[PATCH v3 00/16] mm: expand mmap_prepare functionality and usage

[PATCH v3 00/16] mm: expand mmap_prepare functionality and usage

[Lorenzo Stoakes (Oracle)]

This series expands the mmap_prepare functionality, which is intended to
replace the deprecated f_op->mmap hook which has been the source of bugs
and security issues for some time.

This series starts with some cleanup of existing mmap_prepare logic, then
adds documentation for the mmap_prepare call to make it easier for
filesystem and driver writers to understand how it works.

It then importantly adds a vm_ops->mapped hook, a key feature that was
missing from mmap_prepare previously - this is invoked when a driver which
specifies mmap_prepare has successfully been mapped but not merged with
another VMA.

mmap_prepare is invoked prior to a merge being attempted, so you cannot
manipulate state such as reference counts as if it were a new mapping.

The vm_ops->mapped hook allows a driver to perform tasks required at this
stage, and provides symmetry against subsequent vm_ops->open,close calls.

The series uses this to correct the afs implementation which wrongly
manipulated reference count at mmap_prepare time.

It then adds an mmap_prepare equivalent of vm_iomap_memory() -
mmap_action_simple_ioremap(), then uses this to update a number of drivers.

It then splits out the mmap_prepare compatibility layer (which allows for
invocation of mmap_prepare hooks in an mmap() hook) in such a way as to
allow for more incremental implementation of mmap_prepare hooks.

It then uses this to extend mmap_prepare usage in drivers.

Finally it adds an mmap_prepare equivalent of vm_map_pages(), which lays
the foundation for future work which will extend mmap_prepare to DMA
coherent mappings.


v3:
* Propagated tags (thanks Suren, Richard!)
* Updated 12/16 to correctly clear the vm_area_desc data structure in
  set_desc_from_vma() as per Joshua Hahn (thanks! :)
* Fixed type in 12/16 as per Suren (cheers!)
* Fixed up 6/16 to use mmap_action_ioremap_full() in simple_ioremap_prepare() as
  suggested by Suren.
* Also fixed up 6/16 to call io_remap_pfn_range_prepare() direct rather than
  mmap_action_prepare() as per Suren.
* Also fixed up 6/16 to pass vm_len rather than vm_[start, end] to
  __simple_ioremap_prep() as per Suren (thanks for all the above! :)
* Fixed issue in rmap lock being held - we were referencing a vma->vm_file after
  the VMA was unmapped, so UAF. Avoid that. Also do_munmap() relies on rmap lock
  NOT being held or may deadlock, so extend functionality to ensure we drop it
  when it is held on error paths.
* Updated 'area' -> 'vma' variable in 3/16 in VMA test dup.h.
* Fixed up reference to __compat_vma_mmap() in 12/16 commit message.
* Updated 1/16 to no longer duplicatively apply io_remap_pfn_range_pfn().
* Updated 1/16 to delegate I/O remap complete to remap complete logic.
* Fixed various typos in 12/16.
* Fixed stale comment typos in 13/16.
* Fixed commit msg and comment typos in 14/16.
* Removed accidental sneak peak to future functionality in 15/16 commit message
  :).
* Fixed up field names to be identical in VMA tests + mm_types.h in 6/16,
  15/16.

v2:
* Rebased on
  https://lore.kernel.org/all/cover.1773665966.git.ljs@kernel.org/ to make
  Andrew's life easier :)
* Folded all interim fixes into series (thanks Randy for many doc fixes!))
* As per Suren, removed a comment about allocations too small to fail.
* As per Randy, fixed up typo in documentation for vm_area_desc.
* Fixed mmap_action_prepare() not returning if invalid action->type
  specified, as updated from Andrew's interim fix (thanks!) and also
  reported by kernel test bot.
* Updated mmap_action_prepare() and specific prepare functions to only
  pass vm_area_desc parameter as per Suren.
* Fixed up whitespace as per Suren.
* Updated vm_op->open comment in vm_operations_struct to reference forking
  as per Suren.
* Added a commit to check that input range is within VMA on remap as per
  Suren (this also covers I/O remap and all other cases already asserted).
* Updated AFS to not incorrectly reference count on mmap prepare as per
  Usama.
* Also updated various static AFS functions to be consistent with each
  other.
* Updated AFS commit message to reflect mmap_prepare being before any VMA
  merging as per Suren.
* Updated __compat_vma_mapped() to check for NULL vm_ops as per Usama.
* Updated __compat_vma_mapped() to not reference an unmapped VMA's fields
  as per Usama.
* Updated __vma_check_mmap_hook() to check for NULL vm_ops as per Usama.
* Dropped comment about preferring mmap_prepare as seems overly confusing,
  as per Suren.
* Updated the mmap lock assert in unmap_vma_locked() to a write lock assert
  as per Suren.
* Copied vm_ops->open comment over to VMA tests in appropriate patch as per
  Suren.
* Updated mmap_prepare documentation to reflect the fact that no resources
  should be allocated upon mmap_prepare.
* Updated mmap_prepare documentation to reference the vm_ops->mapped
  callback.
* Fixed stray markdown '## How to use' in documentation.
* Fixed bug reported by kernel test bot re: overlooked
  vma_desc_test_flags() -> vma_desc_test() in MTD driver for nommu.
https://lore.kernel.org/linux-mm/cover.1773695307.git.ljs@kernel.org/

v1:
https://lore.kernel.org/linux-mm/cover.1773346620.git.ljs@kernel.org/

Lorenzo Stoakes (Oracle) (16):
  mm: various small mmap_prepare cleanups
  mm: add documentation for the mmap_prepare file operation callback
  mm: document vm_operations_struct->open the same as close()
  mm: add vm_ops->mapped hook
  fs: afs: correctly drop reference count on mapping failure
  mm: add mmap_action_simple_ioremap()
  misc: open-dice: replace deprecated mmap hook with mmap_prepare
  hpet: replace deprecated mmap hook with mmap_prepare
  mtdchar: replace deprecated mmap hook with mmap_prepare, clean up
  stm: replace deprecated mmap hook with mmap_prepare
  staging: vme_user: replace deprecated mmap hook with mmap_prepare
  mm: allow handling of stacked mmap_prepare hooks in more drivers
  drivers: hv: vmbus: replace deprecated mmap hook with mmap_prepare
  uio: replace deprecated mmap hook with mmap_prepare in uio_info
  mm: add mmap_action_map_kernel_pages[_full]()
  mm: on remap assert that input range within the proposed VMA

