+ userfaultfd-introduce-vm_uffd_ops-fix.patch added to mm-unstable branch

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

The patch titled
     Subject: userfaultfd: allow registration of WP_ASYNC for any VMA
has been added to the -mm mm-unstable branch.  Its filename is
     userfaultfd-introduce-vm_uffd_ops-fix.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/userfaultfd-introduce-vm_uffd_ops-fix.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
Subject: userfaultfd: allow registration of WP_ASYNC for any VMA
Date: Wed, 11 Mar 2026 20:21:38 +0200

Registration of a VMA with WP_ASYNC userfaulfd context in write-protect
mode does not require any VMA-specific resolution of user faults and these
faults are completely handled by the generic page fault handler.

This functionality existed since the introduction of WP_ASYNC mode and it
allows tracking writes to SysV shared memory mappings (shmget(2) and
shmat(2)).

Move the check for WP mode before checking for presence of ->uffd_ops in a
VMA to restore the original behaviour.

Link: https://lkml.kernel.org/r/abG5HFV8yoEHOFkh@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nikita Kalyazin <kalyazin@amazon.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/userfaultfd.c |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

--- a/mm/userfaultfd.c~userfaultfd-introduce-vm_uffd_ops-fix
+++ a/mm/userfaultfd.c
@@ -2044,22 +2044,22 @@ bool vma_can_userfault(struct vm_area_st
 {
 	const struct vm_uffd_ops *ops = vma_uffd_ops(vma);
 
-	/* only VMAs that implement vm_uffd_ops are supported */
-	if (!ops)
-		return false;
-
 	vm_flags &= __VM_UFFD_FLAGS;
 
-	if (vma->vm_flags & VM_DROPPABLE)
-		return false;
-
 	/*
-	 * If wp async enabled, and WP is the only mode enabled, allow any
+	 * If WP is the only mode enabled and context is wp async, allow any
 	 * memory type.
 	 */
 	if (wp_async && (vm_flags == VM_UFFD_WP))
 		return true;
 
+	/* For any other mode reject VMAs that don't implement vm_uffd_ops */
+	if (!ops)
+		return false;
+
+	if (vma->vm_flags & VM_DROPPABLE)
+		return false;
+
 	/*
 	 * If user requested uffd-wp but not enabled pte markers for
 	 * uffd-wp, then only anonymous memory is supported
_

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

mm-dont-special-case-mmu-for-is_zero_pfn-and-my_zero_pfn.patch
mm-rename-my_zero_pfn-to-zero_pfn.patch
arch-mm-consolidate-empty_zero_page.patch
mm-cache-struct-page-for-empty_zero_page-and-return-it-from-zero_page.patch
userfaultfd-introduce-mfill_copy_folio_locked-helper.patch
userfaultfd-introduce-struct-mfill_state.patch
userfaultfd-introduce-mfill_get_pmd-helper.patch
userfaultfd-introduce-mfill_get_vma-and-mfill_put_vma.patch
userfaultfd-retry-copying-with-locks-dropped-in-mfill_atomic_pte_copy.patch
userfaultfd-move-vma_can_userfault-out-of-line.patch
userfaultfd-introduce-vm_uffd_ops.patch
userfaultfd-introduce-vm_uffd_ops-fix.patch
shmem-userfaultfd-use-a-vma-callback-to-handle-uffdio_continue.patch
userfaultfd-introduce-vm_uffd_ops-alloc_folio.patch
shmem-userfaultfd-implement-shmem-uffd-operations-using-vm_uffd_ops.patch
userfaultfd-mfill_atomic-remove-retry-logic.patch
selftests-mm-pagemap_ioctl-remove-hungarian-notation.patch