[PATCH 00/15] mm/rmap: index MAP_PRIVATE file-backed folios by virt pgoff

[PATCH 00/15] mm/rmap: index MAP_PRIVATE file-backed folios by virt pgoff

[Lorenzo Stoakes (ARM)]

In memory management we've managed to manufacture a great deal of confusion
around the concept of anonymous memory. We have:

1. 'Pure anon' memory - anonymous VMAs whose folios are anonymous and
   swap-backed (thus for reclaim purposes, treated as anonymous). These are
   simple enough.

2. shmem - file-backed VMAs, file-backed folios (from rmap perspective) so
   present in the page cache and mapped by an address_space object, but
   whose folios are also swap-backed (thus treated as anonymous for reclaim
   purposes).

3. MAP_PRIVATE-mapped /dev/zero - a strange beast whose VMAs have
   vma->vm_file set, but whose mmap_prepare callback clears vma->vm_ops to
   satisfy vma_is_anonymous(), which results in VMAs that were mmap()'d
   referencing a file and whose VMAs reference a file, but are in every other
   sense anonymous, including the folios.

4. Other MAP_PRIVATE-file backed mappings - These possess file-backed VMAs
   and have file-backed folios until CoW'd, at which point those CoW'd
   folios are anonymous.

This series focuses upon issue 4.

In order for us to traverse VMAs using the reverse mapping, we require two
fields - folio->mapping and folio->index. The first tells the rmap code
where to look for VMAs, and the second tells it at which offset the folio
starts within the referenced object.

For anonymous folios, folio->mapping points at an anon_vma object. For
file-backed folios, it points at an address_space. And:

* For file-backed folios folio->index is simply the page offset of the start
  of the folio within the file.

* For anonymous folios belonging to pure anon mappings, folio->index is
  equal to the virtual page offset of the folio.

* For anonymous folios belonging to file-backed mappings (i.e. CoW'd folios
  of a MAP_PRIVATE file-backed mapping), folio->index is equal to the file
  page offset.

This series establishes a new virtual page offset property of VMAs to
allow us to map anonymous folios at their virtual page offset, consistent
with pure anon.

The purpose of doing so is to lay the foundations for the scalable CoW
work. This is necessary because firstly the approach first looks in the
maple tree for the VMA located at folio->index << PAGE_SHIFT, before
falling back to looking up tracked remaps if necessary.

The MAP_PRIVATE file-backed case means that folio indices will very often
conflict with one another and this remap tracking becomes substantially
more contended, and of course the fast path can never be used.

This also makes it possible, in future, to unshare anonymously mapped
folios with deep fork hierarchies on remap, eliminating the need for remap
tracking in the vast majority of cases.

Similar to page offset of pure anonymous VMAs, we update the virtual page
offset of unfaulted file-backed VMAs on remap, but do not once
CoW'd:(i.e. vma->anon_vma is non-NULL).

Overall, there is little impact on mergeability - for shared file-backed
mappings, we treat the anonymous page offset as equal to the file-backed
one (via vma_start_anon_pgoff()), so merge behaviour remains the same
there.

The only impact is on MAP_PRIVATE-mapped file-backed mappings, which must
now match on virtual page offset as well as file page offset to be merged.

To fail to merge like this would require CoW'ing the mapping, then finding
another VMA with identical file and compatible page offset to remap next
to. This is therefore very much an edge case that should have very little
impact (and which scalable CoW may very well address in any case).

We also address the outlier case of MAP_PRIVATE-/dev/zero mappings which
have file page offset but satisfy vma_is_anonymous() by making them truly
anonymous.

This is low-risk as for anything meaningful these mappings behave
anonymously, but it is very beneficial to do so as we eliminate an odd
corner case, and those are notorious for attracting subtle bugs.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
v1:
- Rebased onto mm-new.
- Dependent series heavily reviewed and looks highly likely to land, so
  un-RFC.
- Added explicit check for /dev/zero and removed ability for arbitrary
  mmap/mmap_prepare hooks to make themselves anonymous.
- Made MAP_PRIVATE-/dev/zero mappings truly anonymous.
- Added MAP_PRIVATE file-backed mapping merge test to selftests.
- Added a MAP_PRIVATE-/dev/zero VMA userland test to assert that the VMA
  really is made anonymous.
- Added MAP_PRIVATE-/dev/zero merge tests to selftests.
- Fixed missed virtual page index site in try_to_merge_with_ksm_page().
- Updated folio_within_range() to use virtual page offset for anon
  folio. This had no impact as it is only called for large folios at the
  moment (and MAP_PRIVATE-file backed mappings can't currently be backed by
  a large folio) but making the change now protects us for the future.
- Fixed typos etc.

RFC:
https://patch.msgid.link/cover.1782745153.git.ljs@kernel.org

To: Andrew Morton <akpm@linux-foundation.org>
To: David Hildenbrand <david@kernel.org>
To: "Liam R. Howlett" <liam@infradead.org>
To: Vlastimil Babka <vbabka@kernel.org>
To: Mike Rapoport <rppt@kernel.org>
To: Suren Baghdasaryan <surenb@google.com>
To: Michal Hocko <mhocko@suse.com>
To: Jann Horn <jannh@google.com>
To: Pedro Falcato <pfalcato@suse.de>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
To: Miaohe Lin <linmiaohe@huawei.com>
To: Naoya Horiguchi <nao.horiguchi@gmail.com>
To: Rik van Riel <riel@surriel.com>
To: Harry Yoo <harry@kernel.org>
To: Lance Yang <lance.yang@linux.dev>
To: Kees Cook <kees@kernel.org>
To: Zi Yan <ziy@nvidia.com>
To: Baolin Wang <baolin.wang@linux.alibaba.com>
To: Nico Pache <npache@redhat.com>
To: Ryan Roberts <ryan.roberts@arm.com>
To: Dev Jain <dev.jain@arm.com>
To: Barry Song <baohua@kernel.org>
To: Usama Arif <usama.arif@linux.dev>
To: Matthew Brost <matthew.brost@intel.com>
To: Joshua Hahn <joshua.hahnjy@gmail.com>
To: Rakie Kim <rakie.kim@sk.com>
To: Byungchul Park <byungchul@sk.com>
To: Gregory Price <gourry@gourry.net>
To: Ying Huang <ying.huang@linux.alibaba.com>
To: Alistair Popple <apopple@nvidia.com>
To: Peter Xu <peterx@redhat.com>
To: Xu Xin <xu.xin16@zte.com.cn>
To: Chengming Zhou <chengming.zhou@linux.dev>
To: Arnd Bergmann <arnd@arndb.de>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: ljs@kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org

---
Lorenzo Stoakes (ARM) (15):
      mm/vma: introduce VMA virtual page offset field and add helpers
      mm: introduce linear_virt_page_index()
      mm: abstract vma_address() and introduce vma_anon_address()
      mm: update print_bad_page_map() to show virtual page index
      mm: introduce and use vma_filebacked_address()
      mm: propagate VMA virtual page offset on map, remap, split + merge
      mm/rmap: track whether the page VMA mapped walk is anonymous
      mm: introduce and use linear_folio_page_index()
      mm/rmap: use virt pgoff for MAP_PRIVATE file-backed anon folios
      tools/testing/vma: expand VMA merge tests to assert virt pgoff
      tools/testing/selftests/mm: test virtual page offset merge behaviour
      mm/vma: only permit MAP_PRIVATE /dev/zero to be mapped anonymous
      mm/vma: make MAP_PRIVATE-mapped /dev/zero mappings truly anonymous
      tools/testing/vma: add test to assert MAP_PRIVATE-/dev/zero is anon
      tools/testing/selftests/mm: add MAP_PRIVATE-/dev/zero merge tests

 drivers/char/mem.c                 |   8 +-
 include/linux/mm.h                 |  74 ++++++++++++++---
 include/linux/mm_types.h           |   4 +
 include/linux/pagemap.h            |  66 +++++++++++++++
 include/linux/rmap.h               |   2 +
 mm/huge_memory.c                   |   3 +-
 mm/internal.h                      |  76 ++++++++++++-----
 mm/interval_tree.c                 |   4 +-
 mm/ksm.c                           |   7 +-
 mm/memory-failure.c                |   4 +-
 mm/memory.c                        |   8 +-
 mm/migrate.c                       |   6 +-
 mm/mremap.c                        |   6 +-
 mm/page_vma_mapped.c               |   6 +-
 mm/rmap.c                          |  23 +++---
 mm/userfaultfd.c                   |   6 +-
 mm/vma.c                           | 116 ++++++++++++++++++++------
 mm/vma.h                           | 144 +++++++++++++++++++++++++--------
 mm/vma_exec.c                      |   2 +-
 mm/vma_init.c                      |   1 +
 mm/vma_internal.h                  |   1 +
 tools/testing/selftests/mm/merge.c | 161 +++++++++++++++++++++++++++++++++++++
 tools/testing/vma/include/dup.h    |  77 ++++++++++++++++++
 tools/testing/vma/shared.c         |   3 +-
 tools/testing/vma/tests/merge.c    |  22 ++++-
 tools/testing/vma/tests/mmap.c     |  49 +++++++++++
 tools/testing/vma/tests/vma.c      |   4 +-
 tools/testing/vma/vma_internal.h   |   1 +
 28 files changed, 764 insertions(+), 120 deletions(-)
---
base-commit: 5093dba1014c1d7f7e247fd118f0fa8f22136046
change-id: 20260711-b4-scalable-cow-virt-pgoff-a0cc0eb14bc6

Cheers,
-- 
Lorenzo Stoakes (ARM) <ljs@kernel.org>

[PATCH 01/15] mm/vma: introduce VMA virtual page offset field and add helpers

[Lorenzo Stoakes (ARM)]

This patch establishes fields within the vm_area_struct type to store the
virtual page offset of VMAs.

The virtual page offset of a VMA is equal to vma->vm_start >> PAGE_SHIFT if
they are unfaulted or were not remapped, otherwise it is equal to this
value at the point of first fault.

Currently, anonymous folios belonging to CoW'd MAP_PRIVATE-mapped
file-backed VMAs are tracked by their file offset. By adding virtual offset
as a property of VMAs, we can now track them by their virtual page offset
instead.

By tracking this, we provide the means by which to eliminate this
inconsistency, and more importantly lay the foundations for future work for
the scalable CoW anonymous rmap rework.

This patch simply adds the fields and some simple helpers. Subsequent
patches will update mm code to make use of these fields correctly.

The fields chosen are packed in the VMA such that, for 64-bit kernel
builds, no additional space is taken up.

The first field is present on cacheline 0 containing key VMA fields, and
the second on cacheline 3, which contains file-backed reverse mapping
fields.

Given the relative time spent accessing reverse mapping fields as well as
updating them, there shouldn't be any performance impact here from false
sharing.

Update the VMA userland tests to account for this change.

No callsites are updated yet, so no functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 include/linux/mm.h              | 59 +++++++++++++++++++++++++++++++++++++++++
 include/linux/mm_types.h        |  4 +++
 mm/vma.h                        | 14 ++++++++++
 mm/vma_init.c                   |  1 +
 tools/testing/vma/include/dup.h | 26 ++++++++++++++++++
 5 files changed, 104 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 87feaa5a2b78..59b98cc60402 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4393,6 +4393,65 @@ static inline pgoff_t vma_last_pgoff(const struct vm_area_struct *vma)
 	return vma_end_pgoff(vma) - 1;
 }
 
+/**
+ * vma_start_virt_pgoff() - Get the virtual page offset of the start of @vma
+ * @vma: The VMA whose virtual page offset is required.
+ *
+ * If unfaulted, then this is vma->vm_start >> PAGE_SHIFT, if faulted then the
+ * virtual page offset at the time of first fault.
+ *
+ * If the VMA is anonymous, this returns the same value as vma_start_pgoff().
+ *
+ * This value is used for tracking MAP_PRIVATE file-backed mappings by their
+ * virtual page offset.
+ *
+ * Returns: The virtual page offset of the start of @vma.
+ */
+static inline pgoff_t vma_start_virt_pgoff(const struct vm_area_struct *vma)
+{
+	pgoff_t pgoff = 0;
+
+#ifdef CONFIG_64BIT
+	pgoff += vma->__vm_virt_pgoff_hi;
+	pgoff <<= 32;
+#endif
+	pgoff += vma->__vm_virt_pgoff_lo;
+	return pgoff;
+}
+
+/**
+ * vma_end_virt_pgoff() - Get the virtual page offset of the exclusive end of
+ * @vma.
+ * @vma: The VMA whose end virtual page offset is required.
+ *
+ * This returns the virtual exclusive end page offset of @vma, which is useful
+ * for expressing page offset ranges.
+ *
+ * See the description of vma_start_virt_pgoff() for a description of VMA
+ * virtual page offsets.
+ *
+ * Returns: The exclusive end virtual page offset of @vma.
+ */
+static inline pgoff_t vma_end_virt_pgoff(const struct vm_area_struct *vma)
+{
+	return vma_start_virt_pgoff(vma) + vma_pages(vma);
+}
+
+/**
+ * vma_last_virt_pgoff() - Get the virtual page offset of the last page in
+ * @vma.
+ * @vma: The VMA whose last virtual page offset is required.
+ *
+ * See the description of vma_start_virt_pgoff() for a description of VMA
+ * virtual page offsets.
+ *
+ * Returns: The last virtual page offset of @vma.
+ */
+static inline pgoff_t vma_last_virt_pgoff(const struct vm_area_struct *vma)
+{
+	return vma_end_virt_pgoff(vma) - 1;
+}
+
 static inline unsigned long vma_desc_size(const struct vm_area_desc *desc)
 {
 	return desc->end - desc->start;
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 939b5ea8c9e0..2710628059b1 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -967,6 +967,7 @@ struct vm_area_struct {
 	 */
 	unsigned int vm_lock_seq;
 #endif
+	unsigned int __vm_virt_pgoff_lo; /* Low 32-bits of virtual pgoff. */
 	/*
 	 * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
 	 * list, after a COW of one of the file pages.	A MAP_SHARED vma
@@ -1041,6 +1042,9 @@ struct vm_area_struct {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map vmlock_dep_map;
 #endif
+#endif
+#ifdef CONFIG_64BIT
+	unsigned int __vm_virt_pgoff_hi;  /* High 32-bits of virtual pgoff. */
 #endif
 	/*
 	 * For areas with an address space and backing store,
diff --git a/mm/vma.h b/mm/vma.h
index 0bc7d521e976..04c5c1c546f6 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -283,6 +283,20 @@ static inline void vma_set_pgoff(struct vm_area_struct *vma, pgoff_t pgoff)
 	vma->vm_pgoff = pgoff;
 }
 
+static inline void __vma_set_virt_pgoff(struct vm_area_struct *vma, pgoff_t pgoff)
+{
+#ifdef CONFIG_64BIT
+	vma->__vm_virt_pgoff_hi = pgoff >> 32;
+#endif
+	vma->__vm_virt_pgoff_lo = pgoff & GENMASK(31, 0);
+}
+
+static inline void vma_set_virt_pgoff(struct vm_area_struct *vma, pgoff_t pgoff)
+{
+	vma_assert_can_modify(vma);
+	__vma_set_virt_pgoff(vma, pgoff);
+}
+
 static inline void vma_add_pgoff(struct vm_area_struct *vma, pgoff_t delta)
 {
 	vma_assert_can_modify(vma);
diff --git a/mm/vma_init.c b/mm/vma_init.c
index 715feee283f0..710b18849a36 100644
--- a/mm/vma_init.c
+++ b/mm/vma_init.c
@@ -51,6 +51,7 @@ static void vm_area_init_from(const struct vm_area_struct *src,
 	dest->vm_end = src->vm_end;
 	dest->anon_vma = src->anon_vma;
 	dest->vm_pgoff = vma_start_pgoff(src);
+	__vma_set_virt_pgoff(dest, vma_start_virt_pgoff(src));
 	dest->vm_file = src->vm_file;
 	dest->vm_private_data = src->vm_private_data;
 	vm_flags_init(dest, src->vm_flags);
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index c52b23773cd2..00d416d79ec1 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -577,6 +577,7 @@ struct vm_area_struct {
 	 */
 	unsigned int vm_lock_seq;
 #endif
+	unsigned int __vm_virt_pgoff_lo;
 
