Linux 6.14-rc3

[linux.git] / mm / vma.c

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

/*
 * VMA-specific functions.
 */

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

struct mmap_state {
        struct mm_struct *mm;
        struct vma_iterator *vmi;

        unsigned long addr;
        unsigned long end;
        pgoff_t pgoff;
        unsigned long pglen;
        unsigned long flags;
        struct file *file;

        unsigned long charged;
        bool retry_merge;

        struct vm_area_struct *prev;
        struct vm_area_struct *next;

        /* Unmapping state. */
        struct vma_munmap_struct vms;
        struct ma_state mas_detach;
        struct maple_tree mt_detach;
};

#define MMAP_STATE(name, mm_, vmi_, addr_, len_, pgoff_, flags_, file_) \
        struct mmap_state name = {                                      \
                .mm = mm_,                                              \
                .vmi = vmi_,                                            \
                .addr = addr_,                                          \
                .end = (addr_) + (len_),                                \
                .pgoff = pgoff_,                                        \
                .pglen = PHYS_PFN(len_),                                \
                .flags = flags_,                                        \
                .file = file_,                                          \
        }

#define VMG_MMAP_STATE(name, map_, vma_)                                \
        struct vma_merge_struct name = {                                \
                .mm = (map_)->mm,                                       \
                .vmi = (map_)->vmi,                                     \
                .start = (map_)->addr,                                  \
                .end = (map_)->end,                                     \
                .flags = (map_)->flags,                                 \
                .pgoff = (map_)->pgoff,                                 \
                .file = (map_)->file,                                   \
                .prev = (map_)->prev,                                   \
                .vma = vma_,                                            \
                .next = (vma_) ? NULL : (map_)->next,                   \
                .state = VMA_MERGE_START,                               \
                .merge_flags = VMG_FLAG_DEFAULT,                        \
        }

static inline bool is_mergeable_vma(struct vma_merge_struct *vmg, bool merge_next)
{
        struct vm_area_struct *vma = merge_next ? vmg->next : vmg->prev;

        if (!mpol_equal(vmg->policy, vma_policy(vma)))
                return false;
        /*
         * 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 ^ vmg->flags) & ~VM_SOFTDIRTY)
                return false;
        if (vma->vm_file != vmg->file)
                return false;
        if (!is_mergeable_vm_userfaultfd_ctx(vma, vmg->uffd_ctx))
                return false;
        if (!anon_vma_name_eq(anon_vma_name(vma), vmg->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;
}

/* Are the anon_vma's belonging to each VMA compatible with one another? */
static inline bool are_anon_vmas_compatible(struct vm_area_struct *vma1,
                                            struct vm_area_struct *vma2)
{
        return is_mergeable_anon_vma(vma1->anon_vma, vma2->anon_vma, NULL);
}

/*
 * 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.
 */
static bool can_vma_merge_before(struct vma_merge_struct *vmg)
{
        pgoff_t pglen = PHYS_PFN(vmg->end - vmg->start);

        if (is_mergeable_vma(vmg, /* merge_next = */ true) &&
            is_mergeable_anon_vma(vmg->anon_vma, vmg->next->anon_vma, vmg->next)) {
                if (vmg->next->vm_pgoff == vmg->pgoff + pglen)
                        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.
 */
static bool can_vma_merge_after(struct vma_merge_struct *vmg)
{
        if (is_mergeable_vma(vmg, /* merge_next = */ false) &&
            is_mergeable_anon_vma(vmg->anon_vma, vmg->prev->anon_vma, vmg->prev)) {
                if (vmg->prev->vm_pgoff + vma_pages(vmg->prev) == vmg->pgoff)
                        return true;
        }
        return false;
}

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);
}

/*
 * 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.
 */
static 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 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);
}

/*
 * vma_prepare() - Helper function for handling locking VMAs prior to altering
 * @vp: The initialized vma_prepare struct
 */
static 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);
        }

}

/*
 * 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
 */
static 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);
}

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

/*
 * Can the proposed VMA be merged with the left (previous) VMA taking into
 * account the start position of the proposed range.
 */
static bool can_vma_merge_left(struct vma_merge_struct *vmg)

{
        return vmg->prev && vmg->prev->vm_end == vmg->start &&
                can_vma_merge_after(vmg);
}

/*
 * Can the proposed VMA be merged with the right (next) VMA taking into
 * account the end position of the proposed range.
 *
 * In addition, if we can merge with the left VMA, ensure that left and right
 * anon_vma's are also compatible.
 */
static bool can_vma_merge_right(struct vma_merge_struct *vmg,
                                bool can_merge_left)
{
        if (!vmg->next || vmg->end != vmg->next->vm_start ||
            !can_vma_merge_before(vmg))
                return false;

        if (!can_merge_left)
                return true;

        /*
         * If we can merge with prev (left) and next (right), indicating that
         * each VMA's anon_vma is compatible with the proposed anon_vma, this
         * does not mean prev and next are compatible with EACH OTHER.
         *
         * We therefore check this in addition to mergeability to either side.
         */
        return are_anon_vmas_compatible(vmg->prev, vmg->next);
}

/*
 * Close a vm structure and free it.
 */
void remove_vma(struct vm_area_struct *vma, bool unreachable)
{
        might_sleep();
        vma_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 ma_state *mas, struct vm_area_struct *vma,
                struct vm_area_struct *prev, struct vm_area_struct *next)
{
        struct mm_struct *mm = vma->vm_mm;
        struct mmu_gather tlb;

        tlb_gather_mmu(&tlb, mm);
        update_hiwater_rss(mm);
        unmap_vmas(&tlb, mas, vma, vma->vm_start, vma->vm_end, vma->vm_end,
                   /* mm_wr_locked = */ true);
        mas_set(mas, vma->vm_end);
        free_pgtables(&tlb, mas, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
                      next ? next->vm_start : USER_PGTABLES_CEILING,
                      /* mm_wr_locked = */ true);
        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 original VMA.
 */
static __must_check 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);
        validate_mm(vma->vm_mm);

        /* Success. */
        if (new_below)
                vma_next(vmi);
        else
                vma_prev(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);
}

/*
 * 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
                /* Check for a infinite loop */
                if (++i > mm->map_count + 10) {
                        i = -1;
                        break;
                }
        }
        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 */

/* Actually perform the VMA merge operation. */
static int commit_merge(struct vma_merge_struct *vmg,
                        struct vm_area_struct *adjust,
                        struct vm_area_struct *remove,
                        struct vm_area_struct *remove2,
                        long adj_start,
                        bool expanded)
{
        struct vma_prepare vp;

        init_multi_vma_prep(&vp, vmg->vma, adjust, remove, remove2);

        VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
                   vp.anon_vma != adjust->anon_vma);

        if (expanded) {
                /* Note: vma iterator must be pointing to 'start'. */
                vma_iter_config(vmg->vmi, vmg->start, vmg->end);
        } else {
                vma_iter_config(vmg->vmi, adjust->vm_start + adj_start,
                                adjust->vm_end);
        }

        if (vma_iter_prealloc(vmg->vmi, vmg->vma))
                return -ENOMEM;

        vma_prepare(&vp);
        vma_adjust_trans_huge(vmg->vma, vmg->start, vmg->end, adj_start);
        vma_set_range(vmg->vma, vmg->start, vmg->end, vmg->pgoff);

        if (expanded)
                vma_iter_store(vmg->vmi, vmg->vma);

        if (adj_start) {
                adjust->vm_start += adj_start;
                adjust->vm_pgoff += PHYS_PFN(adj_start);
                if (adj_start < 0) {
                        WARN_ON(expanded);
                        vma_iter_store(vmg->vmi, adjust);
                }
        }

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

        return 0;
}

/* We can only remove VMAs when merging if they do not have a close hook. */
static bool can_merge_remove_vma(struct vm_area_struct *vma)
{
        return !vma->vm_ops || !vma->vm_ops->close;
}

/*
 * vma_merge_existing_range - Attempt to merge VMAs based on a VMA having its
 * attributes modified.
 *
 * @vmg: Describes the modifications being made to a VMA and associated
 *       metadata.
 *
 * When the attributes of a range within a VMA change, then it might be possible
 * for immediately adjacent VMAs to be merged into that VMA due to having
 * identical properties.
 *
 * This function checks for the existence of any such mergeable VMAs and updates
 * the maple tree describing the @vmg->vma->vm_mm address space to account for
 * this, as well as any VMAs shrunk/expanded/deleted as a result of this merge.
 *
 * As part of this operation, if a merge occurs, the @vmg object will have its
 * vma, start, end, and pgoff fields modified to execute the merge. Subsequent
 * calls to this function should reset these fields.
 *
 * Returns: The merged VMA if merge succeeds, or NULL otherwise.
 *
 * ASSUMPTIONS:
 * - The caller must assign the VMA to be modifed to @vmg->vma.
 * - The caller must have set @vmg->prev to the previous VMA, if there is one.
 * - The caller must not set @vmg->next, as we determine this.
 * - The caller must hold a WRITE lock on the mm_struct->mmap_lock.
 * - vmi must be positioned within [@vmg->vma->vm_start, @vmg->vma->vm_end).
 */
static __must_check struct vm_area_struct *vma_merge_existing_range(
                struct vma_merge_struct *vmg)
{
        struct vm_area_struct *vma = vmg->vma;
        struct vm_area_struct *prev = vmg->prev;
        struct vm_area_struct *next, *res;
        struct vm_area_struct *anon_dup = NULL;
        struct vm_area_struct *adjust = NULL;
        unsigned long start = vmg->start;
        unsigned long end = vmg->end;
        bool left_side = vma && start == vma->vm_start;
        bool right_side = vma && end == vma->vm_end;
        int err = 0;
        long adj_start = 0;
        bool merge_will_delete_vma, merge_will_delete_next;
        bool merge_left, merge_right, merge_both;
        bool expanded;

        mmap_assert_write_locked(vmg->mm);
        VM_WARN_ON_VMG(!vma, vmg); /* We are modifying a VMA, so caller must specify. */
        VM_WARN_ON_VMG(vmg->next, vmg); /* We set this. */
        VM_WARN_ON_VMG(prev && start <= prev->vm_start, vmg);
        VM_WARN_ON_VMG(start >= end, vmg);

        /*
         * If vma == prev, then we are offset into a VMA. Otherwise, if we are
         * not, we must span a portion of the VMA.
         */
        VM_WARN_ON_VMG(vma && ((vma != prev && vmg->start != vma->vm_start) ||
                               vmg->end > vma->vm_end), vmg);
        /* The vmi must be positioned within vmg->vma. */
        VM_WARN_ON_VMG(vma && !(vma_iter_addr(vmg->vmi) >= vma->vm_start &&
                                vma_iter_addr(vmg->vmi) < vma->vm_end), vmg);

        vmg->state = VMA_MERGE_NOMERGE;

        /*
         * If a special mapping or if the range being modified is neither at the
         * furthermost left or right side of the VMA, then we have no chance of
         * merging and should abort.
         */
        if (vmg->flags & VM_SPECIAL || (!left_side && !right_side))
                return NULL;

        if (left_side)
                merge_left = can_vma_merge_left(vmg);
        else
                merge_left = false;

        if (right_side) {
                next = vmg->next = vma_iter_next_range(vmg->vmi);
                vma_iter_prev_range(vmg->vmi);

                merge_right = can_vma_merge_right(vmg, merge_left);
        } else {
                merge_right = false;
                next = NULL;
        }

        if (merge_left)         /* If merging prev, position iterator there. */
                vma_prev(vmg->vmi);
        else if (!merge_right)  /* If we have nothing to merge, abort. */
                return NULL;

        merge_both = merge_left && merge_right;
        /* If we span the entire VMA, a merge implies it will be deleted. */
        merge_will_delete_vma = left_side && right_side;

        /*
         * If we need to remove vma in its entirety but are unable to do so,
         * we have no sensible recourse but to abort the merge.
         */
        if (merge_will_delete_vma && !can_merge_remove_vma(vma))
                return NULL;

        /*
         * If we merge both VMAs, then next is also deleted. This implies
         * merge_will_delete_vma also.
         */
        merge_will_delete_next = merge_both;

        /*
         * If we cannot delete next, then we can reduce the operation to merging
         * prev and vma (thereby deleting vma).
         */
        if (merge_will_delete_next && !can_merge_remove_vma(next)) {
                merge_will_delete_next = false;
                merge_right = false;
                merge_both = false;
        }

        /* No matter what happens, we will be adjusting vma. */
        vma_start_write(vma);

        if (merge_left)
                vma_start_write(prev);

        if (merge_right)
                vma_start_write(next);

        if (merge_both) {
                /*
                 *         |<----->|
                 * |-------*********-------|
                 *   prev     vma     next
                 *  extend   delete  delete
                 */

                vmg->vma = prev;
                vmg->start = prev->vm_start;
                vmg->end = next->vm_end;
                vmg->pgoff = prev->vm_pgoff;

                /*
                 * We already ensured anon_vma compatibility above, so now it's
                 * simply a case of, if prev has no anon_vma object, which of
                 * next or vma contains the anon_vma we must duplicate.
                 */
                err = dup_anon_vma(prev, next->anon_vma ? next : vma, &anon_dup);
        } else if (merge_left) {
                /*
                 *         |<----->| OR
                 *         |<--------->|
                 * |-------*************
                 *   prev       vma
                 *  extend shrink/delete
                 */

                vmg->vma = prev;
                vmg->start = prev->vm_start;
                vmg->pgoff = prev->vm_pgoff;

                if (!merge_will_delete_vma) {
                        adjust = vma;
                        adj_start = vmg->end - vma->vm_start;
                }

                err = dup_anon_vma(prev, vma, &anon_dup);
        } else { /* merge_right */
                /*
                 *     |<----->| OR
                 * |<--------->|
                 * *************-------|
                 *      vma       next
                 * shrink/delete extend
                 */

                pgoff_t pglen = PHYS_PFN(vmg->end - vmg->start);

