The patch titled Subject: mm/userfaultfd: fix kmap_local LIFO ordering for CONFIG_HIGHPTE has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-userfaultfd-fix-kmap_local-lifo-ordering-for-config_highpte.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Sasha Levin sashal@kernel.org Subject: mm/userfaultfd: fix kmap_local LIFO ordering for CONFIG_HIGHPTE Date: Thu, 31 Jul 2025 10:44:31 -0400
With CONFIG_HIGHPTE on 32-bit ARM, move_pages_pte() maps PTE pages using kmap_local_page(), which requires unmapping in Last-In-First-Out order.
The current code maps dst_pte first, then src_pte, but unmaps them in the same order (dst_pte, src_pte), violating the LIFO requirement. This causes the warning in kunmap_local_indexed():
WARNING: CPU: 0 PID: 604 at mm/highmem.c:622 kunmap_local_indexed+0x178/0x17c addr != __fix_to_virt(FIX_KMAP_BEGIN + idx)
Fix this by reversing the unmap order to respect LIFO ordering.
This issue follows the same pattern as similar fixes: - commit eca6828403b8 ("crypto: skcipher - fix mismatch between mapping and unmapping order") - commit 8cf57c6df818 ("nilfs2: eliminate staggered calls to kunmap in nilfs_rename")
Both of which addressed the same fundamental requirement that kmap_local operations must follow LIFO ordering.
Link: https://lkml.kernel.org/r/20250731144431.773923-1-sashal@kernel.org Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") Signed-off-by: Sasha Levin sashal@kernel.org Acked-by: David Hildenbrand david@redhat.com Reviewed-by: Suren Baghdasaryan surenb@google.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/userfaultfd.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
--- a/mm/userfaultfd.c~mm-userfaultfd-fix-kmap_local-lifo-ordering-for-config_highpte +++ a/mm/userfaultfd.c @@ -1453,10 +1453,15 @@ out: folio_unlock(src_folio); folio_put(src_folio); } - if (dst_pte) - pte_unmap(dst_pte); + /* + * Unmap in reverse order (LIFO) to maintain proper kmap_local + * index ordering when CONFIG_HIGHPTE is enabled. We mapped dst_pte + * first, then src_pte, so we must unmap src_pte first, then dst_pte. + */ if (src_pte) pte_unmap(src_pte); + if (dst_pte) + pte_unmap(dst_pte); mmu_notifier_invalidate_range_end(&range); if (si) put_swap_device(si); _
Patches currently in -mm which might be from sashal@kernel.org are
mm-userfaultfd-fix-kmap_local-lifo-ordering-for-config_highpte.patch