fremap.c

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    1 /*
    2  *   linux/mm/fremap.c
    3  * 
    4  * Explicit pagetable population and nonlinear (random) mappings support.
    5  *
    6  * started by Ingo Molnar, Copyright (C) 2002, 2003
    7  */
    8 #include <linux/export.h>
    9 #include <linux/backing-dev.h>
   10 #include <linux/mm.h>
   11 #include <linux/swap.h>
   12 #include <linux/file.h>
   13 #include <linux/mman.h>
   14 #include <linux/pagemap.h>
   15 #include <linux/swapops.h>
   16 #include <linux/rmap.h>
   17 #include <linux/syscalls.h>
   18 #include <linux/mmu_notifier.h>
   19 
   20 #include <asm/mmu_context.h>
   21 #include <asm/cacheflush.h>
   22 #include <asm/tlbflush.h>
   23 
   24 #include "internal.h"
   25 
   26 static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
   27                         unsigned long addr, pte_t *ptep)
   28 {
   29         pte_t pte = *ptep;
   30 
   31         if (pte_present(pte)) {
   32                 struct page *page;
   33 
   34                 flush_cache_page(vma, addr, pte_pfn(pte));
   35                 pte = ptep_clear_flush(vma, addr, ptep);
   36                 page = vm_normal_page(vma, addr, pte);
   37                 if (page) {
   38                         if (pte_dirty(pte))
   39                                 set_page_dirty(page);
   40                         page_remove_rmap(page);
   41                         page_cache_release(page);
   42                         update_hiwater_rss(mm);
   43                         dec_mm_counter(mm, MM_FILEPAGES);
   44                 }
   45         } else {
   46                 if (!pte_file(pte))
   47                         free_swap_and_cache(pte_to_swp_entry(pte));
   48                 pte_clear_not_present_full(mm, addr, ptep, 0);
   49         }
   50 }
   51 
   52 /*
   53  * Install a file pte to a given virtual memory address, release any
   54  * previously existing mapping.
   55  */
   56 static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
   57                 unsigned long addr, unsigned long pgoff, pgprot_t prot)
   58 {
   59         int err = -ENOMEM;
   60         pte_t *pte;
   61         spinlock_t *ptl;
   62 
   63         pte = get_locked_pte(mm, addr, &ptl);
   64         if (!pte)
   65                 goto out;
   66 
   67         if (!pte_none(*pte))
   68                 zap_pte(mm, vma, addr, pte);
   69 
   70         set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
   71         /*
   72          * We don't need to run update_mmu_cache() here because the "file pte"
   73          * being installed by install_file_pte() is not a real pte - it's a
   74          * non-present entry (like a swap entry), noting what file offset should
   75          * be mapped there when there's a fault (in a non-linear vma where
   76          * that's not obvious).
   77          */
   78         pte_unmap_unlock(pte, ptl);
   79         err = 0;
   80 out:
   81         return err;
   82 }
   83 
   84 int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
   85                              unsigned long size, pgoff_t pgoff)
   86 {
   87         struct mm_struct *mm = vma->vm_mm;
   88         int err;
   89 
   90         do {
   91                 err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
   92                 if (err)
   93                         return err;
   94 
   95                 size -= PAGE_SIZE;
   96                 addr += PAGE_SIZE;
   97                 pgoff++;
   98         } while (size);
   99 
  100         return 0;
  101 }
  102 EXPORT_SYMBOL(generic_file_remap_pages);
  103 
  104 /**
  105  * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
  106  * @start: start of the remapped virtual memory range
  107  * @size: size of the remapped virtual memory range
  108  * @prot: new protection bits of the range (see NOTE)
  109  * @pgoff: to-be-mapped page of the backing store file
  110  * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
  111  *
  112  * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
  113  * (shared backing store file).
  114  *
  115  * This syscall works purely via pagetables, so it's the most efficient
  116  * way to map the same (large) file into a given virtual window. Unlike
  117  * mmap()/mremap() it does not create any new vmas. The new mappings are
  118  * also safe across swapout.
  119  *
  120  * NOTE: the @prot parameter right now is ignored (but must be zero),
  121  * and the vma's default protection is used. Arbitrary protections
  122  * might be implemented in the future.
  123  */
  124 SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
  125                 unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
  126 {
  127         struct mm_struct *mm = current->mm;
  128         struct address_space *mapping;
  129         struct vm_area_struct *vma;
  130         int err = -EINVAL;
  131         int has_write_lock = 0;
  132 
  133         if (prot)
  134                 return err;
  135         /*
  136          * Sanitize the syscall parameters:
  137          */
  138         start = start & PAGE_MASK;
  139         size = size & PAGE_MASK;
  140 
  141         /* Does the address range wrap, or is the span zero-sized? */
  142         if (start + size <= start)