 	/*
 	 * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
@@ -612,6 +613,9 @@ struct vm_area_struct {
 #ifdef CONFIG_PER_VMA_LOCK
 	/* Unstable RCU readers are allowed to read this. */
 	refcount_t vm_refcnt;
+#endif
+#ifdef CONFIG_64BIT
+	unsigned int __vm_virt_pgoff_hi;
 #endif
 	/*
 	 * For areas with an address space and backing store,
@@ -1320,6 +1324,28 @@ static inline pgoff_t vma_end_pgoff(const struct vm_area_struct *vma)
 	return vma_start_pgoff(vma) + vma_pages(vma);
 }
 
+static inline pgoff_t vma_start_virt_pgoff(const struct vm_area_struct *vma)
+{
+	pgoff_t pgoff = 0;
+
+#ifdef CONFIG_64BIT
+	pgoff += vma->__vm_virt_pgoff_hi;
+	pgoff <<= 32;
+#endif
+	pgoff += vma->__vm_virt_pgoff_lo;
+	return pgoff;
+}
+
+static inline pgoff_t vma_end_virt_pgoff(const struct vm_area_struct *vma)
+{
+	return vma_start_virt_pgoff(vma) + vma_pages(vma);
+}
+
+static inline pgoff_t vma_last_virt_pgoff(const struct vm_area_struct *vma)
+{
+	return vma_end_virt_pgoff(vma) - 1;
+}
+
 static inline int vfs_mmap_prepare(struct file *file, struct vm_area_desc *desc)
 {
 	return file->f_op->mmap_prepare(desc);

-- 
2.55.0

[PATCH 02/15] mm: introduce linear_virt_page_index()

[Lorenzo Stoakes (ARM)]

This function provides the virtual equivalent of linear_page_index(),
instead offsetting based on the virtual page offset of the VMA.

It is valid only for anonymous or MAP_PRIVATE file-backed mappings. It must
not be called for shared file-backed mappings.

For pure anon VMAs, this will be equal to linear_page_index().

We implement the algorithm in __linear_virt_page_index(), which is provided
for internal mm code that might be interacting with shared VMAs.

In linear_virt_page_index() we assert that both of these invariants are
true.

Note that MAP_PRIVATE-/dev/zero mappings will satisfy vma_is_anonymous()
but not fulfill this invariant, so when asserting this we check
vma->vm_file to account for this.

We do not update callsites yet, so no functional change intended.

Also const-ify vma_is_anonymous() to make it compatible with the
const-ified linear_virt_page_index().

VMA userland tests are updated accordingly.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 include/linux/mm.h              |  2 +-
 include/linux/pagemap.h         | 41 +++++++++++++++++++++++++++++++++++++++++
 tools/testing/vma/include/dup.h | 22 ++++++++++++++++++++++
 3 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 59b98cc60402..b6503b5f0010 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1556,7 +1556,7 @@ static inline void vma_desc_set_anonymous(struct vm_area_desc *desc)
 	desc->vm_ops = NULL;
 }
 
-static inline bool vma_is_anonymous(struct vm_area_struct *vma)
+static inline bool vma_is_anonymous(const struct vm_area_struct *vma)
 {
 	return !vma->vm_ops;
 }
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c6fc783aaee5..81da91e103b3 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1101,6 +1101,47 @@ static inline pgoff_t linear_page_index(const struct vm_area_struct *vma,
 	return pgoff;
 }
 
+static inline pgoff_t __linear_virt_page_index(const struct vm_area_struct *vma,
+					       const unsigned long address)
+{
+	pgoff_t pgoff;
+
+	pgoff = linear_page_delta(vma, address);
+	pgoff += vma_start_virt_pgoff(vma);
+	return pgoff;
+}
+
+/**
+ * linear_virt_page_index() - Determine the absolute virtual page offset of
+ * @address within @vma.
+ * @vma: An anonymous or MAP_PRIVATE file-backed VMA in which @address resides.
+ * @address: The address whose absolute page offset is required.
+ *
+ * This returns the virtual page offset of @address, which is the page offset
+ * the address possessed at the time the VMA was first faulted.
+ *
+ * For anonymous mappings, this returns the same value as linear_page_index().
+ *
+ * For MAP_PRIVATE file-backed mappings, this returns the virtual page offset of
+ * @address, which is the page offset the address possessed at the time the VMA
+ * was first faulted.
+ *
+ * It is not valid to call this function for shared file-backed mappings.
+ *
+ * Returns: The absolute virtual page offset of @address within @vma.
+ */
+static inline pgoff_t linear_virt_page_index(const struct vm_area_struct *vma,
+					     const unsigned long address)
+{
+	const pgoff_t pgoff = __linear_virt_page_index(vma, address);
+
+	VM_WARN_ON_ONCE(vma_test(vma, VMA_SHARED_BIT));
+	if (!vma->vm_file) /* Is anonymous except MAP_PRIVATE-/dev/zero */
+		VM_WARN_ON_ONCE(pgoff != linear_page_index(vma, address));
+
+	return pgoff;
+}
+
 struct wait_page_key {
 	struct folio *folio;
 	int bit_nr;
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 00d416d79ec1..51605ade06fb 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -1610,3 +1610,25 @@ static inline pgprot_t vma_get_page_prot(const struct vm_area_struct *vma)
 {
 	return vma_flags_to_page_prot(vma->flags);
 }
+
+static inline pgoff_t __linear_virt_page_index(const struct vm_area_struct *vma,
+					       const unsigned long address)
+{
+	pgoff_t pgoff;
+
+	pgoff = linear_page_delta(vma, address);
+	pgoff += vma_start_virt_pgoff(vma);
+	return pgoff;
+}
+
+static inline pgoff_t linear_virt_page_index(const struct vm_area_struct *vma,
+					     const unsigned long address)
+{
+	const pgoff_t pgoff = __linear_virt_page_index(vma, address);
+
+	VM_WARN_ON_ONCE(vma_test(vma, VMA_SHARED_BIT));
+	if (!vma->vm_file) /* Is anonymous except MAP_PRIVATE-/dev/zero */
+		VM_WARN_ON_ONCE(pgoff != linear_page_index(vma, address));
+
+	return pgoff;
+}

-- 
2.55.0

[PATCH 03/15] mm: abstract vma_address() and introduce vma_anon_address()

[Lorenzo Stoakes (ARM)]

Introduce __vma_address() which abstracts the VMA start page offset field
as pgoff_start, then update vma_address() to use it.

Then introduce vma_anon_address() which does the equivalent of
vma_address(), only using the virtual page offset of the VMA rather than
the file-backed one.

Also add an assert to ensure that the function is not called for mappings
which are file-backed but not MAP_PRIVATE to ensure it is only used in the
correct places.

This will be necessary for determining the address of a folio's index
within a VMA when the folio belongs to a MAP_PRIVATE file-backed VMA but
has been CoW'd, and thus is anonymous, once the anonymous VMA page offset
field is used for the reverse mapping.

No callers are updated, so no functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 mm/internal.h | 49 +++++++++++++++++++++++++++++++++++++------------
 1 file changed, 37 insertions(+), 12 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index f26423de4ca2..04acfeffa066 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1005,19 +1005,9 @@ void mlock_drain_remote(int cpu);
 
 extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
 
-/**
- * vma_address - Find the virtual address a page range is mapped at
- * @vma: The vma which maps this object.
- * @pgoff: The page offset within its object.
- * @nr_pages: The number of pages to consider.
- *
- * If any page in this range is mapped by this VMA, return the first address
- * where any of these pages appear.  Otherwise, return -EFAULT.
- */
-static inline unsigned long vma_address(const struct vm_area_struct *vma,
-		pgoff_t pgoff, unsigned long nr_pages)
+static inline unsigned long __vma_address(const struct vm_area_struct *vma,
+		pgoff_t pgoff, pgoff_t pgoff_start, unsigned long nr_pages)
 {
-	const pgoff_t pgoff_start = vma_start_pgoff(vma);
 	unsigned long address;
 
 	if (pgoff >= pgoff_start) {
@@ -1035,6 +1025,41 @@ static inline unsigned long vma_address(const struct vm_area_struct *vma,
 	return address;
 }
 
+/**
+ * vma_address - Find the virtual address a page range is mapped at.
+ * @vma: The vma which maps this object.
+ * @pgoff: The page offset within its object.
+ * @nr_pages: The number of pages to consider.
+ *
+ * If any page in this range is mapped by this VMA, return the first address
+ * where any of these pages appear.  Otherwise, return -EFAULT.
+ */
+static inline unsigned long vma_address(const struct vm_area_struct *vma,
+		pgoff_t pgoff, unsigned long nr_pages)
+{
+	return __vma_address(vma, pgoff, vma_start_pgoff(vma), nr_pages);
+}
+
+/**
+ * vma_anon_address - Find the address an anonymous folio with index @pgoff_virt
+ * is mapped at.
+ * @vma: The vma which maps this object.
+ * @pgoff_virt: The virtual page index belonging to the folio.
+ * @nr_pages: The number of pages to consider.
+ *
+ * This is only valid for anonymous or MAP_PRIVATE-mapped file-backed VMAs.
+ *
+ * Returns: If any page in this range is mapped by this VMA, return the first address
+ * where any of these pages appear. Otherwise, return -EFAULT.
+ */
+static inline unsigned long vma_anon_address(const struct vm_area_struct *vma,
+		pgoff_t pgoff_virt, unsigned long nr_pages)
+{
+	VM_WARN_ON_ONCE(!vma_is_anonymous(vma) && vma_test(vma, VMA_SHARED_BIT));
+
+	return __vma_address(vma, pgoff_virt, vma_start_virt_pgoff(vma), nr_pages);
+}
+
 /*
  * Then at what user virtual address will none of the range be found in vma?
  * Assumes that vma_address() already returned a good starting address.

-- 
2.55.0

[PATCH 04/15] mm: update print_bad_page_map() to show virtual page index

[Lorenzo Stoakes (ARM)]

This is potentially useful debugging information and matches the existing
page offset provided.

Use the raw __linear_virt_page_index() function so as to always output this
value regardless of whether the mapping is file-backed or not.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 mm/memory.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index d5e87624f692..56b244552f13 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -631,13 +631,14 @@ static void print_bad_page_map(struct vm_area_struct *vma,
 {
 	struct address_space *mapping;
 	char entry_str[PTVAL_STR_MAX];
-	pgoff_t index;
+	pgoff_t index, virt_index;
 
 	if (is_bad_page_map_ratelimited())
 		return;
 
 	mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
 	index = linear_page_index(vma, addr);
+	virt_index = __linear_virt_page_index(vma, addr);
 
 	ptval_bytes_to_hex_str(entry_str, sizeof(entry_str), entry, entry_size);
 	pr_alert("BUG: Bad page map in process %s  %s:%s", current->comm,
@@ -645,8 +646,9 @@ static void print_bad_page_map(struct vm_area_struct *vma,
 	__print_bad_page_map_pgtable(vma->vm_mm, addr);
 	if (page)
 		dump_page(page, "bad page map");
-	pr_alert("addr:%px vm_flags:%08lx anon_vma:%px mapping:%px index:%lx\n",
-		 (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
+	pr_alert("addr:%px vm_flags:%08lx anon_vma:%px mapping:%px index:%lx virt_index:%lx\n",
+		 (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index,
+		 virt_index);
 	pr_alert("file:%pD fault:%ps mmap:%ps mmap_prepare: %ps read_folio:%ps\n",
 		 vma->vm_file,
 		 vma->vm_ops ? vma->vm_ops->fault : NULL,

-- 
2.55.0

[PATCH 05/15] mm: introduce and use vma_filebacked_address()

[Lorenzo Stoakes (ARM)]

In cases where we know that the VMA is file-backed, use
vma_filebacked_address() rather than vma_address().

This lays the foundation for using the virtual page offset for anonymous
VMAs via vma_anon_address().

Also add an assert to ensure that the VMA whose address is required is not
anonymous.

No functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 mm/internal.h        | 18 ++++++++++++++++++
 mm/memory-failure.c  |  4 ++--
 mm/page_vma_mapped.c |  6 +++++-
 mm/rmap.c            | 10 ++++++----
 4 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 04acfeffa066..73f90aaa979d 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1025,6 +1025,24 @@ static inline unsigned long __vma_address(const struct vm_area_struct *vma,
 	return address;
 }
 
+/**
+ * vma_filebacked_address - Find the virtual address a file-backed page range is
+ * mapped at.
+ * @vma: The vma which maps this object.
+ * @pgoff: The page offset within its object.
+ * @nr_pages: The number of pages to consider.
+ *
+ * Returns: If any page in this range is mapped by this VMA, return the first
+ * address where any of these pages appear.  Otherwise, return -EFAULT.
+ */
+static inline unsigned long vma_filebacked_address(const struct vm_area_struct *vma,
+		pgoff_t pgoff, unsigned long nr_pages)
+{
+	VM_WARN_ON_ONCE(vma_is_anonymous(vma));
+
+	return __vma_address(vma, pgoff, vma_start_pgoff(vma), nr_pages);
+}
+
 /**
  * vma_address - Find the virtual address a page range is mapped at.
  * @vma: The vma which maps this object.
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index aaf14608b30e..a8b03e2920ba 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -620,7 +620,7 @@ static void add_to_kill_fsdax(struct task_struct *tsk, const struct page *p,
 			      struct vm_area_struct *vma,
 			      struct list_head *to_kill, pgoff_t pgoff)
 {
-	unsigned long addr = vma_address(vma, pgoff, 1);
+	unsigned long addr = vma_filebacked_address(vma, pgoff, 1);
 	__add_to_kill(tsk, p, vma, to_kill, addr);
 }
 
@@ -2265,7 +2265,7 @@ static void add_to_kill_pgoff(struct task_struct *tsk,
 	}
 
 	/* Check for pgoff not backed by struct page */
-	tk->addr = vma_address(vma, pgoff, 1);
+	tk->addr = vma_filebacked_address(vma, pgoff, 1);
 	tk->size_shift = PAGE_SHIFT;
 
 	if (tk->addr == -EFAULT)
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index d7670ba4147b..081e483cc7bf 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -356,6 +356,7 @@ unsigned long page_mapped_in_vma(const struct page *page,
 		struct vm_area_struct *vma)
 {
 	const struct folio *folio = page_folio(page);
+	const pgoff_t pgoff = page_pgoff(folio, page);
 	struct page_vma_mapped_walk pvmw = {
 		.pfn = page_to_pfn(page),
 		.nr_pages = 1,
@@ -363,7 +364,10 @@ unsigned long page_mapped_in_vma(const struct page *page,
 		.flags = PVMW_SYNC,
 	};
 
-	pvmw.address = vma_address(vma, page_pgoff(folio, page), 1);
+	if (folio_test_anon(folio))
+		pvmw.address = vma_address(vma, pgoff, 1);
+	else
+		pvmw.address = vma_filebacked_address(vma, pgoff, 1);
 	if (pvmw.address == -EFAULT)
 		goto out;
 	if (!page_vma_mapped_walk(&pvmw))
diff --git a/mm/rmap.c b/mm/rmap.c
index ad820fe86f7d..5798427d007f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -865,14 +865,15 @@ unsigned long page_address_in_vma(const struct folio *folio,
 		if (!vma->anon_vma || !anon_vma ||
 		    vma->anon_vma->root != anon_vma->root)
 			return -EFAULT;
+		/* KSM folios don't reach here because of the !anon_vma check */
+		return vma_address(vma, page_pgoff(folio, page), 1);
 	} else if (!vma->vm_file) {
 		return -EFAULT;
 	} else if (vma->vm_file->f_mapping != folio->mapping) {
 		return -EFAULT;
 	}
 
-	/* KSM folios don't reach here because of the !anon_vma check */
-	return vma_address(vma, page_pgoff(folio, page), 1);
+	return vma_filebacked_address(vma, page_pgoff(folio, page), 1);
 }
 
 /*
@@ -1321,7 +1322,7 @@ int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
 	if (invalid_mkclean_vma(vma, NULL))
 		return 0;
 
-	pvmw.address = vma_address(vma, pgoff, nr_pages);
+	pvmw.address = vma_filebacked_address(vma, pgoff, nr_pages);
 	VM_BUG_ON_VMA(pvmw.address == -EFAULT, vma);
 
 	return page_vma_mkclean_one(&pvmw);
@@ -3100,7 +3101,8 @@ static void __rmap_walk_file(struct folio *folio, struct address_space *mapping,
 	}
 lookup:
 	mapping_rmap_tree_foreach(vma, mapping, pgoff_start, pgoff_end) {
-		unsigned long address = vma_address(vma, pgoff_start, nr_pages);
+		unsigned long address = vma_filebacked_address(vma, pgoff_start,
+							       nr_pages);
 
 		VM_BUG_ON_VMA(address == -EFAULT, vma);
 		cond_resched();

-- 
2.55.0

[PATCH 06/15] mm: propagate VMA virtual page offset on map, remap, split + merge

[Lorenzo Stoakes (ARM)]

We must correctly update VMA virtual page offset state on all VMA
operations that would result in it changing, with special attention given
to remapping.

