flags))
                          return i ? : -EFAULT;
  
                  if (is_vm_hugetlb_page(vma)) {
                          i = follow_hugetlb_page(mm, vma, pages, vmas,
                                          &start, &nr_pages, i, gup_flags);
                          continue;
                  }
  
                  do {
                          struct page *page;
                          unsigned int foll_flags = gup_flags;
  
                          /*
                           * If we have a pending SIGKILL, don't keep faulting
                           * pages and potentially allocating memory.
                           */
                          if (unlikely(fatal_signal_pending(current)))
                                  return i ? i : -ERESTARTSYS;
  
                          cond_resched();
                          while (!(page = follow_page(vma, start, foll_flags))) {
                                  int ret;
                                  unsigned int fault_flags = 0;
  
                                  /* For mlock, just skip the stack guard page. */
                                  if (foll_flags & FOLL_MLOCK) {
                                          if (stack_guard_page(vma, start))
                                                  goto next_page;
                                  }
                                  if (foll_flags & FOLL_WRITE)
                                          fault_flags |= FAULT_FLAG_WRITE;
                                  if (nonblocking)
                                          fault_flags |= FAULT_FLAG_ALLOW_RETRY;
                                  if (foll_flags & FOLL_NOWAIT)
                                          fault_flags |= (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT);
  
                                  ret = handle_mm_fault(mm, vma, start,
                                                          fault_flags);
  
                                  if (ret & VM_FAULT_ERROR) {
                                          if (ret & VM_FAULT_OOM)
                                                  return i ? i : -ENOMEM;
                                          if (ret & (VM_FAULT_HWPOISON |
                                                     VM_FAULT_HWPOISON_LARGE)) {
                                                  if (i)
                                                          return i;
                                                  else if (gup_flags & FOLL_HWPOISON)
                                                          return -EHWPOISON;
                                                  else
                                                          return -EFAULT;
                                          }
                                          if (ret & VM_FAULT_SIGBUS)
                                                  return i ? i : -EFAULT;
                                          BUG();
                                  }
  
                                  if (tsk) {
                                          if (ret & VM_FAULT_MAJOR)
                                                  tsk->maj_flt++;
                                          else
                                                  tsk->min_flt++;
                                  }
  
                                  if (ret & VM_FAULT_RETRY) {
                                          if (nonblocking)
                                                  *nonblocking = 0;
                                          return i;
                                  }
  
                                  /*
                                   * The VM_FAULT_WRITE bit tells us that
                                   * do_wp_page has broken COW when necessary,
                                   * even if maybe_mkwrite decided not to set
                                   * pte_write. We can thus safely do subsequent
                                   * page lookups as if they were reads. But only
                                   * do so when looping for pte_write is futile:
                                   * in some cases userspace may also be wanting
                                   * to write to the gotten user page, which a
                                   * read fault here might prevent (a readonly
                                   * page might get reCOWed by userspace write).
                                   */
                                  if ((ret & VM_FAULT_WRITE) &&
                                      !(vma->vm_flags & VM_WRITE))
                                          foll_flags &= ~FOLL_WRITE;
  
                                  cond_resched();
                          }
                          if (IS_ERR(page))
                                  return i ? i : PTR_ERR(page);
                          if (pages) {
                                  pages[i] = page;
  
                                  flush_anon_page(vma, page, start);
                                  flush_dcache_page(page);
                          }
  next_page:
                          if (vmas)
                                  vmas[i] = vma;
                          i++;
                          start += PAGE_SIZE;
                          nr_pages--;
                  } while (nr_pages && start < vma->vm_end);
          } while (nr_pages);
          return i;
  }
  EXPORT_SYMBOL(__get_user_pages);
  
  /*
   * fixup_user_fault() - manually resolve a user page fault
   * @tsk:        the task_struct to use for page fault accounting, or
   *              NULL if faults are not to be recorded.
   * @mm:         mm_struct of target mm
   * @address:    user address
   * @fault_flags:flags to pass down to handle_mm_fault()
   *
   * This is meant to be called in the specific scenario where for locking reasons
   * we try to access user memory in atomic context (within a pagefault_disable()
   * section), this returns -EFAULT, and we want to resolve the user fault before
   * trying again.
   *
   * Typically this is meant to be used by the futex code.
   *
   * The main difference with get_user_pages() is that this function will
   * unconditionally call handle_mm_fault() which will in turn perform all the
   * necessary SW fixup of the dirty and young bits in the PTE, while
   * handle_mm_fault() only guarantees to update these in the struct page.
   *
   * This is important for some architectures where those bits also gate the
   * access permission to the page because they are maintained in software.  On
   * such architectures, gup() will not be enough to make a subsequent access
   * succeed.
   *
   * This should be called with the mm_sem held for read.
   */
  int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
                       unsigned long address, unsigned int fault_flags)
  {
          struct vm_area_struct *vma;
          int ret;
  
          vma = find_extend_vma(mm, address);
          if (!vma || address < vma->vm_start)
                  return -EFAULT;
  
          ret = handle_mm_fault(mm, vma, address, fault_flags);
          if (ret & VM_FAULT_ERROR) {
                  if (ret & VM_FAULT_OOM)
                          return -ENOMEM;
                  if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
                          return -EHWPOISON;
                  if (ret & VM_FAULT_SIGBUS)
                          return -EFAULT;
                  BUG();
          }
          if (tsk) {
                  if (ret & VM_FAULT_MAJOR)
                          tsk->maj_flt++;
                  else
                          tsk->min_flt++;
          }
          return 0;
  }
  
  /*
   * get_user_pages() - pin user pages in memory
   * @tsk:        the task_struct to use for page fault accounting, or
   *              NULL if faults are not to be recorded.
   * @mm:         mm_struct of target mm
   * @start:      starting user address
   * @nr_pages:   number of pages from start to pin
   * @write:      whether pages will be written to by the caller
   * @force:      whether to force write access even if user mapping is
   *              readonly. This will result in the page being COWed even
   *              in MAP_SHARED mappings. You do not want this.
   * @pages:      array that receives pointers to the pages pinned.
   *              Should be at least nr_pages long. Or NULL, if caller
   *              only intends to ensure the pages are faulted in.
   * @vmas:       array of pointers to vmas corresponding to each page.
   *              Or NULL if the caller does not require them.
   *
   * Returns number of pages pinned. This may be fewer than the number
   * requested. If nr_pages is 0 or negative, returns 0. If no pages
   * were pinned, returns -errno. Each page returned must be released
   * with a put_page() call when it is finished with. vmas will only
   * remain valid while mmap_sem is held.
   *
   * Must be called with mmap_sem held for read or write.
   *
   * get_user_pages walks a process's page tables and takes a reference to
   * each struct page that each user address corresponds to at a given
   * instant. That is, it takes the page that would be accessed if a user
   * thread accesses the given user virtual address at that instant.
   *
   * This does not guarantee that the page exists in the user mappings when
   * get_user_pages returns, and there may even be a completely different
   * page there in some cases (eg. if mmapped pagecache has been invalidated
   * and subsequently re faulted). However it does guarantee that the page
   * won't be freed completely. And mostly callers simply care that the page
   * contains data that was valid *at some point in time*. Typically, an IO
   * or similar operation cannot guarantee anything stronger anyway because
   * locks can't be held over the syscall boundary.
   *
   * If write=0, the page must not be written to. If the page is written to,
   * set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
   * after the page is finished with, and before put_page is called.
   *
   * get_user_pages is typically used for fewer-copy IO operations, to get a
   * handle on the memory by some means other than accesses via the user virtual
   * addresses. The pages may be submitted for DMA to devices or accessed via
   * their kernel linear mapping (via the kmap APIs). Care should be taken to
   * use the correct cache flushing APIs.
   *
   * See also get_user_pages_fast, for performance critical applications.
   */
  int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                  unsigned long start, int nr_pages, int write, int force,
                  struct page **pages, struct vm_area_struct **vmas)
  {
          int flags = FOLL_TOUCH;
  
          if (pages)
                  flags |= FOLL_GET;
          if (write)
                  flags |= FOLL_WRITE;
          if (force)
                  flags |= FOLL_FORCE;
  
          return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas,
                                  NULL);
  }
  EXPORT_SYMBOL(get_user_pages);
  
  /**
   * get_dump_page() - pin user page in memory while writing it to core dump
   * @addr: user address
   *
   * Returns struct page pointer of user page pinned for dump,
   * to be freed afterwards by page_cache_release() or put_page().
   *
   * Returns NULL on any kind of failure - a hole must then be inserted into
   * the corefile, to preserve alignment with its headers; and also returns
   * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
   * allowing a hole to be left in the corefile to save diskspace.
   *
   * Called without mmap_sem, but after all other threads have been killed.
   */
  #ifdef CONFIG_ELF_CORE
  struct page *get_dump_page(unsigned long addr)
  {
          struct vm_area_struct *vma;
          struct page *page;
  
          if (__get_user_pages(current, current->mm, addr, 1,
                               FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
                               NULL) < 1)
                  return NULL;
          flush_cache_page(vma, addr, page_to_pfn(page));
          return page;
  }
  #endif /* CONFIG_ELF_CORE */
  
  pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
                          spinlock_t **ptl)
  {
          pgd_t * pgd = pgd_offset(mm, addr);
          pud_t * pud = pud_alloc(mm, pgd, addr);
          if (pud) {
                  pmd_t * pmd = pmd_alloc(mm, pud, addr);
                  if (pmd) {
                          VM_BUG_ON(pmd_trans_huge(*pmd));
                          return pte_alloc_map_lock(mm, pmd, addr, ptl);
                  }
          }
          return NULL;
  }
  
  /*
   * This is the old fallback for page remapping.
   *
   * For historical reasons, it only allows reserved pages. Only
   * old drivers should use this, and they needed to mark their
   * pages reserved for the old functions anyway.
   */
  static int insert_page(struct vm_area_struct *vma, unsigned long addr,
                          struct page *page, pgprot_t prot)
  {
          struct mm_struct *mm = vma->vm_mm;
          int retval;
          pte_t *pte;
          spinlock_t *ptl;
  
          retval = -EINVAL;
          if (PageAnon(page))
                  goto out;
          retval = -ENOMEM;
          flush_dcache_page(page);
          pte = get_locked_pte(mm, addr, &ptl);
          if (!pte)
                  goto out;
          retval = -EBUSY;
          if (!pte_none(*pte))
                  goto out_unlock;
  