 Documentation/driver-api/vme.rst           |   2 +-
 Documentation/filesystems/index.rst        |   1 +
 Documentation/filesystems/mmap_prepare.rst | 168 ++++++++++++++
 drivers/char/hpet.c                        |  12 +-
 drivers/hv/hyperv_vmbus.h                  |   4 +-
 drivers/hv/vmbus_drv.c                     |  31 ++-
 drivers/hwtracing/stm/core.c               |  31 ++-
 drivers/misc/open-dice.c                   |  19 +-
 drivers/mtd/mtdchar.c                      |  21 +-
 drivers/staging/vme_user/vme.c             |  20 +-
 drivers/staging/vme_user/vme.h             |   2 +-
 drivers/staging/vme_user/vme_user.c        |  51 +++--
 drivers/target/target_core_user.c          |  26 ++-
 drivers/uio/uio.c                          |  10 +-
 drivers/uio/uio_hv_generic.c               |  11 +-
 fs/afs/file.c                              |  36 ++-
 include/linux/fs.h                         |  14 +-
 include/linux/hyperv.h                     |   4 +-
 include/linux/mm.h                         | 159 ++++++++++++-
 include/linux/mm_types.h                   |  17 +-
 include/linux/uio_driver.h                 |   4 +-
 mm/internal.h                              |  41 ++--
 mm/memory.c                                | 175 ++++++++++----
 mm/util.c                                  | 251 ++++++++++++++-------
 mm/vma.c                                   |  53 +++--
 mm/vma.h                                   |   2 +-
 tools/testing/vma/include/dup.h            | 152 ++++++++++---
 tools/testing/vma/include/stubs.h          |   9 +-
 28 files changed, 990 insertions(+), 336 deletions(-)
 create mode 100644 Documentation/filesystems/mmap_prepare.rst

--
2.53.0

[PATCH v3 01/16] mm: various small mmap_prepare cleanups

[Lorenzo Stoakes (Oracle)]

Rather than passing arbitrary fields, pass a vm_area_desc pointer to mmap
prepare functions to mmap prepare, and an action and vma pointer to mmap
complete in order to put all the action-specific logic in the function
actually doing the work.

Additionally, allow mmap prepare functions to return an error so we can
error out as soon as possible if there is something logically incorrect in
the input.

Update remap_pfn_range_prepare() to properly check the input range for the
CoW case.

Also remove io_remap_pfn_range_complete(), as we can simply set up the
fields correctly in io_remap_pfn_range_prepare() and use
remap_pfn_range_complete() for this.

While we're here, make remap_pfn_range_prepare_vma() a little neater, and
pass mmap_action directly to call_action_complete().

Then, update compat_vma_mmap() to perform its logic directly, as
__compat_vma_map() is not used by anything so we don't need to export it.

Also update compat_vma_mmap() to use vfs_mmap_prepare() rather than
calling the mmap_prepare op directly.

Finally, update the VMA userland tests to reflect the changes.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 include/linux/fs.h                |   2 -
 include/linux/mm.h                |   7 +-
 mm/internal.h                     |  32 ++++----
 mm/memory.c                       |  45 +++++++----
 mm/util.c                         | 121 +++++++++++++-----------------
 mm/vma.c                          |  24 +++---
 tools/testing/vma/include/dup.h   |   7 +-
 tools/testing/vma/include/stubs.h |   8 +-
 8 files changed, 126 insertions(+), 120 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8b3dd145b25e..a2628a12bd2b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2058,8 +2058,6 @@ static inline bool can_mmap_file(struct file *file)
 	return true;
 }
 
-int __compat_vma_mmap(const struct file_operations *f_op,
-		struct file *file, struct vm_area_struct *vma);
 int compat_vma_mmap(struct file *file, struct vm_area_struct *vma);
 
 static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 42cc40aa63d9..1e63b3a44a47 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4320,10 +4320,9 @@ static inline void mmap_action_ioremap_full(struct vm_area_desc *desc,
 	mmap_action_ioremap(desc, desc->start, start_pfn, vma_desc_size(desc));
 }
 
-void mmap_action_prepare(struct mmap_action *action,
-			 struct vm_area_desc *desc);
-int mmap_action_complete(struct mmap_action *action,
-			 struct vm_area_struct *vma);
+int mmap_action_prepare(struct vm_area_desc *desc);
+int mmap_action_complete(struct vm_area_struct *vma,
+			 struct mmap_action *action);
 
 /* Look up the first VMA which exactly match the interval vm_start ... vm_end */
 static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
diff --git a/mm/internal.h b/mm/internal.h
index 708d240b4198..0256ca44115a 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1793,26 +1793,28 @@ int walk_page_range_debug(struct mm_struct *mm, unsigned long start,
 void dup_mm_exe_file(struct mm_struct *mm, struct mm_struct *oldmm);
 int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm);
 
-void remap_pfn_range_prepare(struct vm_area_desc *desc, unsigned long pfn);
-int remap_pfn_range_complete(struct vm_area_struct *vma, unsigned long addr,
-		unsigned long pfn, unsigned long size, pgprot_t pgprot);
+int remap_pfn_range_prepare(struct vm_area_desc *desc);
+int remap_pfn_range_complete(struct vm_area_struct *vma,
+			     struct mmap_action *action);
 
-static inline void io_remap_pfn_range_prepare(struct vm_area_desc *desc,
-		unsigned long orig_pfn, unsigned long size)
+static inline int io_remap_pfn_range_prepare(struct vm_area_desc *desc)
 {
+	struct mmap_action *action = &desc->action;
+	const unsigned long orig_pfn = action->remap.start_pfn;
+	const pgprot_t orig_pgprot = action->remap.pgprot;
+	const unsigned long size = action->remap.size;
 	const unsigned long pfn = io_remap_pfn_range_pfn(orig_pfn, size);
+	int err;
 
-	return remap_pfn_range_prepare(desc, pfn);
-}
+	action->remap.start_pfn = pfn;
+	action->remap.pgprot = pgprot_decrypted(orig_pgprot);
+	err = remap_pfn_range_prepare(desc);
+	if (err)
+		return err;
 
-static inline int io_remap_pfn_range_complete(struct vm_area_struct *vma,
-		unsigned long addr, unsigned long orig_pfn, unsigned long size,
-		pgprot_t orig_prot)
-{
-	const unsigned long pfn = io_remap_pfn_range_pfn(orig_pfn, size);
-	const pgprot_t prot = pgprot_decrypted(orig_prot);
-
-	return remap_pfn_range_complete(vma, addr, pfn, size, prot);
+	/* Remap does the actual work. */
+	action->type = MMAP_REMAP_PFN;
+	return 0;
 }
 
 #ifdef CONFIG_MMU_NOTIFIER
diff --git a/mm/memory.c b/mm/memory.c
index 219b9bf6cae0..9dec67a18116 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3099,26 +3099,34 @@ static int do_remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
 }
 #endif
 
-void remap_pfn_range_prepare(struct vm_area_desc *desc, unsigned long pfn)
+int remap_pfn_range_prepare(struct vm_area_desc *desc)
 {
-	/*
-	 * We set addr=VMA start, end=VMA end here, so this won't fail, but we
-	 * check it again on complete and will fail there if specified addr is
-	 * invalid.
-	 */
-	get_remap_pgoff(vma_desc_is_cow_mapping(desc), desc->start, desc->end,
-			desc->start, desc->end, pfn, &desc->pgoff);
+	const struct mmap_action *action = &desc->action;
+	const unsigned long start = action->remap.start;
+	const unsigned long end = start + action->remap.size;
+	const unsigned long pfn = action->remap.start_pfn;
+	const bool is_cow = vma_desc_is_cow_mapping(desc);
+	int err;
+
+	err = get_remap_pgoff(is_cow, start, end, desc->start, desc->end, pfn,
+			      &desc->pgoff);
+	if (err)
+		return err;
+
 	vma_desc_set_flags_mask(desc, VMA_REMAP_FLAGS);
+	return 0;
 }
 
