From fed15f1345dc8a7fc8baa81e8b55c3ba010d7f4b Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Wed, 4 Jan 2023 17:52:05 -0500 Subject: [PATCH] mm/hugetlb: pre-allocate pgtable pages for uffd wr-protects 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 Reported-by: James Houghton Reviewed-by: Mike Kravetz Acked-by: David Hildenbrand Acked-by: James Houghton Cc: Andrea Arcangeli Cc: Axel Rasmussen Cc: Muchun Song Cc: Nadav Amit Cc: [5.19+] Signed-off-by: Andrew Morton --- mm/hugetlb.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 2ce912c915eb..f96794be71d5 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6660,8 +6660,17 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, 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)) {