async: Asynchronous function calls to speed up kernel boot

[linux-2.6/linux-2.6-openrd.git] / mm / mmap.c

/*
 * mm/mmap.c
 *
 * Written by obz.
 *
 * Address space accounting code        <alan@lxorguk.ukuu.org.uk>
 */

#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 <linux/mmu_notifier.h>

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

#include "internal.h"

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

#ifndef arch_rebalance_pgtables
#define arch_rebalance_pgtables(addr, len)              (addr)
#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 __pgprot(pgprot_val(protection_map[vm_flags &
                                (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
                        pgprot_val(arch_vm_get_page_prot(vm_flags)));
}
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_long_t vm_committed_space = ATOMIC_LONG_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 */
        if (mm)
                allowed -= mm->total_vm / 32;

        /*
         * cast `allowed' as a signed long because vm_committed_space
         * sometimes has a negative value
         */
        if (atomic_long_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);
                if (vma->vm_flags & VM_EXECUTABLE)
                        removed_exe_file_vma(vma->vm_mm);
        }
        mpol_put(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;
        unsigned long min_brk;

        down_write(&mm->mmap_sem);

#ifdef CONFIG_COMPAT_BRK
        min_brk = mm->end_code;
#else
        min_brk = mm->start_brk;
#endif
        if (brk < min_brk)
                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_brk) +
                        (mm->end_data - 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)
                                break;
                        __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 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);
                        if (next->vm_flags & VM_EXECUTABLE)
                                removed_exe_file_vma(mm);
                }
                mm->map_count--;
                mpol_put(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.
 */
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:
                        /*
                         * Ignore pgoff.
                         */
                        pgoff = 0;
                        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 (flags & MAP_NORESERVE)
                vm_flags |= VM_NORESERVE;

        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 = vma_merge(mm, prev, addr, addr + len, vm_flags,
                                        NULL, NULL, pgoff, NULL);
                if (vma)
                        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;
                if (vm_flags & VM_EXECUTABLE)
                        added_exe_file_vma(mm);
        } 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))) {
                mpol_put(vma_policy(vma));
                kmem_cache_free(vm_area_cachep, vma);
                fput(file);
                if (vm_flags & VM_EXECUTABLE)
                        removed_exe_file_vma(mm);
        } else {
                vma_link(mm, vma, prev, rb_link, rb_parent);
                file = vma->vm_file;
        }

        /* Once vma denies write, undo our temporary denial count */
        if (correct_wcount)
                atomic_inc(&inode->i_writecount);
out:
        mm->total_vm += len >> PAGE_SHIFT;
        vm_stat_account(mm, vm_flags, file, len >> PAGE_SHIFT);
        if (vm_flags & VM_LOCKED) {
                /*
                 * makes pages present; downgrades, drops, reacquires mmap_sem
                 */
                long nr_pages = mlock_vma_pages_range(vma, addr, addr + len);
                if (nr_pages < 0)
                        return nr_pages;        /* vma gone! */
                mm->locked_vm += (len >> PAGE_SHIFT) - nr_pages;
        } else 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 arch_rebalance_pgtables(addr, len);
}

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
#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 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(NULL, 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) {
                if (mlock_vma_pages_range(prev, addr, prev->vm_end) < 0)
                        return NULL;    /* vma gone! */
        }
        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) {
                if (mlock_vma_pages_range(vma, addr, start) < 0)
                        return NULL;    /* vma gone! */
        }
        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;
                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 &
                                        ~(huge_page_mask(hstate_vma(vma)))))
                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_dup(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 (vma->vm_flags & VM_EXECUTABLE)
                        added_exe_file_vma(mm);
        }

        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;

        /*
         * unlock any mlock()ed ranges before detaching vmas
         */
        if (mm->locked_vm) {
                struct vm_area_struct *tmp = vma;
                while (tmp && tmp->vm_start < end) {
                        if (tmp->vm_flags & VM_LOCKED) {
                                mm->locked_vm -= vma_pages(tmp);
                                munlock_vma_pages_all(tmp);
                        }
                        tmp = tmp->vm_next;
                }
        }

        /*
         * 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(NULL, 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? */
        vma = vma_merge(mm, prev, addr, addr + len, flags,
                                        NULL, NULL, pgoff, NULL);
        if (vma)
                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) {
                if (!mlock_vma_pages_range(vma, addr, addr + len))
                        mm->locked_vm += (len >> PAGE_SHIFT);
        }
        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;
        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);
        mmu_notifier_release(mm);

        if (!mm->mmap)  /* Can happen if dup_mmap() received an OOM */
                return;

        if (mm->locked_vm) {
                vma = mm->mmap;
                while (vma) {
                        if (vma->vm_flags & VM_LOCKED)
                                munlock_vma_pages_all(vma);
                        vma = vma->vm_next;
                }
        }
        vma = mm->mmap;
        lru_add_drain();
        flush_cache_mm(mm);
        tlb = tlb_gather_mmu(mm, 1);
        /* update_hiwater_rss(mm) here? but nobody should be looking */
        /* 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_dup(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 (vma->vm_flags & VM_EXECUTABLE)
                                        added_exe_file_vma(mm);
                        }
                        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 int special_mapping_fault(struct vm_area_struct *vma,
                                struct vm_fault *vmf)
{
        pgoff_t pgoff;
        struct page **pages;

