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    Subject[PATCH v7 26/70] mm/mmap: Use advanced maple tree API for mmap_region()
    Date
    From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

    Changing mmap_region() to use the maple tree state and the advanced
    maple tree interface allows for a lot less tree walking.

    This change removes the last caller of munmap_vma_range(), so drop this
    unused function.

    Add vma_expand() to expand a VMA if possible by doing the necessary
    hugepage check, uprobe_munmap of files, dcache flush, modifications then
    undoing the detaches, etc.

    Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
    ---
    mm/mmap.c | 234 +++++++++++++++++++++++++++++++++++++++++++-----------
    1 file changed, 187 insertions(+), 47 deletions(-)

    diff --git a/mm/mmap.c b/mm/mmap.c
    index 1e6a72147480..be5ecb515d1e 100644
    --- a/mm/mmap.c
    +++ b/mm/mmap.c
    @@ -511,28 +511,6 @@ static inline struct vm_area_struct *__vma_next(struct mm_struct *mm,
    return vma->vm_next;
    }

    -/*
    - * munmap_vma_range() - munmap VMAs that overlap a range.
    - * @mm: The mm struct
    - * @start: The start of the range.
    - * @len: The length of the range.
    - * @pprev: pointer to the pointer that will be set to previous vm_area_struct
    - *
    - * Find all the vm_area_struct that overlap from @start to
    - * @end and munmap them. Set @pprev to the previous vm_area_struct.
    - *
    - * Returns: -ENOMEM on munmap failure or 0 on success.
    - */
    -static inline int
    -munmap_vma_range(struct mm_struct *mm, unsigned long start, unsigned long len,
    - struct vm_area_struct **pprev, struct list_head *uf)
    -{
    - while (range_has_overlap(mm, start, start + len, pprev))
    - if (do_munmap(mm, start, len, uf))
    - return -ENOMEM;
    - return 0;
    -}
    -
    static unsigned long count_vma_pages_range(struct mm_struct *mm,
    unsigned long addr, unsigned long end)
    {
    @@ -634,6 +612,117 @@ static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma,
    mm->map_count++;
    }