          /* Ok, finally just insert the thing.. */
          get_page(page);
          inc_mm_counter_fast(mm, MM_FILEPAGES);
          page_add_file_rmap(page);
          set_pte_at(mm, addr, pte, mk_pte(page, prot));
  
          retval = 0;
          pte_unmap_unlock(pte, ptl);
          return retval;
  out_unlock:
          pte_unmap_unlock(pte, ptl);
  out:
          return retval;
  }
  
  /**
   * vm_insert_page - insert single page into user vma
   * @vma: user vma to map to
   * @addr: target user address of this page
   * @page: source kernel page
   *
   * This allows drivers to insert individual pages they've allocated
   * into a user vma.
   *
   * The page has to be a nice clean _individual_ kernel allocation.
   * If you allocate a compound page, you need to have marked it as
   * such (__GFP_COMP), or manually just split the page up yourself
   * (see split_page()).
   *
   * NOTE! Traditionally this was done with "remap_pfn_range()" which
   * took an arbitrary page protection parameter. This doesn't allow
   * that. Your vma protection will have to be set up correctly, which
   * means that if you want a shared writable mapping, you'd better
   * ask for a shared writable mapping!
   *
   * The page does not need to be reserved.
   *
   * Usually this function is called from f_op->mmap() handler
   * under mm->mmap_sem write-lock, so it can change vma->vm_flags.
   * Caller must set VM_MIXEDMAP on vma if it wants to call this
   * function from other places, for example from page-fault handler.
   */
  int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
                          struct page *page)
  {
          if (addr < vma->vm_start || addr >= vma->vm_end)
                  return -EFAULT;
          if (!page_count(page))
                  return -EINVAL;
          if (!(vma->vm_flags & VM_MIXEDMAP)) {
                  BUG_ON(down_read_trylock(&vma->vm_mm->mmap_sem));
                  BUG_ON(vma->vm_flags & VM_PFNMAP);
                  vma->vm_flags |= VM_MIXEDMAP;
          }
          return insert_page(vma, addr, page, vma->vm_page_prot);
  }
  EXPORT_SYMBOL(vm_insert_page);
  
  static int insert_pfn(struct vm_area_struct *vma, unsigned long addr,
                          unsigned long pfn, pgprot_t prot)
  {
          struct mm_struct *mm = vma->vm_mm;
          int retval;
          pte_t *pte, entry;
          spinlock_t *ptl;
  
          retval = -ENOMEM;
          pte = get_locked_pte(mm, addr, &ptl);
          if (!pte)
                  goto out;
          retval = -EBUSY;
          if (!pte_none(*pte))
                  goto out_unlock;
  
          /* Ok, finally just insert the thing.. */
          entry = pte_mkspecial(pfn_pte(pfn, prot));
          set_pte_at(mm, addr, pte, entry);
          update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */
  
          retval = 0;
  out_unlock:
          pte_unmap_unlock(pte, ptl);
  out:
          return retval;
  }
  
  /**
   * vm_insert_pfn - insert single pfn into user vma
   * @vma: user vma to map to
   * @addr: target user address of this page
   * @pfn: source kernel pfn
   *
   * Similar to vm_insert_page, this allows drivers to insert individual pages
   * they've allocated into a user vma. Same comments apply.
   *
   * This function should only be called from a vm_ops->fault handler, and
   * in that case the handler should return NULL.
   *
   * vma cannot be a COW mapping.
   *
   * As this is called only for pages that do not currently exist, we
   * do not need to flush old virtual caches or the TLB.
   */
  int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
                          unsigned long pfn)
  {
          int ret;
          pgprot_t pgprot = vma->vm_page_prot;
          /*
           * Technically, architectures with pte_special can avoid all these
           * restrictions (same for remap_pfn_range).  However we would like
           * consistency in testing and feature parity among all, so we should
           * try to keep these invariants in place for everybody.
           */
          BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
          BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
                                                  (VM_PFNMAP|VM_MIXEDMAP));
          BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
          BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
  
          if (addr < vma->vm_start || addr >= vma->vm_end)
                  return -EFAULT;
          if (track_pfn_insert(vma, &pgprot, pfn))
                  return -EINVAL;
  
          ret = insert_pfn(vma, addr, pfn, pgprot);
  
          return ret;
  }
  EXPORT_SYMBOL(vm_insert_pfn);
  
  int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
                          unsigned long pfn)
  {
          BUG_ON(!(vma->vm_flags & VM_MIXEDMAP));
  
          if (addr < vma->vm_start || addr >= vma->vm_end)
                  return -EFAULT;
  
          /*
           * If we don't have pte special, then we have to use the pfn_valid()
           * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must*
           * refcount the page if pfn_valid is true (hence insert_page rather
           * than insert_pfn).  If a zero_pfn were inserted into a VM_MIXEDMAP
           * without pte special, it would there be refcounted as a normal page.
           */
          if (!HAVE_PTE_SPECIAL && pfn_valid(pfn)) {
                  struct page *page;
  
                  page = pfn_to_page(pfn);
                  return insert_page(vma, addr, page, vma->vm_page_prot);
          }
          return insert_pfn(vma, addr, pfn, vma->vm_page_prot);
  }
  EXPORT_SYMBOL(vm_insert_mixed);
  
  /*
   * maps a range of physical memory into the requested pages. the old
   * mappings are removed. any references to nonexistent pages results
   * in null mappings (currently treated as "copy-on-access")
   */
  static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
                          unsigned long addr, unsigned long end,
                          unsigned long pfn, pgprot_t prot)
  {
          pte_t *pte;
          spinlock_t *ptl;
  
          pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
          if (!pte)
                  return -ENOMEM;
          arch_enter_lazy_mmu_mode();
          do {
                  BUG_ON(!pte_none(*pte));
                  set_pte_at(mm, addr, pte, pte_mkspecial(pfn_pte(pfn, prot)));
                  pfn++;
          } while (pte++, addr += PAGE_SIZE, addr != end);
          arch_leave_lazy_mmu_mode();
          pte_unmap_unlock(pte - 1, ptl);
          return 0;
  }
  
  static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud,
                          unsigned long addr, unsigned long end,
                          unsigned long pfn, pgprot_t prot)
  {
          pmd_t *pmd;
          unsigned long next;
  
          pfn -= addr >> PAGE_SHIFT;
          pmd = pmd_alloc(mm, pud, addr);
          if (!pmd)
                  return -ENOMEM;
          VM_BUG_ON(pmd_trans_huge(*pmd));
          do {
                  next = pmd_addr_end(addr, end);
                  if (remap_pte_range(mm, pmd, addr, next,
                                  pfn + (addr >> PAGE_SHIFT), prot))
                          return -ENOMEM;
          } while (pmd++, addr = next, addr != end);
          return 0;
  }
  
  static inline int remap_pud_range(struct mm_struct *mm, pgd_t *pgd,
                          unsigned long addr, unsigned long end,
                          unsigned long pfn, pgprot_t prot)
  {
          pud_t *pud;
          unsigned long next;
  
          pfn -= addr >> PAGE_SHIFT;
          pud = pud_alloc(mm, pgd, addr);
          if (!pud)
                  return -ENOMEM;
          do {
                  next = pud_addr_end(addr, end);
                  if (remap_pmd_range(mm, pud, addr, next,
                                  pfn + (addr >> PAGE_SHIFT), prot))
                          return -ENOMEM;
          } while (pud++, addr = next, addr != end);
          return 0;
  }
  
  /**
   * remap_pfn_range - remap kernel memory to userspace
   * @vma: user vma to map to
   * @addr: target user address to start at
   * @pfn: physical address of kernel memory
   * @size: size of map area
   * @prot: page protection flags for this mapping
   *
   *  Note: this is only safe if the mm semaphore is held when called.
   */
  int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
                      unsigned long pfn, unsigned long size, pgprot_t prot)
  {
          pgd_t *pgd;
          unsigned long next;
          unsigned long end = addr + PAGE_ALIGN(size);
          struct mm_struct *mm = vma->vm_mm;
          int err;
  
          /*
           * Physically remapped pages are special. Tell the
           * rest of the world about it:
           *   VM_IO tells people not to look at these pages
           *      (accesses can have side effects).
           *   VM_PFNMAP tells the core MM that the base pages are just
           *      raw PFN mappings, and do not have a "struct page" associated
           *      with them.
           *   VM_DONTEXPAND
           *      Disable vma merging and expanding with mremap().
           *   VM_DONTDUMP
           *      Omit vma from core dump, even when VM_IO turned off.
           *
           * There's a horrible special case to handle copy-on-write
           * behaviour that some programs depend on. We mark the "original"
           * un-COW'ed pages by matching them up with "vma->vm_pgoff".
           * See vm_normal_page() for details.
           */
          if (is_cow_mapping(vma->vm_flags)) {
                  if (addr != vma->vm_start || end != vma->vm_end)
                          return -EINVAL;
                  vma->vm_pgoff = pfn;
          }
  
          err = track_pfn_remap(vma, &prot, pfn, addr, PAGE_ALIGN(size));
          if (err)
                  return -EINVAL;
  
          vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
  
          BUG_ON(addr >= end);
          pfn -= addr >> PAGE_SHIFT;
          pgd = pgd_offset(mm, addr);
          flush_cache_range(vma, addr, end);
          do {
                  next = pgd_addr_end(addr, end);
                  err = remap_pud_range(mm, pgd, addr, next,
                                  pfn + (addr >> PAGE_SHIFT), prot);
                  if (err)
                          break;
          } while (pgd++, addr = next, addr != end);
  
          if (err)
                  untrack_pfn(vma, pfn, PAGE_ALIGN(size));
  
          return err;
  }
  EXPORT_SYMBOL(remap_pfn_range);
  
  static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
                                       unsigned long addr, unsigned long end,
                                       pte_fn_t fn, void *data)
  {
          pte_t *pte;
          int err;
          pgtable_t token;
          spinlock_t *uninitialized_var(ptl);
  
          pte = (mm == &init_mm) ?
                  pte_alloc_kernel(pmd, addr) :
                  pte_alloc_map_lock(mm, pmd, addr, &ptl);
          if (!pte)
                  return -ENOMEM;
  
