+ mm-hugetlb-tolerate-uffd-bits-set-without-uffd-for-prot_none-ptes.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/hugetlb: tolerate uffd bits set without uffd for PROT_NONE PTEs
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-hugetlb-tolerate-uffd-bits-set-without-uffd-for-prot_none-ptes.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-tolerate-uffd-bits-set-without-uffd-for-prot_none-ptes.patch

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: "David Hildenbrand (Arm)" <david@kernel.org>
Subject: mm/hugetlb: tolerate uffd bits set without uffd for PROT_NONE PTEs
Date: Thu, 15 Oct 2026 18:07:13 +0200

The whole uffd handling when a VMA is unregistered from UFFD is shaky:
there are still some scenarios where we might have stale uffd PTE bits
in VMAs no longer registered for UFFD, which confuses other code.

Let's just tolerate that for now and simply clear the PTE bit. Add a
TODO to really clean up any uffd leftovers when unregistering a VMA from
userfaultfd.

The handling is now more similar to what we have in handle_pte_fault().

Link: https://lore.kernel.org/20261015-urgent_fixes-v1-7-42796911043b@kernel.org
Fixes: 2d427bb01639 ("mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP")
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Adam Litke <agl@us.ibm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Rik van Riel <riel@surriel.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: <stable@vger.kernel.org>
---

 mm/hugetlb.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-tolerate-uffd-bits-set-without-uffd-for-prot_none-ptes
+++ a/mm/hugetlb.c
@@ -6138,16 +6138,20 @@ vm_fault_t hugetlb_fault(struct mm_struc
 	 * NUMA hinting), so let normal hugetlb fault handling proceed.
 	 */
 	if (pte_protnone(vmf.orig_pte) && vma_is_accessible(vma) &&
-	    userfaultfd_rwp(vma) && huge_pte_uffd(vmf.orig_pte)) {
+	    huge_pte_uffd(vmf.orig_pte)) {
 		spinlock_t *ptl;
 		pte_t pte;
 
 		/* Sync: drop hugetlb locks before blocking in handle_userfault() */
-		if (!userfaultfd_rwp_async(vma))
+		if (userfaultfd_rwp(vma) && !userfaultfd_rwp_async(vma))
 			return hugetlb_handle_userfault(&vmf, mapping, VM_UFFD_RWP);
 
 		ptl = huge_pte_lock(h, mm, vmf.pte);
 		pte = huge_ptep_get(mm, vmf.address, vmf.pte);
+		/*
+		 * TODO: fix all cases where uffd PTE bits remain in VMAs that
+		 * are no longer registered with uffd.
+		 */
 		if (pte_protnone(pte) && huge_pte_uffd(pte)) {
 			unsigned int shift = huge_page_shift(h);
 
_

Patches currently in -mm which might be from david@kernel.org are

mm-fix-address-wraparound-when-scanning-large-folio-ptes.patch
mm-hugetlb-fix-use-after-free-in-hugetlb_mfill_atomic_pte.patch
mm-hugetlb-tolerate-uffd-bits-set-without-uffd-for-prot_none-ptes.patch
mm-hugetlb-tolerate-uffd_wp-markers-outside-uffd-wp-vmas.patch
mm-mremap-fix-calling-fixup_hugetlb_reservations-on-the-wrong-vma.patch
arm64-mm-move-__check_safe_pte_update-fix.patch
mm-sparse-move-mem_section-init-to-sparse_extreme_init.patch
mm-sparse-refactor-sparse_sections_init.patch
mm-sparse-move-initialization-of-section-metadata-to-sparse_metadata_init.patch
mm-sparse-rename-and-cleanup-sparse_init_nid.patch
mm-sparse-cleanup-sparse_init_one_section.patch
mm-sparse-rename-__highest_present_section_nr-to-__highest_used_section_nr.patch
mm-sparse-remove-pfn_in_present_section.patch
mm-sparse-move-__highest_used_section_nr-handling.patch
scripts-gdb-mmpy-remove-fallbacks-for-section_has_mem_map-and-section_is_early.patch
mm-sparse-remove-section_marked_present.patch
mm-sparse-remove-flags-parameter-from-sparse_init_one_section.patch
fs-proc-page-clarify-comment-in-get_max_dump_pfn.patch
mm-memory_hotplug-drop-config_have_arch_pfn_valid-handling-from-pfn_to_online_page.patch
vmcoreinfo-export-section_has_mem_map.patch
mm-disallow-ioremaping-ordinary-ram-in-generic_access_phys.patch
mm-userfaultfd-only-allocate-anon_vma-in-cow-mappings.patch