We cover most cases by simply updating vma_set_range() to do so (with a new
virtual page offset parameter), but also notably must update the merging
and mapping logic to propagate this parameter correctly.

The remap logic remains the same - we may update the virtual page offset if
the VMA is unfaulted, but now this applies to MAP_PRIVATE file-backed
mappings too, so we update the code to reflect this.

Note that we use __linear_virt_page_index() upon remap as the VMA may be
shared, in order that we update the field consistently regardless of VMA
type.

Also while we're here, replace a VM_BUG_ON_VMA() with a
VM_WARN_ON_ONCE_VMA().

We also introduce vma_anon_pgoff_addr(), vma_start_anon_pgoff(), and
vma_end_anon_pgoff() which differ from their virtual page offset
equivalents in that a shared file-backed mapping returns its file page
offset otherwise the virtual page offset is used.

This means we don't predicate merges for shared file-backed mappings on
virtual page offset.

We simply ensure state is correctly propagated here, so no functional
changes are intended.

Finally, we update insert_vm_struct() to correctly set the virtual page
offset on insertion of a VMA.

Also update VMA userland tests to reflect this change.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 mm/mremap.c                      |   6 +-
 mm/vma.c                         |  56 ++++++++++++-----
 mm/vma.h                         | 127 ++++++++++++++++++++++++++++++---------
 mm/vma_exec.c                    |   2 +-
 tools/testing/vma/shared.c       |   3 +-
 tools/testing/vma/tests/merge.c  |   4 +-
 tools/testing/vma/tests/vma.c    |   4 +-
 tools/testing/vma/vma_internal.h |   1 +
 8 files changed, 152 insertions(+), 51 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index b64aa1f6e07e..f07fc4e3ef2e 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -1265,7 +1265,9 @@ static void unmap_source_vma(struct vma_remap_struct *vrm)
 static int copy_vma_and_data(struct vma_remap_struct *vrm,
 			     struct vm_area_struct **new_vma_ptr)
 {
-	const unsigned long new_pgoff = linear_page_index(vrm->vma, vrm->addr);
+	const pgoff_t new_pgoff = linear_page_index(vrm->vma, vrm->addr);
+	const pgoff_t new_virt_pgoff =
+		__linear_virt_page_index(vrm->vma, vrm->addr);
 	struct vm_area_struct *vma = vrm->vma;
 	struct vm_area_struct *new_vma;
 	unsigned long moved_len;
@@ -1273,7 +1275,7 @@ static int copy_vma_and_data(struct vma_remap_struct *vrm,
 	PAGETABLE_MOVE(pmc, NULL, NULL, vrm->addr, vrm->new_addr, vrm->old_len);
 
 	new_vma = copy_vma(&vma, vrm->new_addr, vrm->new_len, new_pgoff,
-			   &pmc.need_rmap_locks);
+			   new_virt_pgoff, &pmc.need_rmap_locks);
 	if (!new_vma) {
 		vrm_uncharge(vrm);
 		*new_vma_ptr = NULL;
diff --git a/mm/vma.c b/mm/vma.c
index b5bc3eec961c..e45d43493446 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -18,6 +18,7 @@ struct mmap_state {
 	unsigned long addr;
 	unsigned long end;
 	pgoff_t pgoff;
+	pgoff_t virt_pgoff;
 	unsigned long pglen;
 	union {
 		vm_flags_t vm_flags;
@@ -46,13 +47,22 @@ struct mmap_state {
 	bool file_doesnt_need_get :1;
 };
 
-#define MMAP_STATE(name, mm_, vmi_, addr_, len_, pgoff_, vma_flags_, file_) \
+static inline pgoff_t map_anon_pgoff(const struct mmap_state *map)
+{
+	if (vma_flags_test(&map->vma_flags, VMA_SHARED_BIT))
+		return map->pgoff;
+
+	return map->virt_pgoff;
+}
+
+#define MMAP_STATE(name, mm_, vmi_, addr_, len_, pgoff_, virt_pgoff_, vma_flags_, file_) \
 	struct mmap_state name = {					\
 		.mm = mm_,						\
 		.vmi = vmi_,						\
 		.addr = addr_,						\
 		.end = (addr_) + (len_),				\
 		.pgoff = pgoff_,					\
+		.virt_pgoff = virt_pgoff_,				\
 		.pglen = PHYS_PFN(len_),				\
 		.vma_flags = vma_flags_,				\
 		.file = file_,						\
@@ -67,6 +77,7 @@ struct mmap_state {
 		.end = (map_)->end,					\
 		.vma_flags = (map_)->vma_flags,				\
 		.pgoff = (map_)->pgoff,					\
+		.anon_pgoff = map_anon_pgoff(map_),			\
 		.file = (map_)->file,					\
 		.prev = (map_)->prev,					\
 		.middle = vma_,						\
@@ -82,10 +93,11 @@ static void __vma_set_range(struct vm_area_struct *vma, unsigned long start,
 }
 
 static void vma_set_range(struct vm_area_struct *vma, unsigned long start,
-			  unsigned long end, pgoff_t pgoff)
+			  unsigned long end, pgoff_t pgoff, pgoff_t virt_pgoff)
 {
 	__vma_set_range(vma, start, end);
 	vma_set_pgoff(vma, pgoff);
+	vma_set_virt_pgoff(vma, virt_pgoff);
 }
 
 /* Was this VMA ever forked from a parent, i.e. maybe contains CoW mappings? */
@@ -812,7 +824,8 @@ static int commit_merge(struct vma_merge_struct *vmg)
 	 */
 	vma_adjust_trans_huge(vma, vmg->start, vmg->end,
 			      vmg->__adjust_middle_start ? vmg->middle : NULL);
-	vma_set_range(vma, vmg->start, vmg->end, vmg_start_pgoff(vmg));
+	vma_set_range(vma, vmg->start, vmg->end, vmg_start_pgoff(vmg),
+		      vmg_start_anon_pgoff(vmg));
 	vmg_adjust_set_range(vmg);
 	vma_iter_store_overwrite(vmg->vmi, vmg->target);
 
@@ -982,6 +995,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
 		vmg->start = prev->vm_start;
 		vmg->end = next->vm_end;
 		vmg->pgoff = vma_start_pgoff(prev);
+		vmg->anon_pgoff = vma_start_anon_pgoff(prev);
 
 		/*
 		 * We already ensured anon_vma compatibility above, so now it's
@@ -1000,6 +1014,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
 		 */
 		vmg->start = prev->vm_start;
 		vmg->pgoff = vma_start_pgoff(prev);
+		vmg->anon_pgoff = vma_start_anon_pgoff(prev);
 
 		if (!vmg->__remove_middle)
 			vmg->__adjust_middle_start = true;
@@ -1022,12 +1037,14 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
 		if (vmg->__remove_middle) {
 			vmg->end = next->vm_end;
 			vmg->pgoff = vma_start_pgoff(next) - pglen;
+			vmg->anon_pgoff = vma_start_anon_pgoff(next) - pglen;
 		} else {
 			/* We shrink middle and expand next. */
 			vmg->__adjust_next_start = true;
 			vmg->start = middle->vm_start;
 			vmg->end = start;
 			vmg->pgoff = vma_start_pgoff(middle);
+			vmg->anon_pgoff = vma_start_anon_pgoff(middle);
 		}
 
 		err = dup_anon_vma(next, middle, &anon_dup);
@@ -1137,6 +1154,7 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
 		vmg->start = prev->vm_start;
 		vmg->target = prev;
 		vmg->pgoff = vma_start_pgoff(prev);
+		vmg->anon_pgoff = vma_start_anon_pgoff(prev);
 
 		/*
 		 * If this merge would result in removal of the next VMA but we
@@ -1908,9 +1926,10 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
  */
 struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	unsigned long addr, unsigned long len, pgoff_t pgoff,
-	bool *need_rmap_locks)
+	pgoff_t virt_pgoff, bool *need_rmap_locks)
 {
 	struct vm_area_struct *vma = *vmap;
+	const bool is_shared = vma_test(vma, VMA_SHARED_BIT);
 	unsigned long vma_start = vma->vm_start;
 	struct mm_struct *mm = vma->vm_mm;
 	struct vm_area_struct *new_vma;
@@ -1919,11 +1938,14 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	VMG_VMA_STATE(vmg, &vmi, NULL, vma, addr, addr + len);
 
 	/*
-	 * If anonymous vma has not yet been faulted, update new pgoff
-	 * to match new location, to increase its chance of merging.
+	 * If a vma has not yet been faulted, update its virtual pgoff to match
+	 * the new location to increase its chance of merging.
 	 */
-	if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) {
-		pgoff = addr >> PAGE_SHIFT;
+	if (!vma->anon_vma && !is_shared) {
+		virt_pgoff = addr >> PAGE_SHIFT;
+
+		if (vma_is_anonymous(vma))
+			pgoff = virt_pgoff;
 		faulted_in_anon_vma = false;
 	}
 
@@ -1940,6 +1962,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 		return NULL;	/* should never get here */
 
 	vmg.pgoff = pgoff;
+	vmg.anon_pgoff = is_shared ? pgoff : virt_pgoff;
 	vmg.next = vma_iter_next_rewind(&vmi, NULL);
 	new_vma = vma_merge_copied_range(&vmg);
 
@@ -1961,7 +1984,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 			 * safe. It is only safe to keep the vm_pgoff
 			 * linear if there are no pages mapped yet.
 			 */
-			VM_BUG_ON_VMA(faulted_in_anon_vma, new_vma);
+			VM_WARN_ON_ONCE_VMA(faulted_in_anon_vma, new_vma);
 			*vmap = vma = new_vma;
 		}
 		*need_rmap_locks =
@@ -1970,7 +1993,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 		new_vma = vm_area_dup(vma);
 		if (!new_vma)
 			goto out;
-		vma_set_range(new_vma, addr, addr + len, pgoff);
+		vma_set_range(new_vma, addr, addr + len, pgoff, virt_pgoff);
 		if (vma_dup_policy(vma, new_vma))
 			goto out_free_vma;
 		if (anon_vma_clone(new_vma, vma, VMA_OP_REMAP))
@@ -2612,7 +2635,7 @@ static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap,
 	if (is_anon)
 		vma_set_anonymous(vma);
 
-	vma_set_range(vma, map->addr, map->end, map->pgoff);
+	vma_set_range(vma, map->addr, map->end, map->pgoff, map->virt_pgoff);
 	vma->flags = map->vma_flags;
 	vma->vm_page_prot = map->page_prot;
 
@@ -2801,7 +2824,8 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr,
 	struct vm_area_struct *vma = NULL;
 	bool have_mmap_prepare = file && file->f_op->mmap_prepare;
 	VMA_ITERATOR(vmi, mm, addr);
-	MMAP_STATE(map, mm, &vmi, addr, len, pgoff, vma_flags, file);
+	const pgoff_t virt_pgoff = addr >> PAGE_SHIFT;
+	MMAP_STATE(map, mm, &vmi, addr, len, pgoff, virt_pgoff, vma_flags, file);
 	struct vm_area_desc desc = {
 		.mm = mm,
 		.file = file,
@@ -2946,6 +2970,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		 unsigned long addr, unsigned long len, vma_flags_t vma_flags)
 {
 	struct mm_struct *mm = current->mm;
+	const pgoff_t pgoff = addr >> PAGE_SHIFT;
 
 	/*
 	 * Check against address space limits by the changed size
@@ -2970,7 +2995,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	 * occur after forking, so the expand will only happen on new VMAs.
 	 */
 	if (vma && vma->vm_end == addr) {
-		VMG_STATE(vmg, mm, vmi, addr, addr + len, vma_flags, PHYS_PFN(addr));
+		VMG_STATE(vmg, mm, vmi, addr, addr + len, vma_flags, pgoff, pgoff);
 
 		vmg.prev = vma;
 		/* vmi is positioned at prev, which this mode expects. */
@@ -2990,7 +3015,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		goto unacct_fail;
 
 	vma_set_anonymous(vma);
-	vma_set_range(vma, addr, addr + len, addr >> PAGE_SHIFT);
+	vma_set_range(vma, addr, addr + len, pgoff, pgoff);
 	vma->flags = vma_flags;
 	vma->vm_page_prot = vm_get_page_prot(vma_flags_to_legacy(vma_flags));
 	vma_start_write(vma);
@@ -3382,6 +3407,7 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
 		WARN_ON_ONCE(vma->anon_vma);
 		vma_set_pgoff(vma, vma->vm_start >> PAGE_SHIFT);
 	}
+	vma_set_virt_pgoff(vma, vma->vm_start >> PAGE_SHIFT);
 
 	if (vma_link(mm, vma)) {
 		if (vma_test(vma, VMA_ACCOUNT_BIT))
@@ -3437,7 +3463,7 @@ struct vm_area_struct *__install_special_mapping(
 
 	vma->vm_ops = ops;
 	vma->vm_private_data = priv;
-	vma_set_range(vma, addr, addr + len, 0);
+	vma_set_range(vma, addr, addr + len, 0, addr >> PAGE_SHIFT);
 
 	ret = insert_vm_struct(mm, vma);
 	if (ret)
diff --git a/mm/vma.h b/mm/vma.h
index 04c5c1c546f6..c1d65060071f 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -104,6 +104,7 @@ struct vma_merge_struct {
 	unsigned long start;
 	unsigned long end;
 	pgoff_t pgoff;
+	pgoff_t anon_pgoff;
 
 	union {
 		/* Temporary while VMA flags are being converted. */
@@ -237,11 +238,6 @@ static inline bool vmg_nomem(struct vma_merge_struct *vmg)
 	return vmg->state == VMA_MERGE_ERROR_NOMEM;
 }
 
