mm: add optional close() to struct vm_special_mapping

[linux.git] / mm / vma.c

// SPDX-License-Identifier: GPL-2.0-or-later

/*
 * VMA-specific functions.
 */

#include "vma_internal.h"
#include "vma.h"

/*
 * 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 if the caller indicates
 * the current vma may be removed as part of the merge.
 */
static inline bool is_mergeable_vma(struct vm_area_struct *vma,
                struct file *file, unsigned long vm_flags,
                struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
                struct anon_vma_name *anon_name, bool may_remove_vma)
{
        /*
         * VM_SOFTDIRTY should not prevent from VMA merging, if we
         * match the flags but dirty bit -- the caller should mark
         * merged VMA as dirty. If dirty bit won't be excluded from
         * comparison, we increase pressure on the memory system forcing
         * the kernel to generate new VMAs when old one could be
         * extended instead.
         */
        if ((vma->vm_flags ^ vm_flags) & ~VM_SOFTDIRTY)
                return false;
        if (vma->vm_file != file)
                return false;
        if (may_remove_vma && vma->vm_ops && vma->vm_ops->close)
                return false;
        if (!is_mergeable_vm_userfaultfd_ctx(vma, vm_userfaultfd_ctx))
                return false;
        if (!anon_vma_name_eq(anon_vma_name(vma), anon_name))
                return false;
        return true;
}

static inline bool 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 true;
        return anon_vma1 == anon_vma2;
}

/*
 * init_multi_vma_prep() - Initializer for struct vma_prepare
 * @vp: The vma_prepare struct
 * @vma: The vma that will be altered once locked
 * @next: The next vma if it is to be adjusted
 * @remove: The first vma to be removed
 * @remove2: The second vma to be removed
 */
static void init_multi_vma_prep(struct vma_prepare *vp,
                                struct vm_area_struct *vma,
                                struct vm_area_struct *next,
                                struct vm_area_struct *remove,
                                struct vm_area_struct *remove2)
{
        memset(vp, 0, sizeof(struct vma_prepare));
        vp->vma = vma;
        vp->anon_vma = vma->anon_vma;
        vp->remove = remove;
        vp->remove2 = remove2;
        vp->adj_next = next;
        if (!vp->anon_vma && next)
                vp->anon_vma = next->anon_vma;

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

}

/*
 * 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() does not permit mmap's which
 * wrap, nor mmaps which cover the final page at index -1UL.
 *
 * We assume the vma may be removed as part of the merge.
 */
bool
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, struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
                struct anon_vma_name *anon_name)
{
        if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name, true) &&
            is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
                if (vma->vm_pgoff == vm_pgoff)
                        return true;
        }
        return false;
}

/*
 * 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.
 *
 * We assume that vma is not removed as part of the merge.
 */
bool
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, struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
                struct anon_vma_name *anon_name)
{
        if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name, false) &&
            is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
                pgoff_t vm_pglen;

                vm_pglen = vma_pages(vma);
                if (vma->vm_pgoff + vm_pglen == vm_pgoff)
                        return true;
        }
        return false;
}

/*
 * Close a vm structure and free it.
 */
void remove_vma(struct vm_area_struct *vma, bool unreachable)
{
        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));
        if (unreachable)
                __vm_area_free(vma);
        else
                vm_area_free(vma);
}

/*
 * Get rid of page table information in the indicated region.
 *
 * Called with the mm semaphore held.
 */
void unmap_region(struct mm_struct *mm, struct ma_state *mas,
                struct vm_area_struct *vma, struct vm_area_struct *prev,
                struct vm_area_struct *next, unsigned long start,
                unsigned long end, unsigned long tree_end, bool mm_wr_locked)
{
        struct mmu_gather tlb;
        unsigned long mt_start = mas->index;

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm);
        update_hiwater_rss(mm);
        unmap_vmas(&tlb, mas, vma, start, end, tree_end, mm_wr_locked);
        mas_set(mas, mt_start);
        free_pgtables(&tlb, mas, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
                                 next ? next->vm_start : USER_PGTABLES_CEILING,
                                 mm_wr_locked);
        tlb_finish_mmu(&tlb);
}

/*
 * __split_vma() bypasses sysctl_max_map_count checking.  We use this where it
 * has already been checked or doesn't make sense to fail.
 * VMA Iterator will point to the end VMA.
 */
static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
                       unsigned long addr, int new_below)
{
        struct vma_prepare vp;
        struct vm_area_struct *new;
        int err;

        WARN_ON(vma->vm_start >= addr);
        WARN_ON(vma->vm_end <= addr);

        if (vma->vm_ops && vma->vm_ops->may_split) {
                err = vma->vm_ops->may_split(vma, addr);
                if (err)
                        return err;
        }

        new = vm_area_dup(vma);
        if (!new)
                return -ENOMEM;

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

        err = -ENOMEM;
        vma_iter_config(vmi, new->vm_start, new->vm_end);
        if (vma_iter_prealloc(vmi, new))
                goto out_free_vma;

        err = vma_dup_policy(vma, new);
        if (err)
                goto out_free_vmi;

        err = anon_vma_clone(new, vma);
        if (err)
                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);

        vma_start_write(vma);
        vma_start_write(new);

        init_vma_prep(&vp, vma);
        vp.insert = new;
        vma_prepare(&vp);
        vma_adjust_trans_huge(vma, vma->vm_start, addr, 0);

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

        /* vma_complete stores the new vma */
        vma_complete(&vp, vmi, vma->vm_mm);

