+ mm-uffd-use-predicates-for-userfaultfd-checks.patch added to mm-new branch

+ mm-uffd-use-predicates-for-userfaultfd-checks.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/uffd: use predicates for userfaultfd checks
has been added to the -mm mm-new branch.  Its filename is
     mm-uffd-use-predicates-for-userfaultfd-checks.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-uffd-use-predicates-for-userfaultfd-checks.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: mm/uffd: use predicates for userfaultfd checks
Date: Mon, 14 Sep 2026 15:57:52 +0100

Rather than directly checking VMA flags, use the newly introduced
vma_is_kernel_owned() and vma_is_persistent() helpers in userfaultfd when
assessing VMA suitability for userfaultfd and UFFDIO_MOVE.

Update vma_move_compatible() so it's expressed in terms of VMA
characteristics rather than arbitrary flags.

Additionally, update the use of the deprecated VMA flag API when checking
VMA_SHADOW_STACK_BIT.

A VMA_IO_BIT check is no longer required but that is fine as a hard
invariant has been established that only kernel-owned mappings may set
VMA_IO_BIT so the check is now redundant.

Link: https://lore.kernel.org/20260914-b4-mmap-prepare-vma-flag-sanify-v2-32-7d9781ed5361@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/userfaultfd.c |   21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

--- a/mm/userfaultfd.c~mm-uffd-use-predicates-for-userfaultfd-checks
+++ a/mm/userfaultfd.c
@@ -1754,10 +1754,18 @@ static inline bool move_splits_huge_pmd(
 }
 #endif
 
-static inline bool vma_move_compatible(struct vm_area_struct *vma)
+static inline bool vma_move_compatible(const struct vm_area_struct *vma)
 {
-	return !(vma->vm_flags & (VM_PFNMAP | VM_IO |  VM_HUGETLB |
-				  VM_MIXEDMAP | VM_SHADOW_STACK));
+	/* uffd is generally incompatible with kernel-owned mappings. */
+	if (vma_is_kernel_owned(vma))
+		return false;
+	/* The shadow stack should not be written to by userspace. */
+	if (vma_test_single_mask(vma, VMA_SHADOW_STACK))
+		return false;
+	/* hugetlb mappings cannot be safely moved. */
+	if (vma_is_hugetlb(vma))
+		return false;
+	return true;
 }
 
 static int validate_move_areas(struct userfaultfd_ctx *ctx,
@@ -2146,10 +2154,11 @@ static bool vma_can_userfault(struct vm_
 {
 	const struct vm_uffd_ops *ops = vma_uffd_ops(vma);
 
-	if (vma->vm_flags & (VM_DROPPABLE | VM_SHADOW_STACK))
+	/* Non-persistent memory is inherently not controllable by userspace. */
+	if (!vma_is_persistent(vma))
 		return false;
-
-	if (!vma_is_hugetlb(vma) && (vma->vm_flags & VM_SPECIAL))
+	/* The shadow stack should not be written to by userspace. */
+	if (vma_test_single_mask(vma, VMA_SHADOW_STACK))
 		return false;
 