-static int remap_pfn_range_prepare_vma(struct vm_area_struct *vma, unsigned long addr,
-		unsigned long pfn, unsigned long size)
+static int remap_pfn_range_prepare_vma(struct vm_area_struct *vma,
+				       unsigned long addr, unsigned long pfn,
+				       unsigned long size)
 {
-	unsigned long end = addr + PAGE_ALIGN(size);
+	const unsigned long end = addr + PAGE_ALIGN(size);
+	const bool is_cow = is_cow_mapping(vma->vm_flags);
 	int err;
 
-	err = get_remap_pgoff(is_cow_mapping(vma->vm_flags), addr, end,
-			      vma->vm_start, vma->vm_end, pfn, &vma->vm_pgoff);
+	err = get_remap_pgoff(is_cow, addr, end, vma->vm_start, vma->vm_end,
+			      pfn, &vma->vm_pgoff);
 	if (err)
 		return err;
 
@@ -3151,10 +3159,15 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
 }
 EXPORT_SYMBOL(remap_pfn_range);
 
-int remap_pfn_range_complete(struct vm_area_struct *vma, unsigned long addr,
-		unsigned long pfn, unsigned long size, pgprot_t prot)
+int remap_pfn_range_complete(struct vm_area_struct *vma,
+			     struct mmap_action *action)
 {
-	return do_remap_pfn_range(vma, addr, pfn, size, prot);
+	const unsigned long start = action->remap.start;
+	const unsigned long pfn = action->remap.start_pfn;
+	const unsigned long size = action->remap.size;
+	const pgprot_t prot = action->remap.pgprot;
+
+	return do_remap_pfn_range(vma, start, pfn, size, prot);
 }
 
 /**
diff --git a/mm/util.c b/mm/util.c
index ce7ae80047cf..73c97a748d8e 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1163,43 +1163,6 @@ void flush_dcache_folio(struct folio *folio)
 EXPORT_SYMBOL(flush_dcache_folio);
 #endif
 
-/**
- * __compat_vma_mmap() - See description for compat_vma_mmap()
- * for details. This is the same operation, only with a specific file operations
- * struct which may or may not be the same as vma->vm_file->f_op.
- * @f_op: The file operations whose .mmap_prepare() hook is specified.
- * @file: The file which backs or will back the mapping.
- * @vma: The VMA to apply the .mmap_prepare() hook to.
- * Returns: 0 on success or error.
- */
-int __compat_vma_mmap(const struct file_operations *f_op,
-		struct file *file, struct vm_area_struct *vma)
-{
-	struct vm_area_desc desc = {
-		.mm = vma->vm_mm,
-		.file = file,
-		.start = vma->vm_start,
-		.end = vma->vm_end,
-
-		.pgoff = vma->vm_pgoff,
-		.vm_file = vma->vm_file,
-		.vma_flags = vma->flags,
-		.page_prot = vma->vm_page_prot,
-
-		.action.type = MMAP_NOTHING, /* Default */
-	};
-	int err;
-
-	err = f_op->mmap_prepare(&desc);
-	if (err)
-		return err;
-
-	mmap_action_prepare(&desc.action, &desc);
-	set_vma_from_desc(vma, &desc);
-	return mmap_action_complete(&desc.action, vma);
-}
-EXPORT_SYMBOL(__compat_vma_mmap);
-
 /**
  * compat_vma_mmap() - Apply the file's .mmap_prepare() hook to an
  * existing VMA and execute any requested actions.
@@ -1228,7 +1191,31 @@ EXPORT_SYMBOL(__compat_vma_mmap);
  */
 int compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	return __compat_vma_mmap(file->f_op, file, vma);
+	struct vm_area_desc desc = {
+		.mm = vma->vm_mm,
+		.file = file,
+		.start = vma->vm_start,
+		.end = vma->vm_end,
+
+		.pgoff = vma->vm_pgoff,
+		.vm_file = vma->vm_file,
+		.vma_flags = vma->flags,
+		.page_prot = vma->vm_page_prot,
+
+		.action.type = MMAP_NOTHING, /* Default */
+	};
+	int err;
+
+	err = vfs_mmap_prepare(file, &desc);
+	if (err)
+		return err;
+
+	err = mmap_action_prepare(&desc);
+	if (err)
+		return err;
+
+	set_vma_from_desc(vma, &desc);
+	return mmap_action_complete(vma, &desc.action);
 }
 EXPORT_SYMBOL(compat_vma_mmap);
 
@@ -1320,8 +1307,8 @@ void snapshot_page(struct page_snapshot *ps, const struct page *page)
 	}
 }
 
-static int mmap_action_finish(struct mmap_action *action,
-		const struct vm_area_struct *vma, int err)
+static int mmap_action_finish(struct vm_area_struct *vma,
+			      struct mmap_action *action, int err)
 {
 	/*
 	 * If an error occurs, unmap the VMA altogether and return an error. We
@@ -1353,37 +1340,38 @@ static int mmap_action_finish(struct mmap_action *action,
 /**
  * mmap_action_prepare - Perform preparatory setup for an VMA descriptor
  * action which need to be performed.
- * @desc: The VMA descriptor to prepare for @action.
- * @action: The action to perform.
+ * @desc: The VMA descriptor to prepare for its @desc->action.
+ *
+ * Returns: %0 on success, otherwise error.
  */
-void mmap_action_prepare(struct mmap_action *action,
-			 struct vm_area_desc *desc)
+int mmap_action_prepare(struct vm_area_desc *desc)
 {
-	switch (action->type) {
+	switch (desc->action.type) {
 	case MMAP_NOTHING:
-		break;
+		return 0;
 	case MMAP_REMAP_PFN:
-		remap_pfn_range_prepare(desc, action->remap.start_pfn);
-		break;
+		return remap_pfn_range_prepare(desc);
 	case MMAP_IO_REMAP_PFN:
-		io_remap_pfn_range_prepare(desc, action->remap.start_pfn,
-					   action->remap.size);
-		break;
+		return io_remap_pfn_range_prepare(desc);
 	}
+
+	WARN_ON_ONCE(1);
+	return -EINVAL;
 }
 EXPORT_SYMBOL(mmap_action_prepare);
 
 /**
  * mmap_action_complete - Execute VMA descriptor action.
- * @action: The action to perform.
  * @vma: The VMA to perform the action upon.
+ * @action: The action to perform.
  *
  * Similar to mmap_action_prepare().
  *
  * Return: 0 on success, or error, at which point the VMA will be unmapped.
  */
-int mmap_action_complete(struct mmap_action *action,
-			 struct vm_area_struct *vma)
+int mmap_action_complete(struct vm_area_struct *vma,
+			 struct mmap_action *action)
+
 {
 	int err = 0;
 
