The patch titled Subject: mm/hugetlb: pre-allocate pgtable pages for uffd wr-protects has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-hugetlb-pre-allocate-pgtable-pages-for-uffd-wr-protects.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/hugetlb: pre-allocate pgtable pages for uffd wr-protects Date: Wed, 4 Jan 2023 17:52:05 -0500

Userfaultfd-wp uses pte markers to mark wr-protected pages for both shmem and hugetlb. Shmem has pre-allocation ready for markers, but hugetlb path was overlooked.

Doing so by calling huge_pte_alloc() if the initial pgtable walk fails to find the huge ptep. It's possible that huge_pte_alloc() can fail with high memory pressure, in that case stop the loop immediately and fail silently. This is not the most ideal solution but it matches with what we do with shmem meanwhile it avoids the splat in dmesg.

Link: https://lkml.kernel.org/r/20230104225207.1066932-2-peterx@redhat.com Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes") Signed-off-by: Peter Xu peterx@redhat.com Reported-by: James Houghton jthoughton@google.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Axel Rasmussen axelrasmussen@google.com Cc: David Hildenbrand david@redhat.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Muchun Song songmuchun@bytedance.com Cc: Nadav Amit nadav.amit@gmail.com Cc: stable@vger.kernel.org [5.19+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/hugetlb.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-pre-allocate-pgtable-pages-for-uffd-wr-protects +++ a/mm/hugetlb.c @@ -6660,8 +6660,17 @@ unsigned long hugetlb_change_protection( spinlock_t *ptl; ptep = huge_pte_offset(mm, address, psize); if (!ptep) { - address |= last_addr_mask; - continue; + if (!uffd_wp) { + address |= last_addr_mask; + continue; + } + /* + * Userfaultfd wr-protect requires pgtable + * pre-allocations to install pte markers. + */ + ptep = huge_pte_alloc(mm, vma, address, psize); + if (!ptep) + break; } ptl = huge_pte_lock(h, mm, ptep); if (huge_pmd_unshare(mm, vma, address, ptep)) { _

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

mm-hugetlb-pre-allocate-pgtable-pages-for-uffd-wr-protects.patch mm-uffd-fix-pte-marker-when-fork-without-fork-event.patch mm-fix-a-few-rare-cases-of-using-swapin-error-pte-marker.patch mm-uffd-always-wr-protect-pte-in-ptepmd_mkuffd_wp.patch mm-hugetlb-let-vma_offset_start-to-return-start.patch mm-hugetlb-dont-wait-for-migration-entry-during-follow-page.patch mm-hugetlb-document-huge_pte_offset-usage.patch mm-hugetlb-move-swap-entry-handling-into-vma-lock-when-faulted.patch mm-hugetlb-make-userfaultfd_huge_must_wait-safe-to-pmd-unshare.patch mm-hugetlb-make-hugetlb_follow_page_mask-safe-to-pmd-unshare.patch mm-hugetlb-make-follow_hugetlb_page-safe-to-pmd-unshare.patch mm-hugetlb-make-walk_hugetlb_range-safe-to-pmd-unshare.patch mm-hugetlb-introduce-hugetlb_walk.patch mm-mprotect-use-long-for-page-accountings-and-retval.patch mm-uffd-detect-pgtable-allocation-failures.patch