[to-be-updated] mm-vma-fix-self-merge-check-in-copy_vma.patch removed from -mm tree
Andrew Morton <[email protected]>
| Newsgroups | org.kernel.vger.mm-commits |
|---|---|
| Message-ID | <[email protected]> |
The quilt patch titled
Subject: mm/vma: fix self-merge check in copy_vma()
has been removed from the -mm tree. Its filename was
mm-vma-fix-self-merge-check-in-copy_vma.patch
This patch was dropped because an updated version will be issued
------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <[email protected]>
Subject: mm/vma: fix self-merge check in copy_vma()
Date: Thu, 06 Aug 2026 21:21:32 +0100
The existing logic is very confusing so improve things. Firstly rename
the confusing faulted_in_anon_vma variable to can_self_merge and update
this when the page offset is updated.
What is being checked for is a 'self-merge' - that is between the VMA
being remapped and its prior VMA (remember that this is copy_vma() - if a
non-MREMAP_DONTUNMAP remap the original VMA is only removed afterwards).
This can happen if the VMA is moved immediately adjacent to itself, either
before or after it:
|----------------|----------------|
| | |
v | v
|...............||---------------||...............|
| new || old || new |
|...............||---------------||---------------|
In these cases the old VMA is simply expanded to cover the new range.
It is also possible for the move to both self-merge and merge with a prior
VMA if it is placed between a preceding VMA and its old self:
|---------------|
| |
v |
|---------------||...............||---------------|
| prev || new || old |
|---------------||...............||---------------|
In this case, the old VMA is removed and 'prev' is expanded and replaces
it.
Since copy_vma_and_data() which calls copy_vma() intends to reference the
old VMA after the merge, it must have this pointer updated.
This kind of self-merge is not possible with a succeeding merge, as the
merge always prefers to expand the preceding VMA if possible.
copy_vma() accounts for this by explicitly checking to see if a self-merge
occurred and updating the vmap pointer if so. However it incorrect did so
even for a subsequent merge (this is simply a noop so it had no impact).
So change this to only check for the case which matters - a backwards
merge - and rearrange the parameters to make it clearer we're doing that -
i.e. check new_vma->vm_start < old_vma_start (having already renamed
vma_start to old_vma_start to make it clear this is the previous VMA).
Also update the existing wall-of-text comment to be a lot clearer.
While we're here, replace the VM_BUG_ON_VMA() with a VM_WARN_ON_ONCE_VMA()
and update the VMA userland tests accordingly.
No functional change intended.
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]>
Acked-by: David Hildenbrand (Arm) <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Deucher <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Boris Brezillon <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Chengming Zhou <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Christan König <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Claudio Imbrenda <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: Gerald Schaefer <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Gregory Price (Meta) <[email protected]>
Cc: Harry Yoo <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Huang Ray <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Clark <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Janosch Frank <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Kemeng Shi <[email protected]>
Cc: Lance Yang <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Liviu Dudau <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Marc Rutland <[email protected]>
Cc: "Masami Hiramatsu (Google)" <[email protected]>
Cc: Matthew Auld <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Namhyung kim <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Nhat Pham <[email protected]>
Cc: Nico Pache <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Pedro Falcato <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Steven Price <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: <[email protected]>
Cc: Thomas Hellström <[email protected]>
Cc: Thomas Zimemrmann <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xu Xin <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
mm/vma.c | 35 +++++++++++++----------------
tools/testing/vma/vma_internal.h | 1
2 files changed, 17 insertions(+), 19 deletions(-)
--- a/mm/vma.c~mm-vma-fix-self-merge-check-in-copy_vma
+++ a/mm/vma.c
@@ -1911,10 +1911,10 @@ struct vm_area_struct *copy_vma(struct v
bool *need_rmap_locks)
{
struct vm_area_struct *vma = *vmap;
- unsigned long vma_start = vma->vm_start;
+ unsigned long old_vma_start = vma->vm_start;
struct mm_struct *mm = vma->vm_mm;
struct vm_area_struct *new_vma;
- bool faulted_in_anon_vma = true;
+ bool can_self_merge = false;
VMA_ITERATOR(vmi, mm, addr);
VMG_VMA_STATE(vmg, &vmi, NULL, vma, addr, addr + len);
@@ -1924,7 +1924,7 @@ struct vm_area_struct *copy_vma(struct v
*/
if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) {
pgoff = addr >> PAGE_SHIFT;
- faulted_in_anon_vma = false;
+ can_self_merge = true;
}
/*
@@ -1944,24 +1944,21 @@ struct vm_area_struct *copy_vma(struct v
new_vma = vma_merge_copied_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)) {
+ /* Self-merged and VMA replaced. */
+ if (unlikely(new_vma->vm_start < old_vma_start &&
+ new_vma->vm_end > old_vma_start)) {
/*
- * 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.
+ * The only way a VMA can both self-merge and be
+ * replaced is if the remap places the new VMA
+ * immediately prior to its old self ('next') and
+ * immediately after another VMA ('prev') causing the
+ * next to be removed and prev to be expanded to cover
+ * the entire range.
+ *
+ * This should only be possible if the page offset was
+ * updated, i.e. the VMA is unfaulted.
*/
- VM_BUG_ON_VMA(faulted_in_anon_vma, new_vma);
+ VM_WARN_ON_ONCE_VMA(!can_self_merge, new_vma);
*vmap = vma = new_vma;
}
*need_rmap_locks =
--- a/tools/testing/vma/vma_internal.h~mm-vma-fix-self-merge-check-in-copy_vma
+++ a/tools/testing/vma/vma_internal.h
@@ -53,6 +53,7 @@ typedef __bitwise unsigned int vm_fault_
#define VM_WARN_ON(_expr) (WARN_ON(_expr))
#define VM_WARN_ON_ONCE(_expr) (WARN_ON_ONCE(_expr))
+#define VM_WARN_ON_ONCE_VMA(_expr, _vma) (WARN_ON_ONCE(_expr))
#define VM_WARN_ON_VMG(_expr, _vmg) (WARN_ON(_expr))
#define VM_BUG_ON(_expr) (BUG_ON(_expr))
#define VM_BUG_ON_VMA(_expr, _vma) (BUG_ON(_expr))
_
Patches currently in -mm which might be from [email protected] are
tools-testing-vma-add-tests-for-copy_vma-self-merge.patch
mm-propagate-vma-anonymous-page-offset-on-map-remap-split-merge.patch
mm-rmap-track-whether-the-page-vma-mapped-pgoff-is-anonymous.patch
mm-clean-up-vma_address_end.patch
mm-huge_memory-update-remove_migration_pmd-to-accept-a-folio.patch
mm-migrate-calculate-large-folio-page-index-using-pfn.patch
mm-rmap-use-anon-pgoff-to-track-map_private-file-backed-anon-folios.patch
tools-testing-vma-expand-vma-merge-tests-to-assert-anon-pgoff.patch
tools-testing-selftests-mm-test-anonymous-page-offset-merge-behaviour.patch
mm-vma-only-permit-map_private-dev-zero-to-be-mapped-anonymous.patch
mm-vma-make-map_private-mapped-dev-zero-mappings-truly-anonymous.patch
tools-testing-vma-add-test-to-assert-map_private-dev-zero-is-anon.patch
tools-testing-selftests-mm-add-map_private-dev-zero-merge-tests.patch
mm-add-some-missing-includes-to-mm-local-headers.patch
maintainers-add-drivers-char-memc-to-mm-misc-memory-mapping-sections.patch