          BUG_ON(pmd_huge(*pmd));
  
          arch_enter_lazy_mmu_mode();
  
          token = pmd_pgtable(*pmd);
  
          do {
                  err = fn(pte++, token, addr, data);
                  if (err)
                          break;
          } while (addr += PAGE_SIZE, addr != end);
  
          arch_leave_lazy_mmu_mode();
  
          if (mm != &init_mm)
                  pte_unmap_unlock(pte-1, ptl);
          return err;
  }
  
  static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
                                       unsigned long addr, unsigned long end,
                                       pte_fn_t fn, void *data)
  {
          pmd_t *pmd;
          unsigned long next;
          int err;
  
          BUG_ON(pud_huge(*pud));
  
          pmd = pmd_alloc(mm, pud, addr);
          if (!pmd)
                  return -ENOMEM;
          do {
                  next = pmd_addr_end(addr, end);
                  err = apply_to_pte_range(mm, pmd, addr, next, fn, data);
                  if (err)
                          break;
          } while (pmd++, addr = next, addr != end);
          return err;
  }
  
  static int apply_to_pud_range(struct mm_struct *mm, pgd_t *pgd,
                                       unsigned long addr, unsigned long end,
                                       pte_fn_t fn, void *data)
  {
          pud_t *pud;
          unsigned long next;
          int err;
  
          pud = pud_alloc(mm, pgd, addr);
          if (!pud)
                  return -ENOMEM;
          do {
                  next = pud_addr_end(addr, end);
                  err = apply_to_pmd_range(mm, pud, addr, next, fn, data);
                  if (err)
                          break;
          } while (pud++, addr = next, addr != end);
          return err;
  }
  
  /*
   * Scan a region of virtual memory, filling in page tables as necessary
   * and calling a provided function on each leaf page table.
   */
  int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
                          unsigned long size, pte_fn_t fn, void *data)
  {
          pgd_t *pgd;
          unsigned long next;
          unsigned long end = addr + size;
          int err;
  
          BUG_ON(addr >= end);
          pgd = pgd_offset(mm, addr);
          do {
                  next = pgd_addr_end(addr, end);
                  err = apply_to_pud_range(mm, pgd, addr, next, fn, data);
                  if (err)
                          break;
          } while (pgd++, addr = next, addr != end);
  
          return err;
  }
  EXPORT_SYMBOL_GPL(apply_to_page_range);
  
  /*
   * handle_pte_fault chooses page fault handler according to an entry
   * which was read non-atomically.  Before making any commitment, on
   * those architectures or configurations (e.g. i386 with PAE) which
   * might give a mix of unmatched parts, do_swap_page and do_nonlinear_fault
   * must check under lock before unmapping the pte and proceeding
   * (but do_wp_page is only called after already making such a check;
   * and do_anonymous_page can safely check later on).
   */
  static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
                                  pte_t *page_table, pte_t orig_pte)
  {
          int same = 1;
  #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
          if (sizeof(pte_t) > sizeof(unsigned long)) {
                  spinlock_t *ptl = pte_lockptr(mm, pmd);
                  spin_lock(ptl);
                  same = pte_same(*page_table, orig_pte);
                  spin_unlock(ptl);
          }
  #endif
          pte_unmap(page_table);
          return same;
  }
  
  static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
  {
          /*
           * If the source page was a PFN mapping, we don't have
           * a "struct page" for it. We do a best-effort copy by
           * just copying from the original user address. If that
           * fails, we just zero-fill it. Live with it.
           */
          if (unlikely(!src)) {
                  void *kaddr = kmap_atomic(dst);
                  void __user *uaddr = (void __user *)(va & PAGE_MASK);
  
                  /*
                   * This really shouldn't fail, because the page is there
                   * in the page tables. But it might just be unreadable,
                   * in which case we just give up and fill the result with
                   * zeroes.
                   */
                  if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
                          clear_page(kaddr);
                  kunmap_atomic(kaddr);
                  flush_dcache_page(dst);
          } else
                  copy_user_highpage(dst, src, va, vma);
  }
  
  /*
   * This routine handles present pages, when users try to write
   * to a shared page. It is done by copying the page to a new address
   * and decrementing the shared-page counter for the old page.
   *
   * Note that this routine assumes that the protection checks have been
   * done by the caller (the low-level page fault routine in most cases).
   * Thus we can safely just mark it writable once we've done any necessary
   * COW.
   *
   * We also mark the page dirty at this point even though the page will
   * change only once the write actually happens. This avoids a few races,
   * and potentially makes it more efficient.
   *
   * We enter with non-exclusive mmap_sem (to exclude vma changes,
   * but allow concurrent faults), with pte both mapped and locked.
   * We return with mmap_sem still held, but pte unmapped and unlocked.
   */
  static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
                  unsigned long address, pte_t *page_table, pmd_t *pmd,
                  spinlock_t *ptl, pte_t orig_pte)
          __releases(ptl)
  {
          struct page *old_page, *new_page = NULL;
          pte_t entry;
          int ret = 0;
          int page_mkwrite = 0;
          struct page *dirty_page = NULL;
          unsigned long mmun_start = 0;   /* For mmu_notifiers */
          unsigned long mmun_end = 0;     /* For mmu_notifiers */
  
          old_page = vm_normal_page(vma, address, orig_pte);
          if (!old_page) {
                  /*
                   * VM_MIXEDMAP !pfn_valid() case
                   *
                   * We should not cow pages in a shared writeable mapping.
                   * Just mark the pages writable as we can't do any dirty
                   * accounting on raw pfn maps.
                   */
                  if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
                                       (VM_WRITE|VM_SHARED))
                          goto reuse;
                  goto gotten;
          }
  
          /*
           * Take out anonymous pages first, anonymous shared vmas are
           * not dirty accountable.
           */
          if (PageAnon(old_page) && !PageKsm(old_page)) {
                  if (!trylock_page(old_page)) {
                          page_cache_get(old_page);
                          pte_unmap_unlock(page_table, ptl);
                          lock_page(old_page);
                          page_table = pte_offset_map_lock(mm, pmd, address,
                                                           &ptl);
                          if (!pte_same(*page_table, orig_pte)) {
                                  unlock_page(old_page);
                                  goto unlock;
                          }
                          page_cache_release(old_page);
                  }
                  if (reuse_swap_page(old_page)) {
                          /*
                           * The page is all ours.  Move it to our anon_vma so
                           * the rmap code will not search our parent or siblings.
                           * Protected against the rmap code by the page lock.
                           */
                          page_move_anon_rmap(old_page, vma, address);
                          unlock_page(old_page);
                          goto reuse;
                  }
                  unlock_page(old_page);
          } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
                                          (VM_WRITE|VM_SHARED))) {
                  /*
                   * Only catch write-faults on shared writable pages,
                   * read-only shared pages can get COWed by
                   * get_user_pages(.write=1, .force=1).
                   */
                  if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
                          struct vm_fault vmf;
                          int tmp;
  
                          vmf.virtual_address = (void __user *)(address &
                                                                  PAGE_MASK);
                          vmf.pgoff = old_page->index;
                          vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
                          vmf.page = old_page;
  
                          /*
                           * Notify the address space that the page is about to
                           * become writable so that it can prohibit this or wait
                           * for the page to get into an appropriate state.
                           *
                           * We do this without the lock held, so that it can
                           * sleep if it needs to.
                           */
                          page_cache_get(old_page);
                          pte_unmap_unlock(page_table, ptl);
  
                          tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
                          if (unlikely(tmp &
                                          (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
                                  ret = tmp;
                                  goto unwritable_page;
                          }
                          if (unlikely(!(tmp & VM_FAULT_LOCKED))) {
                                  lock_page(old_page);
                                  if (!old_page->mapping) {
                                          ret = 0; /* retry the fault */
                                          unlock_page(old_page);
                                          goto unwritable_page;
                                  }
                          } else
                                  VM_BUG_ON(!PageLocked(old_page));
  
                          /*
                           * Since we dropped the lock we need to revalidate
                           * the PTE as someone else may have changed it.  If
                           * they did, we just return, as we can count on the
                           * MMU to tell us if they didn't also make it writable.
                           */
                          page_table = pte_offset_map_lock(mm, pmd, address,
                                                           &ptl);
                          if (!pte_same(*page_table, orig_pte)) {
                                  unlock_page(old_page);
                                  goto unlock;
                          }
  
                          page_mkwrite = 1;
                  }
                  dirty_page = old_page;
                  get_page(dirty_page);
  
  reuse:
                  flush_cache_page(vma, address, pte_pfn(orig_pte));
                  entry = pte_mkyoung(orig_pte);
                  entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                  if (ptep_set_access_flags(vma, address, page_table, entry,1))
                          update_mmu_cache(vma, address, page_table);
                  pte_unmap_unlock(page_table, ptl);
                  ret |= VM_FAULT_WRITE;
  
                  if (!dirty_page)
                          return ret;
  
                  /*
                   * Yes, Virginia, this is actually required to prevent a race
                   * with clear_page_dirty_for_io() from clearing the page dirty
                   * bit after it clear all dirty ptes, but before a racing
                   * do_wp_page installs a dirty pte.
                   *
                   * __do_fault is protected similarly.
                   */
                  if (!page_mkwrite) {
                          wait_on_page_locked(dirty_page);
                          set_page_dirty_balance(dirty_page, page_mkwrite);
                          /* file_update_time outside page_lock */
                          if (vma->vm_file)
                                  file_update_time(vma->vm_file);
                  }
                  put_page(dirty_page);
                  if (page_mkwrite) {
                          struct address_space *mapping = dirty_page->mapping;
  