-static inline pgoff_t vmg_start_pgoff(const struct vma_merge_struct *vmg)
-{
-	return vmg->pgoff;
-}
-
 static inline pgoff_t vmg_pages(const struct vma_merge_struct *vmg)
 {
 	const unsigned long size = vmg->end - vmg->start;
@@ -249,6 +245,11 @@ static inline pgoff_t vmg_pages(const struct vma_merge_struct *vmg)
 	return size >> PAGE_SHIFT;
 }
 
+static inline pgoff_t vmg_start_pgoff(const struct vma_merge_struct *vmg)
+{
+	return vmg->pgoff;
+}
+
 static inline pgoff_t vmg_end_pgoff(const struct vma_merge_struct *vmg)
 {
 	return vmg_start_pgoff(vmg) + vmg_pages(vmg);
@@ -283,6 +284,16 @@ static inline void vma_set_pgoff(struct vm_area_struct *vma, pgoff_t pgoff)
 	vma->vm_pgoff = pgoff;
 }
 
+static inline pgoff_t vmg_start_anon_pgoff(const struct vma_merge_struct *vmg)
+{
+	return vmg->anon_pgoff;
+}
+
+static inline pgoff_t vmg_end_anon_pgoff(const struct vma_merge_struct *vmg)
+{
+	return vmg_start_anon_pgoff(vmg) + vmg_pages(vmg);
+}
+
 static inline void __vma_set_virt_pgoff(struct vm_area_struct *vma, pgoff_t pgoff)
 {
 #ifdef CONFIG_64BIT
@@ -301,44 +312,102 @@ static inline void vma_add_pgoff(struct vm_area_struct *vma, pgoff_t delta)
 {
 	vma_assert_can_modify(vma);
 	vma_set_pgoff(vma, vma_start_pgoff(vma) + delta);
+	vma_set_virt_pgoff(vma, vma_start_virt_pgoff(vma) + delta);
 }
 
 static inline void vma_sub_pgoff(struct vm_area_struct *vma, pgoff_t delta)
 {
 	vma_assert_can_modify(vma);
 	vma_set_pgoff(vma, vma_start_pgoff(vma) - delta);
+	vma_set_virt_pgoff(vma, vma_start_virt_pgoff(vma) - delta);
+}
+
+/**
+ * vma_anon_pgoff_addr() - Calculates the absolute anonymous page offset of
+ * @address.
+ * @vma: The VMA whose anonymous page offset is required.
+ * @address: The address whose absolute page offset is required.
+ *
+ * If the VMA is a shared file-backed mapping, then the file-based page offset
+ * is returned.
+ *
+ * Otherwise, the virtual page offset is returned.
+ *
+ * This means that shared file-backed mappings are correctly merged based on
+ * their file page offset compatibility.
+ *
+ * Returns: The absolute anonymous page offset of @address within @vma.
+ */
+static inline pgoff_t vma_anon_pgoff_addr(const struct vm_area_struct *vma,
+					  unsigned long address)
+{
+	if (vma_test(vma, VMA_SHARED_BIT))
+		return linear_page_index(vma, address);
+
+	return linear_virt_page_index(vma, address);
+}
+
+/**
+ * vma_start_anon_pgoff() - Calculates the absolute anonymous page offset used
+ * for purposes of merge compatibility.
+ * @vma: The VMA whose anonymous page offset is required.
+ *
+ * See vma_anon_pgoff_addr().
+ *
+ * Returns: The absolute anonymous page offset of @vma for purposes of merging.
+ */
+static inline pgoff_t vma_start_anon_pgoff(const struct vm_area_struct *vma)
+{
+	return vma_anon_pgoff_addr(vma, vma->vm_start);
 }
 
-#define VMG_STATE(name, mm_, vmi_, start_, end_, vma_flags_, pgoff_)	\
+/**
+ * vma_end_anon_pgoff() - Calculates the absolute exclusive end anonymous page
+ * offset used for purposes of merge compatibility.
+ * @vma: The VMA whosse anonymous end page offset is required.
+ *
+ * See vma_start_anon_pgoff().
+ *
+ * Returns: The absolute exclusive end anonymous page offset of @vma for
+ * purposes of merging.
+ */
+static inline pgoff_t vma_end_anon_pgoff(const struct vm_area_struct *vma)
+{
+	return vma_start_anon_pgoff(vma) + vma_pages(vma);
+}
+
+#define VMG_STATE(name, mm_, vmi_, start_, end_, vma_flags_, pgoff_, anon_pgoff_) \
+	struct vma_merge_struct name = {					  \
+		.mm = mm_,							  \
+		.vmi = vmi_,							  \
+		.start = start_,						  \
+		.end = end_,							  \
+		.vma_flags = vma_flags_,					  \
+		.pgoff = pgoff_,						  \
+		.anon_pgoff = anon_pgoff_,					  \
+		.state = VMA_MERGE_START,					  \
+	}
+
+#define VMG_VMA_STATE(name, vmi_, prev_, vma_, start_, end_)		\
 	struct vma_merge_struct name = {				\
-		.mm = mm_,						\
+		.mm = vma_->vm_mm,					\
 		.vmi = vmi_,						\
+		.prev = prev_,						\
+		.middle = vma_,						\
+		.next = NULL,						\
 		.start = start_,					\
 		.end = end_,						\
-		.vma_flags = vma_flags_,				\
-		.pgoff = pgoff_,					\
+		.vm_flags = vma_->vm_flags,				\
+		.pgoff = linear_page_index(vma_, start_),		\
+		.anon_pgoff = vma_anon_pgoff_addr(vma_, start_),	\
+		.file = vma_->vm_file,					\
+		.anon_vma = vma_->anon_vma,				\
+		.policy = vma_policy(vma_),				\
+		.uffd_ctx = vma_->vm_userfaultfd_ctx,			\
+		.anon_name = anon_vma_name(vma_),			\
 		.state = VMA_MERGE_START,				\
 	}
 
-#define VMG_VMA_STATE(name, vmi_, prev_, vma_, start_, end_)	\
-	struct vma_merge_struct name = {			\
-		.mm = vma_->vm_mm,				\
-		.vmi = vmi_,					\
-		.prev = prev_,					\
-		.middle = vma_,					\
-		.next = NULL,					\
-		.start = start_,				\
-		.end = end_,					\
-		.vm_flags = vma_->vm_flags,			\
-		.pgoff = linear_page_index(vma_, start_),	\
-		.file = vma_->vm_file,				\
-		.anon_vma = vma_->anon_vma,			\
-		.policy = vma_policy(vma_),			\
-		.uffd_ctx = vma_->vm_userfaultfd_ctx,		\
-		.anon_name = anon_vma_name(vma_),		\
-		.state = VMA_MERGE_START,			\
-	}
-
 #ifdef CONFIG_DEBUG_VM_MAPLE_TREE
 void validate_mm(struct mm_struct *mm);
 #else
@@ -520,7 +589,7 @@ void unlink_file_vma_batch_add(struct unlink_vma_file_batch *vb,
 
 struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	unsigned long addr, unsigned long len, pgoff_t pgoff,
-	bool *need_rmap_locks);
+	pgoff_t anon_pgoff, bool *need_rmap_locks);
 
 struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma);
 
diff --git a/mm/vma_exec.c b/mm/vma_exec.c
index 7af1260689b9..586c52155942 100644
--- a/mm/vma_exec.c
+++ b/mm/vma_exec.c
@@ -41,7 +41,7 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift)
 	unsigned long new_end = old_end - shift;
 	VMA_ITERATOR(vmi, mm, new_start);
 	VMG_STATE(vmg, mm, &vmi, new_start, old_end, EMPTY_VMA_FLAGS,
-		  vma_start_pgoff(vma));
+		  vma_start_pgoff(vma), vma_start_anon_pgoff(vma));
 	struct vm_area_struct *next;
 	struct mmu_gather tlb;
 	PAGETABLE_MOVE(pmc, vma, vma, old_start, new_start, length);
diff --git a/tools/testing/vma/shared.c b/tools/testing/vma/shared.c
index bea9ea6db02a..f410bb6f858e 100644
--- a/tools/testing/vma/shared.c
+++ b/tools/testing/vma/shared.c
@@ -23,7 +23,8 @@ struct vm_area_struct *alloc_vma(struct mm_struct *mm,
 
 	vma->vm_start = start;
 	vma->vm_end = end;
-	vma->vm_pgoff = pgoff;
+	vma_set_pgoff(vma, pgoff);
+	vma_set_virt_pgoff(vma, start >> PAGE_SHIFT);
 	vma->flags = vma_flags;
 	vma_assert_detached(vma);
 
diff --git a/tools/testing/vma/tests/merge.c b/tools/testing/vma/tests/merge.c
index e357accc8499..48418b82b01d 100644
--- a/tools/testing/vma/tests/merge.c
+++ b/tools/testing/vma/tests/merge.c
@@ -45,6 +45,7 @@ void vmg_set_range(struct vma_merge_struct *vmg, unsigned long start,
 	vmg->start = start;
 	vmg->end = end;
 	vmg->pgoff = pgoff;
+	vmg->anon_pgoff = start >> PAGE_SHIFT;
 	vmg->vma_flags = vma_flags;
 
 	vmg->just_expand = false;
@@ -108,6 +109,7 @@ static bool test_simple_merge(void)
 		.end = 0x2000,
 		.vma_flags = vma_flags,
 		.pgoff = 1,
+		.anon_pgoff = 1,
 	};
 
 	ASSERT_FALSE(attach_vma(&mm, vma_left));
@@ -1431,7 +1433,7 @@ static bool test_expand_only_mode(void)
 	struct mm_struct mm = {};
 	VMA_ITERATOR(vmi, &mm, 0);
 	struct vm_area_struct *vma_prev, *vma;
-	VMG_STATE(vmg, &mm, &vmi, 0x5000, 0x9000, vma_flags, 5);
+	VMG_STATE(vmg, &mm, &vmi, 0x5000, 0x9000, vma_flags, 5, 5);
 
 	/*
 	 * Place a VMA prior to the one we're expanding so we assert that we do
diff --git a/tools/testing/vma/tests/vma.c b/tools/testing/vma/tests/vma.c
index 754a2da06321..7ca5289e0f95 100644
--- a/tools/testing/vma/tests/vma.c
+++ b/tools/testing/vma/tests/vma.c
@@ -38,7 +38,7 @@ static bool test_copy_vma(void)
 	/* Move backwards and do not merge. */
 
 	vma = alloc_and_link_vma(&mm, 0x3000, 0x5000, 3, vma_flags);
-	vma_new = copy_vma(&vma, 0, 0x2000, 0, &need_locks);
+	vma_new = copy_vma(&vma, 0, 0x2000, 0, 3, &need_locks);
 	ASSERT_NE(vma_new, vma);
 	ASSERT_EQ(vma_new->vm_start, 0);
 	ASSERT_EQ(vma_new->vm_end, 0x2000);
@@ -51,7 +51,7 @@ static bool test_copy_vma(void)
 
 	vma = alloc_and_link_vma(&mm, 0, 0x2000, 0, vma_flags);
 	vma_next = alloc_and_link_vma(&mm, 0x6000, 0x8000, 6, vma_flags);
-	vma_new = copy_vma(&vma, 0x4000, 0x2000, 4, &need_locks);
+	vma_new = copy_vma(&vma, 0x4000, 0x2000, 4, 4, &need_locks);
 	vma_assert_attached(vma_new);
 
 	ASSERT_EQ(vma_new, vma_next);
diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
index 4f6c5666ac07..8a48b231aa7a 100644
--- a/tools/testing/vma/vma_internal.h
+++ b/tools/testing/vma/vma_internal.h
@@ -53,6 +53,7 @@ typedef __bitwise unsigned int vm_fault_t;
 
 #define VM_WARN_ON(_expr) (WARN_ON(_expr))
 #define VM_WARN_ON_ONCE(_expr) (WARN_ON_ONCE(_expr))
+#define VM_WARN_ON_ONCE_VMA(_expr, _vma) (WARN_ON_ONCE(_expr))
 #define VM_WARN_ON_VMG(_expr, _vmg) (WARN_ON(_expr))
 #define VM_BUG_ON(_expr) (BUG_ON(_expr))
 #define VM_BUG_ON_VMA(_expr, _vma) (BUG_ON(_expr))

-- 
2.55.0

[PATCH 07/15] mm/rmap: track whether the page VMA mapped walk is anonymous

[Lorenzo Stoakes (ARM)]

Update the page_vma_mapped_walk structure to track whether the walk is over
an anonymous folio or not.

This is necessary in order to determine the correct VMA page
offset (virtual or not) in vma_address_end() ready for a subsequent change
which adjusts which page offset to use depending on this parameter, and
update the comment slightly.

No functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 include/linux/rmap.h |  2 ++
 mm/internal.h        | 13 ++++++++-----
 mm/rmap.c            |  3 +++
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 8dc0871e5f00..a48ae9575bd2 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -871,6 +871,7 @@ struct page_vma_mapped_walk {
 	pte_t *pte;
 	spinlock_t *ptl;
 	unsigned int flags;
+	bool is_anon_walk;
 };
 
 #define DEFINE_FOLIO_VMA_WALK(name, _folio, _vma, _address, _flags)	\
@@ -881,6 +882,7 @@ struct page_vma_mapped_walk {
 		.vma = _vma,						\
 		.address = _address,					\
 		.flags = _flags,					\
+		.is_anon_walk = folio_test_anon(_folio),		\
 	}
 
 static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
diff --git a/mm/internal.h b/mm/internal.h
index 73f90aaa979d..7ed8bde7890d 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1079,22 +1079,25 @@ static inline unsigned long vma_anon_address(const struct vm_area_struct *vma,
 }
 
 /*
- * Then at what user virtual address will none of the range be found in vma?
+ * At what user virtual address will none of the range be found in vma?
  * Assumes that vma_address() already returned a good starting address.
  */
 static inline unsigned long vma_address_end(struct page_vma_mapped_walk *pvmw)
 {
-	struct vm_area_struct *vma = pvmw->vma;
-	pgoff_t pgoff;
+	const struct vm_area_struct *vma = pvmw->vma;
+	const pgoff_t pgoff = pvmw->pgoff;
+	pgoff_t pgoff_vma_start;
 	unsigned long address;
+	pgoff_t pgoff_end;
 
 	/* Common case, plus ->pgoff is invalid for KSM */
 	if (pvmw->nr_pages == 1)
 		return pvmw->address + PAGE_SIZE;
 
-	pgoff = pvmw->pgoff + pvmw->nr_pages;
+	pgoff_vma_start = vma_start_pgoff(vma);
+	pgoff_end = pgoff + pvmw->nr_pages;
 	address = vma->vm_start +
-		((pgoff - vma_start_pgoff(vma)) << PAGE_SHIFT);
+		((pgoff_end - pgoff_vma_start) << PAGE_SHIFT);
 	/* Check for address beyond vma (or wrapped through 0?) */
 	if (address < vma->vm_start || address > vma->vm_end)
 		address = vma->vm_end;
diff --git a/mm/rmap.c b/mm/rmap.c
index 5798427d007f..cfd4195ff1ae 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1240,8 +1240,10 @@ static bool mapping_wrprotect_range_one(struct folio *folio,
 		.vma		= vma,
 		.address	= address,
 		.flags		= PVMW_SYNC,
+		.is_anon_walk   = false,
 	};
 
+	VM_WARN_ON_ONCE(folio_test_anon(folio));
 	state->cleaned += page_vma_mkclean_one(&pvmw);
 
 	return true;
@@ -1317,6 +1319,7 @@ int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
 		.pgoff		= pgoff,
 		.vma		= vma,
 		.flags		= PVMW_SYNC,
+		.is_anon_walk   = false,
 	};
 
 	if (invalid_mkclean_vma(vma, NULL))

-- 
2.55.0

Re: [PATCH 07/15] mm/rmap: track whether the page VMA mapped walk is anonymous

[Lorenzo Stoakes (ARM)]

On Fri, Jul 17, 2026 at 07:19:45PM +0100, Lorenzo Stoakes (ARM) wrote:
<snip>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 5798427d007f..cfd4195ff1ae 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1240,8 +1240,10 @@ static bool mapping_wrprotect_range_one(struct folio *folio,
>  		.vma		= vma,
>  		.address	= address,
>  		.flags		= PVMW_SYNC,
> +		.is_anon_walk   = false,
>  	};
>
> +	VM_WARN_ON_ONCE(folio_test_anon(folio));

Andrew - can you drop this line please? It's incorrect (folio is always NULL here).

