From 8146c6478224d8f6395c6b08a19c344a56d79867 Mon Sep 17 00:00:00 2001 From: "Lorenzo Stoakes (ARM)" Date: Fri, 23 Oct 2026 16:17:31 +0100 Subject: [PATCH] mm/vma: fix expansion of VMA_MIXEDMAP_BIT VMAs MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Commit ca3d76b0aa80 ("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: ca3d76b0aa80 ("mm: add merging after mremap resize") Signed-off-by: Lorenzo Stoakes (ARM) Signed-off-by: Andrew Morton Reported-by: Luiz Capitulino Closes: https://lore.kernel.org/all/20261023023106.515365-1-luizcap@redhat.com/ Acked-by: Vlastimil Babka (SUSE) Reviewed-by: Pedro Falcato Cc: Liam R. Howlett Cc: Jann Horn Cc: Jakub Matěna Cc: --- mm/vma.c | 19 ++++++++++++++++--- tools/testing/vma/include/dup.h | 5 +++++ 2 files changed, 21 insertions(+), 3 deletions(-) diff --git a/mm/vma.c b/mm/vma.c index 1be613044b4a..88ef92ab24ec 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -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) diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h index f449129ea97a..e0eab4eca998 100644 --- a/tools/testing/vma/include/dup.h +++ b/tools/testing/vma/include/dup.h @@ -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); +}