        /* Success. */
        if (new_below)
                vma_next(vmi);
        return 0;

out_free_mpol:
        mpol_put(vma_policy(new));
out_free_vmi:
        vma_iter_free(vmi);
out_free_vma:
        vm_area_free(new);
        return err;
}

/*
 * Split a vma into two pieces at address 'addr', a new vma is allocated
 * either for the first part or the tail.
 */
static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
                     unsigned long addr, int new_below)
{
        if (vma->vm_mm->map_count >= sysctl_max_map_count)
                return -ENOMEM;

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

/*
 * Ok - we have the memory areas we should free on a maple tree so release them,
 * and do the vma updates.
 *
 * Called with the mm semaphore held.
 */
static inline void remove_mt(struct mm_struct *mm, struct ma_state *mas)
{
        unsigned long nr_accounted = 0;
        struct vm_area_struct *vma;

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

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

/*
 * init_vma_prep() - Initializer wrapper for vma_prepare struct
 * @vp: The vma_prepare struct
 * @vma: The vma that will be altered once locked
 */
void init_vma_prep(struct vma_prepare *vp,
                   struct vm_area_struct *vma)
{
        init_multi_vma_prep(vp, vma, NULL, NULL, NULL);
}

/*
 * Requires inode->i_mapping->i_mmap_rwsem
 */
static void __remove_shared_vm_struct(struct vm_area_struct *vma,
                                      struct address_space *mapping)
{
        if (vma_is_shared_maywrite(vma))
                mapping_unmap_writable(mapping);

        flush_dcache_mmap_lock(mapping);
        vma_interval_tree_remove(vma, &mapping->i_mmap);
        flush_dcache_mmap_unlock(mapping);
}

/*
 * 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_lock and by
 * the root anon_vma's mutex.
 */
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);
}

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 void __vma_link_file(struct vm_area_struct *vma,
                            struct address_space *mapping)
{
        if (vma_is_shared_maywrite(vma))
                mapping_allow_writable(mapping);

        flush_dcache_mmap_lock(mapping);
        vma_interval_tree_insert(vma, &mapping->i_mmap);
        flush_dcache_mmap_unlock(mapping);
}

/*
 * vma_prepare() - Helper function for handling locking VMAs prior to altering
 * @vp: The initialized vma_prepare struct
 */
void vma_prepare(struct vma_prepare *vp)
{
        if (vp->file) {
                uprobe_munmap(vp->vma, vp->vma->vm_start, vp->vma->vm_end);

                if (vp->adj_next)
                        uprobe_munmap(vp->adj_next, vp->adj_next->vm_start,
                                      vp->adj_next->vm_end);

                i_mmap_lock_write(vp->mapping);
                if (vp->insert && vp->insert->vm_file) {
                        /*
                         * 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(vp->insert,
                                        vp->insert->vm_file->f_mapping);
                }
        }

        if (vp->anon_vma) {
                anon_vma_lock_write(vp->anon_vma);
                anon_vma_interval_tree_pre_update_vma(vp->vma);
                if (vp->adj_next)
                        anon_vma_interval_tree_pre_update_vma(vp->adj_next);
        }

        if (vp->file) {
                flush_dcache_mmap_lock(vp->mapping);
                vma_interval_tree_remove(vp->vma, &vp->mapping->i_mmap);
                if (vp->adj_next)
                        vma_interval_tree_remove(vp->adj_next,
                                                 &vp->mapping->i_mmap);
        }

}

/*
 * dup_anon_vma() - Helper function to duplicate anon_vma
 * @dst: The destination VMA
 * @src: The source VMA
 * @dup: Pointer to the destination VMA when successful.
 *
 * Returns: 0 on success.
 */
static int dup_anon_vma(struct vm_area_struct *dst,
                        struct vm_area_struct *src, struct vm_area_struct **dup)
{
        /*
         * 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 (src->anon_vma && !dst->anon_vma) {
                int ret;

                vma_assert_write_locked(dst);
                dst->anon_vma = src->anon_vma;
                ret = anon_vma_clone(dst, src);
                if (ret)
                        return ret;

                *dup = dst;
        }

        return 0;
}

#ifdef CONFIG_DEBUG_VM_MAPLE_TREE
void validate_mm(struct mm_struct *mm)
{
        int bug = 0;
        int i = 0;
        struct vm_area_struct *vma;
        VMA_ITERATOR(vmi, mm, 0);

        mt_validate(&mm->mm_mt);
        for_each_vma(vmi, vma) {
#ifdef CONFIG_DEBUG_VM_RB
                struct anon_vma *anon_vma = vma->anon_vma;
                struct anon_vma_chain *avc;
#endif
                unsigned long vmi_start, vmi_end;
                bool warn = 0;

                vmi_start = vma_iter_addr(&vmi);
                vmi_end = vma_iter_end(&vmi);
                if (VM_WARN_ON_ONCE_MM(vma->vm_end != vmi_end, mm))
                        warn = 1;

                if (VM_WARN_ON_ONCE_MM(vma->vm_start != vmi_start, mm))
                        warn = 1;

                if (warn) {
                        pr_emerg("issue in %s\n", current->comm);
                        dump_stack();
                        dump_vma(vma);
                        pr_emerg("tree range: %px start %lx end %lx\n", vma,
                                 vmi_start, vmi_end - 1);
                        vma_iter_dump_tree(&vmi);
                }

