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mmap.c

/*
 * mm/mmap.c
 *
 * Written by obz.
 *
 * Address space accounting code    <alan@redhat.com>
 */

#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/mm.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/capability.h>
#include <linux/init.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/hugetlb.h>
#include <linux/profile.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>

#include <asm/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/tlb.h>
#include <asm/mmu_context.h>

#ifndef arch_mmap_check
#define arch_mmap_check(addr, len, flags) (0)
#endif

static void unmap_region(struct mm_struct *mm,
            struct vm_area_struct *vma, struct vm_area_struct *prev,
            unsigned long start, unsigned long end);

/*
 * WARNING: the debugging will use recursive algorithms so never enable this
 * unless you know what you are doing.
 */
#undef DEBUG_MM_RB

/* description of effects of mapping type and prot in current implementation.
 * this is due to the limited x86 page protection hardware.  The expected
 * behavior is in parens:
 *
 * map_type prot
 *          PROT_NONE   PROT_READ   PROT_WRITE  PROT_EXEC
 * MAP_SHARED     r: (no) no  r: (yes) yes      r: (no) yes r: (no) yes
 *          w: (no) no  w: (no) no  w: (yes) yes      w: (no) no
 *          x: (no) no  x: (no) yes x: (no) yes x: (yes) yes
 *          
 * MAP_PRIVATE    r: (no) no  r: (yes) yes      r: (no) yes r: (no) yes
 *          w: (no) no  w: (no) no  w: (copy) copy    w: (no) no
 *          x: (no) no  x: (no) yes x: (no) yes x: (yes) yes
 *
 */
pgprot_t protection_map[16] = {
      __P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
      __S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
};

pgprot_t vm_get_page_prot(unsigned long vm_flags)
{
      return protection_map[vm_flags &
                        (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
}
EXPORT_SYMBOL(vm_get_page_prot);

int sysctl_overcommit_memory = OVERCOMMIT_GUESS;  /* heuristic overcommit */
int sysctl_overcommit_ratio = 50;   /* default is 50% */
int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
atomic_t vm_committed_space = ATOMIC_INIT(0);

/*
 * Check that a process has enough memory to allocate a new virtual
 * mapping. 0 means there is enough memory for the allocation to
 * succeed and -ENOMEM implies there is not.
 *
 * We currently support three overcommit policies, which are set via the
 * vm.overcommit_memory sysctl.  See Documentation/vm/overcommit-accounting
 *
 * Strict overcommit modes added 2002 Feb 26 by Alan Cox.
 * Additional code 2002 Jul 20 by Robert Love.
 *
 * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise.
 *
 * Note this is a helper function intended to be used by LSMs which
 * wish to use this logic.
 */
int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
{
      unsigned long free, allowed;

      vm_acct_memory(pages);

      /*
       * Sometimes we want to use more memory than we have
       */
      if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
            return 0;

      if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {
            unsigned long n;

            free = global_page_state(NR_FILE_PAGES);
            free += nr_swap_pages;

            /*
             * Any slabs which are created with the
             * SLAB_RECLAIM_ACCOUNT flag claim to have contents
             * which are reclaimable, under pressure.  The dentry
             * cache and most inode caches should fall into this
             */
            free += global_page_state(NR_SLAB_RECLAIMABLE);

            /*
             * Leave the last 3% for root
             */
            if (!cap_sys_admin)
                  free -= free / 32;

            if (free > pages)
                  return 0;

            /*
             * nr_free_pages() is very expensive on large systems,
             * only call if we're about to fail.
             */
            n = nr_free_pages();

            /*
             * Leave reserved pages. The pages are not for anonymous pages.
             */
            if (n <= totalreserve_pages)
                  goto error;
            else
                  n -= totalreserve_pages;

            /*
             * Leave the last 3% for root
             */
            if (!cap_sys_admin)
                  n -= n / 32;
            free += n;

            if (free > pages)
                  return 0;

            goto error;
      }

      allowed = (totalram_pages - hugetlb_total_pages())
                  * sysctl_overcommit_ratio / 100;
      /*
       * Leave the last 3% for root
       */
      if (!cap_sys_admin)
            allowed -= allowed / 32;
      allowed += total_swap_pages;

      /* Don't let a single process grow too big:
         leave 3% of the size of this process for other processes */
      allowed -= mm->total_vm / 32;

      /*
       * cast `allowed' as a signed long because vm_committed_space
       * sometimes has a negative value
       */
      if (atomic_read(&vm_committed_space) < (long)allowed)
            return 0;
error:
      vm_unacct_memory(pages);

      return -ENOMEM;
}

/*
 * Requires inode->i_mapping->i_mmap_lock
 */
static void __remove_shared_vm_struct(struct vm_area_struct *vma,
            struct file *file, struct address_space *mapping)
{
      if (vma->vm_flags & VM_DENYWRITE)
            atomic_inc(&file->f_path.dentry->d_inode->i_writecount);
      if (vma->vm_flags & VM_SHARED)
            mapping->i_mmap_writable--;

      flush_dcache_mmap_lock(mapping);
      if (unlikely(vma->vm_flags & VM_NONLINEAR))
            list_del_init(&vma->shared.vm_set.list);
      else
            vma_prio_tree_remove(vma, &mapping->i_mmap);
      flush_dcache_mmap_unlock(mapping);
}

/*
 * Unlink a file-based vm structure from its prio_tree, to hide
 * vma from rmap and vmtruncate before freeing its page tables.
 */
void unlink_file_vma(struct vm_area_struct *vma)
{
      struct file *file = vma->vm_file;

      if (file) {
            struct address_space *mapping = file->f_mapping;
            spin_lock(&mapping->i_mmap_lock);
            __remove_shared_vm_struct(vma, file, mapping);
            spin_unlock(&mapping->i_mmap_lock);
      }
}

/*
 * Close a vm structure and free it, returning the next.
 */
static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
{
      struct vm_area_struct *next = vma->vm_next;

      might_sleep();
      if (vma->vm_ops && vma->vm_ops->close)
            vma->vm_ops->close(vma);
      if (vma->vm_file)
            fput(vma->vm_file);
      mpol_free(vma_policy(vma));
      kmem_cache_free(vm_area_cachep, vma);
      return next;
}

asmlinkage unsigned long sys_brk(unsigned long brk)
{
      unsigned long rlim, retval;
      unsigned long newbrk, oldbrk;
      struct mm_struct *mm = current->mm;

      down_write(&mm->mmap_sem);

      if (brk < mm->end_code)
            goto out;

      /*
       * Check against rlimit here. If this check is done later after the test
       * of oldbrk with newbrk then it can escape the test and let the data
       * segment grow beyond its set limit the in case where the limit is
       * not page aligned -Ram Gupta
       */
      rlim = current->signal->rlim[RLIMIT_DATA].rlim_cur;
      if (rlim < RLIM_INFINITY && brk - mm->start_data > rlim)
            goto out;

      newbrk = PAGE_ALIGN(brk);
      oldbrk = PAGE_ALIGN(mm->brk);
      if (oldbrk == newbrk)
            goto set_brk;

      /* Always allow shrinking brk. */
      if (brk <= mm->brk) {
            if (!do_munmap(mm, newbrk, oldbrk-newbrk))
                  goto set_brk;
            goto out;
      }

      /* Check against existing mmap mappings. */
      if (find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE))
            goto out;

      /* Ok, looks good - let it rip. */
      if (do_brk(oldbrk, newbrk-oldbrk) != oldbrk)
            goto out;
set_brk:
      mm->brk = brk;
out:
      retval = mm->brk;
      up_write(&mm->mmap_sem);
      return retval;
}