Thanks!

Cheers, Lorenzo

[PATCH 08/15] mm: introduce and use linear_folio_page_index()

[Lorenzo Stoakes (ARM)]

This function is, for now, a placeholder; it will be used in future to
determine whether to use the virtual page index or not, based on whether
the folio is anonymous or not.

Currently it simply wraps linear_page_index(), so this does not change
behaviour.

We update callers that will, once the change is introduced to track
anonymous folios by virtual page offset if MAP_PRIVATE file-backed, need to
determine which index to use based on folio type.

No functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 include/linux/pagemap.h | 18 ++++++++++++++++++
 mm/huge_memory.c        |  3 ++-
 mm/migrate.c            |  6 ++++--
 mm/userfaultfd.c        |  6 ++++--
 4 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 81da91e103b3..dab355eda0ef 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1142,6 +1142,24 @@ static inline pgoff_t linear_virt_page_index(const struct vm_area_struct *vma,
 	return pgoff;
 }
 
+/**
+ * linear_folio_page_index() - Determine the absolute page offset of
+ * @address within @vma from @folio.
+ * @folio: The folio whose linear page index is sought.
+ * @vma: The VMA in which @address resides.
+ * @address: The address whose absolute page offset is required.
+ *
+ * For compatibility, currently identical to linear_page_index().
+ *
+ * Returns: The absolute page offset of @address within @vma.
+ */
+static inline pgoff_t linear_folio_page_index(const struct folio *folio,
+					      const struct vm_area_struct *vma,
+					      const unsigned long address)
+{
+	return linear_page_index(vma, address);
+}
+
 struct wait_page_key {
 	struct folio *folio;
 	int bit_nr;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9b1f3b24f7e0..abc65d608c23 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2887,7 +2887,8 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm
 		}
 
 		folio_move_anon_rmap(src_folio, dst_vma);
-		src_folio->index = linear_page_index(dst_vma, dst_addr);
+		src_folio->index = linear_folio_page_index(src_folio, dst_vma,
+							   dst_addr);
 
 		_dst_pmd = folio_mk_pmd(src_folio, dst_vma->vm_page_prot);
 		/* Follow mremap() behavior and treat the entry dirty after the move */
diff --git a/mm/migrate.c b/mm/migrate.c
index 222c8c15f782..37fe7a9b3fac 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -363,8 +363,10 @@ static bool remove_migration_pte(struct folio *folio,
 		unsigned long idx = 0;
 
 		/* pgoff is invalid for ksm pages, but they are never large */
-		if (folio_test_large(folio) && !folio_test_hugetlb(folio))
-			idx = linear_page_index(vma, pvmw.address) - pvmw.pgoff;
+		if (folio_test_large(folio) && !folio_test_hugetlb(folio)) {
+			idx += linear_folio_page_index(folio, vma, pvmw.address);
+			idx -= pvmw.pgoff;
+		}
 		new = folio_page(folio, idx);
 
 #ifdef CONFIG_ARCH_HAS_PMD_SOFTLEAVES
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 8fd24c8b428e..258b03182a78 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1352,7 +1352,8 @@ static long move_present_ptes(struct mm_struct *mm,
 		}
 
 		folio_move_anon_rmap(src_folio, dst_vma);
-		src_folio->index = linear_page_index(dst_vma, dst_addr);
+		src_folio->index = linear_folio_page_index(src_folio, dst_vma,
+							   dst_addr);
 
 		orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot);
 		/* Set soft dirty bit so userspace can notice the pte was moved */
@@ -1428,7 +1429,8 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma,
 	 */
 	if (src_folio) {
 		folio_move_anon_rmap(src_folio, dst_vma);
-		src_folio->index = linear_page_index(dst_vma, dst_addr);
+		src_folio->index = linear_folio_page_index(src_folio, dst_vma,
+							   dst_addr);
 	} else {
 		/*
 		 * Check if the swap entry is cached after acquiring the src_pte

-- 
2.55.0

[PATCH 09/15] mm/rmap: use virt pgoff for MAP_PRIVATE file-backed anon folios

[Lorenzo Stoakes (ARM)]

Currently, anonymous folios belonging to CoW'd MAP_PRIVATE file-backed
mappings are indexed by their page offset within the file in which they
were originally mapped.

This differs from anonymous folios belonging to pure anon mappings which
are indexed by their virtual page offset (the address at which they'd
belong in the VMA when first faulted).

This change fixes this inconsistency, always indexing anonymous folios by
their virtual page offset regardless of the VMA to which they belong.

We have laid the foundations for making this change to the point where we
need only 'switch it on', and this patch switches it on by:

* Using linear_virt_page_index() in __folio_set_anon() to assign the
  folio's index to the anonymous linear index rather than the file-backed
  one.

* Otherwise using linear_virt_page_index() in all instances where
  anonymous folios are being referenced or manipulated.

* Replacing vma_address() with vma_filebacked_address() or
  vma_anon_address() as appropriate.

* Updating the rmap lock logic in copy_vma() to also account for virtual
  page offsets.

* Updating the merging logic to check that virtual page offsets are
  aligned as well as filebacked ones for anonymous or MAP_PRIVATE
  file-backed VMAs.

* Updating linear_folio_page_index() to invoke linear_virt_page_index()
  if the folio is anonymous.

* Correcting folio_within_range() to use virtual page offset for anonymous
  folios.

This will have no impact on merging of anonymous VMAs or shared file-backed
VMAs, whose page offset and anonymous page offset will be identical.

However, MAP_PRIVATE file-backed mappings must now be aligned on virtual
page offset as well.

In most instances this should have no impact on merging of file-backed
mappings, which are usually not merged all that often, let alone
MAP_PRIVATE mapped ones, and rarely remapped and faulted before being moved
back in place (the case in which a merge may now fail).

This change lays the foundations for future scalable CoW work which needs
to track at least some remaps.

This change means that most remap tracking can be avoided, and in nearly
all cases the anonymous page offset can be used to quickly find the VMA in
an mm.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 include/linux/pagemap.h |  9 ++++++++-
 mm/internal.h           | 28 +++++++++-------------------
 mm/interval_tree.c      |  4 ++--
 mm/ksm.c                |  7 ++++---
 mm/page_vma_mapped.c    |  2 +-
 mm/rmap.c               | 12 ++++++------
 mm/vma.c                | 14 ++++++++++++--
 7 files changed, 42 insertions(+), 34 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index dab355eda0ef..90130f28e7a8 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1149,7 +1149,11 @@ static inline pgoff_t linear_virt_page_index(const struct vm_area_struct *vma,
  * @vma: The VMA in which @address resides.
  * @address: The address whose absolute page offset is required.
  *
- * For compatibility, currently identical to linear_page_index().
+ * Determines whether to obtain the virtual linear page index based on whether
+ * @folio is anonymous or not.
+ *
+ * See the descriptions of linear_virt_page_index() and linear_page_index() for
+ * details of each.
  *
  * Returns: The absolute page offset of @address within @vma.
  */
@@ -1157,6 +1161,9 @@ static inline pgoff_t linear_folio_page_index(const struct folio *folio,
 					      const struct vm_area_struct *vma,
 					      const unsigned long address)
 {
+	if (folio_test_anon(folio))
+		return linear_virt_page_index(vma, address);
+
 	return linear_page_index(vma, address);
 }
 
diff --git a/mm/internal.h b/mm/internal.h
index 7ed8bde7890d..22f63cb85bd3 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -933,7 +933,8 @@ folio_within_range(struct folio *folio, struct vm_area_struct *vma,
 		return false;
 
 	pgoff_folio = folio_pgoff(folio);
-	pgoff_vma_start = vma_start_pgoff(vma);
+	pgoff_vma_start = folio_test_anon(folio) ?
+		vma_start_virt_pgoff(vma) : vma_start_pgoff(vma);
 
 	if (start < vma->vm_start)
 		start = vma->vm_start;
@@ -1044,23 +1045,8 @@ static inline unsigned long vma_filebacked_address(const struct vm_area_struct *
 }
 
 /**
- * vma_address - Find the virtual address a page range is mapped at.
- * @vma: The vma which maps this object.
- * @pgoff: The page offset within its object.
- * @nr_pages: The number of pages to consider.
- *
- * If any page in this range is mapped by this VMA, return the first address
- * where any of these pages appear.  Otherwise, return -EFAULT.
- */
-static inline unsigned long vma_address(const struct vm_area_struct *vma,
-		pgoff_t pgoff, unsigned long nr_pages)
-{
-	return __vma_address(vma, pgoff, vma_start_pgoff(vma), nr_pages);
-}
-
-/**
- * vma_anon_address - Find the address an anonymous folio with index @pgoff_virt
- * is mapped at.
+ * vma_anon_address - Find the virtual address an anonymous page range is mapped
+ * at.
  * @vma: The vma which maps this object.
  * @pgoff_virt: The virtual page index belonging to the folio.
  * @nr_pages: The number of pages to consider.
@@ -1094,7 +1080,11 @@ static inline unsigned long vma_address_end(struct page_vma_mapped_walk *pvmw)
 	if (pvmw->nr_pages == 1)
 		return pvmw->address + PAGE_SIZE;
 
-	pgoff_vma_start = vma_start_pgoff(vma);
+	if (pvmw->is_anon_walk)
+		pgoff_vma_start = vma_start_virt_pgoff(vma);
+	else
+		pgoff_vma_start = vma_start_pgoff(vma);
+
 	pgoff_end = pgoff + pvmw->nr_pages;
 	address = vma->vm_start +
 		((pgoff_end - pgoff_vma_start) << PAGE_SHIFT);
diff --git a/mm/interval_tree.c b/mm/interval_tree.c
index 3ae9e106d3af..26b8437e3b1b 100644
--- a/mm/interval_tree.c
+++ b/mm/interval_tree.c
@@ -83,12 +83,12 @@ mapping_rmap_tree_iter_next(struct vm_area_struct *vma,
 
 static pgoff_t avc_start_pgoff(struct anon_vma_chain *avc)
 {
-	return vma_start_pgoff(avc->vma);
+	return vma_start_virt_pgoff(avc->vma);
 }
 
 static pgoff_t avc_last_pgoff(struct anon_vma_chain *avc)
 {
-	return vma_last_pgoff(avc->vma);
+	return vma_last_virt_pgoff(avc->vma);
 }
 
 INTERVAL_TREE_DEFINE(struct anon_vma_chain, rb, pgoff_t, rb_subtree_last,
diff --git a/mm/ksm.c b/mm/ksm.c
index 47006f494fcb..b9b32f7bfb69 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1625,7 +1625,8 @@ static int try_to_merge_with_ksm_page(struct ksm_rmap_item *rmap_item,
 	 * stable_tree, break_cow() will clean it up.
 	 */
 	rmap_item->anon_vma = vma->anon_vma;
-	rmap_item->linear_page_index = linear_page_index(vma, rmap_item->address);
+	/* The VMA is always anon/MAP_PRIVATE-file backed so use anon index. */
+	rmap_item->linear_page_index = linear_virt_page_index(vma, rmap_item->address);
 	get_anon_vma(vma->anon_vma);
 out:
 	mmap_read_unlock(mm);
@@ -3152,7 +3153,7 @@ struct folio *ksm_might_need_to_copy(struct folio *folio,
 			return folio;	/* no need to copy it */
 	} else if (!anon_vma) {
 		return folio;		/* no need to copy it */
-	} else if (folio->index == linear_page_index(vma, addr) &&
+	} else if (folio->index == linear_virt_page_index(vma, addr) &&
 			anon_vma->root == vma->anon_vma->root) {
 		return folio;		/* still no need to copy it */
 	}
@@ -3222,7 +3223,7 @@ void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc)
 		/*
 		 * Currently, KSM folios are always small folios, so it's
 		 * sufficient to search for a single page. We can simply use
-		 * the linear_page_index of the original de-duplicate
+		 * the linear_virt_page_index of the original de-duplicate
 		 * anonymous page that we remembered in the rmap_item while
 		 * de-duplicating. Note that mremap() always de-duplicates KSM
 		 * folios: so if there was mremap() in our parent or our child,
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 081e483cc7bf..4e964545e5e8 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -365,7 +365,7 @@ unsigned long page_mapped_in_vma(const struct page *page,
 	};
 
 	if (folio_test_anon(folio))
-		pvmw.address = vma_address(vma, pgoff, 1);
+		pvmw.address = vma_anon_address(vma, pgoff, 1);
 	else
 		pvmw.address = vma_filebacked_address(vma, pgoff, 1);
 	if (pvmw.address == -EFAULT)
diff --git a/mm/rmap.c b/mm/rmap.c
index cfd4195ff1ae..6854baf4b877 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -866,7 +866,7 @@ unsigned long page_address_in_vma(const struct folio *folio,
 		    vma->anon_vma->root != anon_vma->root)
 			return -EFAULT;
 		/* KSM folios don't reach here because of the !anon_vma check */
-		return vma_address(vma, page_pgoff(folio, page), 1);
+		return vma_anon_address(vma, page_pgoff(folio, page), 1);
 	} else if (!vma->vm_file) {
 		return -EFAULT;
 	} else if (vma->vm_file->f_mapping != folio->mapping) {
@@ -1486,7 +1486,7 @@ static void __folio_set_anon(struct folio *folio, struct vm_area_struct *vma,
 	 */
 	anon_vma = (void *) anon_vma + FOLIO_MAPPING_ANON;
 	WRITE_ONCE(folio->mapping, (struct address_space *) anon_vma);
-	folio->index = linear_page_index(vma, address);
+	folio->index = linear_virt_page_index(vma, address);
 }
 
 /**
@@ -1513,8 +1513,8 @@ static void __page_check_anon_rmap(const struct folio *folio,
 	 */
 	VM_BUG_ON_FOLIO(folio_anon_vma(folio)->root != vma->anon_vma->root,
 			folio);
-	VM_BUG_ON_PAGE(page_pgoff(folio, page) != linear_page_index(vma, address),
-		       page);
+	VM_BUG_ON_PAGE(page_pgoff(folio, page) !=
+		       linear_virt_page_index(vma, address), page);
 }
 
 static __always_inline void __folio_add_anon_rmap(struct folio *folio,
@@ -3041,10 +3041,10 @@ static void rmap_walk_anon(struct folio *folio,
 	pgoff_end = pgoff_start + folio_nr_pages(folio) - 1;
 	anon_rmap_tree_foreach(avc, anon_vma, pgoff_start, pgoff_end) {
 		struct vm_area_struct *vma = avc->vma;
-		unsigned long address = vma_address(vma, pgoff_start,
+		const unsigned long address = vma_anon_address(vma, pgoff_start,
 				folio_nr_pages(folio));
 