 	vm_flags &= __VM_UFFD_FLAGS;
_

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

mm-vmpressure-remove-window-size-todo.patch
tools-testing-selftests-mm-add-missing-gitignore-entries.patch
mm-move-drivers-char-memc-to-mm-char-memc.patch
mm-implement-file_is_dev_zero-to-uniquely-identify-dev-zero.patch
mm-vma-only-permit-map_private-dev-zero-to-be-mapped-anonymous.patch
mm-vma-make-map_private-mapped-dev-zero-mappings-truly-anonymous.patch
tools-testing-vma-add-test-to-assert-map_private-dev-zero-is-anon.patch
tools-testing-selftests-mm-add-map_private-dev-zero-merge-tests.patch
mm-madvise-swap-in-cowd-map_private-file-mappings-on-madv_willneed.patch
mm-huge_memory-zap-deposited-page-tables-after-an-rcu-grace-period.patch
mm-enable-mmu_gather_rcu_table_free-for-most-2-level-architectures.patch
mm-enable-mmu_gather_rcu_table_free-for-mmu-riscv.patch
mm-enable-mmu_gather_rcu_table_free-for-mmu-arm.patch
mm-enable-mmu_gather_rcu_table_free-for-arc-microblaze-xtensa.patch
mm-enable-mmu_gather_rcu_table_free-for-sparc64.patch
mm-enable-mmu_gather_rcu_table_free-for-m68k-coldfire.patch
mm-enable-mmu_gather_rcu_table_free-for-sh-x2.patch
mm-enable-mmu_gather_rcu_table_free-for-m68k-motorola.patch
mm-enable-mmu_gather_rcu_table_free-for-sparc32.patch
mm-make-userland-page-table-freeing-rcu-safe.patch
mm-change-the-contract-for-free_pgtables-update-docs.patch
mm-vma-fix-mmap_prepare-file-handling-remove-file_doesnt_need_get.patch
mm-vma-predicate-setting-mmap_prepare-vma-fields-on-new-vma-alloc.patch
mm-vma-introduce-and-use-vma_can_merge.patch
mm-consistently-validate-vma-state-after-mmap-hooks.patch
mm-vma-ensure-mmap_prepare-doesnt-set-actions-on-a-mergeable-vma.patch
mm-make-map_kernel_pages_-internal-and-unexported.patch
mm-vma-tidy-up-map-kernel-pages-enum-values.patch
mm-add-mmap-action-for-discontiguous-kernel-page-mapping.patch
docs-filesystems-update-mmap_prepare-docs-for-discontig-kernel-pgs.patch
drivers-usb-mon-update-to-use-mmap_prepare-map-kernel-pages.patch
infiniband-update-hfi1-to-use-remap_vmalloc_range.patch
selinux-reject-writable-opens-of-policy-file-drop-mmap-shared-write-check.patch
alsa-pcm-use-vm_insert_page-to-map-pcm-status-page.patch
bpf-arena-mark-arena_map_mmap-mappings-vm_mixedmap.patch
mm-vma-add-vma_is_kernel_owned-predicates.patch
mm-vma-only-allow-mmap-to-clear-vma_maywrite_bit-if-kernel-owned.patch
mm-vma-add-and-use-vma__is_fixed_mapping.patch
scsi-sg-convert-mmap-hook-to-mmap_prepare-and-rework.patch
fbdev-defio-assert-fbinfo_virtfb-drop-vm_io-add-vm_mixedmap.patch
hsi-cmt_speech-convert-mmap-hook-to-mmap_prepare-refactor.patch
mm-gup-error-out-early-on-vma_mayread_bit-vmas.patch
uprobes-remove-vm_io-set-vm_mixedmap-for-mapped-kernel-pages.patch
mm-mlock-clear-vma_locked_mask-over-mmap-callback.patch
mm-mlock-eliminate-weird-vma_io_bit-abuse-and-simplify.patch
mm-vma-enforce-that-only-kernel-owned-mappings-may-set-vma_io_bit.patch
mm-remove-vma_io_bit-check-in-vma_is_kernel_owned.patch
mm-remove-hugetlb_inlineh.patch
mm-rename-is_vm_hugetlb_page-to-vma_is_hugetlb.patch
mm-drop-some-redundant-checks-around-hugetlb-vmas.patch
mm-madvise-update-is_valid_guard_vma-to-use-vma_can_merge.patch
mm-vma-introduce-vma_is_persistent.patch
mm-uffd-use-predicates-for-userfaultfd-checks.patch
mm-madvise-use-predicates-for-madvise-madv_dofork.patch
mm-eliminate-vma_special_flags-usage-when-hugetlb-explicitly-tested.patch
mm-eliminate-vma_special_flags-check-in-lru_gen_look_around.patch
mm-avoid-use-of-vma_special_flags-in-migrate_vma_setup.patch
mm-eliminate-vm_special-vma_special_flags.patch
fuse-dax-do-not-set-vm_mixedmap.patch
mm-huge_memory-remove-vma_is_special_huge.patch
mm-vma-introduce-and-use-vma_can_gup.patch