        /*
         * special mappings have no vm_file, and in that case, the mm
         * uses vm_pgoff internally. So we have to subtract it from here.
         * We are allowed to do this because we are the mm; do not copy
         * this code into drivers!
         */
        pgoff = vmf->pgoff - vma->vm_pgoff;

        for (pages = vma->vm_private_data; pgoff && *pages; ++pages)
                pgoff--;

        if (*pages) {
                struct page *page = *pages;
                get_page(page);
                vmf->page = page;
                return 0;
        }

        return VM_FAULT_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,
        .fault = special_mapping_fault,
};

/*
 * 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;
}

static DEFINE_MUTEX(mm_all_locks_mutex);

static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)
{
        if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) {
                /*
                 * The LSB of head.next can't change from under us
                 * because we hold the mm_all_locks_mutex.
                 */
                spin_lock_nest_lock(&anon_vma->lock, &mm->mmap_sem);
                /*
                 * We can safely modify head.next after taking the
                 * anon_vma->lock. If some other vma in this mm shares
                 * the same anon_vma we won't take it again.
                 *
                 * No need of atomic instructions here, head.next
                 * can't change from under us thanks to the
                 * anon_vma->lock.
                 */
                if (__test_and_set_bit(0, (unsigned long *)
                                       &anon_vma->head.next))
                        BUG();
        }
}

static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
{
        if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
                /*
                 * AS_MM_ALL_LOCKS can't change from under us because
                 * we hold the mm_all_locks_mutex.
                 *
                 * Operations on ->flags have to be atomic because
                 * even if AS_MM_ALL_LOCKS is stable thanks to the
                 * mm_all_locks_mutex, there may be other cpus
                 * changing other bitflags in parallel to us.
                 */
                if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
                        BUG();
                spin_lock_nest_lock(&mapping->i_mmap_lock, &mm->mmap_sem);
        }
}

/*
 * This operation locks against the VM for all pte/vma/mm related
 * operations that could ever happen on a certain mm. This includes
 * vmtruncate, try_to_unmap, and all page faults.
 *
 * The caller must take the mmap_sem in write mode before calling
 * mm_take_all_locks(). The caller isn't allowed to release the
 * mmap_sem until mm_drop_all_locks() returns.
 *
 * mmap_sem in write mode is required in order to block all operations
 * that could modify pagetables and free pages without need of
 * altering the vma layout (for example populate_range() with
 * nonlinear vmas). It's also needed in write mode to avoid new
 * anon_vmas to be associated with existing vmas.
 *
 * A single task can't take more than one mm_take_all_locks() in a row
 * or it would deadlock.
 *
 * The LSB in anon_vma->head.next and the AS_MM_ALL_LOCKS bitflag in
 * mapping->flags avoid to take the same lock twice, if more than one
 * vma in this mm is backed by the same anon_vma or address_space.
 *
 * We can take all the locks in random order because the VM code
 * taking i_mmap_lock or anon_vma->lock outside the mmap_sem never
 * takes more than one of them in a row. Secondly we're protected
 * against a concurrent mm_take_all_locks() by the mm_all_locks_mutex.
 *
 * mm_take_all_locks() and mm_drop_all_locks are expensive operations
 * that may have to take thousand of locks.
 *
 * mm_take_all_locks() can fail if it's interrupted by signals.
 */
int mm_take_all_locks(struct mm_struct *mm)
{
        struct vm_area_struct *vma;
        int ret = -EINTR;

        BUG_ON(down_read_trylock(&mm->mmap_sem));

        mutex_lock(&mm_all_locks_mutex);

        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->vm_file && vma->vm_file->f_mapping)
                        vm_lock_mapping(mm, vma->vm_file->f_mapping);
        }

        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->anon_vma)
                        vm_lock_anon_vma(mm, vma->anon_vma);
        }

        ret = 0;

out_unlock:
        if (ret)
                mm_drop_all_locks(mm);

        return ret;
}

static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
{
        if (test_bit(0, (unsigned long *) &anon_vma->head.next)) {
                /*
                 * The LSB of head.next can't change to 0 from under
                 * us because we hold the mm_all_locks_mutex.
                 *
                 * We must however clear the bitflag before unlocking
                 * the vma so the users using the anon_vma->head will
                 * never see our bitflag.
                 *
                 * No need of atomic instructions here, head.next
                 * can't change from under us until we release the
                 * anon_vma->lock.
                 */
                if (!__test_and_clear_bit(0, (unsigned long *)
                                          &anon_vma->head.next))
                        BUG();
                spin_unlock(&anon_vma->lock);
        }
}

static void vm_unlock_mapping(struct address_space *mapping)
{
        if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
                /*
                 * AS_MM_ALL_LOCKS can't change to 0 from under us
                 * because we hold the mm_all_locks_mutex.
                 */
                spin_unlock(&mapping->i_mmap_lock);
                if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
                                        &mapping->flags))
                        BUG();
        }
}

/*
 * The mmap_sem cannot be released by the caller until
 * mm_drop_all_locks() returns.
 */
void mm_drop_all_locks(struct mm_struct *mm)
{
        struct vm_area_struct *vma;

        BUG_ON(down_read_trylock(&mm->mmap_sem));
        BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));

        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                if (vma->anon_vma)
                        vm_unlock_anon_vma(vma->anon_vma);
                if (vma->vm_file && vma->vm_file->f_mapping)
                        vm_unlock_mapping(vma->vm_file->f_mapping);
        }

        mutex_unlock(&mm_all_locks_mutex);
}