The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/mm/mremap.c

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    1 /*
    2  *      mm/mremap.c
    3  *
    4  *      (C) Copyright 1996 Linus Torvalds
    5  *
    6  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
    7  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
    8  */
    9 
   10 #include <linux/mm.h>
   11 #include <linux/hugetlb.h>
   12 #include <linux/shm.h>
   13 #include <linux/ksm.h>
   14 #include <linux/mman.h>
   15 #include <linux/swap.h>
   16 #include <linux/capability.h>
   17 #include <linux/fs.h>
   18 #include <linux/highmem.h>
   19 #include <linux/security.h>
   20 #include <linux/syscalls.h>
   21 #include <linux/mmu_notifier.h>
   22 
   23 #include <asm/uaccess.h>
   24 #include <asm/cacheflush.h>
   25 #include <asm/tlbflush.h>
   26 
   27 #include "internal.h"
   28 
   29 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
   30 {
   31         pgd_t *pgd;
   32         pud_t *pud;
   33         pmd_t *pmd;
   34 
   35         pgd = pgd_offset(mm, addr);
   36         if (pgd_none_or_clear_bad(pgd))
   37                 return NULL;
   38 
   39         pud = pud_offset(pgd, addr);
   40         if (pud_none_or_clear_bad(pud))
   41                 return NULL;
   42 
   43         pmd = pmd_offset(pud, addr);
   44         if (pmd_none(*pmd))
   45                 return NULL;
   46 
   47         return pmd;
   48 }
   49 
   50 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
   51                             unsigned long addr)
   52 {
   53         pgd_t *pgd;
   54         pud_t *pud;
   55         pmd_t *pmd;
   56 
   57         pgd = pgd_offset(mm, addr);
   58         pud = pud_alloc(mm, pgd, addr);
   59         if (!pud)
   60                 return NULL;
   61 
   62         pmd = pmd_alloc(mm, pud, addr);
   63         if (!pmd)
   64                 return NULL;
   65 
   66         VM_BUG_ON(pmd_trans_huge(*pmd));
   67 
   68         return pmd;
   69 }
   70 
   71 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
   72                 unsigned long old_addr, unsigned long old_end,
   73                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
   74                 unsigned long new_addr, bool need_rmap_locks)
   75 {
   76         struct address_space *mapping = NULL;
   77         struct anon_vma *anon_vma = NULL;
   78         struct mm_struct *mm = vma->vm_mm;
   79         pte_t *old_pte, *new_pte, pte;
   80         spinlock_t *old_ptl, *new_ptl;
   81 
   82         /*
   83          * When need_rmap_locks is true, we take the i_mmap_mutex and anon_vma
   84          * locks to ensure that rmap will always observe either the old or the
   85          * new ptes. This is the easiest way to avoid races with
   86          * truncate_pagecache(), page migration, etc...
   87          *
   88          * When need_rmap_locks is false, we use other ways to avoid
   89          * such races:
   90          *
   91          * - During exec() shift_arg_pages(), we use a specially tagged vma
   92          *   which rmap call sites look for using is_vma_temporary_stack().
   93          *
   94          * - During mremap(), new_vma is often known to be placed after vma
   95          *   in rmap traversal order. This ensures rmap will always observe
   96          *   either the old pte, or the new pte, or both (the page table locks
   97          *   serialize access to individual ptes, but only rmap traversal
   98          *   order guarantees that we won't miss both the old and new ptes).
   99          */
  100         if (need_rmap_locks) {
  101                 if (vma->vm_file) {
  102                         mapping = vma->vm_file->f_mapping;
  103                         mutex_lock(&mapping->i_mmap_mutex);
  104                 }
  105                 if (vma->anon_vma) {
  106                         anon_vma = vma->anon_vma;
  107                         anon_vma_lock_write(anon_vma);
  108                 }
  109         }
  110 
  111         /*
  112          * We don't have to worry about the ordering of src and dst
  113          * pte locks because exclusive mmap_sem prevents deadlock.