#ifdef DEBUG_MM_RB
static int browse_rb(struct rb_root *root)
{
      int i = 0, j;
      struct rb_node *nd, *pn = NULL;
      unsigned long prev = 0, pend = 0;

      for (nd = rb_first(root); nd; nd = rb_next(nd)) {
            struct vm_area_struct *vma;
            vma = rb_entry(nd, struct vm_area_struct, vm_rb);
            if (vma->vm_start < prev)
                  printk("vm_start %lx prev %lx\n", vma->vm_start, prev), i = -1;
            if (vma->vm_start < pend)
                  printk("vm_start %lx pend %lx\n", vma->vm_start, pend);
            if (vma->vm_start > vma->vm_end)
                  printk("vm_end %lx < vm_start %lx\n", vma->vm_end, vma->vm_start);
            i++;
            pn = nd;
            prev = vma->vm_start;
            pend = vma->vm_end;
      }
      j = 0;
      for (nd = pn; nd; nd = rb_prev(nd)) {
            j++;
      }
      if (i != j)
            printk("backwards %d, forwards %d\n", j, i), i = 0;
      return i;
}

void validate_mm(struct mm_struct *mm)
{
      int bug = 0;
      int i = 0;
      struct vm_area_struct *tmp = mm->mmap;
      while (tmp) {
            tmp = tmp->vm_next;
            i++;
      }
      if (i != mm->map_count)
            printk("map_count %d vm_next %d\n", mm->map_count, i), bug = 1;
      i = browse_rb(&mm->mm_rb);
      if (i != mm->map_count)
            printk("map_count %d rb %d\n", mm->map_count, i), bug = 1;
      BUG_ON(bug);
}
#else
#define validate_mm(mm) do { } while (0)
#endif

static struct vm_area_struct *
find_vma_prepare(struct mm_struct *mm, unsigned long addr,
            struct vm_area_struct **pprev, struct rb_node ***rb_link,
            struct rb_node ** rb_parent)
{
      struct vm_area_struct * vma;
      struct rb_node ** __rb_link, * __rb_parent, * rb_prev;

      __rb_link = &mm->mm_rb.rb_node;
      rb_prev = __rb_parent = NULL;
      vma = NULL;

      while (*__rb_link) {
            struct vm_area_struct *vma_tmp;

            __rb_parent = *__rb_link;
            vma_tmp = rb_entry(__rb_parent, struct vm_area_struct, vm_rb);

            if (vma_tmp->vm_end > addr) {
                  vma = vma_tmp;
                  if (vma_tmp->vm_start <= addr)
                        return vma;
                  __rb_link = &__rb_parent->rb_left;
            } else {
                  rb_prev = __rb_parent;
                  __rb_link = &__rb_parent->rb_right;
            }
      }

      *pprev = NULL;
      if (rb_prev)
            *pprev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
      *rb_link = __rb_link;
      *rb_parent = __rb_parent;
      return vma;
}

static inline void
__vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
            struct vm_area_struct *prev, struct rb_node *rb_parent)
{
      if (prev) {
            vma->vm_next = prev->vm_next;
            prev->vm_next = vma;
      } else {
            mm->mmap = vma;
            if (rb_parent)
                  vma->vm_next = rb_entry(rb_parent,
                              struct vm_area_struct, vm_rb);
            else
                  vma->vm_next = NULL;
      }
}

void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
            struct rb_node **rb_link, struct rb_node *rb_parent)
{
      rb_link_node(&vma->vm_rb, rb_parent, rb_link);
      rb_insert_color(&vma->vm_rb, &mm->mm_rb);
}

static inline void __vma_link_file(struct vm_area_struct *vma)
{
      struct file * file;

      file = vma->vm_file;
      if (file) {
            struct address_space *mapping = file->f_mapping;

            if (vma->vm_flags & VM_DENYWRITE)
                  atomic_dec(&file->f_path.dentry->d_inode->i_writecount);
            if (vma->vm_flags & VM_SHARED)
                  mapping->i_mmap_writable++;

            flush_dcache_mmap_lock(mapping);
            if (unlikely(vma->vm_flags & VM_NONLINEAR))
                  vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
            else
                  vma_prio_tree_insert(vma, &mapping->i_mmap);
            flush_dcache_mmap_unlock(mapping);
      }
}

static void
__vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
      struct vm_area_struct *prev, struct rb_node **rb_link,
      struct rb_node *rb_parent)
{
      __vma_link_list(mm, vma, prev, rb_parent);
      __vma_link_rb(mm, vma, rb_link, rb_parent);
      __anon_vma_link(vma);
}

static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
                  struct vm_area_struct *prev, struct rb_node **rb_link,
                  struct rb_node *rb_parent)
{
      struct address_space *mapping = NULL;

      if (vma->vm_file)
            mapping = vma->vm_file->f_mapping;

      if (mapping) {
            spin_lock(&mapping->i_mmap_lock);
            vma->vm_truncate_count = mapping->truncate_count;
      }
      anon_vma_lock(vma);

      __vma_link(mm, vma, prev, rb_link, rb_parent);
      __vma_link_file(vma);

      anon_vma_unlock(vma);
      if (mapping)
            spin_unlock(&mapping->i_mmap_lock);

      mm->map_count++;
      validate_mm(mm);
}

/*
 * Helper for vma_adjust in the split_vma insert case:
 * insert vm structure into list and rbtree and anon_vma,
 * but it has already been inserted into prio_tree earlier.
 */
static void
__insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
{
      struct vm_area_struct * __vma, * prev;
      struct rb_node ** rb_link, * rb_parent;

      __vma = find_vma_prepare(mm, vma->vm_start,&prev, &rb_link, &rb_parent);
      BUG_ON(__vma && __vma->vm_start < vma->vm_end);
      __vma_link(mm, vma, prev, rb_link, rb_parent);
      mm->map_count++;
}

static inline void
__vma_unlink(struct mm_struct *mm, struct vm_area_struct *vma,
            struct vm_area_struct *prev)
{
      prev->vm_next = vma->vm_next;
      rb_erase(&vma->vm_rb, &mm->mm_rb);
      if (mm->mmap_cache == vma)
            mm->mmap_cache = prev;
}

/*
 * We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
 * is already present in an i_mmap tree without adjusting the tree.
 * The following helper function should be used when such adjustments
 * are necessary.  The "insert" vma (if any) is to be inserted
 * before we drop the necessary locks.
 */
void vma_adjust(struct vm_area_struct *vma, unsigned long start,
      unsigned long end, pgoff_t pgoff, struct vm_area_struct *insert)
{
      struct mm_struct *mm = vma->vm_mm;
      struct vm_area_struct *next = vma->vm_next;
      struct vm_area_struct *importer = NULL;
      struct address_space *mapping = NULL;
      struct prio_tree_root *root = NULL;
      struct file *file = vma->vm_file;
      struct anon_vma *anon_vma = NULL;
      long adjust_next = 0;
      int remove_next = 0;

      if (next && !insert) {
            if (end >= next->vm_end) {
                  /*
                   * vma expands, overlapping all the next, and
                   * perhaps the one after too (mprotect case 6).
                   */
again:                  remove_next = 1 + (end > next->vm_end);
                  end = next->vm_end;
                  anon_vma = next->anon_vma;
                  importer = vma;
            } else if (end > next->vm_start) {
                  /*
                   * vma expands, overlapping part of the next:
                   * mprotect case 5 shifting the boundary up.
                   */
                  adjust_next = (end - next->vm_start) >> PAGE_SHIFT;
                  anon_vma = next->anon_vma;
                  importer = vma;
            } else if (end < vma->vm_end) {
                  /*
                   * vma shrinks, and !insert tells it's not
                   * split_vma inserting another: so it must be
                   * mprotect case 4 shifting the boundary down.
                   */
                  adjust_next = - ((vma->vm_end - end) >> PAGE_SHIFT);
                  anon_vma = next->anon_vma;
                  importer = next;
            }
      }

      if (file) {
            mapping = file->f_mapping;
            if (!(vma->vm_flags & VM_NONLINEAR))
                  root = &mapping->i_mmap;
            spin_lock(&mapping->i_mmap_lock);
            if (importer &&
                vma->vm_truncate_count != next->vm_truncate_count) {
                  /*
                   * unmap_mapping_range might be in progress:
                   * ensure that the expanding vma is rescanned.
                   */
                  importer->vm_truncate_count = 0;
            }
            if (insert) {
                  insert->vm_truncate_count = vma->vm_truncate_count;
                  /*
                   * Put into prio_tree now, so instantiated pages
                   * are visible to arm/parisc __flush_dcache_page
                   * throughout; but we cannot insert into address
                   * space until vma start or end is updated.
                   */
                  __vma_link_file(insert);
            }
      }