-		VM_BUG_ON_VMA(address == -EFAULT, vma);
+		VM_WARN_ON_ONCE_VMA(address == -EFAULT, vma);
 		cond_resched();
 
 		if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
diff --git a/mm/vma.c b/mm/vma.c
index e45d43493446..6dc095d03382 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -233,6 +233,8 @@ static bool can_vma_merge_before(struct vma_merge_struct *vmg)
 		return false;
 	if (vmg_end_pgoff(vmg) != vma_start_pgoff(vmg->next))
 		return false;
+	if (vmg_end_anon_pgoff(vmg) != vma_start_anon_pgoff(vmg->next))
+		return false;
 	return true;
 }
 
@@ -253,6 +255,8 @@ static bool can_vma_merge_after(struct vma_merge_struct *vmg)
 		return false;
 	if (vma_end_pgoff(vmg->prev) != vmg_start_pgoff(vmg))
 		return false;
+	if (vma_end_anon_pgoff(vmg->prev) != vmg_start_anon_pgoff(vmg))
+		return false;
 	return true;
 }
 
@@ -1988,7 +1992,8 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 			*vmap = vma = new_vma;
 		}
 		*need_rmap_locks =
-			(vma_start_pgoff(new_vma) <= vma_start_pgoff(vma));
+			(vma_start_pgoff(new_vma) <= vma_start_pgoff(vma)) ||
+			(vma_start_anon_pgoff(new_vma) <= vma_start_anon_pgoff(vma));
 	} else {
 		new_vma = vm_area_dup(vma);
 		if (!new_vma)
@@ -2059,7 +2064,12 @@ static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *
 	if (!vma_flags_empty(&diff))
 		return false;
 	/* Page offset must align. */
-	return vma_end_pgoff(a) == vma_start_pgoff(b);
+	if (vma_end_pgoff(a) != vma_start_pgoff(b))
+		return false;
+	/* Anon page offset must align. */
+	if (vma_end_anon_pgoff(a) != vma_start_anon_pgoff(b))
+		return false;
+	return true;
 }
 
 /*

-- 
2.55.0

[PATCH 10/15] tools/testing/vma: expand VMA merge tests to assert virt pgoff

[Lorenzo Stoakes (ARM)]

Now we have introduced the VMA virtual page offset attribute and update it
when VMAs are manipulated, update VMA merge tests to assert that the
virtual page offset is as expected.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 tools/testing/vma/tests/merge.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tools/testing/vma/tests/merge.c b/tools/testing/vma/tests/merge.c
index 48418b82b01d..a01107ab8e21 100644
--- a/tools/testing/vma/tests/merge.c
+++ b/tools/testing/vma/tests/merge.c
@@ -121,6 +121,7 @@ static bool test_simple_merge(void)
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0x3000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 	ASSERT_FLAGS_SAME_MASK(&vma->flags, vma_flags);
 
 	detach_free_vma(vma);
@@ -153,6 +154,7 @@ static bool test_simple_modify(void)
 	ASSERT_EQ(vma->vm_start, 0x1000);
 	ASSERT_EQ(vma->vm_end, 0x2000);
 	ASSERT_EQ(vma_start_pgoff(vma), 1);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 1);
 
 	/*
 	 * Now walk through the three split VMAs and make sure they are as
@@ -165,6 +167,7 @@ static bool test_simple_modify(void)
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0x1000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 
 	detach_free_vma(vma);
 	vma_iter_clear(&vmi);
@@ -174,6 +177,7 @@ static bool test_simple_modify(void)
 	ASSERT_EQ(vma->vm_start, 0x1000);
 	ASSERT_EQ(vma->vm_end, 0x2000);
 	ASSERT_EQ(vma_start_pgoff(vma), 1);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 1);
 
 	detach_free_vma(vma);
 	vma_iter_clear(&vmi);
@@ -183,6 +187,7 @@ static bool test_simple_modify(void)
 	ASSERT_EQ(vma->vm_start, 0x2000);
 	ASSERT_EQ(vma->vm_end, 0x3000);
 	ASSERT_EQ(vma_start_pgoff(vma), 2);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 2);
 
 	detach_free_vma(vma);
 	mtree_destroy(&mm.mm_mt);
@@ -212,6 +217,7 @@ static bool test_simple_expand(void)
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0x3000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 
 	detach_free_vma(vma);
 	mtree_destroy(&mm.mm_mt);
@@ -234,6 +240,7 @@ static bool test_simple_shrink(void)
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0x1000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 
 	detach_free_vma(vma);
 	mtree_destroy(&mm.mm_mt);
@@ -346,6 +353,7 @@ static bool __test_merge_new(bool is_sticky, bool a_is_sticky, bool b_is_sticky,
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0x5000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 	ASSERT_EQ(vma->anon_vma, &dummy_anon_vma);
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_EQ(mm.map_count, 3);
@@ -367,6 +375,7 @@ static bool __test_merge_new(bool is_sticky, bool a_is_sticky, bool b_is_sticky,
 	ASSERT_EQ(vma->vm_start, 0x6000);
 	ASSERT_EQ(vma->vm_end, 0x9000);
 	ASSERT_EQ(vma_start_pgoff(vma), 6);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 6);
 	ASSERT_EQ(vma->anon_vma, &dummy_anon_vma);
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_EQ(mm.map_count, 3);
@@ -387,6 +396,7 @@ static bool __test_merge_new(bool is_sticky, bool a_is_sticky, bool b_is_sticky,
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0x9000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 	ASSERT_EQ(vma->anon_vma, &dummy_anon_vma);
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_EQ(mm.map_count, 2);
@@ -407,6 +417,7 @@ static bool __test_merge_new(bool is_sticky, bool a_is_sticky, bool b_is_sticky,
 	ASSERT_EQ(vma->vm_start, 0xa000);
 	ASSERT_EQ(vma->vm_end, 0xc000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0xa);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0xa);
 	ASSERT_EQ(vma->anon_vma, &dummy_anon_vma);
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_EQ(mm.map_count, 2);
@@ -426,6 +437,7 @@ static bool __test_merge_new(bool is_sticky, bool a_is_sticky, bool b_is_sticky,
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0xc000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 	ASSERT_EQ(vma->anon_vma, &dummy_anon_vma);
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_EQ(mm.map_count, 1);
@@ -446,6 +458,7 @@ static bool __test_merge_new(bool is_sticky, bool a_is_sticky, bool b_is_sticky,
 		ASSERT_EQ(vma->vm_start, 0);
 		ASSERT_EQ(vma->vm_end, 0xc000);
 		ASSERT_EQ(vma_start_pgoff(vma), 0);
+		ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 		ASSERT_EQ(vma->anon_vma, &dummy_anon_vma);
 
 		detach_free_vma(vma);
@@ -808,6 +821,7 @@ static bool test_vma_merge_new_with_close(void)
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0x5000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 	ASSERT_EQ(vma->vm_ops, &vm_ops);
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_EQ(mm.map_count, 2);
@@ -868,6 +882,7 @@ static bool __test_merge_existing(bool prev_is_sticky, bool middle_is_sticky, bo
 	ASSERT_EQ(vma->vm_start, 0x2000);
 	ASSERT_EQ(vma->vm_end, 0x3000);
 	ASSERT_EQ(vma_start_pgoff(vma), 2);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 2);
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_TRUE(vma_write_started(vma_next));
 	ASSERT_EQ(mm.map_count, 2);
@@ -934,6 +949,7 @@ static bool __test_merge_existing(bool prev_is_sticky, bool middle_is_sticky, bo
 	ASSERT_EQ(vma->vm_start, 0x6000);
 	ASSERT_EQ(vma->vm_end, 0x7000);
 	ASSERT_EQ(vma_start_pgoff(vma), 6);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 6);
 	ASSERT_TRUE(vma_write_started(vma_prev));
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_EQ(mm.map_count, 2);
@@ -1419,6 +1435,7 @@ static bool test_merge_extend(void)
 	ASSERT_EQ(vma->vm_start, 0);
 	ASSERT_EQ(vma->vm_end, 0x4000);
 	ASSERT_EQ(vma_start_pgoff(vma), 0);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0);
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_EQ(mm.map_count, 1);
 
@@ -1459,6 +1476,7 @@ static bool test_expand_only_mode(void)
 	ASSERT_EQ(vma->vm_start, 0x3000);
 	ASSERT_EQ(vma->vm_end, 0x9000);
 	ASSERT_EQ(vma_start_pgoff(vma), 3);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 3);
 	ASSERT_TRUE(vma_write_started(vma));
 	ASSERT_EQ(vma_iter_addr(&vmi), 0x3000);
 	vma_assert_attached(vma);

-- 
2.55.0

[PATCH 11/15] tools/testing/selftests/mm: test virtual page offset merge behaviour

[Lorenzo Stoakes (ARM)]

While maintaining virtual page offsets for VMAs has no impact for most
merge cases, it does impact MAP_PRIVATE-mapped file-backed mappings which
happen to have matching page offset but not matching virtual page offset.

Assert this behaviour by attempting to map an unfaulted MAP_PRIVATE-memfd
region with a faulted one with compatible file page offsets but
incompatible virtual page offsets.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 tools/testing/selftests/mm/merge.c | 57 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/tools/testing/selftests/mm/merge.c b/tools/testing/selftests/mm/merge.c
index 519e5ac02db7..c093e27d0aea 100644
--- a/tools/testing/selftests/mm/merge.c
+++ b/tools/testing/selftests/mm/merge.c
@@ -1305,6 +1305,63 @@ TEST_F(merge, merge_vmas_with_mseal)
 	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 2 * page_size);
 }
 
+TEST_F(merge, virt_and_page_offset_mismatch_memfd)
+{
+	struct procmap_fd *procmap = &self->procmap;
+	unsigned int page_size = self->page_size;
+	char *carveout = self->carveout;
+	char *ptr, *ptr2;
+	int fd;
+
+	/* Create a 10 page memfd descriptor. */
+	fd = memfd_create("virt_page_offset_test", MFD_CLOEXEC);
+	ASSERT_NE(fd, -1);
+	ASSERT_EQ(ftruncate(fd, 10 * page_size), 0);
+
+	/* Map a region using the memfd at page offset 0. */
+	ptr = mmap(carveout, 5 * page_size, PROT_READ | PROT_WRITE,
+		   MAP_FIXED | MAP_PRIVATE, fd, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+
+	/*
+	 * Map another separately, and fault in, at page offset 5:
+	 *
+	 * |-----------|           |---------|
+	 * | unfaulted |           | faulted |
+	 * |-----------|           |---------|
+	 */
+	ptr2 = mmap(&carveout[10 * page_size], 5 * page_size,
+		    PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE,
+		    fd, 5 * page_size);
+	ASSERT_NE(ptr2, MAP_FAILED);
+	ptr2[0] = 'x';
+
+	/*
+	 * Now move it in place:
+	 *
+	 *                   |----------|
+	 *                   |          |
+	 *                   v          |
+	 * |-----------|           |---------|
+	 * | unfaulted |           | faulted |
+	 * |-----------|           |---------|
+	 *
+	 * Because virtual page offset of the faulted region is now
+	 * &carveout[10 * page_size], despite the two regions being mergeable
+	 * due to file page offset, they are NOT mergeable due to virtual page
+	 * offset.
+	 */
+	ptr2 = sys_mremap(ptr2, 5 * page_size, 5 * page_size,
+			  MREMAP_MAYMOVE | MREMAP_FIXED,
+			  &carveout[5 * page_size]);
+	ASSERT_NE(ptr2, MAP_FAILED);
+
+	/* Assert that they did not merge. */
+	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
+	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
+	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 5 * page_size);
+}
+
 TEST_F(merge_with_fork, mremap_faulted_to_unfaulted_prev)
 {
 	struct procmap_fd *procmap = &self->procmap;

-- 
2.55.0

[PATCH 12/15] mm/vma: only permit MAP_PRIVATE /dev/zero to be mapped anonymous

[Lorenzo Stoakes (ARM)]

In order to use mmap_prepare() with MAP_PRIVATE mappings of /dev/zero
without the success_hook hack we explicitly permitted mmap_prepare handlers
to set NULL vm_ops.

However this is dangerous and we really only want to allow this for
MAP_PRIVATE-mapped /dev/zero.

Make it possible to explicitly identify /dev/zero by setting a global
DEVZERO_MINOR device minor number then explicitly check for this in mmap
code for a MAP_PRIVATE mapping and only set the VMA anonymous if we have
positively identified it.

Then remove all ability for mmap_prepare or mmap hooks to set a VMA
anonymous and update mmap_zero_prepare() to leave it to the core mmap code
to mark the VMA anonymous.

Note that this disallows nested MAP_PRIVATE-mappings of /dev/zero
regions. Doing this would be broken in any case.

We therefore do not need to update the mmap_prepare() compatibility layer
to reflect these changes, as the mmap hook check suffices to disallow this
behaviour.

Also update the VMA userland tests to reflect the change.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 drivers/char/mem.c              |  8 ++------
 include/linux/mm.h              |  3 +++
 mm/internal.h                   |  4 ++++
 mm/vma.c                        | 33 +++++++++++++++++++++++++++------
 mm/vma_internal.h               |  1 +
 tools/testing/vma/include/dup.h | 28 ++++++++++++++++++++++++++++
 6 files changed, 65 insertions(+), 12 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 63253d1de5d7..dcfd896b733d 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -506,11 +506,7 @@ static int mmap_zero_prepare(struct vm_area_desc *desc)
 	if (vma_desc_test(desc, VMA_SHARED_BIT))
 		return shmem_zero_setup_desc(desc);
 
-	/*
-	 * This is a highly unique situation where we mark a MAP_PRIVATE mapping
-	 * of /dev/zero anonymous, despite it not being.
-	 */
-	vma_desc_set_anonymous(desc);
+	/* MAP_PRIVATE semantics are taken care for us by core mm. */
 	return 0;
 }
 
@@ -698,7 +694,7 @@ static const struct memdev {
 #ifdef CONFIG_DEVPORT
 	[4] = { "port", &port_fops, 0, 0 },
 #endif
-	[5] = { "zero", &zero_fops, FMODE_NOWAIT, 0666 },
+	[DEVZERO_MINOR] = { "zero", &zero_fops, FMODE_NOWAIT, 0666 },
 	[7] = { "full", &full_fops, 0, 0666 },
 	[8] = { "random", &random_fops, FMODE_NOWAIT, 0666 },
 	[9] = { "urandom", &urandom_fops, FMODE_NOWAIT, 0666 },
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b6503b5f0010..7614afe99c96 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -740,6 +740,9 @@ static inline bool fault_flag_allow_retry_first(enum fault_flag flags)
 	{ FAULT_FLAG_INTERRUPTIBLE,	"INTERRUPTIBLE" }, \
 	{ FAULT_FLAG_VMA_LOCK,		"VMA_LOCK" }
 
+/* /dev/zero minor device number. Special due to MAP_PRIVATE semantics. */
+#define DEVZERO_MINOR	5
+
 /*
  * vm_fault is filled by the pagefault handler and passed to the vma's
  * ->fault function. The vma's ->fault is responsible for returning a bitmask
diff --git a/mm/internal.h b/mm/internal.h
index 22f63cb85bd3..41561fdeb56d 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -240,6 +240,10 @@ static inline int mmap_file(struct file *file, struct vm_area_struct *vma)
 {
 	int err = vfs_mmap(file, vma);
 
+	/* Hooks cannot mark themselves anonymous. */
+	if (WARN_ON_ONCE(vma_is_anonymous(vma)))
+		err = -EINVAL;
+
 	if (likely(!err))
 		return 0;
 
diff --git a/mm/vma.c b/mm/vma.c
index 6dc095d03382..6ccd097b8813 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -2612,6 +2612,27 @@ static int __mmap_new_file_vma(struct mmap_state *map,
 	return 0;
 }
 