  114          */
  115         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
  116         new_pte = pte_offset_map(new_pmd, new_addr);
  117         new_ptl = pte_lockptr(mm, new_pmd);
  118         if (new_ptl != old_ptl)
  119                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
  120         arch_enter_lazy_mmu_mode();
  121 
  122         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
  123                                    new_pte++, new_addr += PAGE_SIZE) {
  124                 if (pte_none(*old_pte))
  125                         continue;
  126                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
  127                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
  128                 set_pte_at(mm, new_addr, new_pte, pte);
  129         }
  130 
  131         arch_leave_lazy_mmu_mode();
  132         if (new_ptl != old_ptl)
  133                 spin_unlock(new_ptl);
  134         pte_unmap(new_pte - 1);
  135         pte_unmap_unlock(old_pte - 1, old_ptl);
  136         if (anon_vma)
  137                 anon_vma_unlock(anon_vma);
  138         if (mapping)
  139                 mutex_unlock(&mapping->i_mmap_mutex);
  140 }
  141 
  142 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
  143 
  144 unsigned long move_page_tables(struct vm_area_struct *vma,
  145                 unsigned long old_addr, struct vm_area_struct *new_vma,
  146                 unsigned long new_addr, unsigned long len,
  147                 bool need_rmap_locks)
  148 {
  149         unsigned long extent, next, old_end;
  150         pmd_t *old_pmd, *new_pmd;
  151         bool need_flush = false;
  152         unsigned long mmun_start;       /* For mmu_notifiers */
  153         unsigned long mmun_end;         /* For mmu_notifiers */
  154 
  155         old_end = old_addr + len;
  156         flush_cache_range(vma, old_addr, old_end);
  157 
  158         mmun_start = old_addr;
  159         mmun_end   = old_end;
  160         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
  161 
  162         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
  163                 cond_resched();
  164                 next = (old_addr + PMD_SIZE) & PMD_MASK;
  165                 /* even if next overflowed, extent below will be ok */
  166                 extent = next - old_addr;
  167                 if (extent > old_end - old_addr)
  168                         extent = old_end - old_addr;
  169                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
  170                 if (!old_pmd)
  171                         continue;
  172                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
  173                 if (!new_pmd)
  174                         break;
  175                 if (pmd_trans_huge(*old_pmd)) {
  176                         int err = 0;
  177                         if (extent == HPAGE_PMD_SIZE)
  178                                 err = move_huge_pmd(vma, new_vma, old_addr,
  179                                                     new_addr, old_end,
  180                                                     old_pmd, new_pmd);
  181                         if (err > 0) {
  182                                 need_flush = true;
  183                                 continue;
  184                         } else if (!err) {
  185                                 split_huge_page_pmd(vma, old_addr, old_pmd);
  186                         }
  187                         VM_BUG_ON(pmd_trans_huge(*old_pmd));
  188                 }
  189                 if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
  190                                                       new_pmd, new_addr))
  191                         break;
  192                 next = (new_addr + PMD_SIZE) & PMD_MASK;
  193                 if (extent > next - new_addr)
  194                         extent = next - new_addr;
  195                 if (extent > LATENCY_LIMIT)
  196                         extent = LATENCY_LIMIT;
  197                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
  198                           new_vma, new_pmd, new_addr, need_rmap_locks);
  199                 need_flush = true;
  200         }
  201         if (likely(need_flush))
  202                 flush_tlb_range(vma, old_end-len, old_addr);
  203 
  204         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
  205 
  206         return len + old_addr - old_end;        /* how much done */
  207 }
  208 
  209 static unsigned long move_vma(struct vm_area_struct *vma,
  210                 unsigned long old_addr, unsigned long old_len,
  211                 unsigned long new_len, unsigned long new_addr)
  212 {
  213         struct mm_struct *mm = vma->vm_mm;
  214         struct vm_area_struct *new_vma;
  215         unsigned long vm_flags = vma->vm_flags;
  216         unsigned long new_pgoff;
  217         unsigned long moved_len;
  218         unsigned long excess = 0;
  219         unsigned long hiwater_vm;
  220         int split = 0;
  221         int err;
  222         bool need_rmap_locks;
  223 
  224         /*
  225          * We'd prefer to avoid failure later on in do_munmap:
  226          * which may split one vma into three before unmapping.