    +/*
    + * vma_expand - Expand an existing VMA
    + *
    + * @mas: The maple state
    + * @vma: The vma to expand
    + * @start: The start of the vma
    + * @end: The exclusive end of the vma
    + * @pgoff: The page offset of vma
    + * @next: The current of next vma.
    + *
    + * Expand @vma to @start and @end. Can expand off the start and end. Will
    + * expand over @next if it's different from @vma and @end == @next->vm_end.
    + * Checking if the @vma can expand and merge with @next needs to be handled by
    + * the caller.
    + *
    + * Returns: 0 on success
    + */
    +inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
    + unsigned long start, unsigned long end, pgoff_t pgoff,
    + struct vm_area_struct *next)
    +{
    + struct mm_struct *mm = vma->vm_mm;
    + struct address_space *mapping = NULL;
    + struct rb_root_cached *root = NULL;
    + struct anon_vma *anon_vma = vma->anon_vma;
    + struct file *file = vma->vm_file;
    + bool remove_next = false;
    +
    + if (next && (vma != next) && (end == next->vm_end)) {
    + remove_next = true;
    + if (next->anon_vma && !vma->anon_vma) {
    + int error;
    +
    + vma->anon_vma = next->anon_vma;
    + error = anon_vma_clone(vma, next);
    + if (error)
    + return error;
    + }
    + }
    +
    + /* Not merging but overwriting any part of next is not handled. */
    + VM_BUG_ON(!remove_next && next != vma && end > next->vm_start);
    + /* Only handles expanding */
    + VM_BUG_ON(vma->vm_start < start || vma->vm_end > end);
    +
    + vma_adjust_trans_huge(vma, start, end, 0);
    +
    + if (file) {
    + mapping = file->f_mapping;
    + root = &mapping->i_mmap;
    + uprobe_munmap(vma, vma->vm_start, vma->vm_end);
    + i_mmap_lock_write(mapping);
    + flush_dcache_mmap_lock(mapping);
    + vma_interval_tree_remove(vma, root);
    + } else if (anon_vma) {
    + anon_vma_lock_write(anon_vma);
    + anon_vma_interval_tree_pre_update_vma(vma);
    + }
    +
    + vma->vm_start = start;
    + vma->vm_end = end;
    + vma->vm_pgoff = pgoff;
    + /* Note: mas must be pointing to the expanding VMA */
    + vma_mas_store(vma, mas);
    +
    + if (file) {
    + vma_interval_tree_insert(vma, root);
    + flush_dcache_mmap_unlock(mapping);
    + }
    +
    + /* Expanding over the next vma */
    + if (remove_next) {
    + /* Remove from mm linked list - also updates highest_vm_end */
    + __vma_unlink_list(mm, next);
    +
    + /* Kill the cache */
    + vmacache_invalidate(mm);
    +
    + if (file)
    + __remove_shared_vm_struct(next, file, mapping);
    +
    + } else if (!next) {
    + mm->highest_vm_end = vm_end_gap(vma);
    + }
    +
    + if (anon_vma) {
    + anon_vma_interval_tree_post_update_vma(vma);
    + anon_vma_unlock_write(anon_vma);
    + }
    +
    + if (file) {
    + i_mmap_unlock_write(mapping);
    + uprobe_mmap(vma);
    + }
    +
    + if (remove_next) {
    + if (file) {
    + uprobe_munmap(next, next->vm_start, next->vm_end);
    + fput(file);
    + }
    + if (next->anon_vma)
    + anon_vma_merge(vma, next);
    + mm->map_count--;
    + mpol_put(vma_policy(next));
    + vm_area_free(next);
    + }
    +
    + validate_mm(mm);
    + return 0;
    +}
    +
    /*
    * We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
    * is already present in an i_mmap tree without adjusting the tree.
    @@ -1623,9 +1712,15 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
    struct list_head *uf)
    {
    struct mm_struct *mm = current->mm;
    - struct vm_area_struct *vma, *prev, *merge;
    - int error;
    + struct vm_area_struct *vma = NULL;
    + struct vm_area_struct *prev, *next;
    + pgoff_t pglen = len >> PAGE_SHIFT;
    unsigned long charged = 0;
    + unsigned long end = addr + len;
    + unsigned long merge_start = addr, merge_end = end;
    + pgoff_t vm_pgoff;
    + int error;
    + MA_STATE(mas, &mm->mm_mt, addr, end - 1);

    /* Check against address space limit. */
    if (!may_expand_vm(mm, vm_flags, len >> PAGE_SHIFT)) {
    @@ -1635,16 +1730,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
    * MAP_FIXED may remove pages of mappings that intersects with
    * requested mapping. Account for the pages it would unmap.
    */
    - nr_pages = count_vma_pages_range(mm, addr, addr + len);
    + nr_pages = count_vma_pages_range(mm, addr, end);

    if (!may_expand_vm(mm, vm_flags,
    (len >> PAGE_SHIFT) - nr_pages))
    return -ENOMEM;
    }

    - /* Clear old maps, set up prev and uf */
    - if (munmap_vma_range(mm, addr, len, &prev, uf))
    + /* Unmap any existing mapping in the area */
    + if (do_munmap(mm, addr, len, uf))
    return -ENOMEM;
    +
    /*
    * Private writable mapping: check memory availability
    */
    @@ -1655,14 +1751,43 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
    vm_flags |= VM_ACCOUNT;
    }

    - /*
    - * Can we just expand an old mapping?
    - */
    - vma = vma_merge(mm, prev, addr, addr + len, vm_flags,
    - NULL, file, pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
    - if (vma)
    - goto out;
    + next = mas_next(&mas, ULONG_MAX);
    + prev = mas_prev(&mas, 0);
    + if (vm_flags & VM_SPECIAL)
    + goto cannot_expand;
    +
    + /* Attempt to expand an old mapping */
    + /* Check next */
    + if (next && next->vm_start == end && !vma_policy(next) &&
    + can_vma_merge_before(next, vm_flags, NULL, file, pgoff+pglen,
    + NULL_VM_UFFD_CTX, NULL)) {
    + merge_end = next->vm_end;
    + vma = next;
    + vm_pgoff = next->vm_pgoff - pglen;
    + }
    +
    + /* Check prev */
    + if (prev && prev->vm_end == addr && !vma_policy(prev) &&
    + (vma ? can_vma_merge_after(prev, vm_flags, vma->anon_vma, file,
    + pgoff, vma->vm_userfaultfd_ctx, NULL) :
    + can_vma_merge_after(prev, vm_flags, NULL, file, pgoff,
    + NULL_VM_UFFD_CTX , NULL))) {
    + merge_start = prev->vm_start;
    + vma = prev;
    + vm_pgoff = prev->vm_pgoff;
    + }