                          set_page_dirty(dirty_page);
                          unlock_page(dirty_page);
                          page_cache_release(dirty_page);
                          if (mapping)    {
                                  /*
                                   * Some device drivers do not set page.mapping
                                   * but still dirty their pages
                                   */
                                  balance_dirty_pages_ratelimited(mapping);
                          }
                  }
  
                  return ret;
          }
  
          /*
           * Ok, we need to copy. Oh, well..
           */
          page_cache_get(old_page);
  gotten:
          pte_unmap_unlock(page_table, ptl);
  
          if (unlikely(anon_vma_prepare(vma)))
                  goto oom;
  
          if (is_zero_pfn(pte_pfn(orig_pte))) {
                  new_page = alloc_zeroed_user_highpage_movable(vma, address);
                  if (!new_page)
                          goto oom;
          } else {
                  new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
                  if (!new_page)
                          goto oom;
                  cow_user_page(new_page, old_page, address, vma);
          }
          __SetPageUptodate(new_page);
  
          if (mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))
                  goto oom_free_new;
  
          mmun_start  = address & PAGE_MASK;
          mmun_end    = mmun_start + PAGE_SIZE;
          mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
  
          /*
           * Re-check the pte - we dropped the lock
           */
          page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
          if (likely(pte_same(*page_table, orig_pte))) {
                  if (old_page) {
                          if (!PageAnon(old_page)) {
                                  dec_mm_counter_fast(mm, MM_FILEPAGES);
                                  inc_mm_counter_fast(mm, MM_ANONPAGES);
                          }
                  } else
                          inc_mm_counter_fast(mm, MM_ANONPAGES);
                  flush_cache_page(vma, address, pte_pfn(orig_pte));
                  entry = mk_pte(new_page, vma->vm_page_prot);
                  entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                  /*
                   * Clear the pte entry and flush it first, before updating the
                   * pte with the new entry. This will avoid a race condition
                   * seen in the presence of one thread doing SMC and another
                   * thread doing COW.
                   */
                  ptep_clear_flush(vma, address, page_table);
                  page_add_new_anon_rmap(new_page, vma, address);
                  /*
                   * We call the notify macro here because, when using secondary
                   * mmu page tables (such as kvm shadow page tables), we want the
                   * new page to be mapped directly into the secondary page table.
                   */
                  set_pte_at_notify(mm, address, page_table, entry);
                  update_mmu_cache(vma, address, page_table);
                  if (old_page) {
                          /*
                           * Only after switching the pte to the new page may
                           * we remove the mapcount here. Otherwise another
                           * process may come and find the rmap count decremented
                           * before the pte is switched to the new page, and
                           * "reuse" the old page writing into it while our pte
                           * here still points into it and can be read by other
                           * threads.
                           *
                           * The critical issue is to order this
                           * page_remove_rmap with the ptp_clear_flush above.
                           * Those stores are ordered by (if nothing else,)
                           * the barrier present in the atomic_add_negative
                           * in page_remove_rmap.
                           *
                           * Then the TLB flush in ptep_clear_flush ensures that
                           * no process can access the old page before the
                           * decremented mapcount is visible. And the old page
                           * cannot be reused until after the decremented
                           * mapcount is visible. So transitively, TLBs to
                           * old page will be flushed before it can be reused.
                           */
                          page_remove_rmap(old_page);
                  }
  
                  /* Free the old page.. */
                  new_page = old_page;
                  ret |= VM_FAULT_WRITE;
          } else
                  mem_cgroup_uncharge_page(new_page);
  
          if (new_page)
                  page_cache_release(new_page);
  unlock:
          pte_unmap_unlock(page_table, ptl);
          if (mmun_end > mmun_start)
                  mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
          if (old_page) {
                  /*
                   * Don't let another task, with possibly unlocked vma,
                   * keep the mlocked page.
                   */
                  if ((ret & VM_FAULT_WRITE) && (vma->vm_flags & VM_LOCKED)) {
                          lock_page(old_page);    /* LRU manipulation */
                          munlock_vma_page(old_page);
                          unlock_page(old_page);
                  }
                  page_cache_release(old_page);
          }
          return ret;
  oom_free_new:
          page_cache_release(new_page);
  oom:
          if (old_page)
                  page_cache_release(old_page);
          return VM_FAULT_OOM;
  
  unwritable_page:
          page_cache_release(old_page);
          return ret;
  }
  
  static void unmap_mapping_range_vma(struct vm_area_struct *vma,
                  unsigned long start_addr, unsigned long end_addr,
                  struct zap_details *details)
  {
          zap_page_range_single(vma, start_addr, end_addr - start_addr, details);
  }
  
  static inline void unmap_mapping_range_tree(struct rb_root *root,
                                              struct zap_details *details)
  {
          struct vm_area_struct *vma;
          pgoff_t vba, vea, zba, zea;
  
          vma_interval_tree_foreach(vma, root,
                          details->first_index, details->last_index) {
  
                  vba = vma->vm_pgoff;
                  vea = vba + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) - 1;
                  /* Assume for now that PAGE_CACHE_SHIFT == PAGE_SHIFT */
                  zba = details->first_index;
                  if (zba < vba)
                          zba = vba;
                  zea = details->last_index;
                  if (zea > vea)
                          zea = vea;
  
                  unmap_mapping_range_vma(vma,
                          ((zba - vba) << PAGE_SHIFT) + vma->vm_start,
                          ((zea - vba + 1) << PAGE_SHIFT) + vma->vm_start,
                                  details);
          }
  }
  
  static inline void unmap_mapping_range_list(struct list_head *head,
                                              struct zap_details *details)
  {
          struct vm_area_struct *vma;
  
          /*
           * In nonlinear VMAs there is no correspondence between virtual address
           * offset and file offset.  So we must perform an exhaustive search
           * across *all* the pages in each nonlinear VMA, not just the pages
           * whose virtual address lies outside the file truncation point.
           */
          list_for_each_entry(vma, head, shared.nonlinear) {
                  details->nonlinear_vma = vma;
                  unmap_mapping_range_vma(vma, vma->vm_start, vma->vm_end, details);
          }
  }
  
  /**
   * unmap_mapping_range - unmap the portion of all mmaps in the specified address_space corresponding to the specified page range in the underlying file.
   * @mapping: the address space containing mmaps to be unmapped.
   * @holebegin: byte in first page to unmap, relative to the start of
   * the underlying file.  This will be rounded down to a PAGE_SIZE
   * boundary.  Note that this is different from truncate_pagecache(), which
   * must keep the partial page.  In contrast, we must get rid of
   * partial pages.
   * @holelen: size of prospective hole in bytes.  This will be rounded
   * up to a PAGE_SIZE boundary.  A holelen of zero truncates to the
   * end of the file.
   * @even_cows: 1 when truncating a file, unmap even private COWed pages;
   * but 0 when invalidating pagecache, don't throw away private data.
   */
  void unmap_mapping_range(struct address_space *mapping,
                  loff_t const holebegin, loff_t const holelen, int even_cows)
  {
          struct zap_details details;
          pgoff_t hba = holebegin >> PAGE_SHIFT;
          pgoff_t hlen = (holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
  
          /* Check for overflow. */
          if (sizeof(holelen) > sizeof(hlen)) {
                  long long holeend =
                          (holebegin + holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
                  if (holeend & ~(long long)ULONG_MAX)
                          hlen = ULONG_MAX - hba + 1;
          }
  
          details.check_mapping = even_cows? NULL: mapping;
          details.nonlinear_vma = NULL;
          details.first_index = hba;
          details.last_index = hba + hlen - 1;
          if (details.last_index < details.first_index)
                  details.last_index = ULONG_MAX;
  
  
          mutex_lock(&mapping->i_mmap_mutex);
          if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap)))
                  unmap_mapping_range_tree(&mapping->i_mmap, &details);
          if (unlikely(!list_empty(&mapping->i_mmap_nonlinear)))
                  unmap_mapping_range_list(&mapping->i_mmap_nonlinear, &details);
          mutex_unlock(&mapping->i_mmap_mutex);
  }
  EXPORT_SYMBOL(unmap_mapping_range);
  
  /*
   * We enter with non-exclusive mmap_sem (to exclude vma changes,
   * but allow concurrent faults), and pte mapped but not yet locked.
   * We return with mmap_sem still held, but pte unmapped and unlocked.
   */
  static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
                  unsigned long address, pte_t *page_table, pmd_t *pmd,
                  unsigned int flags, pte_t orig_pte)
  {
          spinlock_t *ptl;
          struct page *page, *swapcache = NULL;
          swp_entry_t entry;
          pte_t pte;
          int locked;
          struct mem_cgroup *ptr;
          int exclusive = 0;
          int ret = 0;
  
          if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
                  goto out;
  
          entry = pte_to_swp_entry(orig_pte);
          if (unlikely(non_swap_entry(entry))) {
                  if (is_migration_entry(entry)) {
                          migration_entry_wait(mm, pmd, address);
                  } else if (is_hwpoison_entry(entry)) {
                          ret = VM_FAULT_HWPOISON;
                  } else {
                          print_bad_pte(vma, address, orig_pte, NULL);
                          ret = VM_FAULT_SIGBUS;
                  }
                  goto out;
          }
          delayacct_set_flag(DELAYACCT_PF_SWAPIN);
          page = lookup_swap_cache(entry);
          if (!page) {
                  page = swapin_readahead(entry,
                                          GFP_HIGHUSER_MOVABLE, vma, address);
                  if (!page) {
                          /*
                           * Back out if somebody else faulted in this pte
                           * while we released the pte lock.
                           */
                          page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
                          if (likely(pte_same(*page_table, orig_pte)))
                                  ret = VM_FAULT_OOM;
                          delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
                          goto unlock;
                  }
  
                  /* Had to read the page from swap area: Major fault */
                  ret = VM_FAULT_MAJOR;
                  count_vm_event(PGMAJFAULT);
                  mem_cgroup_count_vm_event(mm, PGMAJFAULT);
          } else if (PageHWPoison(page)) {
                  /*
                   * hwpoisoned dirty swapcache pages are kept for killing
                   * owner processes (which may be unknown at hwpoison time)
                   */
                  ret = VM_FAULT_HWPOISON;
                  delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
                  goto out_release;
          }
  
          locked = lock_page_or_retry(page, mm, flags);
  
          delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
          if (!locked) {
                  ret |= VM_FAULT_RETRY;
                  goto out_release;
          }
  