  227          */
  228         if (mm->map_count >= sysctl_max_map_count - 3)
  229                 return -ENOMEM;
  230 
  231         /*
  232          * Advise KSM to break any KSM pages in the area to be moved:
  233          * it would be confusing if they were to turn up at the new
  234          * location, where they happen to coincide with different KSM
  235          * pages recently unmapped.  But leave vma->vm_flags as it was,
  236          * so KSM can come around to merge on vma and new_vma afterwards.
  237          */
  238         err = ksm_madvise(vma, old_addr, old_addr + old_len,
  239                                                 MADV_UNMERGEABLE, &vm_flags);
  240         if (err)
  241                 return err;
  242 
  243         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
  244         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
  245                            &need_rmap_locks);
  246         if (!new_vma)
  247                 return -ENOMEM;
  248 
  249         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
  250                                      need_rmap_locks);
  251         if (moved_len < old_len) {
  252                 /*
  253                  * On error, move entries back from new area to old,
  254                  * which will succeed since page tables still there,
  255                  * and then proceed to unmap new area instead of old.
  256                  */
  257                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
  258                                  true);
  259                 vma = new_vma;
  260                 old_len = new_len;
  261                 old_addr = new_addr;
  262                 new_addr = -ENOMEM;
  263         }
  264 
  265         /* Conceal VM_ACCOUNT so old reservation is not undone */
  266         if (vm_flags & VM_ACCOUNT) {
  267                 vma->vm_flags &= ~VM_ACCOUNT;
  268                 excess = vma->vm_end - vma->vm_start - old_len;
  269                 if (old_addr > vma->vm_start &&
  270                     old_addr + old_len < vma->vm_end)
  271                         split = 1;
  272         }
  273 
  274         /*
  275          * If we failed to move page tables we still do total_vm increment
  276          * since do_munmap() will decrement it by old_len == new_len.
  277          *
  278          * Since total_vm is about to be raised artificially high for a
  279          * moment, we need to restore high watermark afterwards: if stats
  280          * are taken meanwhile, total_vm and hiwater_vm appear too high.
  281          * If this were a serious issue, we'd add a flag to do_munmap().
  282          */
  283         hiwater_vm = mm->hiwater_vm;
  284         vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
  285 
  286         if (do_munmap(mm, old_addr, old_len) < 0) {
  287                 /* OOM: unable to split vma, just get accounts right */
  288                 vm_unacct_memory(excess >> PAGE_SHIFT);
  289                 excess = 0;
  290         }
  291         mm->hiwater_vm = hiwater_vm;
  292 
  293         /* Restore VM_ACCOUNT if one or two pieces of vma left */
  294         if (excess) {
  295                 vma->vm_flags |= VM_ACCOUNT;
  296                 if (split)
  297                         vma->vm_next->vm_flags |= VM_ACCOUNT;
  298         }
  299 
  300         if (vm_flags & VM_LOCKED) {
  301                 mm->locked_vm += new_len >> PAGE_SHIFT;
  302                 if (new_len > old_len)
  303                         mlock_vma_pages_range(new_vma, new_addr + old_len,
  304                                                        new_addr + new_len);
  305         }
  306 
  307         return new_addr;
  308 }
  309 
  310 static struct vm_area_struct *vma_to_resize(unsigned long addr,
  311         unsigned long old_len, unsigned long new_len, unsigned long *p)
  312 {
  313         struct mm_struct *mm = current->mm;
  314         struct vm_area_struct *vma = find_vma(mm, addr);
  315 
  316         if (!vma || vma->vm_start > addr)
  317                 goto Efault;
  318 
  319         if (is_vm_hugetlb_page(vma))
  320                 goto Einval;
  321 
  322         /* We can't remap across vm area boundaries */
  323         if (old_len > vma->vm_end - addr)
  324                 goto Efault;
  325 
  326         /* Need to be careful about a growing mapping */
  327         if (new_len > old_len) {
