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Howlett" , Jann Horn , =?UTF-8?q?Jakub=20Mat=C4=9Bna?= , Sasha Levin Subject: [PATCH 7.3.y] mm/vma: fix expansion of VMA_MIXEDMAP_BIT VMAs Date: Wed, 11 Nov 2026 22:10:50 -0500 Message-ID: <20261112031021.1419377-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261109200136-failed-7.3-8146c6478224@kernel.org> References: <20261109200136-failed-7.3-8146c6478224@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: "Lorenzo Stoakes (ARM)" [ Upstream commit 8146c6478224d8f6395c6b08a19c344a56d79867 ] 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: [ sashal: Replaced vma_can_merge() and vma_is_fixed_mapping() with equivalent flag checks and is_vm_hugetlb_page(). ] Signed-off-by: Sasha Levin --- mm/vma.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/mm/vma.c b/mm/vma.c index e382fd32f0fff..9863668b9d6bc 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -1882,12 +1882,28 @@ 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 bool can_merge = !vma_test_any(vma, VMA_PFNMAP_BIT, + VMA_DONTEXPAND_BIT, VMA_MIXEDMAP_BIT) && + !is_vm_hugetlb_page(vma); + const unsigned long start = + can_merge ? 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 (can_merge) { + 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_test_any(vma, VMA_PFNMAP_BIT, VMA_DONTEXPAND_BIT)); + 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) -- 2.53.0