      /*
       * When changing only vma->vm_end, we don't really need
       * anon_vma lock: but is that case worth optimizing out?
       */
      if (vma->anon_vma)
            anon_vma = vma->anon_vma;
      if (anon_vma) {
            spin_lock(&anon_vma->lock);
            /*
             * Easily overlooked: when mprotect shifts the boundary,
             * make sure the expanding vma has anon_vma set if the
             * shrinking vma had, to cover any anon pages imported.
             */
            if (importer && !importer->anon_vma) {
                  importer->anon_vma = anon_vma;
                  __anon_vma_link(importer);
            }
      }

      if (root) {
            flush_dcache_mmap_lock(mapping);
            vma_prio_tree_remove(vma, root);
            if (adjust_next)
                  vma_prio_tree_remove(next, root);
      }

      vma->vm_start = start;
      vma->vm_end = end;
      vma->vm_pgoff = pgoff;
      if (adjust_next) {
            next->vm_start += adjust_next << PAGE_SHIFT;
            next->vm_pgoff += adjust_next;
      }

      if (root) {
            if (adjust_next)
                  vma_prio_tree_insert(next, root);
            vma_prio_tree_insert(vma, root);
            flush_dcache_mmap_unlock(mapping);
      }

      if (remove_next) {
            /*
             * vma_merge has merged next into vma, and needs
             * us to remove next before dropping the locks.
             */
            __vma_unlink(mm, next, vma);
            if (file)
                  __remove_shared_vm_struct(next, file, mapping);
            if (next->anon_vma)
                  __anon_vma_merge(vma, next);
      } else if (insert) {
            /*
             * split_vma has split insert from vma, and needs
             * us to insert it before dropping the locks
             * (it may either follow vma or precede it).
             */
            __insert_vm_struct(mm, insert);
      }

      if (anon_vma)
            spin_unlock(&anon_vma->lock);
      if (mapping)
            spin_unlock(&mapping->i_mmap_lock);

      if (remove_next) {
            if (file)
                  fput(file);
            mm->map_count--;
            mpol_free(vma_policy(next));
            kmem_cache_free(vm_area_cachep, next);
            /*
             * In mprotect's case 6 (see comments on vma_merge),
             * we must remove another next too. It would clutter
             * up the code too much to do both in one go.
             */
            if (remove_next == 2) {
                  next = vma->vm_next;
                  goto again;
            }
      }

      validate_mm(mm);
}

/*
 * If the vma has a ->close operation then the driver probably needs to release
 * per-vma resources, so we don't attempt to merge those.
 */
#define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP)

static inline int is_mergeable_vma(struct vm_area_struct *vma,
                  struct file *file, unsigned long vm_flags)
{
      if (vma->vm_flags != vm_flags)
            return 0;
      if (vma->vm_file != file)
            return 0;
      if (vma->vm_ops && vma->vm_ops->close)
            return 0;
      return 1;
}

static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
                              struct anon_vma *anon_vma2)
{
      return !anon_vma1 || !anon_vma2 || (anon_vma1 == anon_vma2);
}

/*
 * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
 * in front of (at a lower virtual address and file offset than) the vma.
 *
 * We cannot merge two vmas if they have differently assigned (non-NULL)
 * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
 *
 * We don't check here for the merged mmap wrapping around the end of pagecache
 * indices (16TB on ia32) because do_mmap_pgoff() does not permit mmap's which
 * wrap, nor mmaps which cover the final page at index -1UL.
 */
static int
can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
      struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
{
      if (is_mergeable_vma(vma, file, vm_flags) &&
          is_mergeable_anon_vma(anon_vma, vma->anon_vma)) {
            if (vma->vm_pgoff == vm_pgoff)
                  return 1;
      }
      return 0;
}

/*
 * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
 * beyond (at a higher virtual address and file offset than) the vma.
 *
 * We cannot merge two vmas if they have differently assigned (non-NULL)
 * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
 */
static int
can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
      struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
{
      if (is_mergeable_vma(vma, file, vm_flags) &&
          is_mergeable_anon_vma(anon_vma, vma->anon_vma)) {
            pgoff_t vm_pglen;
            vm_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
            if (vma->vm_pgoff + vm_pglen == vm_pgoff)
                  return 1;
      }
      return 0;
}

/*
 * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
 * whether that can be merged with its predecessor or its successor.
 * Or both (it neatly fills a hole).
 *
 * In most cases - when called for mmap, brk or mremap - [addr,end) is
 * certain not to be mapped by the time vma_merge is called; but when
 * called for mprotect, it is certain to be already mapped (either at
 * an offset within prev, or at the start of next), and the flags of
 * this area are about to be changed to vm_flags - and the no-change
 * case has already been eliminated.
 *
 * The following mprotect cases have to be considered, where AAAA is
 * the area passed down from mprotect_fixup, never extending beyond one
 * vma, PPPPPP is the prev vma specified, and NNNNNN the next vma after:
 *
 *     AAAA             AAAA                AAAA          AAAA
 *    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPNNNNXXXX
 *    cannot merge    might become    might become    might become
 *                    PPNNNNNNNNNN    PPPPPPPPPPNN    PPPPPPPPPPPP 6 or
 *    mmap, brk or    case 4 below    case 5 below    PPPPPPPPXXXX 7 or
 *    mremap move:                                    PPPPNNNNNNNN 8
 *        AAAA
 *    PPPP    NNNN    PPPPPPPPPPPP    PPPPPPPPNNNN    PPPPNNNNNNNN
 *    might become    case 1 below    case 2 below    case 3 below
 *
 * Odd one out? Case 8, because it extends NNNN but needs flags of XXXX:
 * mprotect_fixup updates vm_flags & vm_page_prot on successful return.
 */
struct vm_area_struct *vma_merge(struct mm_struct *mm,
                  struct vm_area_struct *prev, unsigned long addr,
                  unsigned long end, unsigned long vm_flags,
                  struct anon_vma *anon_vma, struct file *file,
                  pgoff_t pgoff, struct mempolicy *policy)
{
      pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
      struct vm_area_struct *area, *next;

      /*
       * We later require that vma->vm_flags == vm_flags,
       * so this tests vma->vm_flags & VM_SPECIAL, too.
       */
      if (vm_flags & VM_SPECIAL)
            return NULL;

      if (prev)
            next = prev->vm_next;
      else
            next = mm->mmap;
      area = next;
      if (next && next->vm_end == end)          /* cases 6, 7, 8 */
            next = next->vm_next;

      /*
       * Can it merge with the predecessor?
       */
      if (prev && prev->vm_end == addr &&
                  mpol_equal(vma_policy(prev), policy) &&
                  can_vma_merge_after(prev, vm_flags,
                                    anon_vma, file, pgoff)) {
            /*
             * OK, it can.  Can we now merge in the successor as well?
             */
            if (next && end == next->vm_start &&
                        mpol_equal(policy, vma_policy(next)) &&
                        can_vma_merge_before(next, vm_flags,
                              anon_vma, file, pgoff+pglen) &&
                        is_mergeable_anon_vma(prev->anon_vma,
                                          next->anon_vma)) {
                                          /* cases 1, 6 */
                  vma_adjust(prev, prev->vm_start,
                        next->vm_end, prev->vm_pgoff, NULL);
            } else                              /* cases 2, 5, 7 */
                  vma_adjust(prev, prev->vm_start,
                        end, prev->vm_pgoff, NULL);
            return prev;
      }

      /*
       * Can this new request be merged in front of next?
       */
      if (next && end == next->vm_start &&
                  mpol_equal(policy, vma_policy(next)) &&
                  can_vma_merge_before(next, vm_flags,
                              anon_vma, file, pgoff+pglen)) {
            if (prev && addr < prev->vm_end)    /* case 4 */
                  vma_adjust(prev, prev->vm_start,
                        addr, prev->vm_pgoff, NULL);
            else                          /* cases 3, 8 */
                  vma_adjust(area, addr, next->vm_end,
                        next->vm_pgoff - pglen, NULL);
            return area;
      }

      return NULL;
}

/*
 * find_mergeable_anon_vma is used by anon_vma_prepare, to check
 * neighbouring vmas for a suitable anon_vma, before it goes off
 * to allocate a new anon_vma.  It checks because a repetitive
 * sequence of mprotects and faults may otherwise lead to distinct
 * anon_vmas being allocated, preventing vma merge in subsequent
 * mprotect.
 */
struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
{
      struct vm_area_struct *near;
      unsigned long vm_flags;

      near = vma->vm_next;
      if (!near)
            goto try_prev;

