mmap.c

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/*
 * mm/mmap.c
 *
 * Written by obz.
 *
 * Address space accounting code    <[email protected]>
 */

#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/export.h>
#include <linux/mount.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>
#include <linux/mmu_notifier.h>
#include <linux/perf_event.h>
#include <linux/audit.h>
#include <linux/khugepaged.h>
#include <linux/uprobes.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);

/* 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 __read_mostly = OVERCOMMIT_GUESS;  /* heuristic overcommit */
int sysctl_overcommit_ratio __read_mostly = 50; /* default is 50% */
int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
/*
 * Make sure vm_committed_as in one cacheline and not cacheline shared with
 * other variables. It can be updated by several CPUs frequently.
 */
struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp;

/*
 * 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) {
        free = global_page_state(NR_FREE_PAGES);
        free += global_page_state(NR_FILE_PAGES);

        /*
         * shmem pages shouldn't be counted as free in this
         * case, they can't be purged, only swapped out, and
         * that won't affect the overall amount of available
         * memory in the system.
         */
        free -= global_page_state(NR_SHMEM);

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

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

        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;

    if (percpu_counter_read_positive(&vm_committed_as) < allowed)
        return 0;
error:
    vm_unacct_memory(pages);

    return -ENOMEM;
}

/*
 * Requires inode->i_mapping->i_mmap_mutex
 */
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.nonlinear);
    else
        vma_interval_tree_remove(vma, &mapping->i_mmap);
    flush_dcache_mmap_unlock(mapping);
}

/*
 * Unlink a file-based vm structure from its interval 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;
        mutex_lock(&mapping->i_mmap_mutex);
        __remove_shared_vm_struct(vma, file, mapping);
        mutex_unlock(&mapping->i_mmap_mutex);
    }
}

/*
 * 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_put(vma_policy(vma));
    kmem_cache_free(vm_area_cachep, vma);
    return next;
}

static unsigned long do_brk(unsigned long addr, unsigned long len);

SYSCALL_DEFINE1(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
    /*
     * CONFIG_COMPAT_BRK can still be overridden by setting
     * randomize_va_space to 2, which will still cause mm->start_brk
     * to be arbitrarily shifted
     */
    if (current->brk_randomized)
        min_brk = mm->start_brk;
    else
        min_brk = mm->end_data;
#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 = rlimit(RLIMIT_DATA);
    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 CONFIG_DEBUG_VM_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 *vma = mm->mmap;
    while (vma) {
        struct anon_vma_chain *avc;
        vma_lock_anon_vma(vma);
        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
            anon_vma_interval_tree_verify(avc);
        vma_unlock_anon_vma(vma);
        vma = vma->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

/*
 * vma has some anon_vma assigned, and is already inserted on that
 * anon_vma's interval trees.
 *
 * Before updating the vma's vm_start / vm_end / vm_pgoff fields, the
 * vma must be removed from the anon_vma's interval trees using
 * anon_vma_interval_tree_pre_update_vma().
 *
 * After the update, the vma will be reinserted using
 * anon_vma_interval_tree_post_update_vma().
 *
 * The entire update must be protected by exclusive mmap_sem and by
 * the root anon_vma's mutex.
 */
static inline void
anon_vma_interval_tree_pre_update_vma(struct vm_area_struct *vma)
{
    struct anon_vma_chain *avc;

    list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
        anon_vma_interval_tree_remove(avc, &avc->anon_vma->rb_root);
}

static inline void
anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
{
    struct anon_vma_chain *avc;

    list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
        anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root);
}

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

    __rb_link = &mm->mm_rb.rb_node;
    rb_prev = __rb_parent = 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) {
            /* Fail if an existing vma overlaps the area */
            if (vma_tmp->vm_start < end)
                return -ENOMEM;
            __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 0;
}

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_interval_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);
}

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)
        mutex_lock(&mapping->i_mmap_mutex);

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

    if (mapping)
        mutex_unlock(&mapping->i_mmap_mutex);

