The patch titled Subject: mm/shmem: use page_mapping() to detect page cache for uffd continue has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-shmem-use-page_mapping-to-detect-page-cache-for-uffd-continue.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: Peter Xu peterx@redhat.com Subject: mm/shmem: use page_mapping() to detect page cache for uffd continue Date: Wed, 2 Nov 2022 14:41:52 -0400

mfill_atomic_install_pte() checks page->mapping to detect whether one page is used in the page cache. However as pointed out by Matthew, the page can logically be a tail page rather than always the head in the case of uffd minor mode with UFFDIO_CONTINUE. It means we could wrongly install one pte with shmem thp tail page assuming it's an anonymous page.

It's not that clear even for anonymous page, since normally anonymous pages also have page->mapping being setup with the anon vma. It's safe here only because the only such caller to mfill_atomic_install_pte() is always passing in a newly allocated page (mcopy_atomic_pte()), whose page->mapping is not yet setup. However that's not extremely obvious either.

For either of above, use page_mapping() instead.

Link: https://lkml.kernel.org/r/Y2K+y7wnhC4vbnP2@x1n Fixes: 153132571f02 ("userfaultfd/shmem: support UFFDIO_CONTINUE for shmem") Signed-off-by: Peter Xu peterx@redhat.com Reported-by: Matthew Wilcox willy@infradead.org Cc: Andrea Arcangeli aarcange@redhat.com Cc: Hugh Dickins hughd@google.com Cc: Axel Rasmussen axelrasmussen@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/userfaultfd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/userfaultfd.c~mm-shmem-use-page_mapping-to-detect-page-cache-for-uffd-continue +++ a/mm/userfaultfd.c @@ -64,7 +64,7 @@ int mfill_atomic_install_pte(struct mm_s pte_t _dst_pte, *dst_pte; bool writable = dst_vma->vm_flags & VM_WRITE; bool vm_shared = dst_vma->vm_flags & VM_SHARED; - bool page_in_cache = page->mapping; + bool page_in_cache = page_mapping(page); spinlock_t *ptl; struct inode *inode; pgoff_t offset, max_off; _

Patches currently in -mm which might be from peterx@redhat.com are

partly-revert-mm-thp-carry-over-dirty-bit-when-thp-splits-on-pmd.patch mm-shmem-use-page_mapping-to-detect-page-cache-for-uffd-continue.patch selftests-vm-use-memfd-for-uffd-hugetlb-tests.patch selftests-vm-use-memfd-for-hugetlb-madvise-test.patch selftests-vm-use-memfd-for-hugepage-mremap-test.patch selftests-vm-drop-mnt-point-for-hugetlb-in-run_vmtestssh.patch mm-hugetlb-unify-clearing-of-restorereserve-for-private-pages.patch revert-mm-uffd-fix-warning-without-pte_marker_uffd_wp-compiled-in.patch