      /*
       * Since only mprotect tries to remerge vmas, match flags
       * which might be mprotected into each other later on.
       * Neither mlock nor madvise tries to remerge at present,
       * so leave their flags as obstructing a merge.
       */
      vm_flags = vma->vm_flags & ~(VM_READ|VM_WRITE|VM_EXEC);
      vm_flags |= near->vm_flags & (VM_READ|VM_WRITE|VM_EXEC);

      if (near->anon_vma && vma->vm_end == near->vm_start &&
                  mpol_equal(vma_policy(vma), vma_policy(near)) &&
                  can_vma_merge_before(near, vm_flags,
                        NULL, vma->vm_file, vma->vm_pgoff +
                        ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT)))
            return near->anon_vma;
try_prev:
      /*
       * It is potentially slow to have to call find_vma_prev here.
       * But it's only on the first write fault on the vma, not
       * every time, and we could devise a way to avoid it later
       * (e.g. stash info in next's anon_vma_node when assigning
       * an anon_vma, or when trying vma_merge).  Another time.
       */
      BUG_ON(find_vma_prev(vma->vm_mm, vma->vm_start, &near) != vma);
      if (!near)
            goto none;

      vm_flags = vma->vm_flags & ~(VM_READ|VM_WRITE|VM_EXEC);
      vm_flags |= near->vm_flags & (VM_READ|VM_WRITE|VM_EXEC);

      if (near->anon_vma && near->vm_end == vma->vm_start &&
                  mpol_equal(vma_policy(near), vma_policy(vma)) &&
                  can_vma_merge_after(near, vm_flags,
                        NULL, vma->vm_file, vma->vm_pgoff))
            return near->anon_vma;
none:
      /*
       * There's no absolute need to look only at touching neighbours:
       * we could search further afield for "compatible" anon_vmas.
       * But it would probably just be a waste of time searching,
       * or lead to too many vmas hanging off the same anon_vma.
       * We're trying to allow mprotect remerging later on,
       * not trying to minimize memory used for anon_vmas.
       */
      return NULL;
}

#ifdef CONFIG_PROC_FS
void vm_stat_account(struct mm_struct *mm, unsigned long flags,
                                    struct file *file, long pages)
{
      const unsigned long stack_flags
            = VM_STACK_FLAGS & (VM_GROWSUP|VM_GROWSDOWN);

      if (file) {
            mm->shared_vm += pages;
            if ((flags & (VM_EXEC|VM_WRITE)) == VM_EXEC)
                  mm->exec_vm += pages;
      } else if (flags & stack_flags)
            mm->stack_vm += pages;
      if (flags & (VM_RESERVED|VM_IO))
            mm->reserved_vm += pages;
}
#endif /* CONFIG_PROC_FS */

/*
 * The caller must hold down_write(current->mm->mmap_sem).
 */

unsigned long do_mmap_pgoff(struct file * file, unsigned long addr,
                  unsigned long len, unsigned long prot,
                  unsigned long flags, unsigned long pgoff)
{
      struct mm_struct * mm = current->mm;
      struct inode *inode;
      unsigned int vm_flags;
      int error;
      int accountable = 1;
      unsigned long reqprot = prot;

      /*
       * Does the application expect PROT_READ to imply PROT_EXEC?
       *
       * (the exception is when the underlying filesystem is noexec
       *  mounted, in which case we dont add PROT_EXEC.)
       */
      if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
            if (!(file && (file->f_path.mnt->mnt_flags & MNT_NOEXEC)))
                  prot |= PROT_EXEC;

      if (!len)
            return -EINVAL;

      if (!(flags & MAP_FIXED))
            addr = round_hint_to_min(addr);

      error = arch_mmap_check(addr, len, flags);
      if (error)
            return error;

      /* Careful about overflows.. */
      len = PAGE_ALIGN(len);
      if (!len || len > TASK_SIZE)
            return -ENOMEM;

      /* offset overflow? */
      if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
               return -EOVERFLOW;

      /* Too many mappings? */
      if (mm->map_count > sysctl_max_map_count)
            return -ENOMEM;

      /* Obtain the address to map to. we verify (or select) it and ensure
       * that it represents a valid section of the address space.
       */
      addr = get_unmapped_area(file, addr, len, pgoff, flags);
      if (addr & ~PAGE_MASK)
            return addr;

      /* Do simple checking here so the lower-level routines won't have
       * to. we assume access permissions have been handled by the open
       * of the memory object, so we don't do any here.
       */
      vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags) |
                  mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

      if (flags & MAP_LOCKED) {
            if (!can_do_mlock())
                  return -EPERM;
            vm_flags |= VM_LOCKED;
      }
      /* mlock MCL_FUTURE? */
      if (vm_flags & VM_LOCKED) {
            unsigned long locked, lock_limit;
            locked = len >> PAGE_SHIFT;
            locked += mm->locked_vm;
            lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
            lock_limit >>= PAGE_SHIFT;
            if (locked > lock_limit && !capable(CAP_IPC_LOCK))
                  return -EAGAIN;
      }

      inode = file ? file->f_path.dentry->d_inode : NULL;

      if (file) {
            switch (flags & MAP_TYPE) {
            case MAP_SHARED:
                  if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
                        return -EACCES;

                  /*
                   * Make sure we don't allow writing to an append-only
                   * file..
                   */
                  if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
                        return -EACCES;

                  /*
                   * Make sure there are no mandatory locks on the file.
                   */
                  if (locks_verify_locked(inode))
                        return -EAGAIN;

                  vm_flags |= VM_SHARED | VM_MAYSHARE;
                  if (!(file->f_mode & FMODE_WRITE))
                        vm_flags &= ~(VM_MAYWRITE | VM_SHARED);

                  /* fall through */
            case MAP_PRIVATE:
                  if (!(file->f_mode & FMODE_READ))
                        return -EACCES;
                  if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) {
                        if (vm_flags & VM_EXEC)
                              return -EPERM;
                        vm_flags &= ~VM_MAYEXEC;
                  }
                  if (is_file_hugepages(file))
                        accountable = 0;

                  if (!file->f_op || !file->f_op->mmap)
                        return -ENODEV;
                  break;

            default:
                  return -EINVAL;
            }
      } else {
            switch (flags & MAP_TYPE) {
            case MAP_SHARED:
                  vm_flags |= VM_SHARED | VM_MAYSHARE;
                  break;
            case MAP_PRIVATE:
                  /*
                   * Set pgoff according to addr for anon_vma.
                   */
                  pgoff = addr >> PAGE_SHIFT;
                  break;
            default:
                  return -EINVAL;
            }
      }

      error = security_file_mmap(file, reqprot, prot, flags, addr, 0);
      if (error)
            return error;

      return mmap_region(file, addr, len, flags, vm_flags, pgoff,
                     accountable);
}
EXPORT_SYMBOL(do_mmap_pgoff);

/*
 * Some shared mappigns will want the pages marked read-only
 * to track write events. If so, we'll downgrade vm_page_prot
 * to the private version (using protection_map[] without the
 * VM_SHARED bit).
 */
int vma_wants_writenotify(struct vm_area_struct *vma)
{
      unsigned int vm_flags = vma->vm_flags;

      /* If it was private or non-writable, the write bit is already clear */
      if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED)))
            return 0;

      /* The backer wishes to know when pages are first written to? */
      if (vma->vm_ops && vma->vm_ops->page_mkwrite)
            return 1;

      /* The open routine did something to the protections already? */
      if (pgprot_val(vma->vm_page_prot) !=
          pgprot_val(vm_get_page_prot(vm_flags)))
            return 0;

      /* Specialty mapping? */
      if (vm_flags & (VM_PFNMAP|VM_INSERTPAGE))
            return 0;

      /* Can the mapping track the dirty pages? */
      return vma->vm_file && vma->vm_file->f_mapping &&
            mapping_cap_account_dirty(vma->vm_file->f_mapping);
}


unsigned long mmap_region(struct file *file, unsigned long addr,
                    unsigned long len, unsigned long flags,
                    unsigned int vm_flags, unsigned long pgoff,
                    int accountable)
{
      struct mm_struct *mm = current->mm;
      struct vm_area_struct *vma, *prev;
      int correct_wcount = 0;
      int error;
      struct rb_node **rb_link, *rb_parent;
      unsigned long charged = 0;
      struct inode *inode =  file ? file->f_path.dentry->d_inode : NULL;

      /* Clear old maps */
      error = -ENOMEM;
munmap_back:
      vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
      if (vma && vma->vm_start < addr + len) {
            if (do_munmap(mm, addr, len))
                  return -ENOMEM;
            goto munmap_back;
      }