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

/*
 * Helper for vma_adjust() in the split_vma insert case: insert a vma into the
 * mm's list and rbtree.  It has already been inserted into the interval tree.
 */
static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
{
    struct vm_area_struct *prev;
    struct rb_node **rb_link, *rb_parent;

    if (find_vma_links(mm, vma->vm_start, vma->vm_end,
               &prev, &rb_link, &rb_parent))
        BUG();
    __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)
{
    struct vm_area_struct *next = vma->vm_next;

    prev->vm_next = next;
    if (next)
        next->vm_prev = prev;
    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.
 */
int 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 rb_root *root = NULL;
    struct anon_vma *anon_vma = NULL;
    struct file *file = vma->vm_file;
    long adjust_next = 0;
    int remove_next = 0;

    if (next && !insert) {
        struct vm_area_struct *exporter = NULL;

        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;
            exporter = next;
            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;
            exporter = next;
            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);
            exporter = vma;
            importer = next;
        }

        /*
         * 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 (exporter && exporter->anon_vma && !importer->anon_vma) {
            if (anon_vma_clone(importer, exporter))
                return -ENOMEM;
            importer->anon_vma = exporter->anon_vma;
        }
    }

    if (file) {
        mapping = file->f_mapping;
        if (!(vma->vm_flags & VM_NONLINEAR)) {
            root = &mapping->i_mmap;
            uprobe_munmap(vma, vma->vm_start, vma->vm_end);

            if (adjust_next)
                uprobe_munmap(next, next->vm_start,
                            next->vm_end);
        }

        mutex_lock(&mapping->i_mmap_mutex);
        if (insert) {
            /*
             * Put into interval 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);
        }
    }

    vma_adjust_trans_huge(vma, start, end, adjust_next);

    anon_vma = vma->anon_vma;
    if (!anon_vma && adjust_next)
        anon_vma = next->anon_vma;
    if (anon_vma) {
        VM_BUG_ON(adjust_next && next->anon_vma &&
              anon_vma != next->anon_vma);
        anon_vma_lock(anon_vma);
        anon_vma_interval_tree_pre_update_vma(vma);
        if (adjust_next)
            anon_vma_interval_tree_pre_update_vma(next);
    }

    if (root) {
        flush_dcache_mmap_lock(mapping);
        vma_interval_tree_remove(vma, root);
        if (adjust_next)
            vma_interval_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_interval_tree_insert(next, root);
        vma_interval_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);
    } 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) {
        anon_vma_interval_tree_post_update_vma(vma);
        if (adjust_next)
            anon_vma_interval_tree_post_update_vma(next);
        anon_vma_unlock(anon_vma);
    }
    if (mapping)
        mutex_unlock(&mapping->i_mmap_mutex);

    if (root) {
        uprobe_mmap(vma);

        if (adjust_next)
            uprobe_mmap(next);
    }

    if (remove_next) {
        if (file) {
            uprobe_munmap(next, next->vm_start, next->vm_end);
            fput(file);
        }
        if (next->anon_vma)
            anon_vma_merge(vma, next);
        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;
        }
    }
    if (insert && file)
        uprobe_mmap(insert);

    validate_mm(mm);

    return 0;
}

/*
 * 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,
                    struct vm_area_struct *vma)
{
    /*
     * The list_is_singular() test is to avoid merging VMA cloned from
     * parents. This can improve scalability caused by anon_vma lock.
     */
    if ((!anon_vma1 || !anon_vma2) && (!vma ||
        list_is_singular(&vma->anon_vma_chain)))
        return 1;
    return 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, 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, 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;
    int err;