                VM_WARN_ON_VMG(!merge_right, vmg);
                /* If we are offset into a VMA, then prev must be vma. */
                VM_WARN_ON_VMG(vmg->start > vma->vm_start && prev && vma != prev, vmg);

                if (merge_will_delete_vma) {
                        vmg->vma = next;
                        vmg->end = next->vm_end;
                        vmg->pgoff = next->vm_pgoff - pglen;
                } else {
                        /*
                         * We shrink vma and expand next.
                         *
                         * IMPORTANT: This is the ONLY case where the final
                         * merged VMA is NOT vmg->vma, but rather vmg->next.
                         */

                        vmg->start = vma->vm_start;
                        vmg->end = start;
                        vmg->pgoff = vma->vm_pgoff;

                        adjust = next;
                        adj_start = -(vma->vm_end - start);
                }

                err = dup_anon_vma(next, vma, &anon_dup);
        }

        if (err)
                goto abort;

        /*
         * In nearly all cases, we expand vmg->vma. There is one exception -
         * merge_right where we partially span the VMA. In this case we shrink
         * the end of vmg->vma and adjust the start of vmg->next accordingly.
         */
        expanded = !merge_right || merge_will_delete_vma;

        if (commit_merge(vmg, adjust,
                         merge_will_delete_vma ? vma : NULL,
                         merge_will_delete_next ? next : NULL,
                         adj_start, expanded)) {
                if (anon_dup)
                        unlink_anon_vmas(anon_dup);

                vmg->state = VMA_MERGE_ERROR_NOMEM;
                return NULL;
        }

        res = merge_left ? prev : next;
        khugepaged_enter_vma(res, vmg->flags);

        vmg->state = VMA_MERGE_SUCCESS;
        return res;

abort:
        vma_iter_set(vmg->vmi, start);
        vma_iter_load(vmg->vmi);
        vmg->state = VMA_MERGE_ERROR_NOMEM;
        return NULL;
}

/*
 * vma_merge_new_range - Attempt to merge a new VMA into address space
 *
 * @vmg: Describes the VMA we are adding, in the range @vmg->start to @vmg->end
 *       (exclusive), which we try to merge with any adjacent VMAs if possible.
 *
 * We are about to add a VMA to the address space starting at @vmg->start and
 * ending at @vmg->end. There are three different possible scenarios:
 *
 * 1. There is a VMA with identical properties immediately adjacent to the
 *    proposed new VMA [@vmg->start, @vmg->end) either before or after it -
 *    EXPAND that VMA:
 *
 * Proposed:       |-----|  or  |-----|
 * Existing:  |----|                  |----|
 *
 * 2. There are VMAs with identical properties immediately adjacent to the
 *    proposed new VMA [@vmg->start, @vmg->end) both before AND after it -
 *    EXPAND the former and REMOVE the latter:
 *
 * Proposed:       |-----|
 * Existing:  |----|     |----|
 *
 * 3. There are no VMAs immediately adjacent to the proposed new VMA or those
 *    VMAs do not have identical attributes - NO MERGE POSSIBLE.
 *
 * In instances where we can merge, this function returns the expanded VMA which
 * will have its range adjusted accordingly and the underlying maple tree also
 * adjusted.
 *
 * Returns: In instances where no merge was possible, NULL. Otherwise, a pointer
 *          to the VMA we expanded.
 *
 * This function adjusts @vmg to provide @vmg->next if not already specified,
 * and adjusts [@vmg->start, @vmg->end) to span the expanded range.
 *
 * ASSUMPTIONS:
 * - The caller must hold a WRITE lock on the mm_struct->mmap_lock.
 * - The caller must have determined that [@vmg->start, @vmg->end) is empty,
     other than VMAs that will be unmapped should the operation succeed.
 * - The caller must have specified the previous vma in @vmg->prev.
 * - The caller must have specified the next vma in @vmg->next.
 * - The caller must have positioned the vmi at or before the gap.
 */
struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
{
        struct vm_area_struct *prev = vmg->prev;
        struct vm_area_struct *next = vmg->next;
        unsigned long end = vmg->end;
        bool can_merge_left, can_merge_right;
        bool just_expand = vmg->merge_flags & VMG_FLAG_JUST_EXPAND;

        mmap_assert_write_locked(vmg->mm);
        VM_WARN_ON_VMG(vmg->vma, vmg);
        /* vmi must point at or before the gap. */
        VM_WARN_ON_VMG(vma_iter_addr(vmg->vmi) > end, vmg);

        vmg->state = VMA_MERGE_NOMERGE;

        /* Special VMAs are unmergeable, also if no prev/next. */
        if ((vmg->flags & VM_SPECIAL) || (!prev && !next))
                return NULL;

        can_merge_left = can_vma_merge_left(vmg);
        can_merge_right = !just_expand && can_vma_merge_right(vmg, can_merge_left);

        /* If we can merge with the next VMA, adjust vmg accordingly. */
        if (can_merge_right) {
                vmg->end = next->vm_end;
                vmg->vma = next;
        }

        /* If we can merge with the previous VMA, adjust vmg accordingly. */
        if (can_merge_left) {
                vmg->start = prev->vm_start;
                vmg->vma = prev;
                vmg->pgoff = prev->vm_pgoff;

                /*
                 * If this merge would result in removal of the next VMA but we
                 * are not permitted to do so, reduce the operation to merging
                 * prev and vma.
                 */
                if (can_merge_right && !can_merge_remove_vma(next))
                        vmg->end = end;

                /* In expand-only case we are already positioned at prev. */
                if (!just_expand) {
                        /* Equivalent to going to the previous range. */
                        vma_prev(vmg->vmi);
                }
        }

        /*
         * Now try to expand adjacent VMA(s). This takes care of removing the
         * following VMA if we have VMAs on both sides.
         */
        if (vmg->vma && !vma_expand(vmg)) {
                khugepaged_enter_vma(vmg->vma, vmg->flags);
                vmg->state = VMA_MERGE_SUCCESS;
                return vmg->vma;
        }

        return NULL;
}

/*
 * vma_expand - Expand an existing VMA
 *
 * @vmg: Describes a VMA expansion operation.
 *
 * Expand @vma to vmg->start and vmg->end.  Can expand off the start and end.
 * Will expand over vmg->next if it's different from vmg->vma and vmg->end ==
 * vmg->next->vm_end.  Checking if the vmg->vma can expand and merge with
 * vmg->next needs to be handled by the caller.
 *
 * Returns: 0 on success.
 *
 * ASSUMPTIONS:
 * - The caller must hold a WRITE lock on vmg->vma->mm->mmap_lock.
 * - The caller must have set @vmg->vma and @vmg->next.
 */
int vma_expand(struct vma_merge_struct *vmg)
{
        struct vm_area_struct *anon_dup = NULL;
        bool remove_next = false;
        struct vm_area_struct *vma = vmg->vma;
        struct vm_area_struct *next = vmg->next;

        mmap_assert_write_locked(vmg->mm);