      /* Check against address space limit. */
      if (!may_expand_vm(mm, len >> PAGE_SHIFT))
            return -ENOMEM;

      if (accountable && (!(flags & MAP_NORESERVE) ||
                      sysctl_overcommit_memory == OVERCOMMIT_NEVER)) {
            if (vm_flags & VM_SHARED) {
                  /* Check memory availability in shmem_file_setup? */
                  vm_flags |= VM_ACCOUNT;
            } else if (vm_flags & VM_WRITE) {
                  /*
                   * Private writable mapping: check memory availability
                   */
                  charged = len >> PAGE_SHIFT;
                  if (security_vm_enough_memory(charged))
                        return -ENOMEM;
                  vm_flags |= VM_ACCOUNT;
            }
      }

      /*
       * Can we just expand an old private anonymous mapping?
       * The VM_SHARED test is necessary because shmem_zero_setup
       * will create the file object for a shared anonymous map below.
       */
      if (!file && !(vm_flags & VM_SHARED) &&
          vma_merge(mm, prev, addr, addr + len, vm_flags,
                              NULL, NULL, pgoff, NULL))
            goto out;

      /*
       * Determine the object being mapped and call the appropriate
       * specific mapper. the address has already been validated, but
       * not unmapped, but the maps are removed from the list.
       */
      vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
      if (!vma) {
            error = -ENOMEM;
            goto unacct_error;
      }

      vma->vm_mm = mm;
      vma->vm_start = addr;
      vma->vm_end = addr + len;
      vma->vm_flags = vm_flags;
      vma->vm_page_prot = vm_get_page_prot(vm_flags);
      vma->vm_pgoff = pgoff;

      if (file) {
            error = -EINVAL;
            if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                  goto free_vma;
            if (vm_flags & VM_DENYWRITE) {
                  error = deny_write_access(file);
                  if (error)
                        goto free_vma;
                  correct_wcount = 1;
            }
            vma->vm_file = file;
            get_file(file);
            error = file->f_op->mmap(file, vma);
            if (error)
                  goto unmap_and_free_vma;
      } else if (vm_flags & VM_SHARED) {
            error = shmem_zero_setup(vma);
            if (error)
                  goto free_vma;
      }

      /* We set VM_ACCOUNT in a shared mapping's vm_flags, to inform
       * shmem_zero_setup (perhaps called through /dev/zero's ->mmap)
       * that memory reservation must be checked; but that reservation
       * belongs to shared memory object, not to vma: so now clear it.
       */
      if ((vm_flags & (VM_SHARED|VM_ACCOUNT)) == (VM_SHARED|VM_ACCOUNT))
            vma->vm_flags &= ~VM_ACCOUNT;

      /* Can addr have changed??
       *
       * Answer: Yes, several device drivers can do it in their
       *         f_op->mmap method. -DaveM
       */
      addr = vma->vm_start;
      pgoff = vma->vm_pgoff;
      vm_flags = vma->vm_flags;

      if (vma_wants_writenotify(vma))
            vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);

      if (!file || !vma_merge(mm, prev, addr, vma->vm_end,
                  vma->vm_flags, NULL, file, pgoff, vma_policy(vma))) {
            file = vma->vm_file;
            vma_link(mm, vma, prev, rb_link, rb_parent);
            if (correct_wcount)
                  atomic_inc(&inode->i_writecount);
      } else {
            if (file) {
                  if (correct_wcount)
                        atomic_inc(&inode->i_writecount);
                  fput(file);
            }
            mpol_free(vma_policy(vma));
            kmem_cache_free(vm_area_cachep, vma);
      }
out:  
      mm->total_vm += len >> PAGE_SHIFT;
      vm_stat_account(mm, vm_flags, file, len >> PAGE_SHIFT);
      if (vm_flags & VM_LOCKED) {
            mm->locked_vm += len >> PAGE_SHIFT;
            make_pages_present(addr, addr + len);
      }
      if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK))
            make_pages_present(addr, addr + len);
      return addr;

unmap_and_free_vma:
      if (correct_wcount)
            atomic_inc(&inode->i_writecount);
      vma->vm_file = NULL;
      fput(file);

      /* Undo any partial mapping done by a device driver. */
      unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
      charged = 0;
free_vma:
      kmem_cache_free(vm_area_cachep, vma);
unacct_error:
      if (charged)
            vm_unacct_memory(charged);
      return error;
}

/* Get an address range which is currently unmapped.
 * For shmat() with addr=0.
 *
 * Ugly calling convention alert:
 * Return value with the low bits set means error value,
 * ie
 *    if (ret & ~PAGE_MASK)
 *          error = ret;
 *
 * This function "knows" that -ENOMEM has the bits set.
 */
#ifndef HAVE_ARCH_UNMAPPED_AREA
unsigned long
arch_get_unmapped_area(struct file *filp, unsigned long addr,
            unsigned long len, unsigned long pgoff, unsigned long flags)
{
      struct mm_struct *mm = current->mm;
      struct vm_area_struct *vma;
      unsigned long start_addr;

      if (len > TASK_SIZE)
            return -ENOMEM;

      if (flags & MAP_FIXED)
            return addr;

      if (addr) {
            addr = PAGE_ALIGN(addr);
            vma = find_vma(mm, addr);
            if (TASK_SIZE - len >= addr &&
                (!vma || addr + len <= vma->vm_start))
                  return addr;
      }
      if (len > mm->cached_hole_size) {
              start_addr = addr = mm->free_area_cache;
      } else {
              start_addr = addr = TASK_UNMAPPED_BASE;
              mm->cached_hole_size = 0;
      }

full_search:
      for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
            /* At this point:  (!vma || addr < vma->vm_end). */
            if (TASK_SIZE - len < addr) {
                  /*
                   * Start a new search - just in case we missed
                   * some holes.
                   */
                  if (start_addr != TASK_UNMAPPED_BASE) {
                        addr = TASK_UNMAPPED_BASE;
                          start_addr = addr;
                        mm->cached_hole_size = 0;
                        goto full_search;
                  }
                  return -ENOMEM;
            }
            if (!vma || addr + len <= vma->vm_start) {
                  /*
                   * Remember the place where we stopped the search:
                   */
                  mm->free_area_cache = addr + len;
                  return addr;
            }
            if (addr + mm->cached_hole_size < vma->vm_start)
                    mm->cached_hole_size = vma->vm_start - addr;
            addr = vma->vm_end;
      }
}
#endif      

void arch_unmap_area(struct mm_struct *mm, unsigned long addr)
{
      /*
       * Is this a new hole at the lowest possible address?
       */
      if (addr >= TASK_UNMAPPED_BASE && addr < mm->free_area_cache) {
            mm->free_area_cache = addr;
            mm->cached_hole_size = ~0UL;
      }
}

/*
 * This mmap-allocator allocates new areas top-down from below the
 * stack's low limit (the base):
 */
#ifndef HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
unsigned long
arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
                    const unsigned long len, const unsigned long pgoff,
                    const unsigned long flags)
{
      struct vm_area_struct *vma;
      struct mm_struct *mm = current->mm;
      unsigned long addr = addr0;

      /* requested length too big for entire address space */
      if (len > TASK_SIZE)
            return -ENOMEM;

      if (flags & MAP_FIXED)
            return addr;

      /* requesting a specific address */
      if (addr) {
            addr = PAGE_ALIGN(addr);
            vma = find_vma(mm, addr);
            if (TASK_SIZE - len >= addr &&
                        (!vma || addr + len <= vma->vm_start))
                  return addr;
      }

      /* check if free_area_cache is useful for us */
      if (len <= mm->cached_hole_size) {
              mm->cached_hole_size = 0;
            mm->free_area_cache = mm->mmap_base;
      }

      /* either no address requested or can't fit in requested address hole */
      addr = mm->free_area_cache;

      /* make sure it can fit in the remaining address space */
      if (addr > len) {
            vma = find_vma(mm, addr-len);
            if (!vma || addr <= vma->vm_start)
                  /* remember the address as a hint for next time */
                  return (mm->free_area_cache = addr-len);
      }

      if (mm->mmap_base < len)
            goto bottomup;

      addr = mm->mmap_base-len;

      do {
            /*
             * Lookup failure means no vma is above this address,
             * else if new region fits below vma->vm_start,
             * return with success:
             */
            vma = find_vma(mm, addr);
            if (!vma || addr+len <= vma->vm_start)
                  /* remember the address as a hint for next time */
                  return (mm->free_area_cache = addr);

            /* remember the largest hole we saw so far */
            if (addr + mm->cached_hole_size < vma->vm_start)
                    mm->cached_hole_size = vma->vm_start - addr;