@@ -1391,25 +1379,22 @@ int mmap_action_complete(struct mmap_action *action,
 	case MMAP_NOTHING:
 		break;
 	case MMAP_REMAP_PFN:
-		err = remap_pfn_range_complete(vma, action->remap.start,
-				action->remap.start_pfn, action->remap.size,
-				action->remap.pgprot);
+		err = remap_pfn_range_complete(vma, action);
 		break;
 	case MMAP_IO_REMAP_PFN:
-		err = io_remap_pfn_range_complete(vma, action->remap.start,
-				action->remap.start_pfn, action->remap.size,
-				action->remap.pgprot);
+		/* Should have been delegated. */
+		WARN_ON_ONCE(1);
+		err = -EINVAL;
 		break;
 	}
 
-	return mmap_action_finish(action, vma, err);
+	return mmap_action_finish(vma, action, err);
 }
 EXPORT_SYMBOL(mmap_action_complete);
 #else
-void mmap_action_prepare(struct mmap_action *action,
-			struct vm_area_desc *desc)
+int mmap_action_prepare(struct vm_area_desc *desc)
 {
-	switch (action->type) {
+	switch (desc->action.type) {
 	case MMAP_NOTHING:
 		break;
 	case MMAP_REMAP_PFN:
@@ -1417,11 +1402,13 @@ void mmap_action_prepare(struct mmap_action *action,
 		WARN_ON_ONCE(1); /* nommu cannot handle these. */
 		break;
 	}
+
+	return 0;
 }
 EXPORT_SYMBOL(mmap_action_prepare);
 
-int mmap_action_complete(struct mmap_action *action,
-			struct vm_area_struct *vma)
+int mmap_action_complete(struct vm_area_struct *vma,
+			 struct mmap_action *action)
 {
 	int err = 0;
 
@@ -1436,7 +1423,7 @@ int mmap_action_complete(struct mmap_action *action,
 		break;
 	}
 
-	return mmap_action_finish(action, vma, err);
+	return mmap_action_finish(vma, action, err);
 }
 EXPORT_SYMBOL(mmap_action_complete);
 #endif
diff --git a/mm/vma.c b/mm/vma.c
index c1f183235756..2a86c7575000 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -2640,15 +2640,18 @@ static void __mmap_complete(struct mmap_state *map, struct vm_area_struct *vma)
 	vma_set_page_prot(vma);
 }
 
-static void call_action_prepare(struct mmap_state *map,
-				struct vm_area_desc *desc)
+static int call_action_prepare(struct mmap_state *map,
+			       struct vm_area_desc *desc)
 {
-	struct mmap_action *action = &desc->action;
+	int err;
 
-	mmap_action_prepare(action, desc);
+	err = mmap_action_prepare(desc);
+	if (err)
+		return err;
 
-	if (action->hide_from_rmap_until_complete)
+	if (desc->action.hide_from_rmap_until_complete)
 		map->hold_file_rmap_lock = true;
+	return 0;
 }
 
 /*
@@ -2672,7 +2675,9 @@ static int call_mmap_prepare(struct mmap_state *map,
 	if (err)
 		return err;
 
-	call_action_prepare(map, desc);
+	err = call_action_prepare(map, desc);
+	if (err)
+		return err;
 
 	/* Update fields permitted to be changed. */
 	map->pgoff = desc->pgoff;
@@ -2727,13 +2732,12 @@ static bool can_set_ksm_flags_early(struct mmap_state *map)
 }
 
 static int call_action_complete(struct mmap_state *map,
-				struct vm_area_desc *desc,
+				struct mmap_action *action,
 				struct vm_area_struct *vma)
 {
-	struct mmap_action *action = &desc->action;
 	int ret;
 
-	ret = mmap_action_complete(action, vma);
+	ret = mmap_action_complete(vma, action);
 
 	/* If we held the file rmap we need to release it. */
 	if (map->hold_file_rmap_lock) {
@@ -2795,7 +2799,7 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr,
 	__mmap_complete(&map, vma);
 
 	if (have_mmap_prepare && allocated_new) {
-		error = call_action_complete(&map, &desc, vma);
+		error = call_action_complete(&map, &desc.action, vma);
 
 		if (error)
 			return error;
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 999357e18eb0..9eada1e0949c 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -1271,9 +1271,12 @@ static inline int __compat_vma_mmap(const struct file_operations *f_op,
 	if (err)
 		return err;
 
-	mmap_action_prepare(&desc.action, &desc);
+	err = mmap_action_prepare(&desc);
+	if (err)
+		return err;
+
 	set_vma_from_desc(vma, &desc);
-	return mmap_action_complete(&desc.action, vma);
+	return mmap_action_complete(vma, &desc.action);
 }
 
 static inline int compat_vma_mmap(struct file *file,
diff --git a/tools/testing/vma/include/stubs.h b/tools/testing/vma/include/stubs.h
index 5afb0afe2d48..a30b8bc84955 100644
--- a/tools/testing/vma/include/stubs.h
+++ b/tools/testing/vma/include/stubs.h
@@ -81,13 +81,13 @@ static inline void free_anon_vma_name(struct vm_area_struct *vma)
 {
 }
 
-static inline void mmap_action_prepare(struct mmap_action *action,
-					   struct vm_area_desc *desc)
+static inline int mmap_action_prepare(struct vm_area_desc *desc)
 {
+	return 0;
 }
 
-static inline int mmap_action_complete(struct mmap_action *action,
-					   struct vm_area_struct *vma)
+static inline int mmap_action_complete(struct vm_area_struct *vma,
+				       struct mmap_action *action)
 {
 	return 0;
 }
-- 
2.53.0

[PATCH v3 02/16] mm: add documentation for the mmap_prepare file operation callback

[Lorenzo Stoakes (Oracle)]

This documentation makes it easier for a driver/file system implementer to
correctly use this callback.

It covers the fundamentals, whilst intentionally leaving the less lovely
possible actions one might take undocumented (for instance - the
success_hook, error_hook fields in mmap_action).

The document also covers the new VMA flags implementation which is the
only one which will work correctly with mmap_prepare.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 Documentation/filesystems/index.rst        |   1 +
 Documentation/filesystems/mmap_prepare.rst | 142 +++++++++++++++++++++
 2 files changed, 143 insertions(+)
 create mode 100644 Documentation/filesystems/mmap_prepare.rst

diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst
index f4873197587d..6cbc3e0292ae 100644
--- a/Documentation/filesystems/index.rst
+++ b/Documentation/filesystems/index.rst
@@ -29,6 +29,7 @@ algorithms work.
    fiemap
    files
    locks
+   mmap_prepare
    multigrain-ts
    mount_api
    quota
diff --git a/Documentation/filesystems/mmap_prepare.rst b/Documentation/filesystems/mmap_prepare.rst
new file mode 100644
index 000000000000..65a1f094e469
--- /dev/null
+++ b/Documentation/filesystems/mmap_prepare.rst
@@ -0,0 +1,142 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========================
+mmap_prepare callback HOWTO
+===========================
+
+Introduction
+============
+
+The ``struct file->f_op->mmap()`` callback has been deprecated as it is both a
+stability and security risk, and doesn't always permit the merging of adjacent
+mappings resulting in unnecessary memory fragmentation.
+
+It has been replaced with the ``file->f_op->mmap_prepare()`` callback which
+solves these problems.
+
+This hook is called right at the beginning of setting up the mapping, and
+importantly it is invoked *before* any merging of adjacent mappings has taken
+place.
+
+If an error arises upon mapping, it might arise after this callback has been
+invoked, therefore it should be treated as effectively stateless.
+
+That is - no resources should be allocated nor state updated to reflect that a
+mapping has been established, as the mapping may either be merged, or fail to be
+mapped after the callback is complete.
+
+How To Use
+==========
+
+In your driver's struct file_operations struct, specify an ``mmap_prepare``
+callback rather than an ``mmap`` one, e.g. for ext4:
+
+.. code-block:: C
+
+    const struct file_operations ext4_file_operations = {
+        ...
+        .mmap_prepare    = ext4_file_mmap_prepare,
+    };
+
+This has a signature of ``int (*mmap_prepare)(struct vm_area_desc *)``.
+
+Examining the struct vm_area_desc type:
+
+.. code-block:: C
+
+    struct vm_area_desc {
+        /* Immutable state. */
+        const struct mm_struct *const mm;
+        struct file *const file; /* May vary from vm_file in stacked callers. */
+        unsigned long start;
+        unsigned long end;
+
+        /* Mutable fields. Populated with initial state. */
+        pgoff_t pgoff;
+        struct file *vm_file;
+        vma_flags_t vma_flags;
+        pgprot_t page_prot;
+
+        /* Write-only fields. */
+        const struct vm_operations_struct *vm_ops;
+        void *private_data;
+
+        /* Take further action? */
+        struct mmap_action action;
+    };
+
+This is straightforward - you have all the fields you need to set up the
+mapping, and you can update the mutable and writable fields, for instance:
+
+.. code-block:: C
+
+    static int ext4_file_mmap_prepare(struct vm_area_desc *desc)
+    {
+        int ret;
+        struct file *file = desc->file;
+        struct inode *inode = file->f_mapping->host;
+
+        ...
+
+        file_accessed(file);
+        if (IS_DAX(file_inode(file))) {
+            desc->vm_ops = &ext4_dax_vm_ops;
+            vma_desc_set_flags(desc, VMA_HUGEPAGE_BIT);
+        } else {
+            desc->vm_ops = &ext4_file_vm_ops;
+        }
+        return 0;
+    }
+
+Importantly, you no longer have to dance around with reference counts or locks
+when updating these fields - **you can simply go ahead and change them**.
+
+Everything is taken care of by the mapping code.
+
+VMA Flags
+---------
+
+Along with ``mmap_prepare``, VMA flags have undergone an overhaul. Where before
+you would invoke one of vm_flags_init(), vm_flags_reset(), vm_flags_set(),
+vm_flags_clear(), and vm_flags_mod() to modify flags (and to have the
+locking done correctly for you, this is no longer necessary.
+
+Also, the legacy approach of specifying VMA flags via ``VM_READ``, ``VM_WRITE``,
+etc. - i.e. using a ``-VM_xxx``- macro has changed too.
+
+When implementing mmap_prepare(), reference flags by their bit number, defined
+as a ``VMA_xxx_BIT`` macro, e.g. ``VMA_READ_BIT``, ``VMA_WRITE_BIT`` etc.,
+and use one of (where ``desc`` is a pointer to struct vm_area_desc):
+
+* ``vma_desc_test_flags(desc, ...)`` - Specify a comma-separated list of flags
+  you wish to test for (whether _any_ are set), e.g. - ``vma_desc_test_flags(
+  desc, VMA_WRITE_BIT, VMA_MAYWRITE_BIT)`` - returns ``true`` if either are set,
+  otherwise ``false``.
+* ``vma_desc_set_flags(desc, ...)`` - Update the VMA descriptor flags to set
+  additional flags specified by a comma-separated list,
+  e.g. - ``vma_desc_set_flags(desc, VMA_PFNMAP_BIT, VMA_IO_BIT)``.
+* ``vma_desc_clear_flags(desc, ...)`` - Update the VMA descriptor flags to clear
+  flags specified by a comma-separated list, e.g. - ``vma_desc_clear_flags(
+  desc, VMA_WRITE_BIT, VMA_MAYWRITE_BIT)``.
+
+Actions
+=======
+
+You can now very easily have actions be performed upon a mapping once set up by
+utilising simple helper functions invoked upon the struct vm_area_desc
+pointer. These are:
+
+* mmap_action_remap() - Remaps a range consisting only of PFNs for a specific
+  range starting a virtual address and PFN number of a set size.
+
+* mmap_action_remap_full() - Same as mmap_action_remap(), only remaps the
+  entire mapping from ``start_pfn`` onward.
+
+* mmap_action_ioremap() - Same as mmap_action_remap(), only performs an I/O
+  remap.
+
+* mmap_action_ioremap_full() - Same as mmap_action_ioremap(), only remaps
+  the entire mapping from ``start_pfn`` onward.
+
+**NOTE:** The ``action`` field should never normally be manipulated directly,
+rather you ought to use one of these helpers.
-- 
2.53.0

[PATCH v3 03/16] mm: document vm_operations_struct->open the same as close()

[Lorenzo Stoakes (Oracle)]

Describe when the operation is invoked and the context in which it is
invoked, matching the description already added for vm_op->close().

While we're here, update all outdated references to an 'area' field for
VMAs to the more consistent 'vma'.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 include/linux/mm.h              | 15 ++++++++++-----
 tools/testing/vma/include/dup.h | 15 ++++++++++-----
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1e63b3a44a47..da94edb287cd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -766,15 +766,20 @@ struct vm_uffd_ops;
  * to the functions called when a no-page or a wp-page exception occurs.
  */
 struct vm_operations_struct {
-	void (*open)(struct vm_area_struct * area);
+	/**
+	 * @open: Called when a VMA is remapped, split or forked. Not called
+	 * upon first mapping a VMA.
+	 * Context: User context.  May sleep.  Caller holds mmap_lock.
+	 */
+	void (*open)(struct vm_area_struct *vma);
 	/**
 	 * @close: Called when the VMA is being removed from the MM.
 	 * Context: User context.  May sleep.  Caller holds mmap_lock.
 	 */
-	void (*close)(struct vm_area_struct * area);
+	void (*close)(struct vm_area_struct *vma);
 	/* Called any time before splitting to check if it's allowed */
-	int (*may_split)(struct vm_area_struct *area, unsigned long addr);
-	int (*mremap)(struct vm_area_struct *area);
+	int (*may_split)(struct vm_area_struct *vma, unsigned long addr);
+	int (*mremap)(struct vm_area_struct *vma);
 	/*
 	 * Called by mprotect() to make driver-specific permission
 	 * checks before mprotect() is finalised.   The VMA must not
@@ -786,7 +791,7 @@ struct vm_operations_struct {
 	vm_fault_t (*huge_fault)(struct vm_fault *vmf, unsigned int order);
 	vm_fault_t (*map_pages)(struct vm_fault *vmf,
 			pgoff_t start_pgoff, pgoff_t end_pgoff);
-	unsigned long (*pagesize)(struct vm_area_struct * area);
+	unsigned long (*pagesize)(struct vm_area_struct *vma);
 