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

                remove_next = true;
                /* This should already have been checked by this point. */
                VM_WARN_ON_VMG(!can_merge_remove_vma(next), vmg);
                vma_start_write(next);
                ret = dup_anon_vma(vma, next, &anon_dup);
                if (ret)
                        return ret;
        }

        /* Not merging but overwriting any part of next is not handled. */
        VM_WARN_ON_VMG(next && !remove_next &&
                       next != vma && vmg->end > next->vm_start, vmg);
        /* Only handles expanding */
        VM_WARN_ON_VMG(vma->vm_start < vmg->start || vma->vm_end > vmg->end, vmg);

        if (commit_merge(vmg, NULL, remove_next ? next : NULL, NULL, 0, true))
                goto nomem;

        return 0;

nomem:
        vmg->state = VMA_MERGE_ERROR_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);
        validate_mm(vma->vm_mm);
        return 0;
}

static inline void vms_clear_ptes(struct vma_munmap_struct *vms,
                    struct ma_state *mas_detach, bool mm_wr_locked)
{
        struct mmu_gather tlb;

        if (!vms->clear_ptes) /* Nothing to do */
                return;

        /*
         * We can free page tables without write-locking mmap_lock because VMAs
         * were isolated before we downgraded mmap_lock.
         */
        mas_set(mas_detach, 1);
        tlb_gather_mmu(&tlb, vms->vma->vm_mm);
        update_hiwater_rss(vms->vma->vm_mm);
        unmap_vmas(&tlb, mas_detach, vms->vma, vms->start, vms->end,
                   vms->vma_count, mm_wr_locked);

        mas_set(mas_detach, 1);
        /* start and end may be different if there is no prev or next vma. */
        free_pgtables(&tlb, mas_detach, vms->vma, vms->unmap_start,
                      vms->unmap_end, mm_wr_locked);
        tlb_finish_mmu(&tlb);
        vms->clear_ptes = false;
}

static void vms_clean_up_area(struct vma_munmap_struct *vms,
                struct ma_state *mas_detach)
{
        struct vm_area_struct *vma;

        if (!vms->nr_pages)
                return;

        vms_clear_ptes(vms, mas_detach, true);
        mas_set(mas_detach, 0);
        mas_for_each(mas_detach, vma, ULONG_MAX)
                vma_close(vma);
}

/*
 * vms_complete_munmap_vmas() - Finish the munmap() operation
 * @vms: The vma munmap struct
 * @mas_detach: The maple state of the detached vmas
 *
 * This updates the mm_struct, unmaps the region, frees the resources
 * used for the munmap() and may downgrade the lock - if requested.  Everything
 * needed to be done once the vma maple tree is updated.
 */
static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
                struct ma_state *mas_detach)
{
        struct vm_area_struct *vma;
        struct mm_struct *mm;

        mm = current->mm;
        mm->map_count -= vms->vma_count;
        mm->locked_vm -= vms->locked_vm;
        if (vms->unlock)
                mmap_write_downgrade(mm);

        if (!vms->nr_pages)
                return;

        vms_clear_ptes(vms, mas_detach, !vms->unlock);
        /* Update high watermark before we lower total_vm */
        update_hiwater_vm(mm);
        /* Stat accounting */
        WRITE_ONCE(mm->total_vm, READ_ONCE(mm->total_vm) - vms->nr_pages);
        /* Paranoid bookkeeping */
        VM_WARN_ON(vms->exec_vm > mm->exec_vm);
        VM_WARN_ON(vms->stack_vm > mm->stack_vm);
        VM_WARN_ON(vms->data_vm > mm->data_vm);
        mm->exec_vm -= vms->exec_vm;
        mm->stack_vm -= vms->stack_vm;
        mm->data_vm -= vms->data_vm;

        /* Remove and clean up vmas */
        mas_set(mas_detach, 0);
        mas_for_each(mas_detach, vma, ULONG_MAX)
                remove_vma(vma, /* unreachable = */ false);

        vm_unacct_memory(vms->nr_accounted);
        validate_mm(mm);
        if (vms->unlock)
                mmap_read_unlock(mm);

        __mt_destroy(mas_detach->tree);
}

/*
 * reattach_vmas() - Undo any munmap work and free resources
 * @mas_detach: The maple state with the detached maple tree
 *
 * Reattach any detached vmas and free up the maple tree used to track the vmas.
 */
static void reattach_vmas(struct ma_state *mas_detach)
{
        struct vm_area_struct *vma;

        mas_set(mas_detach, 0);
        mas_for_each(mas_detach, vma, ULONG_MAX)
                vma_mark_detached(vma, false);

        __mt_destroy(mas_detach->tree);
}

/*
 * vms_gather_munmap_vmas() - Put all VMAs within a range into a maple tree
 * for removal at a later date.  Handles splitting first and last if necessary
 * and marking the vmas as isolated.
 *
 * @vms: The vma munmap struct
 * @mas_detach: The maple state tracking the detached tree
 *
 * Return: 0 on success, error otherwise
 */
static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
                struct ma_state *mas_detach)
{
        struct vm_area_struct *next = NULL;
        int error;

        /*
         * If we need to split any vma, do it now to save pain later.
         * Does it split the first one?
         */
        if (vms->start > vms->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 (vms->end < vms->vma->vm_end &&
                    vms->vma->vm_mm->map_count >= sysctl_max_map_count) {
                        error = -ENOMEM;
                        goto map_count_exceeded;
                }

                /* Don't bother splitting the VMA if we can't unmap it anyway */
                if (!can_modify_vma(vms->vma)) {
                        error = -EPERM;
                        goto start_split_failed;
                }

                error = __split_vma(vms->vmi, vms->vma, vms->start, 1);
                if (error)
                        goto start_split_failed;
        }
        vms->prev = vma_prev(vms->vmi);
        if (vms->prev)
                vms->unmap_start = vms->prev->vm_end;

        /*
         * Detach a range of VMAs from the mm. Using next as a temp variable as
         * it is always overwritten.
         */
        for_each_vma_range(*(vms->vmi), next, vms->end) {
                long nrpages;

                if (!can_modify_vma(next)) {
                        error = -EPERM;
                        goto modify_vma_failed;
                }
                /* Does it split the end? */
                if (next->vm_end > vms->end) {
                        error = __split_vma(vms->vmi, next, vms->end, 0);
                        if (error)
                                goto end_split_failed;
                }
                vma_start_write(next);
                mas_set(mas_detach, vms->vma_count++);
                error = mas_store_gfp(mas_detach, next, GFP_KERNEL);
                if (error)
                        goto munmap_gather_failed;

                vma_mark_detached(next, true);
                nrpages = vma_pages(next);

                vms->nr_pages += nrpages;
                if (next->vm_flags & VM_LOCKED)
                        vms->locked_vm += nrpages;

                if (next->vm_flags & VM_ACCOUNT)
                        vms->nr_accounted += nrpages;

                if (is_exec_mapping(next->vm_flags))
                        vms->exec_vm += nrpages;
                else if (is_stack_mapping(next->vm_flags))
                        vms->stack_vm += nrpages;
                else if (is_data_mapping(next->vm_flags))
                        vms->data_vm += nrpages;