            /* try just below the current vma->vm_start */
            addr = vma->vm_start-len;
      } while (len < vma->vm_start);

bottomup:
      /*
       * A failed mmap() very likely causes application failure,
       * so fall back to the bottom-up function here. This scenario
       * can happen with large stack limits and large mmap()
       * allocations.
       */
      mm->cached_hole_size = ~0UL;
      mm->free_area_cache = TASK_UNMAPPED_BASE;
      addr = arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
      /*
       * Restore the topdown base:
       */
      mm->free_area_cache = mm->mmap_base;
      mm->cached_hole_size = ~0UL;

      return addr;
}
#endif

void arch_unmap_area_topdown(struct mm_struct *mm, unsigned long addr)
{
      /*
       * Is this a new hole at the highest possible address?
       */
      if (addr > mm->free_area_cache)
            mm->free_area_cache = addr;

      /* dont allow allocations above current base */
      if (mm->free_area_cache > mm->mmap_base)
            mm->free_area_cache = mm->mmap_base;
}

unsigned long
get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
            unsigned long pgoff, unsigned long flags)
{
      unsigned long (*get_area)(struct file *, unsigned long,
                          unsigned long, unsigned long, unsigned long);

      get_area = current->mm->get_unmapped_area;
      if (file && file->f_op && file->f_op->get_unmapped_area)
            get_area = file->f_op->get_unmapped_area;
      addr = get_area(file, addr, len, pgoff, flags);
      if (IS_ERR_VALUE(addr))
            return addr;

      if (addr > TASK_SIZE - len)
            return -ENOMEM;
      if (addr & ~PAGE_MASK)
            return -EINVAL;

      return addr;
}

EXPORT_SYMBOL(get_unmapped_area);

/* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long addr)
{
      struct vm_area_struct *vma = NULL;

      if (mm) {
            /* Check the cache first. */
            /* (Cache hit rate is typically around 35%.) */
            vma = mm->mmap_cache;
            if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
                  struct rb_node * rb_node;

                  rb_node = mm->mm_rb.rb_node;
                  vma = NULL;

                  while (rb_node) {
                        struct vm_area_struct * vma_tmp;

                        vma_tmp = rb_entry(rb_node,
                                    struct vm_area_struct, vm_rb);

                        if (vma_tmp->vm_end > addr) {
                              vma = vma_tmp;
                              if (vma_tmp->vm_start <= addr)
                                    break;
                              rb_node = rb_node->rb_left;
                        } else
                              rb_node = rb_node->rb_right;
                  }
                  if (vma)
                        mm->mmap_cache = vma;
            }
      }
      return vma;
}

EXPORT_SYMBOL(find_vma);

/* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
struct vm_area_struct *
find_vma_prev(struct mm_struct *mm, unsigned long addr,
                  struct vm_area_struct **pprev)
{
      struct vm_area_struct *vma = NULL, *prev = NULL;
      struct rb_node * rb_node;
      if (!mm)
            goto out;

      /* Guard against addr being lower than the first VMA */
      vma = mm->mmap;

      /* Go through the RB tree quickly. */
      rb_node = mm->mm_rb.rb_node;

      while (rb_node) {
            struct vm_area_struct *vma_tmp;
            vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);

            if (addr < vma_tmp->vm_end) {
                  rb_node = rb_node->rb_left;
            } else {
                  prev = vma_tmp;
                  if (!prev->vm_next || (addr < prev->vm_next->vm_end))
                        break;
                  rb_node = rb_node->rb_right;
            }
      }

out:
      *pprev = prev;
      return prev ? prev->vm_next : vma;
}

/*
 * Verify that the stack growth is acceptable and
 * update accounting. This is shared with both the
 * grow-up and grow-down cases.
 */
static int acct_stack_growth(struct vm_area_struct * vma, unsigned long size, unsigned long grow)
{
      struct mm_struct *mm = vma->vm_mm;
      struct rlimit *rlim = current->signal->rlim;
      unsigned long new_start;

      /* address space limit tests */
      if (!may_expand_vm(mm, grow))
            return -ENOMEM;

      /* Stack limit test */
      if (size > rlim[RLIMIT_STACK].rlim_cur)
            return -ENOMEM;

      /* mlock limit tests */
      if (vma->vm_flags & VM_LOCKED) {
            unsigned long locked;
            unsigned long limit;
            locked = mm->locked_vm + grow;
            limit = rlim[RLIMIT_MEMLOCK].rlim_cur >> PAGE_SHIFT;
            if (locked > limit && !capable(CAP_IPC_LOCK))
                  return -ENOMEM;
      }

      /* Check to ensure the stack will not grow into a hugetlb-only region */
      new_start = (vma->vm_flags & VM_GROWSUP) ? vma->vm_start :
                  vma->vm_end - size;
      if (is_hugepage_only_range(vma->vm_mm, new_start, size))
            return -EFAULT;

      /*
       * Overcommit..  This must be the final test, as it will
       * update security statistics.
       */
      if (security_vm_enough_memory(grow))
            return -ENOMEM;

      /* Ok, everything looks good - let it rip */
      mm->total_vm += grow;
      if (vma->vm_flags & VM_LOCKED)
            mm->locked_vm += grow;
      vm_stat_account(mm, vma->vm_flags, vma->vm_file, grow);
      return 0;
}

#if defined(CONFIG_STACK_GROWSUP) || defined(CONFIG_IA64)
/*
 * PA-RISC uses this for its stack; IA64 for its Register Backing Store.
 * vma is the last one with address > vma->vm_end.  Have to extend vma.
 */
#ifndef CONFIG_IA64
static inline
#endif
int expand_upwards(struct vm_area_struct *vma, unsigned long address)
{
      int error;

      if (!(vma->vm_flags & VM_GROWSUP))
            return -EFAULT;

      /*
       * We must make sure the anon_vma is allocated
       * so that the anon_vma locking is not a noop.
       */
      if (unlikely(anon_vma_prepare(vma)))
            return -ENOMEM;
      anon_vma_lock(vma);

      /*
       * vma->vm_start/vm_end cannot change under us because the caller
       * is required to hold the mmap_sem in read mode.  We need the
       * anon_vma lock to serialize against concurrent expand_stacks.
       * Also guard against wrapping around to address 0.
       */
      if (address < PAGE_ALIGN(address+4))
            address = PAGE_ALIGN(address+4);
      else {
            anon_vma_unlock(vma);
            return -ENOMEM;
      }
      error = 0;

      /* Somebody else might have raced and expanded it already */
      if (address > vma->vm_end) {
            unsigned long size, grow;

            size = address - vma->vm_start;
            grow = (address - vma->vm_end) >> PAGE_SHIFT;

            error = acct_stack_growth(vma, size, grow);
            if (!error)
                  vma->vm_end = address;
      }
      anon_vma_unlock(vma);
      return error;
}
#endif /* CONFIG_STACK_GROWSUP || CONFIG_IA64 */

/*
 * vma is the first one with address < vma->vm_start.  Have to extend vma.
 */
static inline int expand_downwards(struct vm_area_struct *vma,
                           unsigned long address)
{
      int error;

      /*
       * We must make sure the anon_vma is allocated
       * so that the anon_vma locking is not a noop.
       */
      if (unlikely(anon_vma_prepare(vma)))
            return -ENOMEM;

      address &= PAGE_MASK;
      error = security_file_mmap(0, 0, 0, 0, address, 1);
      if (error)
            return error;

      anon_vma_lock(vma);

      /*
       * vma->vm_start/vm_end cannot change under us because the caller
       * is required to hold the mmap_sem in read mode.  We need the
       * anon_vma lock to serialize against concurrent expand_stacks.
       */

      /* Somebody else might have raced and expanded it already */
      if (address < vma->vm_start) {
            unsigned long size, grow;

            size = vma->vm_end - address;
            grow = (vma->vm_start - address) >> PAGE_SHIFT;

            error = acct_stack_growth(vma, size, grow);
            if (!error) {
                  vma->vm_start = address;
                  vma->vm_pgoff -= grow;
            }
      }
      anon_vma_unlock(vma);
      return error;
}

int expand_stack_downwards(struct vm_area_struct *vma, unsigned long address)
{
      return expand_downwards(vma, address);
}