#ifdef CONFIG_DEBUG_VM_RB
                if (anon_vma) {
                        anon_vma_lock_read(anon_vma);
                        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                                anon_vma_interval_tree_verify(avc);
                        anon_vma_unlock_read(anon_vma);
                }
#endif
                i++;
        }
        if (i != mm->map_count) {
                pr_emerg("map_count %d vma iterator %d\n", mm->map_count, i);
                bug = 1;
        }
        VM_BUG_ON_MM(bug, mm);
}
#endif /* CONFIG_DEBUG_VM_MAPLE_TREE */

/*
 * vma_expand - Expand an existing VMA
 *
 * @vmi: The vma iterator
 * @vma: The vma to expand
 * @start: The start of the vma
 * @end: The exclusive end of the vma
 * @pgoff: The page offset of vma
 * @next: The current of next vma.
 *
 * Expand @vma to @start and @end.  Can expand off the start and end.  Will
 * expand over @next if it's different from @vma and @end == @next->vm_end.
 * Checking if the @vma can expand and merge with @next needs to be handled by
 * the caller.
 *
 * Returns: 0 on success
 */
int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
               unsigned long start, unsigned long end, pgoff_t pgoff,
               struct vm_area_struct *next)
{
        struct vm_area_struct *anon_dup = NULL;
        bool remove_next = false;
        struct vma_prepare vp;

        vma_start_write(vma);
        if (next && (vma != next) && (end == next->vm_end)) {
                int ret;

                remove_next = true;
                vma_start_write(next);
                ret = dup_anon_vma(vma, next, &anon_dup);
                if (ret)
                        return ret;
        }

        init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL);
        /* Not merging but overwriting any part of next is not handled. */
        VM_WARN_ON(next && !vp.remove &&
                  next != vma && end > next->vm_start);
        /* Only handles expanding */
        VM_WARN_ON(vma->vm_start < start || vma->vm_end > end);

        /* Note: vma iterator must be pointing to 'start' */
        vma_iter_config(vmi, start, end);
        if (vma_iter_prealloc(vmi, vma))
                goto nomem;

        vma_prepare(&vp);
        vma_adjust_trans_huge(vma, start, end, 0);
        vma_set_range(vma, start, end, pgoff);
        vma_iter_store(vmi, vma);

        vma_complete(&vp, vmi, vma->vm_mm);
        return 0;

nomem:
        if (anon_dup)
                unlink_anon_vmas(anon_dup);
        return -ENOMEM;
}

/*
 * vma_shrink() - Reduce an existing VMAs memory area
 * @vmi: The vma iterator
 * @vma: The VMA to modify
 * @start: The new start
 * @end: The new end
 *
 * Returns: 0 on success, -ENOMEM otherwise
 */
int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
               unsigned long start, unsigned long end, pgoff_t pgoff)
{
        struct vma_prepare vp;

        WARN_ON((vma->vm_start != start) && (vma->vm_end != end));

        if (vma->vm_start < start)
                vma_iter_config(vmi, vma->vm_start, start);
        else
                vma_iter_config(vmi, end, vma->vm_end);

        if (vma_iter_prealloc(vmi, NULL))
                return -ENOMEM;

        vma_start_write(vma);

        init_vma_prep(&vp, vma);
        vma_prepare(&vp);
        vma_adjust_trans_huge(vma, start, end, 0);

        vma_iter_clear(vmi);
        vma_set_range(vma, start, end, pgoff);
        vma_complete(&vp, vmi, vma->vm_mm);
        return 0;
}

/*
 * vma_complete- Helper function for handling the unlocking after altering VMAs,
 * or for inserting a VMA.
 *
 * @vp: The vma_prepare struct
 * @vmi: The vma iterator
 * @mm: The mm_struct
 */
void vma_complete(struct vma_prepare *vp,
                  struct vma_iterator *vmi, struct mm_struct *mm)
{
        if (vp->file) {
                if (vp->adj_next)
                        vma_interval_tree_insert(vp->adj_next,
                                                 &vp->mapping->i_mmap);
                vma_interval_tree_insert(vp->vma, &vp->mapping->i_mmap);
                flush_dcache_mmap_unlock(vp->mapping);
        }

        if (vp->remove && vp->file) {
                __remove_shared_vm_struct(vp->remove, vp->mapping);
                if (vp->remove2)
                        __remove_shared_vm_struct(vp->remove2, vp->mapping);
        } else if (vp->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).
                 */
                vma_iter_store(vmi, vp->insert);
                mm->map_count++;
        }

        if (vp->anon_vma) {
                anon_vma_interval_tree_post_update_vma(vp->vma);
                if (vp->adj_next)
                        anon_vma_interval_tree_post_update_vma(vp->adj_next);
                anon_vma_unlock_write(vp->anon_vma);
        }

        if (vp->file) {
                i_mmap_unlock_write(vp->mapping);
                uprobe_mmap(vp->vma);

                if (vp->adj_next)
                        uprobe_mmap(vp->adj_next);
        }

        if (vp->remove) {
again:
                vma_mark_detached(vp->remove, true);
                if (vp->file) {
                        uprobe_munmap(vp->remove, vp->remove->vm_start,
                                      vp->remove->vm_end);
                        fput(vp->file);
                }
                if (vp->remove->anon_vma)
                        anon_vma_merge(vp->vma, vp->remove);
                mm->map_count--;
                mpol_put(vma_policy(vp->remove));
                if (!vp->remove2)
                        WARN_ON_ONCE(vp->vma->vm_end < vp->remove->vm_end);
                vm_area_free(vp->remove);