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

        vms->next = vma_next(vms->vmi);
        if (vms->next)
                vms->unmap_end = vms->next->vm_start;

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

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

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

        vms->clear_ptes = true;
        return 0;

userfaultfd_error:
munmap_gather_failed:
end_split_failed:
modify_vma_failed:
        reattach_vmas(mas_detach);
start_split_failed:
map_count_exceeded:
        return error;
}

/*
 * init_vma_munmap() - Initializer wrapper for vma_munmap_struct
 * @vms: The vma munmap struct
 * @vmi: The vma iterator
 * @vma: The first vm_area_struct to munmap
 * @start: The aligned start address to munmap
 * @end: The aligned end address to munmap
 * @uf: The userfaultfd list_head
 * @unlock: Unlock after the operation.  Only unlocked on success
 */
static void init_vma_munmap(struct vma_munmap_struct *vms,
                struct vma_iterator *vmi, struct vm_area_struct *vma,
                unsigned long start, unsigned long end, struct list_head *uf,
                bool unlock)
{
        vms->vmi = vmi;
        vms->vma = vma;
        if (vma) {
                vms->start = start;
                vms->end = end;
        } else {
                vms->start = vms->end = 0;
        }
        vms->unlock = unlock;
        vms->uf = uf;
        vms->vma_count = 0;
        vms->nr_pages = vms->locked_vm = vms->nr_accounted = 0;
        vms->exec_vm = vms->stack_vm = vms->data_vm = 0;
        vms->unmap_start = FIRST_USER_ADDRESS;
        vms->unmap_end = USER_PGTABLES_CEILING;
        vms->clear_ptes = false;
}

/*
 * 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 maple_tree mt_detach;
        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);
        struct vma_munmap_struct vms;
        int error;

        init_vma_munmap(&vms, vmi, vma, start, end, uf, unlock);
        error = vms_gather_munmap_vmas(&vms, &mas_detach);
        if (error)
                goto gather_failed;

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

        /* Point of no return */
        vms_complete_munmap_vmas(&vms, &mas_detach);
        return 0;

clear_tree_failed:
        reattach_vmas(&mas_detach);
gather_failed:
        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.
 *
 * 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;

        /* 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);
}

/*
 * 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.
 */
static struct vm_area_struct *vma_modify(struct vma_merge_struct *vmg)
{
        struct vm_area_struct *vma = vmg->vma;
        struct vm_area_struct *merged;

        /* First, try to merge. */
        merged = vma_merge_existing_range(vmg);
        if (merged)
                return merged;

        /* Split any preceding portion of the VMA. */
        if (vma->vm_start < vmg->start) {
                int err = split_vma(vmg->vmi, vma, vmg->start, 1);

                if (err)
                        return ERR_PTR(err);
        }

        /* Split any trailing portion of the VMA. */
        if (vma->vm_end > vmg->end) {
                int err = split_vma(vmg->vmi, vma, vmg->end, 0);

                if (err)
                        return ERR_PTR(err);
        }

        return vma;
}

struct vm_area_struct *vma_modify_flags(
        struct vma_iterator *vmi, struct vm_area_struct *prev,
        struct vm_area_struct *vma, unsigned long start, unsigned long end,
        unsigned long new_flags)
{
        VMG_VMA_STATE(vmg, vmi, prev, vma, start, end);

        vmg.flags = new_flags;

        return vma_modify(&vmg);
}

struct vm_area_struct
*vma_modify_flags_name(struct vma_iterator *vmi,
                       struct vm_area_struct *prev,
                       struct vm_area_struct *vma,
                       unsigned long start,
                       unsigned long end,
                       unsigned long new_flags,
                       struct anon_vma_name *new_name)
{
        VMG_VMA_STATE(vmg, vmi, prev, vma, start, end);

        vmg.flags = new_flags;
        vmg.anon_name = new_name;

        return vma_modify(&vmg);
}

struct vm_area_struct
*vma_modify_policy(struct vma_iterator *vmi,
                   struct vm_area_struct *prev,
                   struct vm_area_struct *vma,
                   unsigned long start, unsigned long end,
                   struct mempolicy *new_pol)
{
        VMG_VMA_STATE(vmg, vmi, prev, vma, start, end);

        vmg.policy = new_pol;

        return vma_modify(&vmg);
}

struct vm_area_struct
*vma_modify_flags_uffd(struct vma_iterator *vmi,
                       struct vm_area_struct *prev,
                       struct vm_area_struct *vma,
                       unsigned long start, unsigned long end,
                       unsigned long new_flags,
                       struct vm_userfaultfd_ctx new_ctx)
{
        VMG_VMA_STATE(vmg, vmi, prev, vma, start, end);

        vmg.flags = new_flags;
        vmg.uffd_ctx = new_ctx;

        return vma_modify(&vmg);
}

/*
 * 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)
{
        VMG_VMA_STATE(vmg, vmi, vma, vma, vma->vm_end, vma->vm_end + delta);

        vmg.next = vma_iter_next_rewind(vmi, NULL);
        vmg.vma = NULL; /* We use the VMA to populate VMG fields only. */

        return vma_merge_new_range(&vmg);
}

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;
        bool faulted_in_anon_vma = true;
        VMA_ITERATOR(vmi, mm, addr);
        VMG_VMA_STATE(vmg, &vmi, NULL, vma, addr, addr + len);

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

        vmg.vma = NULL; /* New VMA range. */
        vmg.pgoff = pgoff;
        vmg.next = vma_iter_next_rewind(&vmi, NULL);
        new_vma = vma_merge_new_range(&vmg);

        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:
        vma_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);
}

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);
}

/*
 * We account for memory if it's a private writeable mapping,
 * not hugepages and VM_NORESERVE wasn't set.
 */
static bool 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 false;

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

/*
 * vms_abort_munmap_vmas() - Undo as much as possible from an aborted munmap()
 * operation.
 * @vms: The vma unmap structure
 * @mas_detach: The maple state with the detached maple tree
 *
 * Reattach any detached vmas, free up the maple tree used to track the vmas.
 * If that's not possible because the ptes are cleared (and vm_ops->closed() may
 * have been called), then a NULL is written over the vmas and the vmas are
 * removed (munmap() completed).
 */
static void vms_abort_munmap_vmas(struct vma_munmap_struct *vms,
                struct ma_state *mas_detach)
{
        struct ma_state *mas = &vms->vmi->mas;

        if (!vms->nr_pages)
                return;

        if (vms->clear_ptes)
                return reattach_vmas(mas_detach);

        /*
         * Aborting cannot just call the vm_ops open() because they are often
         * not symmetrical and state data has been lost.  Resort to the old
         * failure method of leaving a gap where the MAP_FIXED mapping failed.
         */
        mas_set_range(mas, vms->start, vms->end - 1);
        mas_store_gfp(mas, NULL, GFP_KERNEL|__GFP_NOFAIL);
        /* Clean up the insertion of the unfortunate gap */
        vms_complete_munmap_vmas(vms, mas_detach);
}