#ifdef CONFIG_STACK_GROWSUP
int expand_stack(struct vm_area_struct *vma, unsigned long address)
{
      return expand_upwards(vma, address);
}

struct vm_area_struct *
find_extend_vma(struct mm_struct *mm, unsigned long addr)
{
      struct vm_area_struct *vma, *prev;

      addr &= PAGE_MASK;
      vma = find_vma_prev(mm, addr, &prev);
      if (vma && (vma->vm_start <= addr))
            return vma;
      if (!prev || expand_stack(prev, addr))
            return NULL;
      if (prev->vm_flags & VM_LOCKED)
            make_pages_present(addr, prev->vm_end);
      return prev;
}
#else
int expand_stack(struct vm_area_struct *vma, unsigned long address)
{
      return expand_downwards(vma, address);
}

struct vm_area_struct *
find_extend_vma(struct mm_struct * mm, unsigned long addr)
{
      struct vm_area_struct * vma;
      unsigned long start;

      addr &= PAGE_MASK;
      vma = find_vma(mm,addr);
      if (!vma)
            return NULL;
      if (vma->vm_start <= addr)
            return vma;
      if (!(vma->vm_flags & VM_GROWSDOWN))
            return NULL;
      start = vma->vm_start;
      if (expand_stack(vma, addr))
            return NULL;
      if (vma->vm_flags & VM_LOCKED)
            make_pages_present(addr, start);
      return vma;
}
#endif

/*
 * Ok - we have the memory areas we should free on the vma list,
 * so release them, and do the vma updates.
 *
 * Called with the mm semaphore held.
 */
static void remove_vma_list(struct mm_struct *mm, struct vm_area_struct *vma)
{
      /* Update high watermark before we lower total_vm */
      update_hiwater_vm(mm);
      do {
            long nrpages = vma_pages(vma);

            mm->total_vm -= nrpages;
            if (vma->vm_flags & VM_LOCKED)
                  mm->locked_vm -= nrpages;
            vm_stat_account(mm, vma->vm_flags, vma->vm_file, -nrpages);
            vma = remove_vma(vma);
      } while (vma);
      validate_mm(mm);
}

/*
 * Get rid of page table information in the indicated region.
 *
 * Called with the mm semaphore held.
 */
static void unmap_region(struct mm_struct *mm,
            struct vm_area_struct *vma, struct vm_area_struct *prev,
            unsigned long start, unsigned long end)
{
      struct vm_area_struct *next = prev? prev->vm_next: mm->mmap;
      struct mmu_gather *tlb;
      unsigned long nr_accounted = 0;

      lru_add_drain();
      tlb = tlb_gather_mmu(mm, 0);
      update_hiwater_rss(mm);
      unmap_vmas(&tlb, vma, start, end, &nr_accounted, NULL);
      vm_unacct_memory(nr_accounted);
      free_pgtables(&tlb, vma, prev? prev->vm_end: FIRST_USER_ADDRESS,
                         next? next->vm_start: 0);
      tlb_finish_mmu(tlb, start, end);
}

/*
 * Create a list of vma's touched by the unmap, removing them from the mm's
 * vma list as we go..
 */
static void
detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
      struct vm_area_struct *prev, unsigned long end)
{
      struct vm_area_struct **insertion_point;
      struct vm_area_struct *tail_vma = NULL;
      unsigned long addr;

      insertion_point = (prev ? &prev->vm_next : &mm->mmap);
      do {
            rb_erase(&vma->vm_rb, &mm->mm_rb);
            mm->map_count--;
            tail_vma = vma;
            vma = vma->vm_next;
      } while (vma && vma->vm_start < end);
      *insertion_point = vma;
      tail_vma->vm_next = NULL;
      if (mm->unmap_area == arch_unmap_area)
            addr = prev ? prev->vm_end : mm->mmap_base;
      else
            addr = vma ?  vma->vm_start : mm->mmap_base;
      mm->unmap_area(mm, addr);
      mm->mmap_cache = NULL;        /* Kill the cache. */
}

/*
 * Split a vma into two pieces at address 'addr', a new vma is allocated
 * either for the first part or the tail.
 */
int split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
            unsigned long addr, int new_below)
{
      struct mempolicy *pol;
      struct vm_area_struct *new;

      if (is_vm_hugetlb_page(vma) && (addr & ~HPAGE_MASK))
            return -EINVAL;

      if (mm->map_count >= sysctl_max_map_count)
            return -ENOMEM;

      new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
      if (!new)
            return -ENOMEM;

      /* most fields are the same, copy all, and then fixup */
      *new = *vma;

      if (new_below)
            new->vm_end = addr;
      else {
            new->vm_start = addr;
            new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
      }

      pol = mpol_copy(vma_policy(vma));
      if (IS_ERR(pol)) {
            kmem_cache_free(vm_area_cachep, new);
            return PTR_ERR(pol);
      }
      vma_set_policy(new, pol);

      if (new->vm_file)
            get_file(new->vm_file);

      if (new->vm_ops && new->vm_ops->open)
            new->vm_ops->open(new);

      if (new_below)
            vma_adjust(vma, addr, vma->vm_end, vma->vm_pgoff +
                  ((addr - new->vm_start) >> PAGE_SHIFT), new);
      else
            vma_adjust(vma, vma->vm_start, addr, vma->vm_pgoff, new);

      return 0;
}

/* Munmap is split into 2 main parts -- this part which finds
 * what needs doing, and the areas themselves, which do the
 * work.  This now handles partial unmappings.
 * Jeremy Fitzhardinge <jeremy@goop.org>
 */
int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
{
      unsigned long end;
      struct vm_area_struct *vma, *prev, *last;

      if ((start & ~PAGE_MASK) || start > TASK_SIZE || len > TASK_SIZE-start)
            return -EINVAL;

      if ((len = PAGE_ALIGN(len)) == 0)
            return -EINVAL;

      /* Find the first overlapping VMA */
      vma = find_vma_prev(mm, start, &prev);
      if (!vma)
            return 0;
      /* we have  start < vma->vm_end  */

      /* if it doesn't overlap, we have nothing.. */
      end = start + len;
      if (vma->vm_start >= end)
            return 0;

      /*
       * If we need to split any vma, do it now to save pain later.
       *
       * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
       * unmapped vm_area_struct will remain in use: so lower split_vma
       * places tmp vma above, and higher split_vma places tmp vma below.
       */
      if (start > vma->vm_start) {
            int error = split_vma(mm, vma, start, 0);
            if (error)
                  return error;
            prev = vma;
      }

      /* Does it split the last one? */
      last = find_vma(mm, end);
      if (last && end > last->vm_start) {
            int error = split_vma(mm, last, end, 1);
            if (error)
                  return error;
      }
      vma = prev? prev->vm_next: mm->mmap;

      /*
       * Remove the vma's, and unmap the actual pages
       */
      detach_vmas_to_be_unmapped(mm, vma, prev, end);
      unmap_region(mm, vma, prev, start, end);

      /* Fix up all other VM information */
      remove_vma_list(mm, vma);

      return 0;
}

EXPORT_SYMBOL(do_munmap);

asmlinkage long sys_munmap(unsigned long addr, size_t len)
{
      int ret;
      struct mm_struct *mm = current->mm;

      profile_munmap(addr);

      down_write(&mm->mmap_sem);
      ret = do_munmap(mm, addr, len);
      up_write(&mm->mmap_sem);
      return ret;
}

static inline void verify_mm_writelocked(struct mm_struct *mm)
{
#ifdef CONFIG_DEBUG_VM
      if (unlikely(down_read_trylock(&mm->mmap_sem))) {
            WARN_ON(1);
            up_read(&mm->mmap_sem);
      }
#endif
}

/*
 *  this is really a simplified "do_mmap".  it only handles
 *  anonymous maps.  eventually we may be able to do some
 *  brk-specific accounting here.
 */
unsigned long do_brk(unsigned long addr, unsigned long len)
{
      struct mm_struct * mm = current->mm;
      struct vm_area_struct * vma, * prev;
      unsigned long flags;
      struct rb_node ** rb_link, * rb_parent;
      pgoff_t pgoff = addr >> PAGE_SHIFT;
      int error;

      len = PAGE_ALIGN(len);
      if (!len)
            return addr;

      if ((addr + len) > TASK_SIZE || (addr + len) < addr)
            return -EINVAL;

      if (is_hugepage_only_range(mm, addr, len))
            return -EINVAL;

      error = security_file_mmap(0, 0, 0, 0, addr, 1);
      if (error)
            return error;

      flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;

      error = arch_mmap_check(addr, len, flags);
      if (error)
            return error;

      /*
       * mlock MCL_FUTURE?
       */
      if (mm->def_flags & VM_LOCKED) {
            unsigned long locked, lock_limit;
            locked = len >> PAGE_SHIFT;
            locked += mm->locked_vm;
            lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
            lock_limit >>= PAGE_SHIFT;
            if (locked > lock_limit && !capable(CAP_IPC_LOCK))
                  return -EAGAIN;
      }