          /*
           * Make sure try_to_free_swap or reuse_swap_page or swapoff did not
           * release the swapcache from under us.  The page pin, and pte_same
           * test below, are not enough to exclude that.  Even if it is still
           * swapcache, we need to check that the page's swap has not changed.
           */
          if (unlikely(!PageSwapCache(page) || page_private(page) != entry.val))
                  goto out_page;
  
          if (ksm_might_need_to_copy(page, vma, address)) {
                  swapcache = page;
                  page = ksm_does_need_to_copy(page, vma, address);
  
                  if (unlikely(!page)) {
                          ret = VM_FAULT_OOM;
                          page = swapcache;
                          swapcache = NULL;
                          goto out_page;
                  }
          }
  
          if (mem_cgroup_try_charge_swapin(mm, page, GFP_KERNEL, &ptr)) {
                  ret = VM_FAULT_OOM;
                  goto out_page;
          }
  
          /*
           * Back out if somebody else already faulted in this pte.
           */
          page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
          if (unlikely(!pte_same(*page_table, orig_pte)))
                  goto out_nomap;
  
          if (unlikely(!PageUptodate(page))) {
                  ret = VM_FAULT_SIGBUS;
                  goto out_nomap;
          }
  
          /*
           * The page isn't present yet, go ahead with the fault.
           *
           * Be careful about the sequence of operations here.
           * To get its accounting right, reuse_swap_page() must be called
           * while the page is counted on swap but not yet in mapcount i.e.
           * before page_add_anon_rmap() and swap_free(); try_to_free_swap()
           * must be called after the swap_free(), or it will never succeed.
           * Because delete_from_swap_page() may be called by reuse_swap_page(),
           * mem_cgroup_commit_charge_swapin() may not be able to find swp_entry
           * in page->private. In this case, a record in swap_cgroup  is silently
           * discarded at swap_free().
           */
  
          inc_mm_counter_fast(mm, MM_ANONPAGES);
          dec_mm_counter_fast(mm, MM_SWAPENTS);
          pte = mk_pte(page, vma->vm_page_prot);
          if ((flags & FAULT_FLAG_WRITE) && reuse_swap_page(page)) {
                  pte = maybe_mkwrite(pte_mkdirty(pte), vma);
                  flags &= ~FAULT_FLAG_WRITE;
                  ret |= VM_FAULT_WRITE;
                  exclusive = 1;
          }
          flush_icache_page(vma, page);
          set_pte_at(mm, address, page_table, pte);
          do_page_add_anon_rmap(page, vma, address, exclusive);
          /* It's better to call commit-charge after rmap is established */
          mem_cgroup_commit_charge_swapin(page, ptr);
  
          swap_free(entry);
          if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
                  try_to_free_swap(page);
          unlock_page(page);
          if (swapcache) {
                  /*
                   * Hold the lock to avoid the swap entry to be reused
                   * until we take the PT lock for the pte_same() check
                   * (to avoid false positives from pte_same). For
                   * further safety release the lock after the swap_free
                   * so that the swap count won't change under a
                   * parallel locked swapcache.
                   */
                  unlock_page(swapcache);
                  page_cache_release(swapcache);
          }
  
          if (flags & FAULT_FLAG_WRITE) {
                  ret |= do_wp_page(mm, vma, address, page_table, pmd, ptl, pte);
                  if (ret & VM_FAULT_ERROR)
                          ret &= VM_FAULT_ERROR;
                  goto out;
          }
  
          /* No need to invalidate - it was non-present before */
          update_mmu_cache(vma, address, page_table);
  unlock:
          pte_unmap_unlock(page_table, ptl);
  out:
          return ret;
  out_nomap:
          mem_cgroup_cancel_charge_swapin(ptr);
          pte_unmap_unlock(page_table, ptl);
  out_page:
          unlock_page(page);
  out_release:
          page_cache_release(page);
          if (swapcache) {
                  unlock_page(swapcache);
                  page_cache_release(swapcache);
          }
          return ret;
  }
  
  /*
   * This is like a special single-page "expand_{down|up}wards()",
   * except we must first make sure that 'address{-|+}PAGE_SIZE'
   * doesn't hit another vma.
   */
  static inline int check_stack_guard_page(struct vm_area_struct *vma, unsigned long address)
  {
          address &= PAGE_MASK;
          if ((vma->vm_flags & VM_GROWSDOWN) && address == vma->vm_start) {
                  struct vm_area_struct *prev = vma->vm_prev;
  
                  /*
                   * Is there a mapping abutting this one below?
                   *
                   * That's only ok if it's the same stack mapping
                   * that has gotten split..
                   */
                  if (prev && prev->vm_end == address)
                          return prev->vm_flags & VM_GROWSDOWN ? 0 : -ENOMEM;
  
                  expand_downwards(vma, address - PAGE_SIZE);
          }
          if ((vma->vm_flags & VM_GROWSUP) && address + PAGE_SIZE == vma->vm_end) {
                  struct vm_area_struct *next = vma->vm_next;
  
                  /* As VM_GROWSDOWN but s/below/above/ */
                  if (next && next->vm_start == address + PAGE_SIZE)
                          return next->vm_flags & VM_GROWSUP ? 0 : -ENOMEM;
  
                  expand_upwards(vma, address + PAGE_SIZE);
          }
          return 0;
  }
  
  /*
   * We enter with non-exclusive mmap_sem (to exclude vma changes,
   * but allow concurrent faults), and pte mapped but not yet locked.
   * We return with mmap_sem still held, but pte unmapped and unlocked.
   */
  static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
                  unsigned long address, pte_t *page_table, pmd_t *pmd,
                  unsigned int flags)
  {
          struct page *page;
          spinlock_t *ptl;
          pte_t entry;
  
          pte_unmap(page_table);
  
          /* Check if we need to add a guard page to the stack */
          if (check_stack_guard_page(vma, address) < 0)
                  return VM_FAULT_SIGBUS;
  
          /* Use the zero-page for reads */
          if (!(flags & FAULT_FLAG_WRITE)) {
                  entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
                                                  vma->vm_page_prot));
                  page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
                  if (!pte_none(*page_table))
                          goto unlock;
                  goto setpte;
          }
  
          /* Allocate our own private page. */
          if (unlikely(anon_vma_prepare(vma)))
                  goto oom;
          page = alloc_zeroed_user_highpage_movable(vma, address);
          if (!page)
                  goto oom;
          __SetPageUptodate(page);
  
          if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))
                  goto oom_free_page;
  
          entry = mk_pte(page, vma->vm_page_prot);
          if (vma->vm_flags & VM_WRITE)
                  entry = pte_mkwrite(pte_mkdirty(entry));
  
          page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
          if (!pte_none(*page_table))
                  goto release;
  
          inc_mm_counter_fast(mm, MM_ANONPAGES);
          page_add_new_anon_rmap(page, vma, address);
  setpte:
          set_pte_at(mm, address, page_table, entry);
  
          /* No need to invalidate - it was non-present before */
          update_mmu_cache(vma, address, page_table);
  unlock:
          pte_unmap_unlock(page_table, ptl);
          return 0;
  release:
          mem_cgroup_uncharge_page(page);
          page_cache_release(page);
          goto unlock;
  oom_free_page:
          page_cache_release(page);
  oom:
          return VM_FAULT_OOM;
  }
  
  /*
   * __do_fault() tries to create a new page mapping. It aggressively
   * tries to share with existing pages, but makes a separate copy if
   * the FAULT_FLAG_WRITE is set in the flags parameter in order to avoid
   * the next page fault.
   *
   * As this is called only for pages that do not currently exist, we
   * do not need to flush old virtual caches or the TLB.
   *
   * We enter with non-exclusive mmap_sem (to exclude vma changes,
   * but allow concurrent faults), and pte neither mapped nor locked.
   * We return with mmap_sem still held, but pte unmapped and unlocked.
   */
  static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                  unsigned long address, pmd_t *pmd,
                  pgoff_t pgoff, unsigned int flags, pte_t orig_pte)
  {
          pte_t *page_table;
          spinlock_t *ptl;
          struct page *page;
          struct page *cow_page;
          pte_t entry;
          int anon = 0;
          struct page *dirty_page = NULL;
          struct vm_fault vmf;
          int ret;
          int page_mkwrite = 0;
  
          /*
           * If we do COW later, allocate page befor taking lock_page()
           * on the file cache page. This will reduce lock holding time.
           */
          if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
  
                  if (unlikely(anon_vma_prepare(vma)))
                          return VM_FAULT_OOM;
  
                  cow_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
                  if (!cow_page)
                          return VM_FAULT_OOM;
  
                  if (mem_cgroup_newpage_charge(cow_page, mm, GFP_KERNEL)) {
                          page_cache_release(cow_page);
                          return VM_FAULT_OOM;
                  }
          } else
                  cow_page = NULL;
  
          vmf.virtual_address = (void __user *)(address & PAGE_MASK);
          vmf.pgoff = pgoff;
          vmf.flags = flags;
          vmf.page = NULL;
  
          ret = vma->vm_ops->fault(vma, &vmf);
          if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
                              VM_FAULT_RETRY)))
                  goto uncharge_out;
  
          if (unlikely(PageHWPoison(vmf.page))) {
                  if (ret & VM_FAULT_LOCKED)
                          unlock_page(vmf.page);
                  ret = VM_FAULT_HWPOISON;
                  goto uncharge_out;
          }
  
          /*
           * For consistency in subsequent calls, make the faulted page always
           * locked.
           */
          if (unlikely(!(ret & VM_FAULT_LOCKED)))
                  lock_page(vmf.page);
          else
                  VM_BUG_ON(!PageLocked(vmf.page));
  