/*
 * __mmap_prepare() - Prepare to gather any overlapping VMAs that need to be
 * unmapped once the map operation is completed, check limits, account mapping
 * and clean up any pre-existing VMAs.
 *
 * @map: Mapping state.
 * @uf:  Userfaultfd context list.
 *
 * Returns: 0 on success, error code otherwise.
 */
static int __mmap_prepare(struct mmap_state *map, struct list_head *uf)
{
        int error;
        struct vma_iterator *vmi = map->vmi;
        struct vma_munmap_struct *vms = &map->vms;

        /* Find the first overlapping VMA and initialise unmap state. */
        vms->vma = vma_find(vmi, map->end);
        init_vma_munmap(vms, vmi, vms->vma, map->addr, map->end, uf,
                        /* unlock = */ false);

        /* OK, we have overlapping VMAs - prepare to unmap them. */
        if (vms->vma) {
                mt_init_flags(&map->mt_detach,
                              vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
                mt_on_stack(map->mt_detach);
                mas_init(&map->mas_detach, &map->mt_detach, /* addr = */ 0);
                /* Prepare to unmap any existing mapping in the area */
                error = vms_gather_munmap_vmas(vms, &map->mas_detach);
                if (error) {
                        /* On error VMAs will already have been reattached. */
                        vms->nr_pages = 0;
                        return error;
                }

                map->next = vms->next;
                map->prev = vms->prev;
        } else {
                map->next = vma_iter_next_rewind(vmi, &map->prev);
        }

        /* Check against address space limit. */
        if (!may_expand_vm(map->mm, map->flags, map->pglen - vms->nr_pages))
                return -ENOMEM;

        /* Private writable mapping: check memory availability. */
        if (accountable_mapping(map->file, map->flags)) {
                map->charged = map->pglen;
                map->charged -= vms->nr_accounted;
                if (map->charged) {
                        error = security_vm_enough_memory_mm(map->mm, map->charged);
                        if (error)
                                return error;
                }

                vms->nr_accounted = 0;
                map->flags |= VM_ACCOUNT;
        }

        /*
         * Clear PTEs while the vma is still in the tree so that rmap
         * cannot race with the freeing later in the truncate scenario.
         * This is also needed for mmap_file(), which is why vm_ops
         * close function is called.
         */
        vms_clean_up_area(vms, &map->mas_detach);

        return 0;
}


static int __mmap_new_file_vma(struct mmap_state *map,
                               struct vm_area_struct *vma)
{
        struct vma_iterator *vmi = map->vmi;
        int error;

        vma->vm_file = get_file(map->file);
        error = mmap_file(vma->vm_file, vma);
        if (error) {
                fput(vma->vm_file);
                vma->vm_file = NULL;

                vma_iter_set(vmi, vma->vm_end);
                /* Undo any partial mapping done by a device driver. */
                unmap_region(&vmi->mas, vma, map->prev, map->next);

                return error;
        }

        /* Drivers cannot alter the address of the VMA. */
        WARN_ON_ONCE(map->addr != vma->vm_start);
        /*
         * Drivers should not permit writability when previously it was
         * disallowed.
         */
        VM_WARN_ON_ONCE(map->flags != vma->vm_flags &&
                        !(map->flags & VM_MAYWRITE) &&
                        (vma->vm_flags & VM_MAYWRITE));

        /* If the flags change (and are mergeable), let's retry later. */
        map->retry_merge = vma->vm_flags != map->flags && !(vma->vm_flags & VM_SPECIAL);
        map->flags = vma->vm_flags;

        return 0;
}

/*
 * __mmap_new_vma() - Allocate a new VMA for the region, as merging was not
 * possible.
 *
 * @map:  Mapping state.
 * @vmap: Output pointer for the new VMA.
 *
 * Returns: Zero on success, or an error.
 */
static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap)
{
        struct vma_iterator *vmi = map->vmi;
        int error = 0;
        struct vm_area_struct *vma;

        /*
         * 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 = vm_area_alloc(map->mm);
        if (!vma)
                return -ENOMEM;

        vma_iter_config(vmi, map->addr, map->end);
        vma_set_range(vma, map->addr, map->end, map->pgoff);
        vm_flags_init(vma, map->flags);
        vma->vm_page_prot = vm_get_page_prot(map->flags);

        if (vma_iter_prealloc(vmi, vma)) {
                error = -ENOMEM;
                goto free_vma;
        }

        if (map->file)
                error = __mmap_new_file_vma(map, vma);
        else if (map->flags & VM_SHARED)
                error = shmem_zero_setup(vma);
        else
                vma_set_anonymous(vma);

        if (error)
                goto free_iter_vma;

#ifdef CONFIG_SPARC64
        /* TODO: Fix SPARC ADI! */
        WARN_ON_ONCE(!arch_validate_flags(map->flags));
#endif

        /* Lock the VMA since it is modified after insertion into VMA tree */
        vma_start_write(vma);
        vma_iter_store(vmi, vma);
        map->mm->map_count++;
        vma_link_file(vma);

        /*
         * vma_merge_new_range() calls khugepaged_enter_vma() too, the below
         * call covers the non-merge case.
         */
        khugepaged_enter_vma(vma, map->flags);
        ksm_add_vma(vma);
        *vmap = vma;
        return 0;

free_iter_vma:
        vma_iter_free(vmi);
free_vma:
        vm_area_free(vma);
        return error;
}

/*
 * __mmap_complete() - Unmap any VMAs we overlap, account memory mapping
 *                     statistics, handle locking and finalise the VMA.
 *
 * @map: Mapping state.
 * @vma: Merged or newly allocated VMA for the mmap()'d region.
 */
static void __mmap_complete(struct mmap_state *map, struct vm_area_struct *vma)
{
        struct mm_struct *mm = map->mm;
        unsigned long vm_flags = vma->vm_flags;

        perf_event_mmap(vma);

        /* Unmap any existing mapping in the area. */
        vms_complete_munmap_vmas(&map->vms, &map->mas_detach);

        vm_stat_account(mm, vma->vm_flags, map->pglen);
        if (vm_flags & VM_LOCKED) {
                if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
                                        is_vm_hugetlb_page(vma) ||
                                        vma == get_gate_vma(mm))
                        vm_flags_clear(vma, VM_LOCKED_MASK);
                else
                        mm->locked_vm += map->pglen;
        }

        if (vma->vm_file)
                uprobe_mmap(vma);

        /*
         * New (or expanded) vma always get soft dirty status.
         * Otherwise user-space soft-dirty page tracker won't
         * be able to distinguish situation when vma area unmapped,
         * then new mapped in-place (which must be aimed as
         * a completely new data area).
         */
        vm_flags_set(vma, VM_SOFTDIRTY);

        vma_set_page_prot(vma);
}

static unsigned long __mmap_region(struct file *file, unsigned long addr,
                unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
                struct list_head *uf)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma = NULL;
        int error;
        VMA_ITERATOR(vmi, mm, addr);
        MMAP_STATE(map, mm, &vmi, addr, len, pgoff, vm_flags, file);

        error = __mmap_prepare(&map, uf);
        if (error)
                goto abort_munmap;

