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mm/vma: fix expansion of VMA_MIXEDMAP_BIT VMAs

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Commit ca3d76b0aa ("mm: add merging after mremap resize") combined
merging with expansion of mremap()'d VMAs, however it also unintentionally
disallowed the expansion of unmergeable VMAs.

Previously it was possible to expand a mixed mapping which mremap() had
already ensured was a legal expansion.

This is clearly seen in the mremap() logic, as it checks
vma_is_fixed_mapping() to determine legality of an expansion rather than
vma_can_merge().

Additionally, copy_vma() allows for a failed merge to result in a new VMA
being instantiated if MREMAP_MAYMOVE is specified.

However, this is not attempted, as a failure in vma_merge_extend() is
assumed to be an -ENOMEM failure.

Since vma_merge_extend() is used exclusively by mremap() to perform a merge
and/or expansion, resolve the issue by invoking vma_expand() for
unmergeable VMAs there.

Explicitly assert that the VMA is both non-fixed and a mixed mapping.
This provides double insurance against broken changes in future.

Note that khugepaged_enter_vma() (which vma_merge_new_range() runs) is
redundant in this case, as a mixed mapping is not subject to khugepaged.

Also update the VMA userland tests to add a required predicate.

Link: https://lore.kernel.org/20261023-vma-expansion-fix-v1-1-6142baf1f46b@kernel.org
Fixes: ca3d76b0aa ("mm: add merging after mremap resize")
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Luiz Capitulino <luizcap@redhat.com>
Closes: https://lore.kernel.org/all/20261023023106.515365-1-luizcap@redhat.com/
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jakub Matěna <matenajakub@gmail.com>
Cc: <stable@vger.kernel.org>
This commit is contained in:
Lorenzo Stoakes (ARM) 2026-10-23 16:17:31 +01:00 committed by Andrew Morton
parent b6732c6d43
commit 8146c64782
2 changed files with 21 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
mm/vma.c
View File

@ -1851,12 +1851,25 @@ 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);
const unsigned long start =
vma_can_merge(vma) ? vma->vm_end : vma->vm_start;
VMG_VMA_STATE(vmg, vmi, vma, vma, start, vma->vm_end + delta);
vmg.next = vma_iter_next_rewind(vmi, NULL);
vmg.middle = NULL; /* We use the VMA to populate VMG fields only. */
return vma_merge_new_range(&vmg);
if (vma_can_merge(vma)) {
vmg.next = vma_iter_next_rewind(vmi, NULL);
return vma_merge_new_range(&vmg);
}
/* Mixed mappings are permitted to be expanded, not merged. */
VM_WARN_ON_ONCE(vma_is_fixed_mapping(vma));
VM_WARN_ON_ONCE(!vma_test(vma, VMA_MIXEDMAP_BIT));
vma_prev(vmi); /* Reposition to start of VMA. */
vmg.target = vma;
if (vma_expand(&vmg))
return NULL;
return vma;
}
void unlink_file_vma_batch_init(struct unlink_vma_file_batch *vb)

5
tools/testing/vma/include/dup.h
View File

@ -1727,3 +1727,8 @@ static inline bool vma_flags_can_merge(const vma_flags_t *flags)
*/
return !vma_flags_is_hugetlb(flags);
}
static inline bool vma_can_merge(const struct vm_area_struct *vma)
{
return vma_flags_can_merge(&vma->flags);
}