          /*
           * Should we do an early C-O-W break?
           */
          page = vmf.page;
          if (flags & FAULT_FLAG_WRITE) {
                  if (!(vma->vm_flags & VM_SHARED)) {
                          page = cow_page;
                          anon = 1;
                          copy_user_highpage(page, vmf.page, address, vma);
                          __SetPageUptodate(page);
                  } else {
                          /*
                           * If the page will be shareable, see if the backing
                           * address space wants to know that the page is about
                           * to become writable
                           */
                          if (vma->vm_ops->page_mkwrite) {
                                  int tmp;
  
                                  unlock_page(page);
                                  vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
                                  tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
                                  if (unlikely(tmp &
                                            (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
                                          ret = tmp;
                                          goto unwritable_page;
                                  }
                                  if (unlikely(!(tmp & VM_FAULT_LOCKED))) {
                                          lock_page(page);
                                          if (!page->mapping) {
                                                  ret = 0; /* retry the fault */
                                                  unlock_page(page);
                                                  goto unwritable_page;
                                          }
                                  } else
                                          VM_BUG_ON(!PageLocked(page));
                                  page_mkwrite = 1;
                          }
                  }
  
          }
  
          page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
  
          /*
           * This silly early PAGE_DIRTY setting removes a race
           * due to the bad i386 page protection. But it's valid
           * for other architectures too.
           *
           * Note that if FAULT_FLAG_WRITE is set, we either now have
           * an exclusive copy of the page, or this is a shared mapping,
           * so we can make it writable and dirty to avoid having to
           * handle that later.
           */
          /* Only go through if we didn't race with anybody else... */
          if (likely(pte_same(*page_table, orig_pte))) {
                  flush_icache_page(vma, page);
                  entry = mk_pte(page, vma->vm_page_prot);
                  if (flags & FAULT_FLAG_WRITE)
                          entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                  if (anon) {
                          inc_mm_counter_fast(mm, MM_ANONPAGES);
                          page_add_new_anon_rmap(page, vma, address);
                  } else {
                          inc_mm_counter_fast(mm, MM_FILEPAGES);
                          page_add_file_rmap(page);
                          if (flags & FAULT_FLAG_WRITE) {
                                  dirty_page = page;
                                  get_page(dirty_page);
                          }
                  }
                  set_pte_at(mm, address, page_table, entry);
  
                  /* no need to invalidate: a not-present page won't be cached */
                  update_mmu_cache(vma, address, page_table);
          } else {
                  if (cow_page)
                          mem_cgroup_uncharge_page(cow_page);
                  if (anon)
                          page_cache_release(page);
                  else
                          anon = 1; /* no anon but release faulted_page */
          }
  
          pte_unmap_unlock(page_table, ptl);
  
          if (dirty_page) {
                  struct address_space *mapping = page->mapping;
                  int dirtied = 0;
  
                  if (set_page_dirty(dirty_page))
                          dirtied = 1;
                  unlock_page(dirty_page);
                  put_page(dirty_page);
                  if ((dirtied || page_mkwrite) && mapping) {
                          /*
                           * Some device drivers do not set page.mapping but still
                           * dirty their pages
                           */
                          balance_dirty_pages_ratelimited(mapping);
                  }
  
                  /* file_update_time outside page_lock */
                  if (vma->vm_file && !page_mkwrite)
                          file_update_time(vma->vm_file);
          } else {
                  unlock_page(vmf.page);
                  if (anon)
                          page_cache_release(vmf.page);
          }
  
          return ret;
  
  unwritable_page:
          page_cache_release(page);
          return ret;
  uncharge_out:
          /* fs's fault handler get error */
          if (cow_page) {
                  mem_cgroup_uncharge_page(cow_page);
                  page_cache_release(cow_page);
          }
          return ret;
  }
  
  static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                  unsigned long address, pte_t *page_table, pmd_t *pmd,
                  unsigned int flags, pte_t orig_pte)
  {
          pgoff_t pgoff = (((address & PAGE_MASK)
                          - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  
          pte_unmap(page_table);
          return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
  }
  
  /*
   * Fault of a previously existing named mapping. Repopulate the pte
   * from the encoded file_pte if possible. This enables swappable
   * nonlinear vmas.
   *
   * We enter with non-exclusive mmap_sem (to exclude vma changes,
   * but allow concurrent faults), and pte mapped but not yet locked.
   * We return with mmap_sem still held, but pte unmapped and unlocked.
   */
  static int do_nonlinear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                  unsigned long address, pte_t *page_table, pmd_t *pmd,
                  unsigned int flags, pte_t orig_pte)
  {
          pgoff_t pgoff;
  
          flags |= FAULT_FLAG_NONLINEAR;
  
          if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
                  return 0;
  
          if (unlikely(!(vma->vm_flags & VM_NONLINEAR))) {
                  /*
                   * Page table corrupted: show pte and kill process.
                   */
                  print_bad_pte(vma, address, orig_pte, NULL);
                  return VM_FAULT_SIGBUS;
          }
  
          pgoff = pte_to_pgoff(orig_pte);
          return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
  }
  
  int numa_migrate_prep(struct page *page, struct vm_area_struct *vma,
                                  unsigned long addr, int current_nid)
  {
          get_page(page);
  
          count_vm_numa_event(NUMA_HINT_FAULTS);
          if (current_nid == numa_node_id())
                  count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
  
          return mpol_misplaced(page, vma, addr);
  }
  
  int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
                     unsigned long addr, pte_t pte, pte_t *ptep, pmd_t *pmd)
  {
          struct page *page = NULL;
          spinlock_t *ptl;
          int current_nid = -1;
          int target_nid;
          bool migrated = false;
  
          /*
          * The "pte" at this point cannot be used safely without
          * validation through pte_unmap_same(). It's of NUMA type but
          * the pfn may be screwed if the read is non atomic.
          *
          * ptep_modify_prot_start is not called as this is clearing
          * the _PAGE_NUMA bit and it is not really expected that there
          * would be concurrent hardware modifications to the PTE.
          */
          ptl = pte_lockptr(mm, pmd);
          spin_lock(ptl);
          if (unlikely(!pte_same(*ptep, pte))) {
                  pte_unmap_unlock(ptep, ptl);
                  goto out;
          }
  
          pte = pte_mknonnuma(pte);
          set_pte_at(mm, addr, ptep, pte);
          update_mmu_cache(vma, addr, ptep);
  
          page = vm_normal_page(vma, addr, pte);
          if (!page) {
                  pte_unmap_unlock(ptep, ptl);
                  return 0;
          }
  
          current_nid = page_to_nid(page);
          target_nid = numa_migrate_prep(page, vma, addr, current_nid);
          pte_unmap_unlock(ptep, ptl);
          if (target_nid == -1) {
                  /*
                   * Account for the fault against the current node if it not
                   * being replaced regardless of where the page is located.
                   */
                  current_nid = numa_node_id();
                  put_page(page);
                  goto out;
          }
  
          /* Migrate to the requested node */
          migrated = migrate_misplaced_page(page, target_nid);
          if (migrated)
                  current_nid = target_nid;
  
  out:
          if (current_nid != -1)
                  task_numa_fault(current_nid, 1, migrated);
          return 0;
  }
  
  /* NUMA hinting page fault entry point for regular pmds */
  #ifdef CONFIG_NUMA_BALANCING
  static int do_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
                       unsigned long addr, pmd_t *pmdp)
  {
          pmd_t pmd;
          pte_t *pte, *orig_pte;
          unsigned long _addr = addr & PMD_MASK;
          unsigned long offset;
          spinlock_t *ptl;
          bool numa = false;
          int local_nid = numa_node_id();
  
          spin_lock(&mm->page_table_lock);
          pmd = *pmdp;
          if (pmd_numa(pmd)) {
                  set_pmd_at(mm, _addr, pmdp, pmd_mknonnuma(pmd));
                  numa = true;
          }
          spin_unlock(&mm->page_table_lock);
  
          if (!numa)
                  return 0;
  
          /* we're in a page fault so some vma must be in the range */
          BUG_ON(!vma);
          BUG_ON(vma->vm_start >= _addr + PMD_SIZE);
          offset = max(_addr, vma->vm_start) & ~PMD_MASK;
          VM_BUG_ON(offset >= PMD_SIZE);
          orig_pte = pte = pte_offset_map_lock(mm, pmdp, _addr, &ptl);
          pte += offset >> PAGE_SHIFT;
          for (addr = _addr + offset; addr < _addr + PMD_SIZE; pte++, addr += PAGE_SIZE) {
                  pte_t pteval = *pte;
                  struct page *page;
                  int curr_nid = local_nid;
                  int target_nid;
                  bool migrated;
                  if (!pte_present(pteval))
                          continue;
                  if (!pte_numa(pteval))
                          continue;
                  if (addr >= vma->vm_end) {
                          vma = find_vma(mm, addr);
                          /* there's a pte present so there must be a vma */
                          BUG_ON(!vma);
                          BUG_ON(addr < vma->vm_start);
                  }
                  if (pte_numa(pteval)) {
                          pteval = pte_mknonnuma(pteval);
                          set_pte_at(mm, addr, pte, pteval);
                  }
                  page = vm_normal_page(vma, addr, pteval);
                  if (unlikely(!page))
                          continue;
                  /* only check non-shared pages */
                  if (unlikely(page_mapcount(page) != 1))
                          continue;
  
                  /*
                   * Note that the NUMA fault is later accounted to either
                   * the node that is currently running or where the page is
                   * migrated to.
                   */
                  curr_nid = local_nid;
                  target_nid = numa_migrate_prep(page, vma, addr,
                                                 page_to_nid(page));
                  if (target_nid == -1) {
                          put_page(page);
                          continue;
                  }
  
                  /* Migrate to the requested node */
                  pte_unmap_unlock(pte, ptl);
                  migrated = migrate_misplaced_page(page, target_nid);
                  if (migrated)
                          curr_nid = target_nid;
                  task_numa_fault(curr_nid, 1, migrated);
  
                  pte = pte_offset_map_lock(mm, pmdp, addr, &ptl);
          }
          pte_unmap_unlock(orig_pte, ptl);
  
          return 0;
  }
  #else
  static int do_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
                       unsigned long addr, pmd_t *pmdp)
  {
          BUG();
          return 0;
  }
  #endif /* CONFIG_NUMA_BALANCING */
  