                /*
                 * In mprotect's case 6 (see comments on vma_merge),
                 * we are removing both mid and next vmas
                 */
                if (vp->remove2) {
                        vp->remove = vp->remove2;
                        vp->remove2 = NULL;
                        goto again;
                }
        }
        if (vp->insert && vp->file)
                uprobe_mmap(vp->insert);
        validate_mm(mm);
}

/*
 * do_vmi_align_munmap() - munmap the aligned region from @start to @end.
 * @vmi: The vma iterator
 * @vma: The starting vm_area_struct
 * @mm: The mm_struct
 * @start: The aligned start address to munmap.
 * @end: The aligned end address to munmap.
 * @uf: The userfaultfd list_head
 * @unlock: Set to true to drop the mmap_lock.  unlocking only happens on
 * success.
 *
 * Return: 0 on success and drops the lock if so directed, error and leaves the
 * lock held otherwise.
 */
int
do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
                    struct mm_struct *mm, unsigned long start,
                    unsigned long end, struct list_head *uf, bool unlock)
{
        struct vm_area_struct *prev, *next = NULL;
        struct maple_tree mt_detach;
        int count = 0;
        int error = -ENOMEM;
        unsigned long locked_vm = 0;
        MA_STATE(mas_detach, &mt_detach, 0, 0);
        mt_init_flags(&mt_detach, vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
        mt_on_stack(mt_detach);

        /*
         * 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.
         */

        /* Does it split the first one? */
        if (start > vma->vm_start) {

                /*
                 * 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)
                        goto map_count_exceeded;

                error = __split_vma(vmi, vma, start, 1);
                if (error)
                        goto start_split_failed;
        }

        /*
         * Detach a range of VMAs from the mm. Using next as a temp variable as
         * it is always overwritten.
         */
        next = vma;
        do {
                /* Does it split the end? */
                if (next->vm_end > end) {
                        error = __split_vma(vmi, next, end, 0);
                        if (error)
                                goto end_split_failed;
                }
                vma_start_write(next);
                mas_set(&mas_detach, count);
                error = mas_store_gfp(&mas_detach, next, GFP_KERNEL);
                if (error)
                        goto munmap_gather_failed;
                vma_mark_detached(next, true);
                if (next->vm_flags & VM_LOCKED)
                        locked_vm += vma_pages(next);

                count++;
                if (unlikely(uf)) {
                        /*
                         * If userfaultfd_unmap_prep returns an error the vmas
                         * will remain split, but userland will get a
                         * highly unexpected error anyway. This is no
                         * different than the case where the first of the two
                         * __split_vma fails, but we don't undo the first
                         * split, despite we could. This is unlikely enough
                         * failure that it's not worth optimizing it for.
                         */
                        error = userfaultfd_unmap_prep(next, start, end, uf);

                        if (error)
                                goto userfaultfd_error;
                }
#ifdef CONFIG_DEBUG_VM_MAPLE_TREE
                BUG_ON(next->vm_start < start);
                BUG_ON(next->vm_start > end);
#endif
        } for_each_vma_range(*vmi, next, end);

#if defined(CONFIG_DEBUG_VM_MAPLE_TREE)
        /* Make sure no VMAs are about to be lost. */
        {
                MA_STATE(test, &mt_detach, 0, 0);
                struct vm_area_struct *vma_mas, *vma_test;
                int test_count = 0;

                vma_iter_set(vmi, start);
                rcu_read_lock();
                vma_test = mas_find(&test, count - 1);
                for_each_vma_range(*vmi, vma_mas, end) {
                        BUG_ON(vma_mas != vma_test);
                        test_count++;
                        vma_test = mas_next(&test, count - 1);
                }
                rcu_read_unlock();
                BUG_ON(count != test_count);
        }
#endif

        while (vma_iter_addr(vmi) > start)
                vma_iter_prev_range(vmi);

        error = vma_iter_clear_gfp(vmi, start, end, GFP_KERNEL);
        if (error)
                goto clear_tree_failed;

        /* Point of no return */
        mm->locked_vm -= locked_vm;
        mm->map_count -= count;
        if (unlock)
                mmap_write_downgrade(mm);

        prev = vma_iter_prev_range(vmi);
        next = vma_next(vmi);
        if (next)
                vma_iter_prev_range(vmi);

        /*
         * We can free page tables without write-locking mmap_lock because VMAs
         * were isolated before we downgraded mmap_lock.
         */
        mas_set(&mas_detach, 1);
        unmap_region(mm, &mas_detach, vma, prev, next, start, end, count,
                     !unlock);
        /* Statistics and freeing VMAs */
        mas_set(&mas_detach, 0);
        remove_mt(mm, &mas_detach);
        validate_mm(mm);
        if (unlock)
                mmap_read_unlock(mm);

        __mt_destroy(&mt_detach);
        return 0;

clear_tree_failed:
userfaultfd_error:
munmap_gather_failed:
end_split_failed:
        mas_set(&mas_detach, 0);
        mas_for_each(&mas_detach, next, end)
                vma_mark_detached(next, false);

        __mt_destroy(&mt_detach);
start_split_failed:
map_count_exceeded:
        validate_mm(mm);
        return error;
}

/*
 * do_vmi_munmap() - munmap a given range.
 * @vmi: The vma iterator
 * @mm: The mm_struct
 * @start: The start address to munmap
 * @len: The length of the range to munmap
 * @uf: The userfaultfd list_head
 * @unlock: set to true if the user wants to drop the mmap_lock on success
 *
 * This function takes a @mas that is either pointing to the previous VMA or set
 * to MA_START and sets it up to remove the mapping(s).  The @len will be
 * aligned and any arch_unmap work will be preformed.
 *
 * Return: 0 on success and drops the lock if so directed, error and leaves the
 * lock held otherwise.
 */
int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
                  unsigned long start, size_t len, struct list_head *uf,
                  bool unlock)
{
        unsigned long end;
        struct vm_area_struct *vma;

        if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE-start)
                return -EINVAL;

        end = start + PAGE_ALIGN(len);
        if (end == start)
                return -EINVAL;