  328                 unsigned long pgoff;
  329 
  330                 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
  331                         goto Efault;
  332                 pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
  333                 pgoff += vma->vm_pgoff;
  334                 if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
  335                         goto Einval;
  336         }
  337 
  338         if (vma->vm_flags & VM_LOCKED) {
  339                 unsigned long locked, lock_limit;
  340                 locked = mm->locked_vm << PAGE_SHIFT;
  341                 lock_limit = rlimit(RLIMIT_MEMLOCK);
  342                 locked += new_len - old_len;
  343                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
  344                         goto Eagain;
  345         }
  346 
  347         if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
  348                 goto Enomem;
  349 
  350         if (vma->vm_flags & VM_ACCOUNT) {
  351                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
  352                 if (security_vm_enough_memory_mm(mm, charged))
  353                         goto Efault;
  354                 *p = charged;
  355         }
  356 
  357         return vma;
  358 
  359 Efault: /* very odd choice for most of the cases, but... */
  360         return ERR_PTR(-EFAULT);
  361 Einval:
  362         return ERR_PTR(-EINVAL);
  363 Enomem:
  364         return ERR_PTR(-ENOMEM);
  365 Eagain:
  366         return ERR_PTR(-EAGAIN);
  367 }
  368 
  369 static unsigned long mremap_to(unsigned long addr,
  370         unsigned long old_len, unsigned long new_addr,
  371         unsigned long new_len)
  372 {
  373         struct mm_struct *mm = current->mm;
  374         struct vm_area_struct *vma;
  375         unsigned long ret = -EINVAL;
  376         unsigned long charged = 0;
  377         unsigned long map_flags;
  378 
  379         if (new_addr & ~PAGE_MASK)
  380                 goto out;
  381 
  382         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
  383                 goto out;
  384 
  385         /* Check if the location we're moving into overlaps the
  386          * old location at all, and fail if it does.
  387          */
  388         if ((new_addr <= addr) && (new_addr+new_len) > addr)
  389                 goto out;
  390 
  391         if ((addr <= new_addr) && (addr+old_len) > new_addr)
  392                 goto out;
  393 
  394         ret = do_munmap(mm, new_addr, new_len);
  395         if (ret)
  396                 goto out;
  397 
  398         if (old_len >= new_len) {
  399                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
  400                 if (ret && old_len != new_len)
  401                         goto out;
  402                 old_len = new_len;
  403         }
  404 
  405         vma = vma_to_resize(addr, old_len, new_len, &charged);
  406         if (IS_ERR(vma)) {
  407                 ret = PTR_ERR(vma);
  408                 goto out;
  409         }
  410 
  411         map_flags = MAP_FIXED;
  412         if (vma->vm_flags & VM_MAYSHARE)
  413                 map_flags |= MAP_SHARED;
  414 
  415         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
  416                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
  417                                 map_flags);
  418         if (ret & ~PAGE_MASK)
  419                 goto out1;
  420 
  421         ret = move_vma(vma, addr, old_len, new_len, new_addr);
  422         if (!(ret & ~PAGE_MASK))
  423                 goto out;
  424 out1:
  425         vm_unacct_memory(charged);
  426 
  427 out:
  428         return ret;
  429 }
  430 
  431 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
  432 {
  433         unsigned long end = vma->vm_end + delta;
  434         if (end < vma->vm_end) /* overflow */
  435                 return 0;
  436         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
  437                 return 0;
  438         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
  439                               0, MAP_FIXED) & ~PAGE_MASK)
  440                 return 0;
  441         return 1;
  442 }
  443 
  444 /*
  445  * Expand (or shrink) an existing mapping, potentially moving it at the
  446  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
  447  *
  448  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
  449  * This option implies MREMAP_MAYMOVE.