  /*
   * These routines also need to handle stuff like marking pages dirty
   * and/or accessed for architectures that don't do it in hardware (most
   * RISC architectures).  The early dirtying is also good on the i386.
   *
   * There is also a hook called "update_mmu_cache()" that architectures
   * with external mmu caches can use to update those (ie the Sparc or
   * PowerPC hashed page tables that act as extended TLBs).
   *
   * We enter with non-exclusive mmap_sem (to exclude vma changes,
   * but allow concurrent faults), and pte mapped but not yet locked.
   * We return with mmap_sem still held, but pte unmapped and unlocked.
   */
  int handle_pte_fault(struct mm_struct *mm,
                       struct vm_area_struct *vma, unsigned long address,
                       pte_t *pte, pmd_t *pmd, unsigned int flags)
  {
          pte_t entry;
          spinlock_t *ptl;
  
          entry = *pte;
          if (!pte_present(entry)) {
                  if (pte_none(entry)) {
                          if (vma->vm_ops) {
                                  if (likely(vma->vm_ops->fault))
                                          return do_linear_fault(mm, vma, address,
                                                  pte, pmd, flags, entry);
                          }
                          return do_anonymous_page(mm, vma, address,
                                                   pte, pmd, flags);
                  }
                  if (pte_file(entry))
                          return do_nonlinear_fault(mm, vma, address,
                                          pte, pmd, flags, entry);
                  return do_swap_page(mm, vma, address,
                                          pte, pmd, flags, entry);
          }
  
          if (pte_numa(entry))
                  return do_numa_page(mm, vma, address, entry, pte, pmd);
  
          ptl = pte_lockptr(mm, pmd);
          spin_lock(ptl);
          if (unlikely(!pte_same(*pte, entry)))
                  goto unlock;
          if (flags & FAULT_FLAG_WRITE) {
                  if (!pte_write(entry))
                          return do_wp_page(mm, vma, address,
                                          pte, pmd, ptl, entry);
                  entry = pte_mkdirty(entry);
          }
          entry = pte_mkyoung(entry);
          if (ptep_set_access_flags(vma, address, pte, entry, flags & FAULT_FLAG_WRITE)) {
                  update_mmu_cache(vma, address, pte);
          } else {
                  /*
                   * This is needed only for protection faults but the arch code
                   * is not yet telling us if this is a protection fault or not.
                   * This still avoids useless tlb flushes for .text page faults
                   * with threads.
                   */
                  if (flags & FAULT_FLAG_WRITE)
                          flush_tlb_fix_spurious_fault(vma, address);
          }
  unlock:
          pte_unmap_unlock(pte, ptl);
          return 0;
  }
  
  /*
   * By the time we get here, we already hold the mm semaphore
   */
  int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                  unsigned long address, unsigned int flags)
  {
          pgd_t *pgd;
          pud_t *pud;
          pmd_t *pmd;
          pte_t *pte;
  
          __set_current_state(TASK_RUNNING);
  
          count_vm_event(PGFAULT);
          mem_cgroup_count_vm_event(mm, PGFAULT);
  
          /* do counter updates before entering really critical section. */
          check_sync_rss_stat(current);
  
          if (unlikely(is_vm_hugetlb_page(vma)))
                  return hugetlb_fault(mm, vma, address, flags);
  
  retry:
          pgd = pgd_offset(mm, address);
          pud = pud_alloc(mm, pgd, address);
          if (!pud)
                  return VM_FAULT_OOM;
          pmd = pmd_alloc(mm, pud, address);
          if (!pmd)
                  return VM_FAULT_OOM;
          if (pmd_none(*pmd) && transparent_hugepage_enabled(vma)) {
                  if (!vma->vm_ops)
                          return do_huge_pmd_anonymous_page(mm, vma, address,
                                                            pmd, flags);
          } else {
                  pmd_t orig_pmd = *pmd;
                  int ret;
  
                  barrier();
                  if (pmd_trans_huge(orig_pmd)) {
                          unsigned int dirty = flags & FAULT_FLAG_WRITE;
  
                          /*
                           * If the pmd is splitting, return and retry the
                           * the fault.  Alternative: wait until the split
                           * is done, and goto retry.
                           */
                          if (pmd_trans_splitting(orig_pmd))
                                  return 0;
  
                          if (pmd_numa(orig_pmd))
                                  return do_huge_pmd_numa_page(mm, vma, address,
                                                               orig_pmd, pmd);
  
                          if (dirty && !pmd_write(orig_pmd)) {
                                  ret = do_huge_pmd_wp_page(mm, vma, address, pmd,
                                                            orig_pmd);
                                  /*
                                   * If COW results in an oom, the huge pmd will
                                   * have been split, so retry the fault on the
                                   * pte for a smaller charge.
                                   */
                                  if (unlikely(ret & VM_FAULT_OOM))
                                          goto retry;
                                  return ret;
                          } else {
                                  huge_pmd_set_accessed(mm, vma, address, pmd,
                                                        orig_pmd, dirty);
                          }
  
                          return 0;
                  }
          }
  
          if (pmd_numa(*pmd))
                  return do_pmd_numa_page(mm, vma, address, pmd);
  
          /*
           * Use __pte_alloc instead of pte_alloc_map, because we can't
           * run pte_offset_map on the pmd, if an huge pmd could
           * materialize from under us from a different thread.
           */
          if (unlikely(pmd_none(*pmd)) &&
              unlikely(__pte_alloc(mm, vma, pmd, address)))
                  return VM_FAULT_OOM;
          /* if an huge pmd materialized from under us just retry later */
          if (unlikely(pmd_trans_huge(*pmd)))
                  return 0;
          /*
           * A regular pmd is established and it can't morph into a huge pmd
           * from under us anymore at this point because we hold the mmap_sem
           * read mode and khugepaged takes it in write mode. So now it's
           * safe to run pte_offset_map().
           */
          pte = pte_offset_map(pmd, address);
  
          return handle_pte_fault(mm, vma, address, pte, pmd, flags);
  }
  
  #ifndef __PAGETABLE_PUD_FOLDED
  /*
   * Allocate page upper directory.
   * We've already handled the fast-path in-line.
   */
  int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
  {
          pud_t *new = pud_alloc_one(mm, address);
          if (!new)
                  return -ENOMEM;
  
          smp_wmb(); /* See comment in __pte_alloc */
  
          spin_lock(&mm->page_table_lock);
          if (pgd_present(*pgd))          /* Another has populated it */
                  pud_free(mm, new);
          else
                  pgd_populate(mm, pgd, new);
          spin_unlock(&mm->page_table_lock);
          return 0;
  }
  #endif /* __PAGETABLE_PUD_FOLDED */
  
  #ifndef __PAGETABLE_PMD_FOLDED
  /*
   * Allocate page middle directory.
   * We've already handled the fast-path in-line.
   */
  int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
  {
          pmd_t *new = pmd_alloc_one(mm, address);
          if (!new)
                  return -ENOMEM;
  
          smp_wmb(); /* See comment in __pte_alloc */
  
          spin_lock(&mm->page_table_lock);
  #ifndef __ARCH_HAS_4LEVEL_HACK
          if (pud_present(*pud))          /* Another has populated it */
                  pmd_free(mm, new);
          else
                  pud_populate(mm, pud, new);
  #else
          if (pgd_present(*pud))          /* Another has populated it */
                  pmd_free(mm, new);
          else
                  pgd_populate(mm, pud, new);
  #endif /* __ARCH_HAS_4LEVEL_HACK */
          spin_unlock(&mm->page_table_lock);
          return 0;
  }
  #endif /* __PAGETABLE_PMD_FOLDED */
  
  int make_pages_present(unsigned long addr, unsigned long end)
  {
          int ret, len, write;
          struct vm_area_struct * vma;
  
          vma = find_vma(current->mm, addr);
          if (!vma)
                  return -ENOMEM;
          /*
           * We want to touch writable mappings with a write fault in order
           * to break COW, except for shared mappings because these don't COW
           * and we would not want to dirty them for nothing.
           */
          write = (vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE;
          BUG_ON(addr >= end);
          BUG_ON(end > vma->vm_end);
          len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
          ret = get_user_pages(current, current->mm, addr,
                          len, write, 0, NULL, NULL);
          if (ret < 0)
                  return ret;
          return ret == len ? 0 : -EFAULT;
  }
  
  #if !defined(__HAVE_ARCH_GATE_AREA)
  
  #if defined(AT_SYSINFO_EHDR)
  static struct vm_area_struct gate_vma;
  
  static int __init gate_vma_init(void)
  {
          gate_vma.vm_mm = NULL;
          gate_vma.vm_start = FIXADDR_USER_START;
          gate_vma.vm_end = FIXADDR_USER_END;
          gate_vma.vm_flags = VM_READ | VM_MAYREAD | VM_EXEC | VM_MAYEXEC;
          gate_vma.vm_page_prot = __P101;
  
          return 0;
  }
  __initcall(gate_vma_init);
  #endif
  
  struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
  {
  #ifdef AT_SYSINFO_EHDR
          return &gate_vma;
  #else
          return NULL;
  #endif
  }
  
  int in_gate_area_no_mm(unsigned long addr)
  {
  #ifdef AT_SYSINFO_EHDR
          if ((addr >= FIXADDR_USER_START) && (addr < FIXADDR_USER_END))
                  return 1;
  #endif
          return 0;
  }
  
  #endif  /* __HAVE_ARCH_GATE_AREA */
  
  static int __follow_pte(struct mm_struct *mm, unsigned long address,
                  pte_t **ptepp, spinlock_t **ptlp)
  {
          pgd_t *pgd;
          pud_t *pud;
          pmd_t *pmd;
          pte_t *ptep;
  
          pgd = pgd_offset(mm, address);
          if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
                  goto out;
  
          pud = pud_offset(pgd, address);
          if (pud_none(*pud) || unlikely(pud_bad(*pud)))
                  goto out;
  
          pmd = pmd_offset(pud, address);
          VM_BUG_ON(pmd_trans_huge(*pmd));
          if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
                  goto out;
  