        /*
         * Check if memory is sealed before arch_unmap.
         * Prevent unmapping a sealed VMA.
         * can_modify_mm assumes we have acquired the lock on MM.
         */
        if (unlikely(!can_modify_mm(mm, start, end)))
                return -EPERM;

         /* arch_unmap() might do unmaps itself.  */
        arch_unmap(mm, start, end);

        /* Find the first overlapping VMA */
        vma = vma_find(vmi, end);
        if (!vma) {
                if (unlock)
                        mmap_write_unlock(mm);
                return 0;
        }

        return do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock);
}

/*
 * Given a mapping request (addr,end,vm_flags,file,pgoff,anon_name),
 * 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 **** is
 * the area passed down from mprotect_fixup, never extending beyond one
 * vma, PPPP is the previous vma, CCCC is a concurrent vma that starts
 * at the same address as **** and is of the same or larger span, and
 * NNNN the next vma after ****:
 *
 *     ****             ****                   ****
 *    PPPPPPNNNNNN    PPPPPPNNNNNN       PPPPPPCCCCCC
 *    cannot merge    might become       might become
 *                    PPNNNNNNNNNN       PPPPPPPPPPCC
 *    mmap, brk or    case 4 below       case 5 below
 *    mremap move:
 *                        ****               ****
 *                    PPPP    NNNN       PPPPCCCCNNNN
 *                    might become       might become
 *                    PPPPPPPPPPPP 1 or  PPPPPPPPPPPP 6 or
 *                    PPPPPPPPNNNN 2 or  PPPPPPPPNNNN 7 or
 *                    PPPPNNNNNNNN 3     PPPPNNNNNNNN 8
 *
 * It is important for case 8 that the vma CCCC overlapping the
 * region **** is never going to extended over NNNN. Instead NNNN must
 * be extended in region **** and CCCC must be removed. This way in
 * all cases where vma_merge succeeds, the moment vma_merge drops the
 * rmap_locks, the properties of the merged vma will be already
 * correct for the whole merged range. Some of those properties like
 * vm_page_prot/vm_flags may be accessed by rmap_walks and they must
 * be correct for the whole merged range immediately after the
 * rmap_locks are released. Otherwise if NNNN would be removed and
 * CCCC would be extended over the NNNN range, remove_migration_ptes
 * or other rmap walkers (if working on addresses beyond the "end"
 * parameter) may establish ptes with the wrong permissions of CCCC
 * instead of the right permissions of NNNN.
 *
 * In the code below:
 * PPPP is represented by *prev
 * CCCC is represented by *curr or not represented at all (NULL)
 * NNNN is represented by *next or not represented at all (NULL)
 * **** is not represented - it will be merged and the vma containing the
 *      area is returned, or the function will return NULL
 */
static struct vm_area_struct
*vma_merge(struct vma_iterator *vmi, struct vm_area_struct *prev,
           struct vm_area_struct *src, unsigned long addr, unsigned long end,
           unsigned long vm_flags, pgoff_t pgoff, struct mempolicy *policy,
           struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
           struct anon_vma_name *anon_name)
{
        struct mm_struct *mm = src->vm_mm;
        struct anon_vma *anon_vma = src->anon_vma;
        struct file *file = src->vm_file;
        struct vm_area_struct *curr, *next, *res;
        struct vm_area_struct *vma, *adjust, *remove, *remove2;
        struct vm_area_struct *anon_dup = NULL;
        struct vma_prepare vp;
        pgoff_t vma_pgoff;
        int err = 0;
        bool merge_prev = false;
        bool merge_next = false;
        bool vma_expanded = false;
        unsigned long vma_start = addr;
        unsigned long vma_end = end;
        pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
        long adj_start = 0;

        /*
         * 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;

        /* Does the input range span an existing VMA? (cases 5 - 8) */
        curr = find_vma_intersection(mm, prev ? prev->vm_end : 0, end);

        if (!curr ||                    /* cases 1 - 4 */
            end == curr->vm_end)        /* cases 6 - 8, adjacent VMA */
                next = vma_lookup(mm, end);
        else
                next = NULL;            /* case 5 */

        if (prev) {
                vma_start = prev->vm_start;
                vma_pgoff = prev->vm_pgoff;

                /* Can we merge the predecessor? */
                if (addr == prev->vm_end && mpol_equal(vma_policy(prev), policy)
                    && can_vma_merge_after(prev, vm_flags, anon_vma, file,
                                           pgoff, vm_userfaultfd_ctx, anon_name)) {
                        merge_prev = true;
                        vma_prev(vmi);
                }
        }

        /* Can we merge the successor? */
        if (next && mpol_equal(policy, vma_policy(next)) &&
            can_vma_merge_before(next, vm_flags, anon_vma, file, pgoff+pglen,
                                 vm_userfaultfd_ctx, anon_name)) {
                merge_next = true;
        }

        /* Verify some invariant that must be enforced by the caller. */
        VM_WARN_ON(prev && addr <= prev->vm_start);
        VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end));
        VM_WARN_ON(addr >= end);

        if (!merge_prev && !merge_next)
                return NULL; /* Not mergeable. */

        if (merge_prev)
                vma_start_write(prev);

        res = vma = prev;
        remove = remove2 = adjust = NULL;

