[PATCH v13 24/70] mm/mmap: use advanced maple tree API for mmap_region()

Liam Howlett
2022-08-22T15:07:26Z

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 | 251 +++++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 203 insertions(+), 48 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 57391f99afe9..ed45c6fafd94 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -470,28 +470,6 @@ 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)
{
@@ -618,6 +596,129 @@ static void __insert_vm_struct(struct mm_struct *mm, struct ma_state *mas,
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;
+
+ anon_vma = next->anon_vma;
+ vma->anon_vma = 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(next && !remove_next && next != vma && end > next->vm_start);
+ /* Only handles expanding */
+ VM_BUG_ON(vma->vm_start < start || vma->vm_end > end);
+
+ if (mas_preallocate(mas, vma, GFP_KERNEL))
+ goto nomem;
+
+ 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);
+ }
+
+ if (anon_vma) {
+ anon_vma_lock_write(anon_vma);
+ anon_vma_interval_tree_pre_update_vma(vma);
+ }
+
+ if (file) {
+ flush_dcache_mmap_lock(mapping);
+ vma_interval_tree_remove(vma, root);
+ }
+
+ 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;
+
+nomem:
+ return -ENOMEM;
+}
+
/*
* 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.
@@ -1630,9 +1731,15 @@ 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 *next, *prev, *merge;
+ 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)) {
@@ -1642,16 +1749,17 @@ 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
*/
@@ -1662,14 +1770,43 @@ 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(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
@@ -1682,7 +1819,7 @@ 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;
@@ -1703,28 +1840,32 @@ 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 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,
NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX, NULL);
if (merge) {
- /* ->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.
+ /*
+ * ->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. */
+ addr = vma->vm_start;
vm_flags = vma->vm_flags;
goto unmap_writable;
}
@@ -1748,7 +1889,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
goto free_vma;
}

- if (vma_link(mm, vma, prev)) {
+ if (mas_preallocate(&mas, vma, GFP_KERNEL)) {
error = -ENOMEM;
if (file)
goto unmap_and_free_vma;
@@ -1756,6 +1897,22 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
goto free_vma;
}

+ 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);
+ }
+
/*
* vma_merge() calls khugepaged_enter_vma() either, the below
* call covers the non-merge case.
@@ -1767,7 +1924,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
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);
@@ -1794,6 +1951,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,

vma_set_page_prot(vma);

+ validate_mm(mm);
return addr;

unmap_and_free_vma:
@@ -1809,6 +1967,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
unacct_error:
if (charged)
vm_unacct_memory(charged);
+ validate_mm(mm);
return error;
}

@@ -2632,10 +2791,6 @@ 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.
*
--
2.35.1