  143                 return err;
  144 
  145         /* Does pgoff wrap? */
  146         if (pgoff + (size >> PAGE_SHIFT) < pgoff)
  147                 return err;
  148 
  149         /* Can we represent this offset inside this architecture's pte's? */
  150 #if PTE_FILE_MAX_BITS < BITS_PER_LONG
  151         if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
  152                 return err;
  153 #endif
  154 
  155         /* We need down_write() to change vma->vm_flags. */
  156         down_read(&mm->mmap_sem);
  157  retry:
  158         vma = find_vma(mm, start);
  159 
  160         /*
  161          * Make sure the vma is shared, that it supports prefaulting,
  162          * and that the remapped range is valid and fully within
  163          * the single existing vma.  vm_private_data is used as a
  164          * swapout cursor in a VM_NONLINEAR vma.
  165          */
  166         if (!vma || !(vma->vm_flags & VM_SHARED))
  167                 goto out;
  168 
  169         if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
  170                 goto out;
  171 
  172         if (!vma->vm_ops || !vma->vm_ops->remap_pages)
  173                 goto out;
  174 
  175         if (start < vma->vm_start || start + size > vma->vm_end)
  176                 goto out;
  177 
  178         /* Must set VM_NONLINEAR before any pages are populated. */
  179         if (!(vma->vm_flags & VM_NONLINEAR)) {
  180                 /* Don't need a nonlinear mapping, exit success */
  181                 if (pgoff == linear_page_index(vma, start)) {
  182                         err = 0;
  183                         goto out;
  184                 }
  185 
  186                 if (!has_write_lock) {
  187                         up_read(&mm->mmap_sem);
  188                         down_write(&mm->mmap_sem);
  189                         has_write_lock = 1;
  190                         goto retry;
  191                 }
  192                 mapping = vma->vm_file->f_mapping;
  193                 /*
  194                  * page_mkclean doesn't work on nonlinear vmas, so if
  195                  * dirty pages need to be accounted, emulate with linear
  196                  * vmas.
  197                  */
  198                 if (mapping_cap_account_dirty(mapping)) {
  199                         unsigned long addr;
  200                         struct file *file = get_file(vma->vm_file);
  201 
  202                         flags &= MAP_NONBLOCK;
  203                         addr = mmap_region(file, start, size,
  204                                         flags, vma->vm_flags, pgoff);
  205                         fput(file);
  206                         if (IS_ERR_VALUE(addr)) {
  207                                 err = addr;
  208                         } else {
  209                                 BUG_ON(addr != start);
  210                                 err = 0;
  211                         }
  212                         goto out;
  213                 }
  214                 mutex_lock(&mapping->i_mmap_mutex);
  215                 flush_dcache_mmap_lock(mapping);
  216                 vma->vm_flags |= VM_NONLINEAR;
  217                 vma_interval_tree_remove(vma, &mapping->i_mmap);
  218                 vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
  219                 flush_dcache_mmap_unlock(mapping);
  220                 mutex_unlock(&mapping->i_mmap_mutex);
  221         }
  222 
  223         if (vma->vm_flags & VM_LOCKED) {
  224                 /*
  225                  * drop PG_Mlocked flag for over-mapped range
  226                  */
  227                 vm_flags_t saved_flags = vma->vm_flags;
  228                 munlock_vma_pages_range(vma, start, start + size);
  229                 vma->vm_flags = saved_flags;
  230         }
  231 
  232         mmu_notifier_invalidate_range_start(mm, start, start + size);
  233         err = vma->vm_ops->remap_pages(vma, start, size, pgoff);
  234         mmu_notifier_invalidate_range_end(mm, start, start + size);
  235         if (!err && !(flags & MAP_NONBLOCK)) {
  236                 if (vma->vm_flags & VM_LOCKED) {
  237                         /*
  238                          * might be mapping previously unmapped range of file
  239                          */
  240                         mlock_vma_pages_range(vma, start, start + size);
  241                 } else {
  242                         if (unlikely(has_write_lock)) {
  243                                 downgrade_write(&mm->mmap_sem);
  244                                 has_write_lock = 0;
  245                         }
  246                         make_pages_present(start, start+size);
  247                 }
  248         }
  249 
  250         /*
  251          * We can't clear VM_NONLINEAR because we'd have to do
  252          * it after ->populate completes, and that would prevent
  253          * downgrading the lock.  (Locks can't be upgraded).
  254          */
  255 
  256 out:
  257         if (likely(!has_write_lock))
  258                 up_read(&mm->mmap_sem);
  259         else
  260                 up_write(&mm->mmap_sem);
  261 
  262         return err;
  263 }

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

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