+static bool map_is_dev_zero(const struct mmap_state *map)
+{
+	const struct file *file = map->file;
+	const struct inode *inode = file_inode(file);
+
+	return imajor(inode) == MEM_MAJOR && iminor(inode) == DEVZERO_MINOR;
+}
+
+static bool map_is_private(const struct mmap_state *map)
+{
+	return !vma_flags_test(&map->vma_flags, VMA_SHARED_BIT);
+}
+
+static bool map_is_anon(const struct mmap_state *map)
+{
+	if (!map_is_private(map))
+		return false;
+
+	return !map->file || map_is_dev_zero(map);
+}
+
 /*
  * __mmap_new_vma() - Allocate a new VMA for the region, as merging was not
  * possible.
@@ -2625,8 +2646,7 @@ static int __mmap_new_file_vma(struct mmap_state *map,
 static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap,
 	struct mmap_action *action)
 {
-	const bool is_anon = !map->file &&
-		!vma_flags_test(&map->vma_flags, VMA_SHARED_BIT);
+	const bool is_anon = map_is_anon(map);
 	struct vma_iterator *vmi = map->vmi;
 	int error = 0;
 	struct vm_area_struct *vma;
@@ -2768,6 +2788,10 @@ static int call_mmap_prepare(struct mmap_state *map,
 	if (err)
 		return err;
 
+	/* Hooks cannot mark themselves anonymous. */
+	if (!desc->vm_ops)
+		return -EINVAL;
+
 	err = call_action_prepare(map, desc);
 	if (err)
 		return err;
@@ -2790,10 +2814,7 @@ static int call_mmap_prepare(struct mmap_state *map,
 static void set_vma_user_defined_fields(struct vm_area_struct *vma,
 		struct mmap_state *map)
 {
-	if (map->vm_ops)
-		vma->vm_ops = map->vm_ops;
-	else	/* Only /dev/zero should do this. */
-		vma_set_anonymous(vma);
+	vma->vm_ops = map->vm_ops;
 	vma->vm_private_data = map->vm_private_data;
 }
 
diff --git a/mm/vma_internal.h b/mm/vma_internal.h
index 4d300e7bbaf4..385c0ab13777 100644
--- a/mm/vma_internal.h
+++ b/mm/vma_internal.h
@@ -23,6 +23,7 @@
 #include <linux/ksm.h>
 #include <linux/khugepaged.h>
 #include <linux/list.h>
+#include <linux/major.h>
 #include <linux/maple_tree.h>
 #include <linux/mempolicy.h>
 #include <linux/mm.h>
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 51605ade06fb..93049241b297 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -15,6 +15,15 @@ struct task_struct *get_current(void);
 #define MMF_HAS_MDWE	28
 #define current get_current()
 
+#define MINORBITS	20
+#define MINORMASK	((1U << MINORBITS) - 1)
+
+#define MAJOR(dev)	((unsigned int) ((dev) >> MINORBITS))
+#define MINOR(dev)	((unsigned int) ((dev) & MINORMASK))
+
+#define MEM_MAJOR		1
+#define DEVZERO_MINOR	5
+
 /*
  * Define the task command name length as enum, then it can be visible to
  * BPF programs.
@@ -45,6 +54,9 @@ struct address_space {
 	unsigned long		flags;
 	atomic_t		i_mmap_writable;
 };
+struct inode {
+	dev_t			i_rdev;
+};
 struct file_operations {
 	int (*mmap)(struct file *, struct vm_area_struct *);
 	int (*mmap_prepare)(struct vm_area_desc *);
@@ -52,6 +64,7 @@ struct file_operations {
 struct file {
 	struct address_space	*f_mapping;
 	const struct file_operations	*f_op;
+	struct inode			*f_inode;
 };
 struct anon_vma_chain {
 	struct anon_vma *anon_vma;
@@ -1632,3 +1645,18 @@ static inline pgoff_t linear_virt_page_index(const struct vm_area_struct *vma,
 
 	return pgoff;
 }
+
+static inline struct inode *file_inode(const struct file *f)
+{
+	return f->f_inode;
+}
+
+static inline unsigned iminor(const struct inode *inode)
+{
+	return MINOR(inode->i_rdev);
+}
+
+static inline unsigned imajor(const struct inode *inode)
+{
+	return MAJOR(inode->i_rdev);
+}

-- 
2.55.0

[PATCH 13/15] mm/vma: make MAP_PRIVATE-mapped /dev/zero mappings truly anonymous

[Lorenzo Stoakes (ARM)]

When mapping /dev/zero with MAP_PRIVATE, one ends up with strange VMAs
originating from Linux's distant past.

These have vma->vm_file set but NULL vma->vm_ops, meaning they satisfy
vma_is_anonymous() but otherwise resemble a file-backed VMA.

The introduction of virtual page offsets and their subsequent use as
indexes for MAP_PRIVATE-file-backed mappings mean the rmap does the right
thing with these but we are left with inconsistencies.

The vma_start_pgoff(vma) == vma_start_virt_pgoff(vma) invariant is true for
all other anonymous VMAs, but not these.

These VMAs are also observable as files in /proc/<pid>/[s]maps but
otherwise behave like anonymous mappings.

Therefore let's make these VMAs actually anonymous at mapping time which
will activate the anonymous code path for mappings.

This means we no longer have to account for this discrepancy anywhere and
no longer have to think about these at all.

A previous commit gave us map_is_dev_zero() to positively identify these
mappings, so we expressly only do so for these alone.

The impact of this change should be low as likely very few are relying upon
this in any case, and in using them are asking for anonymous memory, so no
longer seeing these as file mappings in smaps should have no meaningful
impact.

Update assert_sane_pgoff() and the comment for vma_start_pgoff() to reflect
the change.

We make this change in call_mmap_prepare() alone as /dev/zero has been
converted to an mmap_prepare hook and we do not permit nested MAP_PRIVATE
mapping of /dev/zero.

We also remove the now defunct vma_desc_set_anonymous().

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 include/linux/mm.h | 10 ++--------
 mm/vma.c           | 21 +++++++++++++++++----
 mm/vma.h           |  3 ---
 3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7614afe99c96..7fabe6c66b4b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1554,11 +1554,6 @@ static inline void vma_set_anonymous(struct vm_area_struct *vma)
 	vma->vm_ops = NULL;
 }
 
-static inline void vma_desc_set_anonymous(struct vm_area_desc *desc)
-{
-	desc->vm_ops = NULL;
-}
-
 static inline bool vma_is_anonymous(const struct vm_area_struct *vma)
 {
 	return !vma->vm_ops;
@@ -4352,9 +4347,8 @@ static inline unsigned long vma_pages(const struct vm_area_struct *vma)
  * If @vma is a MAP_PRIVATE file-backed mapping, then this returns the
  * page offset within the file.
  *
- * Edge cases: nommu does not abide by these, MAP_PRIVATE-/dev/zero satisfies
- * vma_is_anonymous() but has file-backed page offset, and MAP_PRIVATE-pfnmap
- * regions have their page offset set to the first PFN in the range.
+ * Edge cases: nommu does not abide by these and CoW MAP_PRIVATE-pfnmap regions
+ * have their page offset set to the first PFN in the range.
  *
  * Returns: The page offset of the start of @vma.
  */
diff --git a/mm/vma.c b/mm/vma.c
index 6ccd097b8813..f8001d5c23aa 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -2620,6 +2620,14 @@ static bool map_is_dev_zero(const struct mmap_state *map)
 	return imajor(inode) == MEM_MAJOR && iminor(inode) == DEVZERO_MINOR;
 }
 
+static void map_set_anon(struct mmap_state *map)
+{
+	map->file = NULL;
+	map->file_doesnt_need_get = false;
+	map->pgoff = map->addr >> PAGE_SHIFT;
+	map->vm_ops = NULL;
+}
+
 static bool map_is_private(const struct mmap_state *map)
 {
 	return !vma_flags_test(&map->vma_flags, VMA_SHARED_BIT);
@@ -2627,10 +2635,7 @@ static bool map_is_private(const struct mmap_state *map)
 
 static bool map_is_anon(const struct mmap_state *map)
 {
-	if (!map_is_private(map))
-		return false;
-
-	return !map->file || map_is_dev_zero(map);
+	return map_is_private(map) && !map->file;
 }
 
 /*
@@ -2808,6 +2813,14 @@ static int call_mmap_prepare(struct mmap_state *map,
 	map->vm_ops = desc->vm_ops;
 	map->vm_private_data = desc->private_data;
 
+	/*
+	 * MAP_PRIVATE-/dev/zero mappings are an ancient way of getting
+	 * anonymous mappings. Rather than allowing these mappings to be odd
+	 * outliers, simply make them truly anonymous.
+	 */
+	if (map_is_private(map) && map_is_dev_zero(map))
+		map_set_anon(map);
+
 	return 0;
 }
 
diff --git a/mm/vma.h b/mm/vma.h
index c1d65060071f..8caee3b4ba26 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -267,9 +267,6 @@ static inline void assert_sane_pgoff(struct vm_area_struct *vma, pgoff_t pgoff)
 	 */
 	if (!vma_is_anonymous(vma))
 		return;
-	/* MAP_PRIVATE-/dev/zero is anon, non-NULL vm_file, but has file pgoff. */
-	if (vma->vm_file)
-		return;
 	/* If faulted in, could have been remapped. */
 	if (vma->anon_vma)
 		return;

-- 
2.55.0

[PATCH 14/15] tools/testing/vma: add test to assert MAP_PRIVATE-/dev/zero is anon

[Lorenzo Stoakes (ARM)]

Now we've made MAP_PRIVATE-mapped /dev/zero mappings truly anonymous, add a
VMA userland test to assert that this is the case and everything is as
we would expect for an anonymous mapping.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 tools/testing/vma/include/dup.h |  1 +
 tools/testing/vma/tests/mmap.c  | 49 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 93049241b297..b4f0f7c24fcb 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -20,6 +20,7 @@ struct task_struct *get_current(void);
 
 #define MAJOR(dev)	((unsigned int) ((dev) >> MINORBITS))
 #define MINOR(dev)	((unsigned int) ((dev) & MINORMASK))
+#define MKDEV(ma, mi)	(((ma) << MINORBITS) | (mi))
 
 #define MEM_MAJOR		1
 #define DEVZERO_MINOR	5
diff --git a/tools/testing/vma/tests/mmap.c b/tools/testing/vma/tests/mmap.c
index c85bc000d1cb..0c8a3446b905 100644
--- a/tools/testing/vma/tests/mmap.c
+++ b/tools/testing/vma/tests/mmap.c
@@ -45,7 +45,56 @@ static bool test_mmap_region_basic(void)
 	return true;
 }
 
+static int dummy_mmap_prepare(struct vm_area_desc *desc)
+{
+	return 0;
+}
+
+static bool test_pure_anon_dev_zero(void)
+{
+	const vma_flags_t vma_flags = mk_vma_flags(VMA_READ_BIT, VMA_WRITE_BIT,
+			VMA_MAYREAD_BIT, VMA_MAYWRITE_BIT);
+	const struct file_operations f_op = {
+		.mmap_prepare = dummy_mmap_prepare,
+	};
+	struct inode inode = {
+		.i_rdev = MKDEV(MEM_MAJOR, DEVZERO_MINOR),
+	};
+	struct file file = {
+		.f_inode = &inode,
+		.f_op = &f_op,
+	};
+	struct mm_struct mm = {};
+	struct vm_area_struct *vma;
+	unsigned long addr;
+	VMA_ITERATOR(vmi, &mm, 0);
+
+	current->mm = &mm;
+
+	/*
+	 * Map a MAP_PRIVATE-/dev/zero mapping at address 0x300000 with a page
+	 * offset of 0x10, which we expect to be reset to the virtual page
+	 * offset.
+	 */
+	addr = __mmap_region(&file, 0x300000, 0x3000, vma_flags, 0x10, NULL);
+	ASSERT_EQ(addr, 0x300000);
+
+	/* Assert that it truly is an anonymous mapping. */
+	vma = vma_lookup(&mm, addr);
+	ASSERT_NE(vma, NULL);
+	ASSERT_TRUE(vma_is_anonymous(vma));
+	ASSERT_EQ(vma->vm_file, NULL);
+	ASSERT_EQ(vma->vm_private_data, NULL);
+	/* Expect virtual page offsets. */
+	ASSERT_EQ(vma->vm_pgoff, 0x300);
+	ASSERT_EQ(vma_start_virt_pgoff(vma), 0x300);
+
+	cleanup_mm(&mm, &vmi);
+	return true;
+}
+
 static void run_mmap_tests(int *num_tests, int *num_fail)
 {
 	TEST(mmap_region_basic);
+	TEST(pure_anon_dev_zero);
 }

-- 
2.55.0

[PATCH 15/15] tools/testing/selftests/mm: add MAP_PRIVATE-/dev/zero merge tests

[Lorenzo Stoakes (ARM)]

Assert that MAP_PRIVATE-mapped /dev/zero mappings behave like they are
anonymous.

We test both unfaulted and faulted/unfaulted merges - each with the regions
having page offset of 0, which would not merge if the mappings were treated
as if they were file-backed.

With the recent change that makes them behave as pure anonymous mappings,
the merges should succeed as their page offsets are equal to their virtual
page offsets.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 tools/testing/selftests/mm/merge.c | 104 +++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)

diff --git a/tools/testing/selftests/mm/merge.c b/tools/testing/selftests/mm/merge.c
index c093e27d0aea..edfbd39ae58e 100644
--- a/tools/testing/selftests/mm/merge.c
+++ b/tools/testing/selftests/mm/merge.c
@@ -1362,6 +1362,110 @@ TEST_F(merge, virt_and_page_offset_mismatch_memfd)
 	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 5 * page_size);
 }
 
