diff mbox series

[v4,14/38] mm/vma: add vma[_flags]_is_mm_managed() predicates

Message ID 20261003-b4-mmap-prepare-vma-flag-sanify-v4-14-a1f052500fd7@kernel.org
State New
Headers show
Series mm: make VMA flag semantics explicit, eliminate VM_SPECIAL | expand

Commit Message

Lorenzo Stoakes (ARM) Oct. 3, 2026, 4:32 p.m. UTC 
Rather than referring to VMA flags with uncertain meaning, add a new
predicate that explicitly describes what absence of the VMA_PFNMAP_BIT and
VMA_MIXEDMAP_BIT flags means, and then refer to that function for
determining VMA mergeability.

If neither of these flags are set, that means the contents of the mapping
are managed by core mm.

Otherwise they are instead owned by some other kernel component, usually a
driver: the memory may be MMIO, kernel-allocated pages or even ordinary
pages the driver maps itself, but core mm must not populate, reclaim,
migrate, copy-on-write or merge the range itself.

We initially also treat VMA_IO_BIT as implying a mapping is not mm-managed,
as by implication it cannot be. (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.

Reviewed-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 include/linux/mm.h              | 53 ++++++++++++++++++++++++++++++++++++++++-
 tools/testing/vma/include/dup.h | 29 +++++++++++++++++++++-
 2 files changed, 80 insertions(+), 2 deletions(-)

Comments

Suren Baghdasaryan Oct. 4, 2026, 5:43 p.m. UTC | #1 
On Sat, Oct 3, 2026 at 6:38 PM Lorenzo Stoakes (ARM) <ljs@kernel.org> wrote:
>
> Rather than referring to VMA flags with uncertain meaning, add a new
> predicate that explicitly describes what absence of the VMA_PFNMAP_BIT and
> VMA_MIXEDMAP_BIT flags means, and then refer to that function for
> determining VMA mergeability.
>
> If neither of these flags are set, that means the contents of the mapping
> are managed by core mm.
>
> Otherwise they are instead owned by some other kernel component, usually a
> driver: the memory may be MMIO, kernel-allocated pages or even ordinary
> pages the driver maps itself, but core mm must not populate, reclaim,
> migrate, copy-on-write or merge the range itself.
>
> We initially also treat VMA_IO_BIT as implying a mapping is not mm-managed,
> as by implication it cannot be. (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.
>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

Reviewed-by: Suren Baghdasaryan <surenb@google.com>


> ---
>  include/linux/mm.h              | 53 ++++++++++++++++++++++++++++++++++++++++-
>  tools/testing/vma/include/dup.h | 29 +++++++++++++++++++++-
>  2 files changed, 80 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 97e1eb4fe3a4..83953757735a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1612,6 +1612,41 @@ static inline bool vma_is_shared_maywrite(const struct vm_area_struct *vma)
>         return is_shared_maywrite(&vma->flags);
>  }
>
> +/**
> + * vma_flags_is_mm_managed() - Do the specified VMA flags indicate that the
> + * contents of the VMA are managed by core mm?
> + * @flags: The VMA flags to test.
> + *
> + * Such a mapping is one established by a simple mmap() or brk() with no driver
> + * or other kernel component involved.
> + *
> + * They are rmappable, and core mm services rmap operations including reclaim,
> + * as well as population, CoW and merge/split (if eligible).
> + *
> + * Mappings which fail this test are those where this is not the case -
> + * e.g. MMIO, user-mapped kernel pages, udmabuf (pfnmap shmem), etc.
> + *
> + * Returns: true if the flags indicate an mm-managed mapping.
> + */
> +static inline bool vma_flags_is_mm_managed(const vma_flags_t *flags)
> +{
> +       return !vma_flags_test_any(flags, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT,
> +                                  VMA_IO_BIT);
> +}
> +
> +/**
> + * vma_is_mm_managed() - Are the contents of @vma managed by core mm?
> + * @vma: The VMA to test.
> + *
> + * See vma_flags_is_mm_managed() for a description of this property.
> + *
> + * Returns: true if the VMA is mm-managed.
> + */
> +static inline bool vma_is_mm_managed(const struct vm_area_struct *vma)
> +{
> +       return vma_flags_is_mm_managed(&vma->flags);
> +}
> +
>  /**
>   * vma_flags_can_merge() - Do the specified VMA flags permit the VMA to be
>   * merged with another?
> @@ -1620,7 +1655,23 @@ static inline bool vma_is_shared_maywrite(const struct vm_area_struct *vma)
>   */
>  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, mappings which are not mm-managed 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_mm_managed(flags))
> +               return false;
> +       /* VMA explicitly marked as being unmergeable. */
> +       if (vma_flags_test(flags, VMA_DONTEXPAND_BIT))
> +               return false;
> +
> +       return true;
>  }
>
>  /**
> diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
> index a6a8e53c4b38..89c645a6ad60 100644
> --- a/tools/testing/vma/include/dup.h
> +++ b/tools/testing/vma/include/dup.h
> @@ -1665,7 +1665,34 @@ static inline bool file_is_dev_zero(const struct file *file)
>         return file && file->f_op == &zero_fops;
>  }
>
> +static inline bool vma_flags_is_mm_managed(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_mm_managed(const struct vm_area_struct *vma)
> +{
> +       return vma_flags_is_mm_managed(&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 a VMA's flags and fields completely describe
> +        * its state.
> +        *
> +        * However, mappings which are not mm-managed 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_mm_managed(flags))
> +               return false;
> +       /* VMA explicitly marked as being unmergeable. */
> +       if (vma_flags_test(flags, VMA_DONTEXPAND_BIT))
> +               return false;
> +
> +       return true;
>  }
>
> --
> 2.55.0
>
diff mbox series