          /* We cannot handle huge page PFN maps. Luckily they don't exist. */
          if (pmd_huge(*pmd))
                  goto out;
  
          ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
          if (!ptep)
                  goto out;
          if (!pte_present(*ptep))
                  goto unlock;
          *ptepp = ptep;
          return 0;
  unlock:
          pte_unmap_unlock(ptep, *ptlp);
  out:
          return -EINVAL;
  }
  
  static inline int follow_pte(struct mm_struct *mm, unsigned long address,
                               pte_t **ptepp, spinlock_t **ptlp)
  {
          int res;
  
          /* (void) is needed to make gcc happy */
          (void) __cond_lock(*ptlp,
                             !(res = __follow_pte(mm, address, ptepp, ptlp)));
          return res;
  }
  
  /**
   * follow_pfn - look up PFN at a user virtual address
   * @vma: memory mapping
   * @address: user virtual address
   * @pfn: location to store found PFN
   *
   * Only IO mappings and raw PFN mappings are allowed.
   *
   * Returns zero and the pfn at @pfn on success, -ve otherwise.
   */
  int follow_pfn(struct vm_area_struct *vma, unsigned long address,
          unsigned long *pfn)
  {
          int ret = -EINVAL;
          spinlock_t *ptl;
          pte_t *ptep;
  
          if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
                  return ret;
  
          ret = follow_pte(vma->vm_mm, address, &ptep, &ptl);
          if (ret)
                  return ret;
          *pfn = pte_pfn(*ptep);
          pte_unmap_unlock(ptep, ptl);
          return 0;
  }
  EXPORT_SYMBOL(follow_pfn);
  
  #ifdef CONFIG_HAVE_IOREMAP_PROT
  int follow_phys(struct vm_area_struct *vma,
                  unsigned long address, unsigned int flags,
                  unsigned long *prot, resource_size_t *phys)
  {
          int ret = -EINVAL;
          pte_t *ptep, pte;
          spinlock_t *ptl;
  
          if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
                  goto out;
  
          if (follow_pte(vma->vm_mm, address, &ptep, &ptl))
                  goto out;
          pte = *ptep;
  
          if ((flags & FOLL_WRITE) && !pte_write(pte))
                  goto unlock;
  
          *prot = pgprot_val(pte_pgprot(pte));
          *phys = (resource_size_t)pte_pfn(pte) << PAGE_SHIFT;
  
          ret = 0;
  unlock:
          pte_unmap_unlock(ptep, ptl);
  out:
          return ret;
  }
  
  int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
                          void *buf, int len, int write)
  {
          resource_size_t phys_addr;
          unsigned long prot = 0;
          void __iomem *maddr;
          int offset = addr & (PAGE_SIZE-1);
  
          if (follow_phys(vma, addr, write, &prot, &phys_addr))
                  return -EINVAL;
  
          maddr = ioremap_prot(phys_addr, PAGE_SIZE, prot);
          if (write)
                  memcpy_toio(maddr + offset, buf, len);
          else
                  memcpy_fromio(buf, maddr + offset, len);
          iounmap(maddr);
  
          return len;
  }
  #endif
  
  /*
   * Access another process' address space as given in mm.  If non-NULL, use the
   * given task for page fault accounting.
   */
  static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
                  unsigned long addr, void *buf, int len, int write)
  {
          struct vm_area_struct *vma;
          void *old_buf = buf;
  
          down_read(&mm->mmap_sem);
          /* ignore errors, just check how much was successfully transferred */
          while (len) {
                  int bytes, ret, offset;
                  void *maddr;
                  struct page *page = NULL;
  
                  ret = get_user_pages(tsk, mm, addr, 1,
                                  write, 1, &page, &vma);
                  if (ret <= 0) {
                          /*
                           * Check if this is a VM_IO | VM_PFNMAP VMA, which
                           * we can access using slightly different code.
                           */
  #ifdef CONFIG_HAVE_IOREMAP_PROT
                          vma = find_vma(mm, addr);
                          if (!vma || vma->vm_start > addr)
                                  break;
                          if (vma->vm_ops && vma->vm_ops->access)
                                  ret = vma->vm_ops->access(vma, addr, buf,
                                                            len, write);
                          if (ret <= 0)
  #endif
                                  break;
                          bytes = ret;
                  } else {
                          bytes = len;
                          offset = addr & (PAGE_SIZE-1);
                          if (bytes > PAGE_SIZE-offset)
                                  bytes = PAGE_SIZE-offset;
  
                          maddr = kmap(page);
                          if (write) {
                                  copy_to_user_page(vma, page, addr,
                                                    maddr + offset, buf, bytes);
                                  set_page_dirty_lock(page);
                          } else {
                                  copy_from_user_page(vma, page, addr,
                                                      buf, maddr + offset, bytes);
                          }
                          kunmap(page);
                          page_cache_release(page);
                  }
                  len -= bytes;
                  buf += bytes;
                  addr += bytes;
          }
          up_read(&mm->mmap_sem);
  
          return buf - old_buf;
  }
  
  /**
   * access_remote_vm - access another process' address space
   * @mm:         the mm_struct of the target address space
   * @addr:       start address to access
   * @buf:        source or destination buffer
   * @len:        number of bytes to transfer
   * @write:      whether the access is a write
   *
   * The caller must hold a reference on @mm.
   */
  int access_remote_vm(struct mm_struct *mm, unsigned long addr,
                  void *buf, int len, int write)
  {
          return __access_remote_vm(NULL, mm, addr, buf, len, write);
  }
  
  /*
   * Access another process' address space.
   * Source/target buffer must be kernel space,
   * Do not walk the page table directly, use get_user_pages
   */
  int access_process_vm(struct task_struct *tsk, unsigned long addr,
                  void *buf, int len, int write)
  {
          struct mm_struct *mm;
          int ret;
  
          mm = get_task_mm(tsk);
          if (!mm)
                  return 0;
  
          ret = __access_remote_vm(tsk, mm, addr, buf, len, write);
          mmput(mm);
  
          return ret;
  }
  
  /*
   * Print the name of a VMA.
   */
  void print_vma_addr(char *prefix, unsigned long ip)
  {
          struct mm_struct *mm = current->mm;
          struct vm_area_struct *vma;
  
          /*
           * Do not print if we are in atomic
           * contexts (in exception stacks, etc.):
           */
          if (preempt_count())
                  return;
  
          down_read(&mm->mmap_sem);
          vma = find_vma(mm, ip);
          if (vma && vma->vm_file) {
                  struct file *f = vma->vm_file;
                  char *buf = (char *)__get_free_page(GFP_KERNEL);
                  if (buf) {
                          char *p;
  
                          p = d_path(&f->f_path, buf, PAGE_SIZE);
                          if (IS_ERR(p))
                                  p = "?";
                          printk("%s%s[%lx+%lx]", prefix, kbasename(p),
                                          vma->vm_start,
                                          vma->vm_end - vma->vm_start);
                          free_page((unsigned long)buf);
                  }
          }
          up_read(&mm->mmap_sem);
  }
  
  #ifdef CONFIG_PROVE_LOCKING
  void might_fault(void)
  {
          /*
           * Some code (nfs/sunrpc) uses socket ops on kernel memory while
           * holding the mmap_sem, this is safe because kernel memory doesn't
           * get paged out, therefore we'll never actually fault, and the
           * below annotations will generate false positives.
           */
          if (segment_eq(get_fs(), KERNEL_DS))
                  return;
  
          might_sleep();
          /*
           * it would be nicer only to annotate paths which are not under
           * pagefault_disable, however that requires a larger audit and
           * providing helpers like get_user_atomic.
           */
          if (!in_atomic() && current->mm)
                  might_lock_read(&current->mm->mmap_sem);
  }
  EXPORT_SYMBOL(might_fault);
  #endif
  
  #if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
  static void clear_gigantic_page(struct page *page,
                                  unsigned long addr,
                                  unsigned int pages_per_huge_page)
  {
          int i;
          struct page *p = page;
  
          might_sleep();
          for (i = 0; i < pages_per_huge_page;
               i++, p = mem_map_next(p, page, i)) {
                  cond_resched();
                  clear_user_highpage(p, addr + i * PAGE_SIZE);
          }
  }
  void clear_huge_page(struct page *page,
                       unsigned long addr, unsigned int pages_per_huge_page)
  {
          int i;
  
          if (unlikely(pages_per_huge_page > MAX_ORDER_NR_PAGES)) {
                  clear_gigantic_page(page, addr, pages_per_huge_page);
                  return;
          }
  
          might_sleep();
          for (i = 0; i < pages_per_huge_page; i++) {
                  cond_resched();
                  clear_user_highpage(page + i, addr + i * PAGE_SIZE);
          }
  }
  
  static void copy_user_gigantic_page(struct page *dst, struct page *src,
                                      unsigned long addr,
                                      struct vm_area_struct *vma,
                                      unsigned int pages_per_huge_page)
  {
          int i;
          struct page *dst_base = dst;
          struct page *src_base = src;
  
          for (i = 0; i < pages_per_huge_page; ) {
                  cond_resched();
                  copy_user_highpage(dst, src, addr + i*PAGE_SIZE, vma);
  
                  i++;
                  dst = mem_map_next(dst, dst_base, i);
                  src = mem_map_next(src, src_base, i);
          }
  }
  
  void copy_user_huge_page(struct page *dst, struct page *src,
                           unsigned long addr, struct vm_area_struct *vma,
                           unsigned int pages_per_huge_page)
  {
          int i;
  
          if (unlikely(pages_per_huge_page > MAX_ORDER_NR_PAGES)) {
                  copy_user_gigantic_page(dst, src, addr, vma,
                                          pages_per_huge_page);
                  return;
          }
  
          might_sleep();
          for (i = 0; i < pages_per_huge_page; i++) {
                  cond_resched();
                  copy_user_highpage(dst + i, src + i, addr + i*PAGE_SIZE, vma);
          }
  }
  #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */