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[70.52.228.144]) by smtp.gmail.com with ESMTPSA id r1-20020a05620a298100b006eeb3165565sm24654710qkp.80.2023.01.04.14.52.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Jan 2023 14:52:11 -0800 (PST) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Mike Kravetz , Muchun Song , peterx@redhat.com, Nadav Amit , Andrea Arcangeli , David Hildenbrand , James Houghton , Axel Rasmussen , Andrew Morton , linux-stable Subject: [PATCH 1/3] mm/hugetlb: Pre-allocate pgtable pages for uffd wr-protects Date: Wed, 4 Jan 2023 17:52:05 -0500 Message-Id: <20230104225207.1066932-2-peterx@redhat.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20230104225207.1066932-1-peterx@redhat.com> References: <20230104225207.1066932-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 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. Cc: linux-stable # 5.19+ Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes") Reported-by: James Houghton Signed-off-by: Peter Xu --- mm/hugetlb.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index bf7a1f628357..017d9159cddf 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6649,8 +6649,17 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, spinlock_t *ptl; ptep = hugetlb_walk(vma, 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)) { -- 2.37.3