        /* Can we merge both the predecessor and the successor? */
        if (merge_prev && merge_next &&
            is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) {
                vma_start_write(next);
                remove = next;                          /* case 1 */
                vma_end = next->vm_end;
                err = dup_anon_vma(prev, next, &anon_dup);
                if (curr) {                             /* case 6 */
                        vma_start_write(curr);
                        remove = curr;
                        remove2 = next;
                        /*
                         * Note that the dup_anon_vma below cannot overwrite err
                         * since the first caller would do nothing unless next
                         * has an anon_vma.
                         */
                        if (!next->anon_vma)
                                err = dup_anon_vma(prev, curr, &anon_dup);
                }
        } else if (merge_prev) {                        /* case 2 */
                if (curr) {
                        vma_start_write(curr);
                        if (end == curr->vm_end) {      /* case 7 */
                                /*
                                 * can_vma_merge_after() assumed we would not be
                                 * removing prev vma, so it skipped the check
                                 * for vm_ops->close, but we are removing curr
                                 */
                                if (curr->vm_ops && curr->vm_ops->close)
                                        err = -EINVAL;
                                remove = curr;
                        } else {                        /* case 5 */
                                adjust = curr;
                                adj_start = (end - curr->vm_start);
                        }
                        if (!err)
                                err = dup_anon_vma(prev, curr, &anon_dup);
                }
        } else { /* merge_next */
                vma_start_write(next);
                res = next;
                if (prev && addr < prev->vm_end) {      /* case 4 */
                        vma_start_write(prev);
                        vma_end = addr;
                        adjust = next;
                        adj_start = -(prev->vm_end - addr);
                        err = dup_anon_vma(next, prev, &anon_dup);
                } else {
                        /*
                         * Note that cases 3 and 8 are the ONLY ones where prev
                         * is permitted to be (but is not necessarily) NULL.
                         */
                        vma = next;                     /* case 3 */
                        vma_start = addr;
                        vma_end = next->vm_end;
                        vma_pgoff = next->vm_pgoff - pglen;
                        if (curr) {                     /* case 8 */
                                vma_pgoff = curr->vm_pgoff;
                                vma_start_write(curr);
                                remove = curr;
                                err = dup_anon_vma(next, curr, &anon_dup);
                        }
                }
        }

        /* Error in anon_vma clone. */
        if (err)
                goto anon_vma_fail;

        if (vma_start < vma->vm_start || vma_end > vma->vm_end)
                vma_expanded = true;

        if (vma_expanded) {
                vma_iter_config(vmi, vma_start, vma_end);
        } else {
                vma_iter_config(vmi, adjust->vm_start + adj_start,
                                adjust->vm_end);
        }

        if (vma_iter_prealloc(vmi, vma))
                goto prealloc_fail;

        init_multi_vma_prep(&vp, vma, adjust, remove, remove2);
        VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
                   vp.anon_vma != adjust->anon_vma);

        vma_prepare(&vp);
        vma_adjust_trans_huge(vma, vma_start, vma_end, adj_start);
        vma_set_range(vma, vma_start, vma_end, vma_pgoff);

        if (vma_expanded)
                vma_iter_store(vmi, vma);

        if (adj_start) {
                adjust->vm_start += adj_start;
                adjust->vm_pgoff += adj_start >> PAGE_SHIFT;
                if (adj_start < 0) {
                        WARN_ON(vma_expanded);
                        vma_iter_store(vmi, next);
                }
        }

        vma_complete(&vp, vmi, mm);
        khugepaged_enter_vma(res, vm_flags);
        return res;

prealloc_fail:
        if (anon_dup)
                unlink_anon_vmas(anon_dup);

anon_vma_fail:
        vma_iter_set(vmi, addr);
        vma_iter_load(vmi);
        return NULL;
}

/*
 * We are about to modify one or multiple of a VMA's flags, policy, userfaultfd
 * context and anonymous VMA name within the range [start, end).
 *
 * As a result, we might be able to merge the newly modified VMA range with an
 * adjacent VMA with identical properties.
 *
 * If no merge is possible and the range does not span the entirety of the VMA,
 * we then need to split the VMA to accommodate the change.
 *
 * The function returns either the merged VMA, the original VMA if a split was
 * required instead, or an error if the split failed.
 */
struct vm_area_struct *vma_modify(struct vma_iterator *vmi,
                                  struct vm_area_struct *prev,
                                  struct vm_area_struct *vma,
                                  unsigned long start, unsigned long end,
                                  unsigned long vm_flags,
                                  struct mempolicy *policy,
                                  struct vm_userfaultfd_ctx uffd_ctx,
                                  struct anon_vma_name *anon_name)
{
        pgoff_t pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
        struct vm_area_struct *merged;

        merged = vma_merge(vmi, prev, vma, start, end, vm_flags,
                           pgoff, policy, uffd_ctx, anon_name);
        if (merged)
                return merged;

        if (vma->vm_start < start) {
                int err = split_vma(vmi, vma, start, 1);

                if (err)
                        return ERR_PTR(err);
        }

        if (vma->vm_end > end) {
                int err = split_vma(vmi, vma, end, 0);

                if (err)
                        return ERR_PTR(err);
        }

        return vma;
}

/*
 * Attempt to merge a newly mapped VMA with those adjacent to it. The caller
 * must ensure that [start, end) does not overlap any existing VMA.
 */
struct vm_area_struct
*vma_merge_new_vma(struct vma_iterator *vmi, struct vm_area_struct *prev,
                   struct vm_area_struct *vma, unsigned long start,
                   unsigned long end, pgoff_t pgoff)
{
        return vma_merge(vmi, prev, vma, start, end, vma->vm_flags, pgoff,
                         vma_policy(vma), vma->vm_userfaultfd_ctx, anon_vma_name(vma));
}

/*
 * Expand vma by delta bytes, potentially merging with an immediately adjacent
 * VMA with identical properties.
 */
struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
                                        struct vm_area_struct *vma,
                                        unsigned long delta)
{
        pgoff_t pgoff = vma->vm_pgoff + vma_pages(vma);

        /* vma is specified as prev, so case 1 or 2 will apply. */
        return vma_merge(vmi, vma, vma, vma->vm_end, vma->vm_end + delta,
                         vma->vm_flags, pgoff, vma_policy(vma),
                         vma->vm_userfaultfd_ctx, anon_vma_name(vma));
}

void unlink_file_vma_batch_init(struct unlink_vma_file_batch *vb)
{
        vb->count = 0;
}

static void unlink_file_vma_batch_process(struct unlink_vma_file_batch *vb)
{
        struct address_space *mapping;
        int i;

        mapping = vb->vmas[0]->vm_file->f_mapping;
        i_mmap_lock_write(mapping);
        for (i = 0; i < vb->count; i++) {
                VM_WARN_ON_ONCE(vb->vmas[i]->vm_file->f_mapping != mapping);
                __remove_shared_vm_struct(vb->vmas[i], mapping);
        }
        i_mmap_unlock_write(mapping);

        unlink_file_vma_batch_init(vb);
}

void unlink_file_vma_batch_add(struct unlink_vma_file_batch *vb,
                               struct vm_area_struct *vma)
{
        if (vma->vm_file == NULL)
                return;

        if ((vb->count > 0 && vb->vmas[0]->vm_file != vma->vm_file) ||
            vb->count == ARRAY_SIZE(vb->vmas))
                unlink_file_vma_batch_process(vb);

        vb->vmas[vb->count] = vma;
        vb->count++;
}

void unlink_file_vma_batch_final(struct unlink_vma_file_batch *vb)
{
        if (vb->count > 0)
                unlink_file_vma_batch_process(vb);
}

/*
 * 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;

                i_mmap_lock_write(mapping);
                __remove_shared_vm_struct(vma, mapping);
                i_mmap_unlock_write(mapping);
        }
}

void vma_link_file(struct vm_area_struct *vma)
{
        struct file *file = vma->vm_file;
        struct address_space *mapping;

        if (file) {
                mapping = file->f_mapping;
                i_mmap_lock_write(mapping);
                __vma_link_file(vma, mapping);
                i_mmap_unlock_write(mapping);
        }
}

int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
{
        VMA_ITERATOR(vmi, mm, 0);

        vma_iter_config(&vmi, vma->vm_start, vma->vm_end);
        if (vma_iter_prealloc(&vmi, vma))
                return -ENOMEM;

        vma_start_write(vma);
        vma_iter_store(&vmi, vma);
        vma_link_file(vma);
        mm->map_count++;
        validate_mm(mm);
        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;
        bool faulted_in_anon_vma = true;
        VMA_ITERATOR(vmi, mm, addr);

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

        new_vma = find_vma_prev(mm, addr, &prev);
        if (new_vma && new_vma->vm_start < addr + len)
                return NULL;    /* should never get here */

        new_vma = vma_merge_new_vma(&vmi, prev, vma, addr, addr + len, pgoff);
        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_VMA(faulted_in_anon_vma, new_vma);
                        *vmap = vma = new_vma;
                }
                *need_rmap_locks = (new_vma->vm_pgoff <= vma->vm_pgoff);
        } else {
                new_vma = vm_area_dup(vma);
                if (!new_vma)
                        goto out;
                vma_set_range(new_vma, addr, addr + len, pgoff);
                if (vma_dup_policy(vma, new_vma))
                        goto out_free_vma;
                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);
                if (vma_link(mm, new_vma))
                        goto out_vma_link;
                *need_rmap_locks = false;
        }
        return new_vma;

out_vma_link:
        if (new_vma->vm_ops && new_vma->vm_ops->close)
                new_vma->vm_ops->close(new_vma);

        if (new_vma->vm_file)
                fput(new_vma->vm_file);

        unlink_anon_vmas(new_vma);
out_free_mempol:
        mpol_put(vma_policy(new_vma));
out_free_vma:
        vm_area_free(new_vma);
out:
        return NULL;
}

/*
 * Rough compatibility 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_ACCESS_FLAGS | VM_SOFTDIRTY)) &&
                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 mmap_lock 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 READ_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 mmap_lock.
 */
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 = READ_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 = NULL;
        struct vm_area_struct *prev, *next;
        VMA_ITERATOR(vmi, vma->vm_mm, vma->vm_end);

        /* Try next first. */
        next = vma_iter_load(&vmi);
        if (next) {
                anon_vma = reusable_anon_vma(next, vma, next);
                if (anon_vma)
                        return anon_vma;
        }

        prev = vma_prev(&vmi);
        VM_BUG_ON_VMA(prev != vma, vma);
        prev = vma_prev(&vmi);
        /* Try prev next. */
        if (prev)
                anon_vma = reusable_anon_vma(prev, prev, vma);

        /*
         * We might reach here with anon_vma == NULL if we can't find
         * any reusable anon_vma.
         * 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 anon_vma;
}

static bool vm_ops_needs_writenotify(const struct vm_operations_struct *vm_ops)
{
        return vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite);
}

static bool vma_is_shared_writable(struct vm_area_struct *vma)
{
        return (vma->vm_flags & (VM_WRITE | VM_SHARED)) ==
                (VM_WRITE | VM_SHARED);
}

static bool vma_fs_can_writeback(struct vm_area_struct *vma)
{
        /* No managed pages to writeback. */
        if (vma->vm_flags & VM_PFNMAP)
                return false;

        return vma->vm_file && vma->vm_file->f_mapping &&
                mapping_can_writeback(vma->vm_file->f_mapping);
}

/*
 * Does this VMA require the underlying folios to have their dirty state
 * tracked?
 */
bool vma_needs_dirty_tracking(struct vm_area_struct *vma)
{
        /* Only shared, writable VMAs require dirty tracking. */
        if (!vma_is_shared_writable(vma))
                return false;

        /* Does the filesystem need to be notified? */
        if (vm_ops_needs_writenotify(vma->vm_ops))
                return true;

        /*
         * Even if the filesystem doesn't indicate a need for writenotify, if it
         * can writeback, dirty tracking is still required.
         */
        return vma_fs_can_writeback(vma);
}

/*
 * Some shared mappings 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).
 */
bool vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
{
        /* If it was private or non-writable, the write bit is already clear */
        if (!vma_is_shared_writable(vma))
                return false;

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

        /* The open routine did something to the protections that pgprot_modify
         * won't preserve? */
        if (pgprot_val(vm_page_prot) !=
            pgprot_val(vm_pgprot_modify(vm_page_prot, vma->vm_flags)))
                return false;

        /*
         * Do we need to track softdirty? hugetlb does not support softdirty
         * tracking yet.
         */
        if (vma_soft_dirty_enabled(vma) && !is_vm_hugetlb_page(vma))
                return true;

        /* Do we need write faults for uffd-wp tracking? */
        if (userfaultfd_wp(vma))
                return true;

        /* Can the mapping track the dirty pages? */
        return vma_fs_can_writeback(vma);
}

unsigned long count_vma_pages_range(struct mm_struct *mm,
                                    unsigned long addr, unsigned long end)
{
        VMA_ITERATOR(vmi, mm, addr);
        struct vm_area_struct *vma;
        unsigned long nr_pages = 0;

        for_each_vma_range(vmi, vma, end) {
                unsigned long vm_start = max(addr, vma->vm_start);
                unsigned long vm_end = min(end, vma->vm_end);

                nr_pages += PHYS_PFN(vm_end - vm_start);
        }

        return nr_pages;
}

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_root.rb_node)) {
                /*
                 * The LSB of head.next can't change from under us
                 * because we hold the mm_all_locks_mutex.
                 */
                down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_lock);
                /*
                 * We can safely modify head.next after taking the
                 * anon_vma->root->rwsem. 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->rwsem.
                 */
                if (__test_and_set_bit(0, (unsigned long *)
                                       &anon_vma->root->rb_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();
                down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_lock);
        }
}

/*
 * 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_lock in write mode before calling
 * mm_take_all_locks(). The caller isn't allowed to release the
 * mmap_lock until mm_drop_all_locks() returns.
 *
 * mmap_lock 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. 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 take locks in following order, accordingly to comment at beginning
 * of mm/rmap.c:
 *   - all hugetlbfs_i_mmap_rwsem_key locks (aka mapping->i_mmap_rwsem for
 *     hugetlb mapping);
 *   - all vmas marked locked
 *   - all i_mmap_rwsem locks;
 *   - all anon_vma->rwseml
 *
 * We can take all locks within these types randomly because the VM code
 * doesn't nest them and we protected from parallel mm_take_all_locks() by
 * 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;
        VMA_ITERATOR(vmi, mm, 0);

        mmap_assert_write_locked(mm);

        mutex_lock(&mm_all_locks_mutex);

        /*
         * vma_start_write() does not have a complement in mm_drop_all_locks()
         * because vma_start_write() is always asymmetrical; it marks a VMA as
         * being written to until mmap_write_unlock() or mmap_write_downgrade()
         * is reached.
         */
        for_each_vma(vmi, vma) {
                if (signal_pending(current))
                        goto out_unlock;
                vma_start_write(vma);
        }

        vma_iter_init(&vmi, mm, 0);
        for_each_vma(vmi, vma) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->vm_file && vma->vm_file->f_mapping &&
                                is_vm_hugetlb_page(vma))
                        vm_lock_mapping(mm, vma->vm_file->f_mapping);
        }

        vma_iter_init(&vmi, mm, 0);
        for_each_vma(vmi, vma) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->vm_file && vma->vm_file->f_mapping &&
                                !is_vm_hugetlb_page(vma))
                        vm_lock_mapping(mm, vma->vm_file->f_mapping);
        }

        vma_iter_init(&vmi, mm, 0);
        for_each_vma(vmi, vma) {
                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_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->rwsem.
                 */
                if (!__test_and_clear_bit(0, (unsigned long *)
                                          &anon_vma->root->rb_root.rb_root.rb_node))
                        BUG();
                anon_vma_unlock_write(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.
                 */
                i_mmap_unlock_write(mapping);
                if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
                                        &mapping->flags))
                        BUG();
        }
}

/*
 * The mmap_lock 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;
        VMA_ITERATOR(vmi, mm, 0);

        mmap_assert_write_locked(mm);
        BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));

        for_each_vma(vmi, vma) {
                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);
}