        /* Attempt to merge with adjacent VMAs... */
        if (map.prev || map.next) {
                VMG_MMAP_STATE(vmg, &map, /* vma = */ NULL);

                vma = vma_merge_new_range(&vmg);
        }

        /* ...but if we can't, allocate a new VMA. */
        if (!vma) {
                error = __mmap_new_vma(&map, &vma);
                if (error)
                        goto unacct_error;
        }

        /* If flags changed, we might be able to merge, so try again. */
        if (map.retry_merge) {
                struct vm_area_struct *merged;
                VMG_MMAP_STATE(vmg, &map, vma);

                vma_iter_config(map.vmi, map.addr, map.end);
                merged = vma_merge_existing_range(&vmg);
                if (merged)
                        vma = merged;
        }

        __mmap_complete(&map, vma);

        return addr;

        /* Accounting was done by __mmap_prepare(). */
unacct_error:
        if (map.charged)
                vm_unacct_memory(map.charged);
abort_munmap:
        vms_abort_munmap_vmas(&map.vms, &map.mas_detach);
        return error;
}

/**
 * mmap_region() - Actually perform the userland mapping of a VMA into
 * current->mm with known, aligned and overflow-checked @addr and @len, and
 * correctly determined VMA flags @vm_flags and page offset @pgoff.
 *
 * This is an internal memory management function, and should not be used
 * directly.
 *
 * The caller must write-lock current->mm->mmap_lock.
 *
 * @file: If a file-backed mapping, a pointer to the struct file describing the
 * file to be mapped, otherwise NULL.
 * @addr: The page-aligned address at which to perform the mapping.
 * @len: The page-aligned, non-zero, length of the mapping.
 * @vm_flags: The VMA flags which should be applied to the mapping.
 * @pgoff: If @file is specified, the page offset into the file, if not then
 * the virtual page offset in memory of the anonymous mapping.
 * @uf: Optionally, a pointer to a list head used for tracking userfaultfd unmap
 * events.
 *
 * Returns: Either an error, or the address at which the requested mapping has
 * been performed.
 */
unsigned long mmap_region(struct file *file, unsigned long addr,
                          unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
                          struct list_head *uf)
{
        unsigned long ret;
        bool writable_file_mapping = false;

        mmap_assert_write_locked(current->mm);

        /* Check to see if MDWE is applicable. */
        if (map_deny_write_exec(vm_flags, vm_flags))
                return -EACCES;

        /* Allow architectures to sanity-check the vm_flags. */
        if (!arch_validate_flags(vm_flags))
                return -EINVAL;

        /* Map writable and ensure this isn't a sealed memfd. */
        if (file && is_shared_maywrite(vm_flags)) {
                int error = mapping_map_writable(file->f_mapping);

                if (error)
                        return error;
                writable_file_mapping = true;
        }

        ret = __mmap_region(file, addr, len, vm_flags, pgoff, uf);

        /* Clear our write mapping regardless of error. */
        if (writable_file_mapping)
                mapping_unmap_writable(file->f_mapping);

        validate_mm(current->mm);
        return ret;
}

/*
 * do_brk_flags() - Increase the brk vma if the flags match.
 * @vmi: The vma iterator
 * @addr: The start address
 * @len: The length of the increase
 * @vma: The vma,
 * @flags: The VMA Flags
 *
 * Extend the brk VMA from addr to addr + len.  If the VMA is NULL or the flags
 * do not match then create a new anonymous VMA.  Eventually we may be able to
 * do some brk-specific accounting here.
 */
int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
                 unsigned long addr, unsigned long len, unsigned long flags)
{
        struct mm_struct *mm = current->mm;

        /*
         * Check against address space limits by the changed size
         * Note: This happens *after* clearing old mappings in some code paths.
         */
        flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
        if (!may_expand_vm(mm, flags, 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;

        /*
         * Expand the existing vma if possible; Note that singular lists do not
         * occur after forking, so the expand will only happen on new VMAs.
         */
        if (vma && vma->vm_end == addr) {
                VMG_STATE(vmg, mm, vmi, addr, addr + len, flags, PHYS_PFN(addr));

                vmg.prev = vma;
                /* vmi is positioned at prev, which this mode expects. */
                vmg.merge_flags = VMG_FLAG_JUST_EXPAND;

                if (vma_merge_new_range(&vmg))
                        goto out;
                else if (vmg_nomem(&vmg))
                        goto unacct_fail;
        }

        if (vma)
                vma_iter_next_range(vmi);
        /* create a vma struct for an anonymous mapping */
        vma = vm_area_alloc(mm);
        if (!vma)
                goto unacct_fail;

        vma_set_anonymous(vma);
        vma_set_range(vma, addr, addr + len, addr >> PAGE_SHIFT);
        vm_flags_init(vma, flags);
        vma->vm_page_prot = vm_get_page_prot(flags);
        vma_start_write(vma);
        if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL))
                goto mas_store_fail;

        mm->map_count++;
        validate_mm(mm);
        ksm_add_vma(vma);
out:
        perf_event_mmap(vma);
        mm->total_vm += len >> PAGE_SHIFT;
        mm->data_vm += len >> PAGE_SHIFT;
        if (flags & VM_LOCKED)
                mm->locked_vm += (len >> PAGE_SHIFT);
        vm_flags_set(vma, VM_SOFTDIRTY);
        return 0;

mas_store_fail:
        vm_area_free(vma);
unacct_fail:
        vm_unacct_memory(len >> PAGE_SHIFT);
        return -ENOMEM;
}

/**
 * unmapped_area() - Find an area between the low_limit and the high_limit with
 * the correct alignment and offset, all from @info. Note: current->mm is used
 * for the search.
 *
 * @info: The unmapped area information including the range [low_limit -
 * high_limit), the alignment offset and mask.
 *
 * Return: A memory address or -ENOMEM.
 */
unsigned long unmapped_area(struct vm_unmapped_area_info *info)
{
        unsigned long length, gap;
        unsigned long low_limit, high_limit;
        struct vm_area_struct *tmp;
        VMA_ITERATOR(vmi, current->mm, 0);

        /* Adjust search length to account for worst case alignment overhead */
        length = info->length + info->align_mask + info->start_gap;
        if (length < info->length)
                return -ENOMEM;

        low_limit = info->low_limit;
        if (low_limit < mmap_min_addr)
                low_limit = mmap_min_addr;
        high_limit = info->high_limit;
retry:
        if (vma_iter_area_lowest(&vmi, low_limit, high_limit, length))
                return -ENOMEM;