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 97e1eb4fe3a4..83953757735a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1612,6 +1612,41 @@  static inline bool vma_is_shared_maywrite(const struct vm_area_struct *vma)
 	return is_shared_maywrite(&vma->flags);
 }
 
+/**
+ * vma_flags_is_mm_managed() - Do the specified VMA flags indicate that the
+ * contents of the VMA are managed by core mm?
+ * @flags: The VMA flags to test.
+ *
+ * Such a mapping is one established by a simple mmap() or brk() with no driver
+ * or other kernel component involved.
+ *
+ * They are rmappable, and core mm services rmap operations including reclaim,
+ * as well as population, CoW and merge/split (if eligible).
+ *
+ * Mappings which fail this test are those where this is not the case -
+ * e.g. MMIO, user-mapped kernel pages, udmabuf (pfnmap shmem), etc.
+ *
+ * Returns: true if the flags indicate an mm-managed mapping.
+ */
+static inline bool vma_flags_is_mm_managed(const vma_flags_t *flags)
+{
+	return !vma_flags_test_any(flags, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT,
+				   VMA_IO_BIT);
+}
+
+/**
+ * vma_is_mm_managed() - Are the contents of @vma managed by core mm?
+ * @vma: The VMA to test.
+ *
+ * See vma_flags_is_mm_managed() for a description of this property.
+ *
+ * Returns: true if the VMA is mm-managed.
+ */
+static inline bool vma_is_mm_managed(const struct vm_area_struct *vma)
+{
+	return vma_flags_is_mm_managed(&vma->flags);
+}
+
 /**
  * vma_flags_can_merge() - Do the specified VMA flags permit the VMA to be
  * merged with another?
@@ -1620,7 +1655,23 @@  static inline bool vma_is_shared_maywrite(const struct vm_area_struct *vma)
  */
 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, mappings which are not mm-managed 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_mm_managed(flags))
+		return false;
+	/* VMA explicitly marked as being unmergeable. */
+	if (vma_flags_test(flags, VMA_DONTEXPAND_BIT))
+		return false;
+
+	return true;
 }
 
 /**
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index a6a8e53c4b38..89c645a6ad60 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -1665,7 +1665,34 @@  static inline bool file_is_dev_zero(const struct file *file)
 	return file && file->f_op == &zero_fops;
 }
 
+static inline bool vma_flags_is_mm_managed(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_mm_managed(const struct vm_area_struct *vma)
+{
+	return vma_flags_is_mm_managed(&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 a VMA's flags and fields completely describe
+	 * its state.
+	 *
+	 * However, mappings which are not mm-managed 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_mm_managed(flags))
+		return false;
+	/* VMA explicitly marked as being unmergeable. */
+	if (vma_flags_test(flags, VMA_DONTEXPAND_BIT))
+		return false;
+
+	return true;
 }