    /*
     * 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, NULL)) {
                            /* cases 1, 6 */
            err = vma_adjust(prev, prev->vm_start,
                next->vm_end, prev->vm_pgoff, NULL);
        } else                  /* cases 2, 5, 7 */
            err = vma_adjust(prev, prev->vm_start,
                end, prev->vm_pgoff, NULL);
        if (err)
            return NULL;
        khugepaged_enter_vma_merge(prev);
        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 */
            err = vma_adjust(prev, prev->vm_start,
                addr, prev->vm_pgoff, NULL);
        else                    /* cases 3, 8 */
            err = vma_adjust(area, addr, next->vm_end,
                next->vm_pgoff - pglen, NULL);
        if (err)
            return NULL;
        khugepaged_enter_vma_merge(area);
        return area;
    }

    return NULL;
}

/*
 * Rough compatbility check to quickly see if it's even worth looking
 * at sharing an anon_vma.
 *
 * They need to have the same vm_file, and the flags can only differ
 * in things that mprotect may change.
 *
 * NOTE! The fact that we share an anon_vma doesn't _have_ to mean that
 * we can merge the two vma's. For example, we refuse to merge a vma if
 * there is a vm_ops->close() function, because that indicates that the
 * driver is doing some kind of reference counting. But that doesn't
 * really matter for the anon_vma sharing case.
 */
static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
{
    return a->vm_end == b->vm_start &&
        mpol_equal(vma_policy(a), vma_policy(b)) &&
        a->vm_file == b->vm_file &&
        !((a->vm_flags ^ b->vm_flags) & ~(VM_READ|VM_WRITE|VM_EXEC)) &&
        b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
}

/*
 * Do some basic sanity checking to see if we can re-use the anon_vma
 * from 'old'. The 'a'/'b' vma's are in VM order - one of them will be
 * the same as 'old', the other will be the new one that is trying
 * to share the anon_vma.
 *
 * NOTE! This runs with mm_sem held for reading, so it is possible that
 * the anon_vma of 'old' is concurrently in the process of being set up
 * by another page fault trying to merge _that_. But that's ok: if it
 * is being set up, that automatically means that it will be a singleton
 * acceptable for merging, so we can do all of this optimistically. But
 * we do that ACCESS_ONCE() to make sure that we never re-load the pointer.
 *
 * IOW: that the "list_is_singular()" test on the anon_vma_chain only
 * matters for the 'stable anon_vma' case (ie the thing we want to avoid
 * is to return an anon_vma that is "complex" due to having gone through
 * a fork).
 *
 * We also make sure that the two vma's are compatible (adjacent,
 * and with the same memory policies). That's all stable, even with just
 * a read lock on the mm_sem.
 */
static struct anon_vma *reusable_anon_vma(struct vm_area_struct *old, struct vm_area_struct *a, struct vm_area_struct *b)
{
    if (anon_vma_compatible(a, b)) {
        struct anon_vma *anon_vma = ACCESS_ONCE(old->anon_vma);

        if (anon_vma && list_is_singular(&old->anon_vma_chain))
            return anon_vma;
    }
    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 anon_vma *anon_vma;
    struct vm_area_struct *near;

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

    anon_vma = reusable_anon_vma(near, vma, near);
    if (anon_vma)
        return anon_vma;
try_prev:
    near = vma->vm_prev;
    if (!near)
        goto none;

    anon_vma = reusable_anon_vma(near, near, vma);
    if (anon_vma)
        return 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);

    mm->total_vm += pages;

    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;
}
#endif /* CONFIG_PROC_FS */

/*
 * If a hint addr is less than mmap_min_addr change hint to be as
 * low as possible but still greater than mmap_min_addr
 */
static inline unsigned long round_hint_to_min(unsigned long hint)
{
    hint &= PAGE_MASK;
    if (((void *)hint != NULL) &&
        (hint < mmap_min_addr))
        return PAGE_ALIGN(mmap_min_addr);
    return hint;
}

/*
 * 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;
    vm_flags_t vm_flags;

    /*
     * 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);

    /* Careful about overflows.. */
    len = PAGE_ALIGN(len);
    if (!len)
        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;

    /* mlock MCL_FUTURE? */
    if (vm_flags & VM_LOCKED) {
        unsigned long locked, lock_limit;
        locked = len >> PAGE_SHIFT;
        locked += mm->locked_vm;
        lock_limit = rlimit(RLIMIT_MEMLOCK);
        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 (!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;
        }
    }