        /*
         * Adjust for the gap first so it doesn't interfere with the
         * later alignment. The first step is the minimum needed to
         * fulill the start gap, the next steps is the minimum to align
         * that. It is the minimum needed to fulill both.
         */
        gap = vma_iter_addr(&vmi) + info->start_gap;
        gap += (info->align_offset - gap) & info->align_mask;
        tmp = vma_next(&vmi);
        if (tmp && (tmp->vm_flags & VM_STARTGAP_FLAGS)) { /* Avoid prev check if possible */
                if (vm_start_gap(tmp) < gap + length - 1) {
                        low_limit = tmp->vm_end;
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        } else {
                tmp = vma_prev(&vmi);
                if (tmp && vm_end_gap(tmp) > gap) {
                        low_limit = vm_end_gap(tmp);
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        }

        return gap;
}

/**
 * unmapped_area_topdown() - Find an area between the low_limit and the
 * high_limit with the correct alignment and offset at the highest available
 * address, all from @info. Note: current->mm is used for the search.
 *
 * @info: The unmapped area information including the range [low_limit -
 * high_limit), the alignment offset and mask.
 *
 * Return: A memory address or -ENOMEM.
 */
unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
{
        unsigned long length, gap, gap_end;
        unsigned long low_limit, high_limit;
        struct vm_area_struct *tmp;
        VMA_ITERATOR(vmi, current->mm, 0);

        /* Adjust search length to account for worst case alignment overhead */
        length = info->length + info->align_mask + info->start_gap;
        if (length < info->length)
                return -ENOMEM;

        low_limit = info->low_limit;
        if (low_limit < mmap_min_addr)
                low_limit = mmap_min_addr;
        high_limit = info->high_limit;
retry:
        if (vma_iter_area_highest(&vmi, low_limit, high_limit, length))
                return -ENOMEM;

        gap = vma_iter_end(&vmi) - info->length;
        gap -= (gap - info->align_offset) & info->align_mask;
        gap_end = vma_iter_end(&vmi);
        tmp = vma_next(&vmi);
        if (tmp && (tmp->vm_flags & VM_STARTGAP_FLAGS)) { /* Avoid prev check if possible */
                if (vm_start_gap(tmp) < gap_end) {
                        high_limit = vm_start_gap(tmp);
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        } else {
                tmp = vma_prev(&vmi);
                if (tmp && vm_end_gap(tmp) > gap) {
                        high_limit = tmp->vm_start;
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        }

        return gap;
}

/*
 * 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;
        unsigned long new_start;

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

        /* Stack limit test */
        if (size > rlimit(RLIMIT_STACK))
                return -ENOMEM;

        /* mlock limit tests */
        if (!mlock_future_ok(mm, vma->vm_flags, grow << PAGE_SHIFT))
                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;

        return 0;
}

#if defined(CONFIG_STACK_GROWSUP)
/*
 * PA-RISC uses this for its stack.
 * 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)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *next;
        unsigned long gap_addr;
        int error = 0;
        VMA_ITERATOR(vmi, mm, vma->vm_start);

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

        mmap_assert_write_locked(mm);

        /* Guard against exceeding limits of the address space. */
        address &= PAGE_MASK;
        if (address >= (TASK_SIZE & PAGE_MASK))
                return -ENOMEM;
        address += PAGE_SIZE;

        /* Enforce stack_guard_gap */
        gap_addr = address + stack_guard_gap;

        /* Guard against overflow */
        if (gap_addr < address || gap_addr > TASK_SIZE)
                gap_addr = TASK_SIZE;

        next = find_vma_intersection(mm, vma->vm_end, gap_addr);
        if (next && vma_is_accessible(next)) {
                if (!(next->vm_flags & VM_GROWSUP))
                        return -ENOMEM;
                /* Check that both stack segments have the same anon_vma? */
        }

        if (next)
                vma_iter_prev_range_limit(&vmi, address);

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

        /* We must make sure the anon_vma is allocated. */
        if (unlikely(anon_vma_prepare(vma))) {
                vma_iter_free(&vmi);
                return -ENOMEM;
        }

        /* Lock the VMA before expanding to prevent concurrent page faults */
        vma_start_write(vma);
        /* We update the anon VMA tree. */
        anon_vma_lock_write(vma->anon_vma);

        /* 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) {
                                if (vma->vm_flags & VM_LOCKED)
                                        mm->locked_vm += grow;
                                vm_stat_account(mm, vma->vm_flags, grow);
                                anon_vma_interval_tree_pre_update_vma(vma);
                                vma->vm_end = address;
                                /* Overwrite old entry in mtree. */
                                vma_iter_store(&vmi, vma);
                                anon_vma_interval_tree_post_update_vma(vma);

                                perf_event_mmap(vma);
                        }
                }
        }
        anon_vma_unlock_write(vma->anon_vma);
        vma_iter_free(&vmi);
        validate_mm(mm);
        return error;
}
#endif /* CONFIG_STACK_GROWSUP */

/*
 * vma is the first one with address < vma->vm_start.  Have to extend vma.
 * mmap_lock held for writing.
 */
int expand_downwards(struct vm_area_struct *vma, unsigned long address)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *prev;
        int error = 0;
        VMA_ITERATOR(vmi, mm, vma->vm_start);

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

        mmap_assert_write_locked(mm);

        address &= PAGE_MASK;
        if (address < mmap_min_addr || address < FIRST_USER_ADDRESS)
                return -EPERM;

        /* Enforce stack_guard_gap */
        prev = vma_prev(&vmi);
        /* Check that both stack segments have the same anon_vma? */
        if (prev) {
                if (!(prev->vm_flags & VM_GROWSDOWN) &&
                    vma_is_accessible(prev) &&
                    (address - prev->vm_end < stack_guard_gap))
                        return -ENOMEM;
        }

        if (prev)
                vma_iter_next_range_limit(&vmi, vma->vm_start);

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

        /* We must make sure the anon_vma is allocated. */
        if (unlikely(anon_vma_prepare(vma))) {
                vma_iter_free(&vmi);
                return -ENOMEM;
        }

        /* Lock the VMA before expanding to prevent concurrent page faults */
        vma_start_write(vma);
        /* We update the anon VMA tree. */
        anon_vma_lock_write(vma->anon_vma);

        /* 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) {
                                if (vma->vm_flags & VM_LOCKED)
                                        mm->locked_vm += grow;
                                vm_stat_account(mm, vma->vm_flags, grow);
                                anon_vma_interval_tree_pre_update_vma(vma);
                                vma->vm_start = address;
                                vma->vm_pgoff -= grow;
                                /* Overwrite old entry in mtree. */
                                vma_iter_store(&vmi, vma);
                                anon_vma_interval_tree_post_update_vma(vma);

                                perf_event_mmap(vma);
                        }
                }
        }
        anon_vma_unlock_write(vma->anon_vma);
        vma_iter_free(&vmi);
        validate_mm(mm);
        return error;
}

int __vm_munmap(unsigned long start, size_t len, bool unlock)
{
        int ret;
        struct mm_struct *mm = current->mm;
        LIST_HEAD(uf);
        VMA_ITERATOR(vmi, mm, start);

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        ret = do_vmi_munmap(&vmi, mm, start, len, &uf, unlock);
        if (ret || !unlock)
                mmap_write_unlock(mm);

        userfaultfd_unmap_complete(mm, &uf);
        return ret;
}