 	/* notification that a previously read-only page is about to become
 	 * writable, if an error is returned it will cause a SIGBUS */
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 9eada1e0949c..8ae525ed1738 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -632,15 +632,20 @@ struct vm_area_struct {
 } __randomize_layout;
 
 struct vm_operations_struct {
-	void (*open)(struct vm_area_struct * area);
+	/**
+	 * @open: Called when a VMA is remapped, split or forked. Not called
+	 * upon first mapping a VMA.
+	 * Context: User context.  May sleep.  Caller holds mmap_lock.
+	 */
+	void (*open)(struct vm_area_struct *vma);
 	/**
 	 * @close: Called when the VMA is being removed from the MM.
 	 * Context: User context.  May sleep.  Caller holds mmap_lock.
 	 */
-	void (*close)(struct vm_area_struct * area);
+	void (*close)(struct vm_area_struct *vma);
 	/* Called any time before splitting to check if it's allowed */
-	int (*may_split)(struct vm_area_struct *area, unsigned long addr);
-	int (*mremap)(struct vm_area_struct *area);
+	int (*may_split)(struct vm_area_struct *vma, unsigned long addr);
+	int (*mremap)(struct vm_area_struct *vma);
 	/*
 	 * Called by mprotect() to make driver-specific permission
 	 * checks before mprotect() is finalised.   The VMA must not
@@ -652,7 +657,7 @@ struct vm_operations_struct {
 	vm_fault_t (*huge_fault)(struct vm_fault *vmf, unsigned int order);
 	vm_fault_t (*map_pages)(struct vm_fault *vmf,
 			pgoff_t start_pgoff, pgoff_t end_pgoff);
-	unsigned long (*pagesize)(struct vm_area_struct * area);
+	unsigned long (*pagesize)(struct vm_area_struct *vma);
 
 	/* notification that a previously read-only page is about to become
 	 * writable, if an error is returned it will cause a SIGBUS */
-- 
2.53.0

[PATCH v3 04/16] mm: add vm_ops->mapped hook

[Lorenzo Stoakes (Oracle)]

Previously, when a driver needed to do something like establish a
reference count, it could do so in the mmap hook in the knowledge that the
mapping would succeed.

With the introduction of f_op->mmap_prepare this is no longer the case, as
it is invoked prior to actually establishing the mapping.

mmap_prepare is not appropriate for this kind of thing as it is called
before any merge might take place, and after which an error might occur
meaning resources could be leaked.

To take this into account, introduce a new vm_ops->mapped callback which
is invoked when the VMA is first mapped (though notably - not when it is
merged - which is correct and mirrors existing mmap/open/close behaviour).

We do better that vm_ops->open() here, as this callback can return an
error, at which point the VMA will be unmapped.

Note that vm_ops->mapped() is invoked after any mmap action is complete
(such as I/O remapping).

We intentionally do not expose the VMA at this point, exposing only the
fields that could be used, and an output parameter in case the operation
needs to update the vma->vm_private_data field.

In order to deal with stacked filesystems which invoke inner filesystem's
mmap() invocations, add __compat_vma_mapped() and invoke it on vfs_mmap()
(via compat_vma_mmap()) to ensure that the mapped callback is handled when
an mmap() caller invokes a nested filesystem's mmap_prepare() callback.

We can now also remove call_action_complete() and invoke
mmap_action_complete() directly, as we separate out the rmap lock logic.

The rmap lock logic, which was added in order to keep hugetlb working (!)
to allow for the rmap lock to be held longer, needs to be propagated to the
error paths on mmap complete and mapped hook error paths.

This is because do_munmap() might otherwise deadlock with the rmap being
held, so instead we unlock at the point of unmap.

This is fine as any reliance on the rmap being held is irrelevant on error.

While we're here, refactor mmap_action_finish() to avoid a big if (err)
branch.

We also abstract unmapping of a VMA on mmap action completion into its own
helper function, unmap_vma_locked().

Update the mmap_prepare documentation to describe the mapped hook and make
it clear what its intended use is.

Additionally, update VMA userland test headers to reflect the change.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 Documentation/filesystems/mmap_prepare.rst |  15 +++
 include/linux/fs.h                         |   9 +-
 include/linux/mm.h                         |  20 +++-
 mm/internal.h                              |   8 ++
 mm/util.c                                  | 129 ++++++++++++++-------
 mm/vma.c                                   |  35 +++---
 tools/testing/vma/include/dup.h            |  27 ++++-
 tools/testing/vma/include/stubs.h          |   3 +-
 8 files changed, 186 insertions(+), 60 deletions(-)

diff --git a/Documentation/filesystems/mmap_prepare.rst b/Documentation/filesystems/mmap_prepare.rst
index 65a1f094e469..20db474915da 100644
--- a/Documentation/filesystems/mmap_prepare.rst
+++ b/Documentation/filesystems/mmap_prepare.rst
@@ -25,6 +25,21 @@ That is - no resources should be allocated nor state updated to reflect that a
 mapping has been established, as the mapping may either be merged, or fail to be
 mapped after the callback is complete.
 
+Mapped callback
+---------------
+
+If resources need to be allocated per-mapping, or state such as a reference
+count needs to be manipulated, this should be done using the ``vm_ops->mapped``
+hook, which itself should be set by the >mmap_prepare hook.
+
+This callback is only invoked if a new mapping has been established and was not
+merged with any other, and is invoked at a point where no error may occur before
+the mapping is established.
+
+You may return an error to the callback itself, which will cause the mapping to
+become unmapped and an error returned to the mmap() caller. This is useful if
+resources need to be allocated, and that allocation might fail.
+
 How To Use
 ==========
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a2628a12bd2b..c390f5c667e3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2059,13 +2059,20 @@ static inline bool can_mmap_file(struct file *file)
 }
 
 int compat_vma_mmap(struct file *file, struct vm_area_struct *vma);
+int __vma_check_mmap_hook(struct vm_area_struct *vma);
 
 static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma)
 {
+	int err;
+
 	if (file->f_op->mmap_prepare)
 		return compat_vma_mmap(file, vma);
 
-	return file->f_op->mmap(file, vma);
+	err = file->f_op->mmap(file, vma);
+	if (err)
+		return err;
+
+	return __vma_check_mmap_hook(vma);
 }
 
 static inline int vfs_mmap_prepare(struct file *file, struct vm_area_desc *desc)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index da94edb287cd..68dee1101313 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -777,6 +777,23 @@ struct vm_operations_struct {
 	 * Context: User context.  May sleep.  Caller holds mmap_lock.
 	 */
 	void (*close)(struct vm_area_struct *vma);
+	/**
+	 * @mapped: Called when the VMA is first mapped in the MM. Not called if
+	 * the new VMA is merged with an adjacent VMA.
+	 *
+	 * The @vm_private_data field is an output field allowing the user to
+	 * modify vma->vm_private_data as necessary.
+	 *
+	 * ONLY valid if set from f_op->mmap_prepare. Will result in an error if
+	 * set from f_op->mmap.
+	 *
+	 * Returns %0 on success, or an error otherwise. On error, the VMA will
+	 * be unmapped.
+	 *
+	 * Context: User context.  May sleep.  Caller holds mmap_lock.
+	 */
+	int (*mapped)(unsigned long start, unsigned long end, pgoff_t pgoff,
+		      const struct file *file, void **vm_private_data);
 	/* Called any time before splitting to check if it's allowed */
 	int (*may_split)(struct vm_area_struct *vma, unsigned long addr);
 	int (*mremap)(struct vm_area_struct *vma);
@@ -4327,7 +4344,8 @@ static inline void mmap_action_ioremap_full(struct vm_area_desc *desc,
 
 int mmap_action_prepare(struct vm_area_desc *desc);
 int mmap_action_complete(struct vm_area_struct *vma,
-			 struct mmap_action *action);
+			 struct mmap_action *action,
+			 bool rmap_lock_held);
 