  450  */
  451 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
  452                 unsigned long, new_len, unsigned long, flags,
  453                 unsigned long, new_addr)
  454 {
  455         struct mm_struct *mm = current->mm;
  456         struct vm_area_struct *vma;
  457         unsigned long ret = -EINVAL;
  458         unsigned long charged = 0;
  459 
  460         down_write(&current->mm->mmap_sem);
  461 
  462         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
  463                 goto out;
  464 
  465         if (addr & ~PAGE_MASK)
  466                 goto out;
  467 
  468         old_len = PAGE_ALIGN(old_len);
  469         new_len = PAGE_ALIGN(new_len);
  470 
  471         /*
  472          * We allow a zero old-len as a special case
  473          * for DOS-emu "duplicate shm area" thing. But
  474          * a zero new-len is nonsensical.
  475          */
  476         if (!new_len)
  477                 goto out;
  478 
  479         if (flags & MREMAP_FIXED) {
  480                 if (flags & MREMAP_MAYMOVE)
  481                         ret = mremap_to(addr, old_len, new_addr, new_len);
  482                 goto out;
  483         }
  484 
  485         /*
  486          * Always allow a shrinking remap: that just unmaps
  487          * the unnecessary pages..
  488          * do_munmap does all the needed commit accounting
  489          */
  490         if (old_len >= new_len) {
  491                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
  492                 if (ret && old_len != new_len)
  493                         goto out;
  494                 ret = addr;
  495                 goto out;
  496         }
  497 
  498         /*
  499          * Ok, we need to grow..
  500          */
  501         vma = vma_to_resize(addr, old_len, new_len, &charged);
  502         if (IS_ERR(vma)) {
  503                 ret = PTR_ERR(vma);
  504                 goto out;
  505         }
  506 
  507         /* old_len exactly to the end of the area..
  508          */
  509         if (old_len == vma->vm_end - addr) {
  510                 /* can we just expand the current mapping? */
  511                 if (vma_expandable(vma, new_len - old_len)) {
  512                         int pages = (new_len - old_len) >> PAGE_SHIFT;
  513 
  514                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
  515                                        vma->vm_pgoff, NULL)) {
  516                                 ret = -ENOMEM;
  517                                 goto out;
  518                         }
  519 
  520                         vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
  521                         if (vma->vm_flags & VM_LOCKED) {
  522                                 mm->locked_vm += pages;
  523                                 mlock_vma_pages_range(vma, addr + old_len,
  524                                                    addr + new_len);
  525                         }
  526                         ret = addr;
  527                         goto out;
  528                 }
  529         }
  530 
  531         /*
  532          * We weren't able to just expand or shrink the area,
  533          * we need to create a new one and move it..
  534          */
  535         ret = -ENOMEM;
  536         if (flags & MREMAP_MAYMOVE) {
  537                 unsigned long map_flags = 0;
  538                 if (vma->vm_flags & VM_MAYSHARE)
  539                         map_flags |= MAP_SHARED;
  540 
  541                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
  542                                         vma->vm_pgoff +
  543                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
  544                                         map_flags);
  545                 if (new_addr & ~PAGE_MASK) {
  546                         ret = new_addr;
  547                         goto out;
  548                 }
  549 
  550                 ret = move_vma(vma, addr, old_len, new_len, new_addr);
  551         }
  552 out:
  553         if (ret & ~PAGE_MASK)
  554                 vm_unacct_memory(charged);
  555         up_write(&current->mm->mmap_sem);
  556         return ret;
  557 }

Cache object: f2ae6e11f1e18b3e35987bad308b9414


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