+TEST_F(merge, merge_map_private_dev_zero_unfaulted)
+{
+	struct procmap_fd *procmap = &self->procmap;
+	unsigned int page_size = self->page_size;
+	char *carveout = self->carveout;
+	char *ptr, *ptr2;
+	int fd_zero;
+
+	if (access("/dev/zero", F_OK))
+		SKIP(return, "No /dev/zero.");
+	fd_zero = open("/dev/zero", O_RDWR);
+	ASSERT_NE(fd_zero, -1);
+
+	/*
+	 * Map two MAP_PRIVATE-/dev/zero VMAs next to one another with offset 0
+	 * each.
+	 *
+	 * With these being made truly anonymous upon mapping, they will
+	 * merge. If they were file-backed VMAs the page offsets would prevent
+	 * merge:
+	 *
+	 * |-----||------|    |-------------|
+	 * | ptr || ptr2 | -> |     ptr     |
+	 * |-----||------|    |-------------|
+	 */
+	ptr = mmap(carveout, 5 * page_size, PROT_READ | PROT_WRITE,
+		   MAP_FIXED | MAP_PRIVATE, fd_zero, 0);
+	if (ptr == MAP_FAILED) {
+		close(fd_zero);
+		ASSERT_TRUE(false);
+	}
+	ptr2 = mmap(&carveout[5 * page_size], 5 * page_size,
+		   PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE, fd_zero, 0);
+	if (ptr2 == MAP_FAILED) {
+		close(fd_zero);
+		ASSERT_TRUE(false);
+	}
+	close(fd_zero);
+
+	/* Assert that they merged. */
+	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
+	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
+	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 10 * page_size);
+}
+
+TEST_F(merge, merge_map_private_dev_zero_faulted_unfaulted)
+{
+	struct procmap_fd *procmap = &self->procmap;
+	unsigned int page_size = self->page_size;
+	char *carveout = self->carveout;
+	char *ptr, *ptr2;
+	int fd_zero;
+
+	if (access("/dev/zero", F_OK))
+		SKIP(return, "No /dev/zero.");
+	fd_zero = open("/dev/zero", O_RDWR);
+	ASSERT_NE(fd_zero, -1);
+
+	/*
+	 * Map a MAP_PRIVATE mapping of /dev/zero with page offset 0, then fault
+	 * it in:
+	 *
+	 * |-------------------------------|
+	 * |           faulted             |
+	 * |-------------------------------|
+	 */
+	ptr = mmap(carveout, 15 * page_size, PROT_READ | PROT_WRITE,
+		   MAP_FIXED | MAP_PRIVATE, fd_zero, 0);
+	if (ptr == MAP_FAILED) {
+		close(fd_zero);
+		ASSERT_TRUE(false);
+	}
+	memset(ptr, 'x', 15 * page_size);
+
+	/*
+	 * Unmap the middle:
+	 *
+	 * |---------|           |---------|
+	 * | faulted |           | faulted |
+	 * |---------|           |---------|
+	 */
+	ASSERT_EQ(munmap(&ptr[5 * page_size], 5 * page_size), 0);
+
+	/*
+	 * Map in a new unfaulted mapping in the middle with page offset 0 -
+	 * this should merge and would not if it were treated as a file rather
+	 * than pure anon:
+	 *
+	 * |---------|-----------|---------|
+	 * | faulted | unfaulted | faulted |
+	 * |---------|-----------|---------|
+	 */
+	ptr2 = mmap(&carveout[5 * page_size], 5 * page_size,
+		    PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE,
+		    fd_zero, 0);
+	close(fd_zero);
+	ASSERT_NE(ptr2, MAP_FAILED);
+
+	/* Assert that they merged. */
+	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
+	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
+	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 15 * page_size);
+}
+
 TEST_F(merge_with_fork, mremap_faulted_to_unfaulted_prev)
 {
 	struct procmap_fd *procmap = &self->procmap;

-- 
2.55.0

[syzbot ci] Re: mm/rmap: index MAP_PRIVATE file-backed folios by virt pgoff

[syzbot ci]

syzbot ci has tested the following series

[v1] mm/rmap: index MAP_PRIVATE file-backed folios by virt pgoff
https://lore.kernel.org/all/20260717-b4-scalable-cow-virt-pgoff-v1-0-cf24910ef094@kernel.org
* [PATCH 01/15] mm/vma: introduce VMA virtual page offset field and add helpers
* [PATCH 02/15] mm: introduce linear_virt_page_index()
* [PATCH 03/15] mm: abstract vma_address() and introduce vma_anon_address()
* [PATCH 04/15] mm: update print_bad_page_map() to show virtual page index
* [PATCH 05/15] mm: introduce and use vma_filebacked_address()
* [PATCH 06/15] mm: propagate VMA virtual page offset on map, remap, split + merge
* [PATCH 07/15] mm/rmap: track whether the page VMA mapped walk is anonymous
* [PATCH 08/15] mm: introduce and use linear_folio_page_index()
* [PATCH 09/15] mm/rmap: use virt pgoff for MAP_PRIVATE file-backed anon folios
* [PATCH 10/15] tools/testing/vma: expand VMA merge tests to assert virt pgoff
* [PATCH 11/15] tools/testing/selftests/mm: test virtual page offset merge behaviour
* [PATCH 12/15] mm/vma: only permit MAP_PRIVATE /dev/zero to be mapped anonymous
* [PATCH 13/15] mm/vma: make MAP_PRIVATE-mapped /dev/zero mappings truly anonymous
* [PATCH 14/15] tools/testing/vma: add test to assert MAP_PRIVATE-/dev/zero is anon
* [PATCH 15/15] tools/testing/selftests/mm: add MAP_PRIVATE-/dev/zero merge tests

and found the following issue:
general protection fault in mapping_wrprotect_range_one

Full report is available here:
https://ci.syzbot.org/series/b5c827e8-78a4-494c-b925-417c34a60e85

***

general protection fault in mapping_wrprotect_range_one

tree:      mm-new
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
base:      5093dba1014c1d7f7e247fd118f0fa8f22136046
arch:      amd64
compiler:  Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6
config:    https://ci.syzbot.org/builds/0d856612-f1b4-4e6e-86af-4ed3215225aa/config
syz repro: https://ci.syzbot.org/findings/3484dc14-c12f-477e-b14a-6b249c47b2fd/syz_repro

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
CPU: 1 UID: 0 PID: 32 Comm: kworker/1:1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: events fb_deferred_io_work
RIP: 0010:folio_test_anon include/linux/page-flags.h:718 [inline]
RIP: 0010:mapping_wrprotect_range_one+0x147/0x230 mm/rmap.c:1246
Code: 7c 24 40 49 8d 7f 28 ba 18 00 00 00 31 f6 e8 e0 2e 14 00 48 c7 84 24 80 00 00 00 01 00 00 00 49 83 c6 18 4c 89 f0 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 f7 e8 ea 2b 14 00 4d 8b 36 44 89 f6 83
RSP: 0018:ffffc90000a777c0 EFLAGS: 00010206
RAX: 0000000000000003 RBX: ffffc90000a779e0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffc90000a77840
RBP: ffffc90000a778e0 R08: ffffc90000a7783f R09: 0000000000000000
R10: ffffc90000a77828 R11: fffff5200014ef08 R12: dffffc0000000000
R13: 1ffff9200014eefc R14: 0000000000000018 R15: ffffc90000a77800
FS:  0000000000000000(0000) GS:ffff8882a920c000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f84a91e9c38 CR3: 000000000e746000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 __rmap_walk_file+0x4cd/0x6a0 mm/rmap.c:3116
 mapping_wrprotect_range+0x110/0x180 mm/rmap.c:1294
 fb_deferred_io_work+0x15a/0x310 drivers/video/fbdev/core/fb_defio.c:399
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:folio_test_anon include/linux/page-flags.h:718 [inline]
RIP: 0010:mapping_wrprotect_range_one+0x147/0x230 mm/rmap.c:1246
Code: 7c 24 40 49 8d 7f 28 ba 18 00 00 00 31 f6 e8 e0 2e 14 00 48 c7 84 24 80 00 00 00 01 00 00 00 49 83 c6 18 4c 89 f0 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 f7 e8 ea 2b 14 00 4d 8b 36 44 89 f6 83
RSP: 0018:ffffc90000a777c0 EFLAGS: 00010206
RAX: 0000000000000003 RBX: ffffc90000a779e0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffc90000a77840
RBP: ffffc90000a778e0 R08: ffffc90000a7783f R09: 0000000000000000
R10: ffffc90000a77828 R11: fffff5200014ef08 R12: dffffc0000000000
R13: 1ffff9200014eefc R14: 0000000000000018 R15: ffffc90000a77800
FS:  0000000000000000(0000) GS:ffff8882a920c000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000025d35e991000 CR3: 0000000110c34000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
   0:	7c 24                	jl     0x26
   2:	40                   	rex
   3:	49 8d 7f 28          	lea    0x28(%r15),%rdi
   7:	ba 18 00 00 00       	mov    $0x18,%edx
   c:	31 f6                	xor    %esi,%esi
   e:	e8 e0 2e 14 00       	call   0x142ef3
  13:	48 c7 84 24 80 00 00 	movq   $0x1,0x80(%rsp)
  1a:	00 01 00 00 00
  1f:	49 83 c6 18          	add    $0x18,%r14
  23:	4c 89 f0             	mov    %r14,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 20 00       	cmpb   $0x0,(%rax,%r12,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	4c 89 f7             	mov    %r14,%rdi
  34:	e8 ea 2b 14 00       	call   0x142c23
  39:	4d 8b 36             	mov    (%r14),%r14
  3c:	44 89 f6             	mov    %r14d,%esi
  3f:	83                   	.byte 0x83


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.

To test a patch for this bug, please reply with `#syz test`
(should be on a separate line).

The patch should be attached to the email.
Note: arguments like custom git repos and branches are not supported.

Re: [syzbot ci] Re: mm/rmap: index MAP_PRIVATE file-backed folios by virt pgoff

[Lorenzo Stoakes (ARM)]

On Fri, Jul 17, 2026 at 11:47:18PM -0700, syzbot ci wrote:
> syzbot ci has tested the following series
>
> [v1] mm/rmap: index MAP_PRIVATE file-backed folios by virt pgoff
> https://lore.kernel.org/all/20260717-b4-scalable-cow-virt-pgoff-v1-0-cf24910ef094@kernel.org
> * [PATCH 01/15] mm/vma: introduce VMA virtual page offset field and add helpers
> * [PATCH 02/15] mm: introduce linear_virt_page_index()
> * [PATCH 03/15] mm: abstract vma_address() and introduce vma_anon_address()
> * [PATCH 04/15] mm: update print_bad_page_map() to show virtual page index
> * [PATCH 05/15] mm: introduce and use vma_filebacked_address()
> * [PATCH 06/15] mm: propagate VMA virtual page offset on map, remap, split + merge
> * [PATCH 07/15] mm/rmap: track whether the page VMA mapped walk is anonymous
> * [PATCH 08/15] mm: introduce and use linear_folio_page_index()
> * [PATCH 09/15] mm/rmap: use virt pgoff for MAP_PRIVATE file-backed anon folios
> * [PATCH 10/15] tools/testing/vma: expand VMA merge tests to assert virt pgoff
> * [PATCH 11/15] tools/testing/selftests/mm: test virtual page offset merge behaviour
> * [PATCH 12/15] mm/vma: only permit MAP_PRIVATE /dev/zero to be mapped anonymous
> * [PATCH 13/15] mm/vma: make MAP_PRIVATE-mapped /dev/zero mappings truly anonymous
> * [PATCH 14/15] tools/testing/vma: add test to assert MAP_PRIVATE-/dev/zero is anon
> * [PATCH 15/15] tools/testing/selftests/mm: add MAP_PRIVATE-/dev/zero merge tests
>
> and found the following issue:
> general protection fault in mapping_wrprotect_range_one
>
> Full report is available here:
> https://ci.syzbot.org/series/b5c827e8-78a4-494c-b925-417c34a60e85
>
> ***
>
> general protection fault in mapping_wrprotect_range_one
>
> tree:      mm-new
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
> base:      5093dba1014c1d7f7e247fd118f0fa8f22136046
> arch:      amd64
> compiler:  Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6
> config:    https://ci.syzbot.org/builds/0d856612-f1b4-4e6e-86af-4ed3215225aa/config
> syz repro: https://ci.syzbot.org/findings/3484dc14-c12f-477e-b14a-6b249c47b2fd/syz_repro
>
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
> CPU: 1 UID: 0 PID: 32 Comm: kworker/1:1 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> Workqueue: events fb_deferred_io_work
> RIP: 0010:folio_test_anon include/linux/page-flags.h:718 [inline]
> RIP: 0010:mapping_wrprotect_range_one+0x147/0x230 mm/rmap.c:1246

Ah yeah, this is:

	VM_WARN_ON_ONCE(folio_test_anon(folio));

In mapping_wrprotect_range_one() and... this test is completely superfluous
actually :)

The only caller is mapping_wrprotect_range() which literally passes a NULL folio
NULL to __rmap_walk_file() (with mapping_wrprotect_range_one set as the
rwc->rmap_one).

I'll ping on the relevant commit and ask Andrew to just drop this line.

Cheers, Lorenzo

> Code: 7c 24 40 49 8d 7f 28 ba 18 00 00 00 31 f6 e8 e0 2e 14 00 48 c7 84 24 80 00 00 00 01 00 00 00 49 83 c6 18 4c 89 f0 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 f7 e8 ea 2b 14 00 4d 8b 36 44 89 f6 83
> RSP: 0018:ffffc90000a777c0 EFLAGS: 00010206
> RAX: 0000000000000003 RBX: ffffc90000a779e0 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffc90000a77840
> RBP: ffffc90000a778e0 R08: ffffc90000a7783f R09: 0000000000000000
> R10: ffffc90000a77828 R11: fffff5200014ef08 R12: dffffc0000000000
> R13: 1ffff9200014eefc R14: 0000000000000018 R15: ffffc90000a77800
> FS:  0000000000000000(0000) GS:ffff8882a920c000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f84a91e9c38 CR3: 000000000e746000 CR4: 00000000000006f0
> Call Trace:
>  <TASK>
>  __rmap_walk_file+0x4cd/0x6a0 mm/rmap.c:3116
>  mapping_wrprotect_range+0x110/0x180 mm/rmap.c:1294
>  fb_deferred_io_work+0x15a/0x310 drivers/video/fbdev/core/fb_defio.c:399
>  process_one_work kernel/workqueue.c:3322 [inline]
>  process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
>  worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
>  kthread+0x388/0x470 kernel/kthread.c:436
>  ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:folio_test_anon include/linux/page-flags.h:718 [inline]
> RIP: 0010:mapping_wrprotect_range_one+0x147/0x230 mm/rmap.c:1246
> Code: 7c 24 40 49 8d 7f 28 ba 18 00 00 00 31 f6 e8 e0 2e 14 00 48 c7 84 24 80 00 00 00 01 00 00 00 49 83 c6 18 4c 89 f0 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 f7 e8 ea 2b 14 00 4d 8b 36 44 89 f6 83
> RSP: 0018:ffffc90000a777c0 EFLAGS: 00010206
> RAX: 0000000000000003 RBX: ffffc90000a779e0 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffc90000a77840
> RBP: ffffc90000a778e0 R08: ffffc90000a7783f R09: 0000000000000000
> R10: ffffc90000a77828 R11: fffff5200014ef08 R12: dffffc0000000000
> R13: 1ffff9200014eefc R14: 0000000000000018 R15: ffffc90000a77800
> FS:  0000000000000000(0000) GS:ffff8882a920c000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000025d35e991000 CR3: 0000000110c34000 CR4: 00000000000006f0
> ----------------
> Code disassembly (best guess):
>    0:	7c 24                	jl     0x26
>    2:	40                   	rex
>    3:	49 8d 7f 28          	lea    0x28(%r15),%rdi
>    7:	ba 18 00 00 00       	mov    $0x18,%edx
>    c:	31 f6                	xor    %esi,%esi
>    e:	e8 e0 2e 14 00       	call   0x142ef3
>   13:	48 c7 84 24 80 00 00 	movq   $0x1,0x80(%rsp)
>   1a:	00 01 00 00 00
>   1f:	49 83 c6 18          	add    $0x18,%r14
>   23:	4c 89 f0             	mov    %r14,%rax
>   26:	48 c1 e8 03          	shr    $0x3,%rax
> * 2a:	42 80 3c 20 00       	cmpb   $0x0,(%rax,%r12,1) <-- trapping instruction
>   2f:	74 08                	je     0x39
>   31:	4c 89 f7             	mov    %r14,%rdi
>   34:	e8 ea 2b 14 00       	call   0x142c23
>   39:	4d 8b 36             	mov    (%r14),%r14
>   3c:	44 89 f6             	mov    %r14d,%esi
>   3f:	83                   	.byte 0x83
>
>
> ***
>
> If these findings have caused you to resend the series or submit a
> separate fix, please add the following tag to your commit message:
>   Tested-by: syzbot@syzkaller.appspotmail.com
>
> ---
> This report is generated by a bot. It may contain errors.
> syzbot ci engineers can be reached at syzkaller@googlegroups.com.
>
> To test a patch for this bug, please reply with `#syz test`
> (should be on a separate line).
>
> The patch should be attached to the email.
> Note: arguments like custom git repos and branches are not supported.