      /*
       * mm->mmap_sem is required to protect against another thread
       * changing the mappings in case we sleep.
       */
      verify_mm_writelocked(mm);

      /*
       * Clear old maps.  this also does some error checking for us
       */
 munmap_back:
      vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
      if (vma && vma->vm_start < addr + len) {
            if (do_munmap(mm, addr, len))
                  return -ENOMEM;
            goto munmap_back;
      }

      /* Check against address space limits *after* clearing old maps... */
      if (!may_expand_vm(mm, len >> PAGE_SHIFT))
            return -ENOMEM;

      if (mm->map_count > sysctl_max_map_count)
            return -ENOMEM;

      if (security_vm_enough_memory(len >> PAGE_SHIFT))
            return -ENOMEM;

      /* Can we just expand an old private anonymous mapping? */
      if (vma_merge(mm, prev, addr, addr + len, flags,
                              NULL, NULL, pgoff, NULL))
            goto out;

      /*
       * create a vma struct for an anonymous mapping
       */
      vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
      if (!vma) {
            vm_unacct_memory(len >> PAGE_SHIFT);
            return -ENOMEM;
      }

      vma->vm_mm = mm;
      vma->vm_start = addr;
      vma->vm_end = addr + len;
      vma->vm_pgoff = pgoff;
      vma->vm_flags = flags;
      vma->vm_page_prot = vm_get_page_prot(flags);
      vma_link(mm, vma, prev, rb_link, rb_parent);
out:
      mm->total_vm += len >> PAGE_SHIFT;
      if (flags & VM_LOCKED) {
            mm->locked_vm += len >> PAGE_SHIFT;
            make_pages_present(addr, addr + len);
      }
      return addr;
}

EXPORT_SYMBOL(do_brk);

/* Release all mmaps. */
void exit_mmap(struct mm_struct *mm)
{
      struct mmu_gather *tlb;
      struct vm_area_struct *vma = mm->mmap;
      unsigned long nr_accounted = 0;
      unsigned long end;

      /* mm's last user has gone, and its about to be pulled down */
      arch_exit_mmap(mm);

      lru_add_drain();
      flush_cache_mm(mm);
      tlb = tlb_gather_mmu(mm, 1);
      /* Don't update_hiwater_rss(mm) here, do_exit already did */
      /* Use -1 here to ensure all VMAs in the mm are unmapped */
      end = unmap_vmas(&tlb, vma, 0, -1, &nr_accounted, NULL);
      vm_unacct_memory(nr_accounted);
      free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
      tlb_finish_mmu(tlb, 0, end);

      /*
       * Walk the list again, actually closing and freeing it,
       * with preemption enabled, without holding any MM locks.
       */
      while (vma)
            vma = remove_vma(vma);

      BUG_ON(mm->nr_ptes > (FIRST_USER_ADDRESS+PMD_SIZE-1)>>PMD_SHIFT);
}

/* Insert vm structure into process list sorted by address
 * and into the inode's i_mmap tree.  If vm_file is non-NULL
 * then i_mmap_lock is taken here.
 */
int insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
{
      struct vm_area_struct * __vma, * prev;
      struct rb_node ** rb_link, * rb_parent;

      /*
       * The vm_pgoff of a purely anonymous vma should be irrelevant
       * until its first write fault, when page's anon_vma and index
       * are set.  But now set the vm_pgoff it will almost certainly
       * end up with (unless mremap moves it elsewhere before that
       * first wfault), so /proc/pid/maps tells a consistent story.
       *
       * By setting it to reflect the virtual start address of the
       * vma, merges and splits can happen in a seamless way, just
       * using the existing file pgoff checks and manipulations.
       * Similarly in do_mmap_pgoff and in do_brk.
       */
      if (!vma->vm_file) {
            BUG_ON(vma->anon_vma);
            vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
      }
      __vma = find_vma_prepare(mm,vma->vm_start,&prev,&rb_link,&rb_parent);
      if (__vma && __vma->vm_start < vma->vm_end)
            return -ENOMEM;
      if ((vma->vm_flags & VM_ACCOUNT) &&
           security_vm_enough_memory_mm(mm, vma_pages(vma)))
            return -ENOMEM;
      vma_link(mm, vma, prev, rb_link, rb_parent);
      return 0;
}

/*
 * Copy the vma structure to a new location in the same mm,
 * prior to moving page table entries, to effect an mremap move.
 */
struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
      unsigned long addr, unsigned long len, pgoff_t pgoff)
{
      struct vm_area_struct *vma = *vmap;
      unsigned long vma_start = vma->vm_start;
      struct mm_struct *mm = vma->vm_mm;
      struct vm_area_struct *new_vma, *prev;
      struct rb_node **rb_link, *rb_parent;
      struct mempolicy *pol;

      /*
       * If anonymous vma has not yet been faulted, update new pgoff
       * to match new location, to increase its chance of merging.
       */
      if (!vma->vm_file && !vma->anon_vma)
            pgoff = addr >> PAGE_SHIFT;

      find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
      new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
                  vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
      if (new_vma) {
            /*
             * Source vma may have been merged into new_vma
             */
            if (vma_start >= new_vma->vm_start &&
                vma_start < new_vma->vm_end)
                  *vmap = new_vma;
      } else {
            new_vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
            if (new_vma) {
                  *new_vma = *vma;
                  pol = mpol_copy(vma_policy(vma));
                  if (IS_ERR(pol)) {
                        kmem_cache_free(vm_area_cachep, new_vma);
                        return NULL;
                  }
                  vma_set_policy(new_vma, pol);
                  new_vma->vm_start = addr;
                  new_vma->vm_end = addr + len;
                  new_vma->vm_pgoff = pgoff;
                  if (new_vma->vm_file)
                        get_file(new_vma->vm_file);
                  if (new_vma->vm_ops && new_vma->vm_ops->open)
                        new_vma->vm_ops->open(new_vma);
                  vma_link(mm, new_vma, prev, rb_link, rb_parent);
            }
      }
      return new_vma;
}

/*
 * Return true if the calling process may expand its vm space by the passed
 * number of pages
 */
int may_expand_vm(struct mm_struct *mm, unsigned long npages)
{
      unsigned long cur = mm->total_vm;   /* pages */
      unsigned long lim;

      lim = current->signal->rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT;

      if (cur + npages > lim)
            return 0;
      return 1;
}


static struct page *special_mapping_nopage(struct vm_area_struct *vma,
                                 unsigned long address, int *type)
{
      struct page **pages;

      BUG_ON(address < vma->vm_start || address >= vma->vm_end);

      address -= vma->vm_start;
      for (pages = vma->vm_private_data; address > 0 && *pages; ++pages)
            address -= PAGE_SIZE;

      if (*pages) {
            struct page *page = *pages;
            get_page(page);
            return page;
      }

      return NOPAGE_SIGBUS;
}

/*
 * Having a close hook prevents vma merging regardless of flags.
 */
static void special_mapping_close(struct vm_area_struct *vma)
{
}

static struct vm_operations_struct special_mapping_vmops = {
      .close = special_mapping_close,
      .nopage     = special_mapping_nopage,
};

/*
 * Called with mm->mmap_sem held for writing.
 * Insert a new vma covering the given region, with the given flags.
 * Its pages are supplied by the given array of struct page *.
 * The array can be shorter than len >> PAGE_SHIFT if it's null-terminated.
 * The region past the last page supplied will always produce SIGBUS.
 * The array pointer and the pages it points to are assumed to stay alive
 * for as long as this mapping might exist.
 */
int install_special_mapping(struct mm_struct *mm,
                      unsigned long addr, unsigned long len,
                      unsigned long vm_flags, struct page **pages)
{
      struct vm_area_struct *vma;

      vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
      if (unlikely(vma == NULL))
            return -ENOMEM;

      vma->vm_mm = mm;
      vma->vm_start = addr;
      vma->vm_end = addr + len;

      vma->vm_flags = vm_flags | mm->def_flags | VM_DONTEXPAND;
      vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);

      vma->vm_ops = &special_mapping_vmops;
      vma->vm_private_data = pages;

      if (unlikely(insert_vm_struct(mm, vma))) {
            kmem_cache_free(vm_area_cachep, vma);
            return -ENOMEM;
      }

      mm->total_vm += len >> PAGE_SHIFT;

      return 0;
}

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