    +
    + /* Actually expand, if possible */
    + if (vma &&
    + !vma_expand(&mas, vma, merge_start, merge_end, vm_pgoff, next)) {
    + khugepaged_enter_vma_merge(vma, vm_flags);
    + goto expanded;
    + }
    +
    + mas.index = addr;
    + mas.last = end - 1;
    +cannot_expand:
    /*
    * Determine the object being mapped and call the appropriate
    * specific mapper. the address has already been validated, but
    @@ -1675,7 +1800,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
    }

    vma->vm_start = addr;
    - vma->vm_end = addr + len;
    + vma->vm_end = end;
    vma->vm_flags = vm_flags;
    vma->vm_page_prot = vm_get_page_prot(vm_flags);
    vma->vm_pgoff = pgoff;
    @@ -1696,28 +1821,30 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
    *
    * Answer: Yes, several device drivers can do it in their
    * f_op->mmap method. -DaveM
    - * Bug: If addr is changed, prev, rb_link, rb_parent should
    - * be updated for vma_link()
    */
    WARN_ON_ONCE(addr != vma->vm_start);

    addr = vma->vm_start;
    + mas_reset(&mas);

    /* If vm_flags changed after call_mmap(), we should try merge vma again
    * as we may succeed this time.
    */
    if (unlikely(vm_flags != vma->vm_flags && prev)) {
    - merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags,
    + next = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags,
    NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
    - if (merge) {
    + if (next) {
    /* ->mmap() can change vma->vm_file and fput the original file. So
    * fput the vma->vm_file here or we would add an extra fput for file
    * and cause general protection fault ultimately.
    */
    fput(vma->vm_file);
    vm_area_free(vma);
    - vma = merge;
    - /* Update vm_flags to pick up the change. */
    + vma = prev;
    + /* Update vm_flags and possible addr to pick up the change. We don't
    + * warn here if addr changed as the vma is not linked by vma_link().
    + */
    + addr = vma->vm_start;
    vm_flags = vma->vm_flags;
    goto unmap_writable;
    }
    @@ -1741,13 +1868,28 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
    goto free_vma;
    }

    - vma_link(mm, vma, prev);
    + if (vma->vm_file)
    + i_mmap_lock_write(vma->vm_file->f_mapping);
    +
    + vma_mas_store(vma, &mas);
    + __vma_link_list(mm, vma, prev);
    + mm->map_count++;
    + if (vma->vm_file) {
    + if (vma->vm_flags & VM_SHARED)
    + mapping_allow_writable(vma->vm_file->f_mapping);
    +
    + flush_dcache_mmap_lock(vma->vm_file->f_mapping);
    + vma_interval_tree_insert(vma, &vma->vm_file->f_mapping->i_mmap);
    + flush_dcache_mmap_unlock(vma->vm_file->f_mapping);
    + i_mmap_unlock_write(vma->vm_file->f_mapping);
    + }
    +
    /* Once vma denies write, undo our temporary denial count */
    unmap_writable:
    if (file && vm_flags & VM_SHARED)
    mapping_unmap_writable(file->f_mapping);
    file = vma->vm_file;
    -out:
    +expanded:
    perf_event_mmap(vma);

    vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
    @@ -1774,6 +1916,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,

    vma_set_page_prot(vma);

    + validate_mm(mm);
    return addr;

    unmap_and_free_vma:
    @@ -1790,6 +1933,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
    unacct_error:
    if (charged)
    vm_unacct_memory(charged);
    + validate_mm(mm);
    return error;
    }

    @@ -2584,10 +2728,6 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
    prev = vma->vm_prev;
    /* we have start < vma->vm_end */

    - /* if it doesn't overlap, we have nothing.. */
    - if (vma->vm_start >= end)
    - return 0;
    -
    /*
    * If we need to split any vma, do it now to save pain later.
    *
    --
    2.34.1
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