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

SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
        unsigned long, prot, unsigned long, flags,
        unsigned long, fd, unsigned long, pgoff)
{
    struct file *file = NULL;
    unsigned long retval = -EBADF;

    if (!(flags & MAP_ANONYMOUS)) {
        audit_mmap_fd(fd, flags);
        if (unlikely(flags & MAP_HUGETLB))
            return -EINVAL;
        file = fget(fd);
        if (!file)
            goto out;
    } else if (flags & MAP_HUGETLB) {
        struct user_struct *user = NULL;
        /*
         * VM_NORESERVE is used because the reservations will be
         * taken when vm_ops->mmap() is called
         * A dummy user value is used because we are not locking
         * memory so no accounting is necessary
         */
        file = hugetlb_file_setup(HUGETLB_ANON_FILE, addr, len,
                        VM_NORESERVE, &user,
                        HUGETLB_ANONHUGE_INODE);
        if (IS_ERR(file))
            return PTR_ERR(file);
    }

    flags &= ~(MAP_EXECUTABLE | MAP_DENYWRITE);

    retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
    if (file)
        fput(file);
out:
    return retval;
}

#ifdef __ARCH_WANT_SYS_OLD_MMAP
struct mmap_arg_struct {
    unsigned long addr;
    unsigned long len;
    unsigned long prot;
    unsigned long flags;
    unsigned long fd;
    unsigned long offset;
};

SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
{
    struct mmap_arg_struct a;

    if (copy_from_user(&a, arg, sizeof(a)))
        return -EFAULT;
    if (a.offset & ~PAGE_MASK)
        return -EINVAL;

    return sys_mmap_pgoff(a.addr, a.len, a.prot, a.flags, a.fd,
                  a.offset >> PAGE_SHIFT);
}
#endif /* __ARCH_WANT_SYS_OLD_MMAP */

/*
 * 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)
{
    vm_flags_t 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)
        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);
}

/*
 * We account for memory if it's a private writeable mapping,
 * not hugepages and VM_NORESERVE wasn't set.
 */
static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
{
    /*
     * hugetlb has its own accounting separate from the core VM
     * VM_HUGETLB may not be set yet so we cannot check for that flag.
     */
    if (file && is_file_hugepages(file))
        return 0;

    return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
}

unsigned long mmap_region(struct file *file, unsigned long addr,
              unsigned long len, unsigned long flags,
              vm_flags_t vm_flags, unsigned long pgoff)
{
    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:
    if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) {
        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;

    /*
     * Set 'VM_NORESERVE' if we should not account for the
     * memory use of this mapping.
     */
    if ((flags & MAP_NORESERVE)) {
        /* We honor MAP_NORESERVE if allowed to overcommit */
        if (sysctl_overcommit_memory != OVERCOMMIT_NEVER)
            vm_flags |= VM_NORESERVE;

        /* hugetlb applies strict overcommit unless MAP_NORESERVE */
        if (file && is_file_hugepages(file))
            vm_flags |= VM_NORESERVE;
    }

    /*
     * Private writable mapping: check memory availability
     */
    if (accountable_mapping(file, vm_flags)) {
        charged = len >> PAGE_SHIFT;
        if (security_vm_enough_memory_mm(mm, charged))
            return -ENOMEM;
        vm_flags |= VM_ACCOUNT;
    }

    /*
     * Can we just expand an old mapping?
     */
    vma = vma_merge(mm, prev, addr, addr + len, vm_flags, NULL, file, 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;
    INIT_LIST_HEAD(&vma->anon_vma_chain);

    error = -EINVAL;    /* when rejecting VM_GROWSDOWN|VM_GROWSUP */

    if (file) {
        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 = get_file(file);
        error = file->f_op->mmap(file, vma);
        if (error)
            goto unmap_and_free_vma;