 /* Look up the first VMA which exactly match the interval vm_start ... vm_end */
 static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
diff --git a/mm/internal.h b/mm/internal.h
index 0256ca44115a..e0f554178143 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -202,6 +202,14 @@ static inline void vma_close(struct vm_area_struct *vma)
 /* unmap_vmas is in mm/memory.c */
 void unmap_vmas(struct mmu_gather *tlb, struct unmap_desc *unmap);
 
+static inline void unmap_vma_locked(struct vm_area_struct *vma)
+{
+	const size_t len = vma_pages(vma) << PAGE_SHIFT;
+
+	mmap_assert_write_locked(vma->vm_mm);
+	do_munmap(vma->vm_mm, vma->vm_start, len, NULL);
+}
+
 #ifdef CONFIG_MMU
 
 static inline void get_anon_vma(struct anon_vma *anon_vma)
diff --git a/mm/util.c b/mm/util.c
index 73c97a748d8e..fc1bd8a8f3ea 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1163,6 +1163,54 @@ void flush_dcache_folio(struct folio *folio)
 EXPORT_SYMBOL(flush_dcache_folio);
 #endif
 
+static int __compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct vm_area_desc desc = {
+		.mm = vma->vm_mm,
+		.file = file,
+		.start = vma->vm_start,
+		.end = vma->vm_end,
+
+		.pgoff = vma->vm_pgoff,
+		.vm_file = vma->vm_file,
+		.vma_flags = vma->flags,
+		.page_prot = vma->vm_page_prot,
+
+		.action.type = MMAP_NOTHING, /* Default */
+	};
+	int err;
+
+	err = vfs_mmap_prepare(file, &desc);
+	if (err)
+		return err;
+
+	err = mmap_action_prepare(&desc);
+	if (err)
+		return err;
+
+	set_vma_from_desc(vma, &desc);
+	return mmap_action_complete(vma, &desc.action, /*rmap_lock_held=*/false);
+}
+
+static int __compat_vma_mapped(struct file *file, struct vm_area_struct *vma)
+{
+	const struct vm_operations_struct *vm_ops = vma->vm_ops;
+	void *vm_private_data = vma->vm_private_data;
+	int err;
+
+	if (!vm_ops || !vm_ops->mapped)
+		return 0;
+
+	err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff, file,
+			     &vm_private_data);
+	if (err)
+		unmap_vma_locked(vma);
+	else if (vm_private_data != vma->vm_private_data)
+		vma->vm_private_data = vm_private_data;
+
+	return err;
+}
+
 /**
  * compat_vma_mmap() - Apply the file's .mmap_prepare() hook to an
  * existing VMA and execute any requested actions.
@@ -1191,34 +1239,26 @@ EXPORT_SYMBOL(flush_dcache_folio);
  */
 int compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	struct vm_area_desc desc = {
-		.mm = vma->vm_mm,
-		.file = file,
-		.start = vma->vm_start,
-		.end = vma->vm_end,
-
-		.pgoff = vma->vm_pgoff,
-		.vm_file = vma->vm_file,
-		.vma_flags = vma->flags,
-		.page_prot = vma->vm_page_prot,
-
-		.action.type = MMAP_NOTHING, /* Default */
-	};
 	int err;
 
-	err = vfs_mmap_prepare(file, &desc);
+	err = __compat_vma_mmap(file, vma);
 	if (err)
 		return err;
 
-	err = mmap_action_prepare(&desc);
-	if (err)
-		return err;
-
-	set_vma_from_desc(vma, &desc);
-	return mmap_action_complete(vma, &desc.action);
+	return __compat_vma_mapped(file, vma);
 }
 EXPORT_SYMBOL(compat_vma_mmap);
 
+int __vma_check_mmap_hook(struct vm_area_struct *vma)
+{
+	/* vm_ops->mapped is not valid if mmap() is specified. */
+	if (vma->vm_ops && WARN_ON_ONCE(vma->vm_ops->mapped))
+		return -EINVAL;
+
+	return 0;
+}
+EXPORT_SYMBOL(__vma_check_mmap_hook);
+
 static void set_ps_flags(struct page_snapshot *ps, const struct folio *folio,
 			 const struct page *page)
 {
@@ -1308,32 +1348,31 @@ void snapshot_page(struct page_snapshot *ps, const struct page *page)
 }
 
 static int mmap_action_finish(struct vm_area_struct *vma,
-			      struct mmap_action *action, int err)
+			      struct mmap_action *action, int err,
+			      bool rmap_lock_held)
 {
+	if (rmap_lock_held)
+		i_mmap_unlock_write(vma->vm_file->f_mapping);
+
+	if (!err) {
+		if (action->success_hook)
+			return action->success_hook(vma);
+		return 0;
+	}
+
 	/*
 	 * If an error occurs, unmap the VMA altogether and return an error. We
 	 * only clear the newly allocated VMA, since this function is only
 	 * invoked if we do NOT merge, so we only clean up the VMA we created.
 	 */
-	if (err) {
-		const size_t len = vma_pages(vma) << PAGE_SHIFT;
-
-		do_munmap(current->mm, vma->vm_start, len, NULL);
-
-		if (action->error_hook) {
-			/* We may want to filter the error. */
-			err = action->error_hook(err);
-
-			/* The caller should not clear the error. */
-			VM_WARN_ON_ONCE(!err);
-		}
-		return err;
+	unmap_vma_locked(vma);
+	if (action->error_hook) {
+		/* We may want to filter the error. */
+		err = action->error_hook(err);
+		/* The caller should not clear the error. */
+		VM_WARN_ON_ONCE(!err);
 	}
-
-	if (action->success_hook)
-		return action->success_hook(vma);
-
-	return 0;
+	return err;
 }
 
 #ifdef CONFIG_MMU
@@ -1364,13 +1403,15 @@ EXPORT_SYMBOL(mmap_action_prepare);
  * mmap_action_complete - Execute VMA descriptor action.
  * @vma: The VMA to perform the action upon.
  * @action: The action to perform.
+ * @rmap_lock_held: Is the file rmap lock held?
  *
  * Similar to mmap_action_prepare().
  *
  * Return: 0 on success, or error, at which point the VMA will be unmapped.
  */
 int mmap_action_complete(struct vm_area_struct *vma,
-			 struct mmap_action *action)
+			 struct mmap_action *action,
+			 bool rmap_lock_held)
 
 {
 	int err = 0;
@@ -1388,7 +1429,8 @@ int mmap_action_complete(struct vm_area_struct *vma,
 		break;
 	}
 
