+ mm-vma-add-vma_is_kernel_owned-predicates.patch added to mm-new branch

+ mm-vma-add-vma_is_kernel_owned-predicates.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/vma: add vma[_flags]_is_kernel_owned() predicates
has been added to the -mm mm-new branch.  Its filename is
     mm-vma-add-vma_is_kernel_owned-predicates.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vma-add-vma_is_kernel_owned-predicates.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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: mm/vma: add vma[_flags]_is_kernel_owned() predicates
Date: Mon, 14 Sep 2026 15:57:35 +0100

Rather than referring to VMA flags with uncertain meaning, add a new
predicate that explicitly describes what possession of the VMA_PFNMAP_BIT
or VMA_MIXEDMAP_BIT flags mean, and then refer to that function for
determining VMA mergeability.

Either flag means the contents of the mapping are owned by the kernel,
usually a driver, rather than by the core mm: the memory may be MMIO,
kernel-allocated pages or even ordinary pages the driver maps itself, but
the core must not populate, reclaim, migrate, copy-on-write or merge the
range on its own initiative.

We initially also include VMA_IO_BIT here, as by implication, these must
be kernel-owned.  (mlock() also sets VMA_IO_BIT transiently on ordinary
VMAs while locking them, which is addressed later in this series.)

However the intent is to in future remove this, as no mapping should be
marked as an I/O mapping without also being marked with VMA_PFNMAP_BIT.

This forms the basis of further work intended to improve how we express
VMA properties such as this.

Also update the VMA userland tests to reflect the change.

No functional change intended.

Link: https://lore.kernel.org/20260914-b4-mmap-prepare-vma-flag-sanify-v2-15-7d9781ed5361@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h              |   56 +++++++++++++++++++++++++++++-
 tools/testing/vma/include/dup.h |   29 +++++++++++++++
 2 files changed, 83 insertions(+), 2 deletions(-)

--- a/include/linux/mm.h~mm-vma-add-vma_is_kernel_owned-predicates
+++ a/include/linux/mm.h
@@ -1613,6 +1613,44 @@ static inline bool vma_is_shared_maywrit
 }
 
 /**
+ * vma_flags_is_kernel_owned() - Do the specified VMA flags indicate that the
+ * contents of the VMA are owned by the kernel rather than the core mm?
+ * @flags: The VMA flags to test.
+ *
+ * A kernel-owned mapping is one whose contents are established and controlled
+ * by the kernel, typically a driver, rather than by the core mm's fault and
+ * rmap machinery.
+ *
+ * The mapping may be memory-mapped I/O, kernel-allocated pages or ordinary
+ * pages the owner has chosen to map itself (shmem via a PFN map, for instance).
+ *
+ * In all cases the core mm must not populate, reclaim, migrate, copy-on-write
+ * or merge it of its own accord.
+ *
+ * Pages mapped this way are not necessarily reference counted or map counted.
+ *
+ * Returns: true if the flags indicate a kernel-owned mapping.
+ */
+static inline bool vma_flags_is_kernel_owned(const vma_flags_t *flags)
+{
+	return vma_flags_test_any(flags, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT,
+				  VMA_IO_BIT);
+}
+
+/**
+ * vma_is_kernel_owned() - Are the contents of @vma owned by the kernel?
+ * @vma: The VMA to test.
+ *
+ * See vma_flags_is_kernel_owned() for a description of this property.
+ *
+ * Returns: true if the VMA is kernel-owned.
+ */
+static inline bool vma_is_kernel_owned(const struct vm_area_struct *vma)
+{
+	return vma_flags_is_kernel_owned(&vma->flags);
+}
+
+/**
  * vma_flags_can_merge() - Do the specified VMA flags permit the VMA to be
  * merged with another?
  * @flags: The VMA flags to test.
@@ -1620,7 +1658,23 @@ static inline bool vma_is_shared_maywrit
  */
 static inline bool vma_flags_can_merge(const vma_flags_t *flags)
 {
-	return !vma_flags_test_any_mask(flags, VMA_SPECIAL_FLAGS);
+	/*
+	 * VMA merging assumes that a VMA's flags and fields completely describe
+	 * its state.
+	 *
+	 * However, kernel-owned mappings may have established state upon mapping
+	 * not embodied in any attribute of the VMA.
+	 *
+	 * Additionally, private (CoW) PFN maps encode the source PFN of the
+	 * range in vma->vm_pgoff, which may otherwise cause spurious merges.
+	 */
+	if (vma_flags_is_kernel_owned(flags))
+		return false;
+	/* VMA explicitly marked as being unmergeable. */
+	if (vma_flags_test(flags, VMA_DONTEXPAND_BIT))
+		return false;
+
+	return true;
 }
 
 /**
--- a/tools/testing/vma/include/dup.h~mm-vma-add-vma_is_kernel_owned-predicates
+++ a/tools/testing/vma/include/dup.h
@@ -1665,7 +1665,34 @@ static inline bool file_is_dev_zero(cons
 	return file && file->f_op == &zero_fops;
 }
 
+static inline bool vma_flags_is_kernel_owned(const vma_flags_t *flags)
+{
+	return vma_flags_test_any(flags, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT,
+				  VMA_IO_BIT);
+}
+
+static inline bool vma_is_kernel_owned(const struct vm_area_struct *vma)
+{
+	return vma_flags_is_kernel_owned(&vma->flags);
+}
+
 static inline bool vma_flags_can_merge(const vma_flags_t *flags)
 {
-	return !vma_flags_test_any_mask(flags, VMA_SPECIAL_FLAGS);
+	/*
+	 * VMA merging assumes that the properties of a VMA completely describe
+	 * the properties of that VMA.
+	 *
+	 * However, kernel-owned mappings may have established state upon mapping
+	 * not embodied in any attribute of the VMA.
+	 *
+	 * Additionally, PFN maps encode the source PFN of the range in
+	 * vma->vm_pgoff, which may otherwise cause spurious merges.
+	 */
+	if (vma_flags_is_kernel_owned(flags))
+		return false;
+	/* VMA explicitly marked as being unmergeable. */
+	if (vma_flags_test(flags, VMA_DONTEXPAND_BIT))
+		return false;
+
+	return true;
 }
_

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