        /* 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;
    } else if (vm_flags & VM_SHARED) {
        if (unlikely(vm_flags & (VM_GROWSDOWN|VM_GROWSUP)))
            goto free_vma;
        error = shmem_zero_setup(vma);
        if (error)
            goto free_vma;
    }

    if (vma_wants_writenotify(vma)) {
        pgprot_t pprot = vma->vm_page_prot;

        /* Can vma->vm_page_prot have changed??
         *
         * Answer: Yes, drivers may have changed it in their
         *         f_op->mmap method.
         *
         * Ensures that vmas marked as uncached stay that way.
         */
        vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);
        if (pgprot_val(pprot) == pgprot_val(pgprot_noncached(pprot)))
            vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
    }

    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:
    perf_event_mmap(vma);

    vm_stat_account(mm, vm_flags, file, len >> PAGE_SHIFT);
    if (vm_flags & VM_LOCKED) {
        if (!mlock_vma_pages_range(vma, addr, addr + len))
            mm->locked_vm += (len >> PAGE_SHIFT);
    } else if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK))
        make_pages_present(addr, addr + len);

    if (file)
        uprobe_mmap(vma);

    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;
}

/*
 * 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, start_addr;

    /* 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;
    }

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

    if (addr < len)
        goto fail;

    addr -= 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);

fail:
    /*
     * if hint left us with no space for the requested
     * mapping then try again:
     *
     * Note: this is different with the case of bottomup
     * which does the fully line-search, but we use find_vma
     * here that causes some holes skipped.
     */
    if (start_addr != mm->mmap_base) {
        mm->free_area_cache = mm->mmap_base;
        mm->cached_hole_size = 0;
        goto try_again;
    }

    /*
     * 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);

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

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

    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;

    addr = arch_rebalance_pgtables(addr, len);
    error = security_mmap_addr(addr);
    return error ? error : 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 (WARN_ON_ONCE(!mm))      /* Remove this in linux-3.6 */
        return NULL;

    /* 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;

    vma = find_vma(mm, addr);
    if (vma) {
        *pprev = vma->vm_prev;
    } else {
        struct rb_node *rb_node = mm->mm_rb.rb_node;
        *pprev = NULL;
        while (rb_node) {
            *pprev = rb_entry(rb_node, struct vm_area_struct, vm_rb);
            rb_node = rb_node->rb_right;
        }
    }
    return 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 > ACCESS_ONCE(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 = ACCESS_ONCE(rlim[RLIMIT_MEMLOCK].rlim_cur);
        limit >>= 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_mm(mm, grow))
        return -ENOMEM;

    /* Ok, everything looks good - let it rip */
    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.
 */
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;
    vma_lock_anon_vma(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 {
        vma_unlock_anon_vma(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 = -ENOMEM;
        if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) {
            error = acct_stack_growth(vma, size, grow);
            if (!error) {
                anon_vma_interval_tree_pre_update_vma(vma);
                vma->vm_end = address;
                anon_vma_interval_tree_post_update_vma(vma);
                perf_event_mmap(vma);
            }
        }
    }
    vma_unlock_anon_vma(vma);
    khugepaged_enter_vma_merge(vma);
    validate_mm(vma->vm_mm);
    return error;
}
#endif /* CONFIG_STACK_GROWSUP || CONFIG_IA64 */

/*
 * vma is the first one with address < vma->vm_start.  Have to extend vma.
 */
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_mmap_addr(address);
    if (error)
        return error;

    vma_lock_anon_vma(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 = -ENOMEM;
        if (grow <= vma->vm_pgoff) {
            error = acct_stack_growth(vma, size, grow);
            if (!error) {
                anon_vma_interval_tree_pre_update_vma(vma);
                vma->vm_start = address;
                vma->vm_pgoff -= grow;
                anon_vma_interval_tree_post_update_vma(vma);
                perf_event_mmap(vma);
            }
        }
    }
    vma_unlock_anon_vma(vma);
    khugepaged_enter_vma_merge(vma);
    validate_mm(vma->vm_mm);
    return error;
}

