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Tue, 26 May 2026 09:05:18 -0400 (EDT) From: Kiryl Shutsemau To: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com, david@kernel.org Cc: ljs@kernel.org, surenb@google.com, vbabka@kernel.org, Liam.Howlett@oracle.com, ziy@nvidia.com, corbet@lwn.net, skhan@linuxfoundation.org, seanjc@google.com, pbonzini@redhat.com, jthoughton@google.com, aarcange@redhat.com, sj@kernel.org, usama.arif@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, kernel-team@meta.com, "Kiryl Shutsemau (Meta)" , stable@vger.kernel.org, Sashiko AI review Subject: [PATCH v5 01/18] fs/proc/task_mmu: fix make_uffd_wp_huge_pte() prot-update race Date: Tue, 26 May 2026 14:04:49 +0100 Message-ID: <20260526130509.2748441-2-kirill@shutemov.name> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260526130509.2748441-1-kirill@shutemov.name> References: <20260526130509.2748441-1-kirill@shutemov.name> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Kiryl Shutsemau (Meta)" make_uffd_wp_huge_pte() arms the UFFD_WP bit on a present HugeTLB PTE by calling huge_ptep_modify_prot_commit() with a ptent snapshot that was fetched without the corresponding huge_ptep_modify_prot_start(). The start helper is what atomically clears the entry so the kernel-owned snapshot stays consistent until the commit; without it, the hardware may set Dirty or Accessed in the live PTE between the original read and the commit, and huge_ptep_modify_prot_commit() (whose generic implementation just calls set_huge_pte_at()) then writes the stale snapshot back over the live hardware bits, losing the update. The non-hugetlb sibling make_uffd_wp_pte() does this correctly via ptep_modify_prot_start() / ptep_modify_prot_commit(). Mirror that pattern for the present-PTE branch. The migration case stays as-is -- migration entries are non-present, so there's no hardware update to race against. Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs") Cc: stable@vger.kernel.org Reported-by: Sashiko AI review Signed-off-by: Kiryl Shutsemau --- fs/proc/task_mmu.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 1e3a15bf46f4..e21a38ac745b 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -2610,12 +2610,16 @@ static void make_uffd_wp_huge_pte(struct vm_area_struct *vma, if (softleaf_is_hwpoison(entry) || softleaf_is_marker(entry)) return; - if (softleaf_is_migration(entry)) + if (softleaf_is_migration(entry)) { set_huge_pte_at(vma->vm_mm, addr, ptep, pte_swp_mkuffd_wp(ptent), psize); - else - huge_ptep_modify_prot_commit(vma, addr, ptep, ptent, - huge_pte_mkuffd_wp(ptent)); + } else { + pte_t old_pte, new_pte; + + old_pte = huge_ptep_modify_prot_start(vma, addr, ptep); + new_pte = huge_pte_mkuffd_wp(old_pte); + huge_ptep_modify_prot_commit(vma, addr, ptep, old_pte, new_pte); + } } #endif /* CONFIG_HUGETLB_PAGE */ -- 2.54.0