#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) {
        mlock_vma_pages_range(prev, 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) {
        mlock_vma_pages_range(vma, 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)
{
    unsigned long nr_accounted = 0;

    /* Update high watermark before we lower total_vm */
    update_hiwater_vm(mm);
    do {
        long nrpages = vma_pages(vma);

        if (vma->vm_flags & VM_ACCOUNT)
            nr_accounted += nrpages;
        vm_stat_account(mm, vma->vm_flags, vma->vm_file, -nrpages);
        vma = remove_vma(vma);
    } while (vma);
    vm_unacct_memory(nr_accounted);
    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;

    lru_add_drain();
    tlb_gather_mmu(&tlb, mm, 0);
    update_hiwater_rss(mm);
    unmap_vmas(&tlb, vma, start, end);
    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);
    vma->vm_prev = NULL;
    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;
    if (vma)
        vma->vm_prev = prev;
    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_vma() bypasses sysctl_max_map_count checking.  We use this on the
 * munmap path where it doesn't make sense to fail.
 */
static 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;
    int err = -ENOMEM;

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

    new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
    if (!new)
        goto out_err;

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

    INIT_LIST_HEAD(&new->anon_vma_chain);

    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)) {
        err = PTR_ERR(pol);
        goto out_free_vma;
    }
    vma_set_policy(new, pol);

    if (anon_vma_clone(new, vma))
        goto out_free_mpol;

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

    /* Success. */
    if (!err)
        return 0;

    /* Clean everything up if vma_adjust failed. */
    if (new->vm_ops && new->vm_ops->close)
        new->vm_ops->close(new);
    if (new->vm_file)
        fput(new->vm_file);
    unlink_anon_vmas(new);
 out_free_mpol:
    mpol_put(pol);
 out_free_vma:
    kmem_cache_free(vm_area_cachep, new);
 out_err:
    return err;
}

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

    return __split_vma(mm, vma, addr, new_below);
}

/* 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 <[email protected]>
 */
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(mm, start);
    if (!vma)
        return 0;
    prev = vma->vm_prev;
    /* 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;

        /*
         * Make sure that map_count on return from munmap() will
         * not exceed its limit; but let map_count go just above
         * its limit temporarily, to help free resources as expected.
         */
        if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
            return -ENOMEM;

        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;
}

int vm_munmap(unsigned long start, size_t len)
{
    int ret;
    struct mm_struct *mm = current->mm;

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

SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
{
    profile_munmap(addr);
    return vm_munmap(addr, len);
}

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.
 */
static 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;

    flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;

    error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
    if (error & ~PAGE_MASK)
        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 = rlimit(RLIMIT_MEMLOCK);
        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:
    if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) {
        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_mm(mm, 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;
    }

    INIT_LIST_HEAD(&vma->anon_vma_chain);
    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:
    perf_event_mmap(vma);
    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;
}

unsigned long vm_brk(unsigned long addr, unsigned long len)
{
    struct mm_struct *mm = current->mm;
    unsigned long ret;

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

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

    if (mm->locked_vm) {
        vma = mm->mmap;
        while (vma) {
            if (vma->vm_flags & VM_LOCKED)
                munlock_vma_pages_all(vma);
            vma = vma->vm_next;
        }
    }

    arch_exit_mmap(mm);

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

    lru_add_drain();
    flush_cache_mm(mm);
    tlb_gather_mmu(&tlb, mm, 1);
    /* update_hiwater_rss(mm) here? but nobody should be looking */
    /* Use -1 here to ensure all VMAs in the mm are unmapped */
    unmap_vmas(&tlb, vma, 0, -1);

    free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
    tlb_finish_mmu(&tlb, 0, -1);

    /*
     * Walk the list again, actually closing and freeing it,
     * with preemption enabled, without holding any MM locks.
     */
    while (vma) {
        if (vma->vm_flags & VM_ACCOUNT)
            nr_accounted += vma_pages(vma);
        vma = remove_vma(vma);
    }
    vm_unacct_memory(nr_accounted);

    WARN_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_mutex is taken here.
 */
int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
{
    struct vm_area_struct *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;
    }
    if (find_vma_links(mm, vma->vm_start, vma->vm_end,
               &prev, &rb_link, &rb_parent))
        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,
    bool *need_rmap_locks)
{
    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;
    bool faulted_in_anon_vma = true;

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

    if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent))
        return NULL;    /* should never get here */
    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 (unlikely(vma_start >= new_vma->vm_start &&
                 vma_start < new_vma->vm_end)) {
            /*
             * The only way we can get a vma_merge with
             * self during an mremap is if the vma hasn't
             * been faulted in yet and we were allowed to
             * reset the dst vma->vm_pgoff to the
             * destination address of the mremap to allow
             * the merge to happen. mremap must change the
             * vm_pgoff linearity between src and dst vmas
             * (in turn preventing a vma_merge) to be
             * safe. It is only safe to keep the vm_pgoff
             * linear if there are no pages mapped yet.
             */
            VM_BUG_ON(faulted_in_anon_vma);
            *vmap = vma = new_vma;
        }
        *need_rmap_locks = (new_vma->vm_pgoff <= vma->vm_pgoff);
    } else {
        new_vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
        if (new_vma) {
            *new_vma = *vma;
            new_vma->vm_start = addr;
            new_vma->vm_end = addr + len;
            new_vma->vm_pgoff = pgoff;
            pol = mpol_dup(vma_policy(vma));
            if (IS_ERR(pol))
                goto out_free_vma;
            vma_set_policy(new_vma, pol);
            INIT_LIST_HEAD(&new_vma->anon_vma_chain);
            if (anon_vma_clone(new_vma, vma))
                goto out_free_mempol;
            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);
            *need_rmap_locks = false;
        }
    }
    return new_vma;

 out_free_mempol:
    mpol_put(pol);
 out_free_vma:
    kmem_cache_free(vm_area_cachep, new_vma);
    return NULL;
}

/*
 * 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 = rlimit(RLIMIT_AS) >> 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 const 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)
{
    int ret;
    struct vm_area_struct *vma;

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

    INIT_LIST_HEAD(&vma->anon_vma_chain);
    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;

    ret = insert_vm_struct(mm, vma);
    if (ret)
        goto out;

    mm->total_vm += len >> PAGE_SHIFT;

    perf_event_mmap(vma);

    return 0;

out:
    kmem_cache_free(vm_area_cachep, vma);
    return ret;
}

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->root->rb_root.rb_node)) {
        /*
         * The LSB of head.next can't change from under us
         * because we hold the mm_all_locks_mutex.
         */
        mutex_lock_nest_lock(&anon_vma->root->mutex, &mm->mmap_sem);
        /*
         * We can safely modify head.next after taking the
         * anon_vma->root->mutex. 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->root->mutex.
         */
        if (__test_and_set_bit(0, (unsigned long *)
                       &anon_vma->root->rb_root.rb_node))
            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();
        mutex_lock_nest_lock(&mapping->i_mmap_mutex, &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->rb_root.rb_node 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_mutex or anon_vma->mutex 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;
    struct anon_vma_chain *avc;

    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)
            list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                vm_lock_anon_vma(mm, avc->anon_vma);
    }

    return 0;

out_unlock:
    mm_drop_all_locks(mm);
    return -EINTR;
}

static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
{
    if (test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_node)) {
        /*
         * 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->rb_root 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->root->mutex.
         */
        if (!__test_and_clear_bit(0, (unsigned long *)
                      &anon_vma->root->rb_root.rb_node))
            BUG();
        anon_vma_unlock(anon_vma);
    }
}

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.
         */
        mutex_unlock(&mapping->i_mmap_mutex);
        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;
    struct anon_vma_chain *avc;

    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)
            list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                vm_unlock_anon_vma(avc->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);
}

/*
 * initialise the VMA slab
 */
void __init mmap_init(void)
{
    int ret;

    ret = percpu_counter_init(&vm_committed_as, 0);
    VM_BUG_ON(ret);
}