-	return mmap_action_finish(vma, action, err);
+	return mmap_action_finish(vma, action, err,
+				  rmap_lock_held);
 }
 EXPORT_SYMBOL(mmap_action_complete);
 #else
@@ -1408,7 +1450,8 @@ int mmap_action_prepare(struct vm_area_desc *desc)
 EXPORT_SYMBOL(mmap_action_prepare);
 
 int mmap_action_complete(struct vm_area_struct *vma,
-			 struct mmap_action *action)
+			 struct mmap_action *action,
+			 bool rmap_lock_held)
 {
 	int err = 0;
 
@@ -1423,7 +1466,7 @@ int mmap_action_complete(struct vm_area_struct *vma,
 		break;
 	}
 
-	return mmap_action_finish(vma, action, err);
+	return mmap_action_finish(vma, action, err, rmap_lock_held);
 }
 EXPORT_SYMBOL(mmap_action_complete);
 #endif
diff --git a/mm/vma.c b/mm/vma.c
index 2a86c7575000..a27d1278ea6d 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -2731,21 +2731,28 @@ static bool can_set_ksm_flags_early(struct mmap_state *map)
 	return false;
 }
 
-static int call_action_complete(struct mmap_state *map,
-				struct mmap_action *action,
-				struct vm_area_struct *vma)
+static int call_mapped_hook(struct mmap_state *map,
+			    struct vm_area_struct *vma)
 {
-	int ret;
-
-	ret = mmap_action_complete(vma, action);
+	const struct vm_operations_struct *vm_ops = vma->vm_ops;
+	void *vm_private_data = vma->vm_private_data;
+	int err;
 
-	/* If we held the file rmap we need to release it. */
-	if (map->hold_file_rmap_lock) {
-		struct file *file = vma->vm_file;
+	if (!vm_ops || !vm_ops->mapped)
+		return 0;
+	err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff,
+			     vma->vm_file, &vm_private_data);
+	if (err) {
+		if (map->hold_file_rmap_lock)
+			i_mmap_unlock_write(vma->vm_file->f_mapping);
 
-		i_mmap_unlock_write(file->f_mapping);
+		unmap_vma_locked(vma);
+		return err;
 	}
-	return ret;
+	/* Update private data if changed. */
+	if (vm_private_data != vma->vm_private_data)
+		vma->vm_private_data = vm_private_data;
+	return 0;
 }
 
 static unsigned long __mmap_region(struct file *file, unsigned long addr,
@@ -2799,8 +2806,10 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr,
 	__mmap_complete(&map, vma);
 
 	if (have_mmap_prepare && allocated_new) {
-		error = call_action_complete(&map, &desc.action, vma);
-
+		error = mmap_action_complete(vma, &desc.action,
+					     map.hold_file_rmap_lock);
+		if (!error)
+			error = call_mapped_hook(&map, vma);
 		if (error)
 			return error;
 	}
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 8ae525ed1738..aa34966cbc62 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -643,6 +643,23 @@ struct vm_operations_struct {
 	 * Context: User context.  May sleep.  Caller holds mmap_lock.
 	 */
 	void (*close)(struct vm_area_struct *vma);
+	/**
+	 * @mapped: Called when the VMA is first mapped in the MM. Not called if
+	 * the new VMA is merged with an adjacent VMA.
+	 *
+	 * The @vm_private_data field is an output field allowing the user to
+	 * modify vma->vm_private_data as necessary.
+	 *
+	 * ONLY valid if set from f_op->mmap_prepare. Will result in an error if
+	 * set from f_op->mmap.
+	 *
+	 * Returns %0 on success, or an error otherwise. On error, the VMA will
+	 * be unmapped.
+	 *
+	 * Context: User context.  May sleep.  Caller holds mmap_lock.
+	 */
+	int (*mapped)(unsigned long start, unsigned long end, pgoff_t pgoff,
+		      const struct file *file, void **vm_private_data);
 	/* Called any time before splitting to check if it's allowed */
 	int (*may_split)(struct vm_area_struct *vma, unsigned long addr);
 	int (*mremap)(struct vm_area_struct *vma);
@@ -1281,7 +1298,7 @@ static inline int __compat_vma_mmap(const struct file_operations *f_op,
 		return err;
 
 	set_vma_from_desc(vma, &desc);
-	return mmap_action_complete(vma, &desc.action);
+	return mmap_action_complete(vma, &desc.action, /*rmap_lock_held=*/false);
 }
 
 static inline int compat_vma_mmap(struct file *file,
@@ -1500,3 +1517,11 @@ static inline pgprot_t vma_get_page_prot(vma_flags_t vma_flags)
 
 	return vm_get_page_prot(vm_flags);
 }
+
+static inline void unmap_vma_locked(struct vm_area_struct *vma)
+{
+	const size_t len = vma_pages(vma) << PAGE_SHIFT;
+
+	mmap_assert_write_locked(vma->vm_mm);
+	do_munmap(vma->vm_mm, vma->vm_start, len, NULL);
+}
diff --git a/tools/testing/vma/include/stubs.h b/tools/testing/vma/include/stubs.h
index a30b8bc84955..d1c3d4ddb5e9 100644
--- a/tools/testing/vma/include/stubs.h
+++ b/tools/testing/vma/include/stubs.h
@@ -87,7 +87,8 @@ static inline int mmap_action_prepare(struct vm_area_desc *desc)
 }
 
 static inline int mmap_action_complete(struct vm_area_struct *vma,
-				       struct mmap_action *action)
+				       struct mmap_action *action,
+				       bool rmap_lock_held)
 {
 	return 0;
 }
-- 
2.53.0

[PATCH v3 05/16] fs: afs: correctly drop reference count on mapping failure

[Lorenzo Stoakes (Oracle)]

Commit 9d5403b1036c ("fs: convert most other generic_file_*mmap() users to
.mmap_prepare()") updated AFS to use the mmap_prepare callback in favour
of the deprecated mmap callback.

However, it did not account for the fact that mmap_prepare is called
pre-merge, and may then be merged, nor that mmap_prepare can fail to map
due to an out of memory error.

Both of those are cases in which we should not be incrementing a reference
count.

With the newly added vm_ops->mapped callback available, we can simply
defer this operation to that callback which is only invoked once the
mapping is successfully in place (but not yet visible to userspace as the
mmap and VMA write locks are held).

Therefore add afs_mapped() to implement this callback for AFS, and remove
the code doing so in afs_mmap_prepare().

Also update afs_vm_open(), afs_vm_close() and afs_vm_map_pages() to be
consistent in how the vnode is accessed.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 fs/afs/file.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index f609366fd2ac..85696ac984cc 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -28,6 +28,8 @@ static ssize_t afs_file_splice_read(struct file *in, loff_t *ppos,
 static void afs_vm_open(struct vm_area_struct *area);
 static void afs_vm_close(struct vm_area_struct *area);
 static vm_fault_t afs_vm_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff);
+static int afs_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
+		      const struct file *file, void **vm_private_data);
 
 const struct file_operations afs_file_operations = {
 	.open		= afs_open,
@@ -61,6 +63,7 @@ const struct address_space_operations afs_file_aops = {
 };
 
 static const struct vm_operations_struct afs_vm_ops = {
+	.mapped		= afs_mapped,
 	.open		= afs_vm_open,
 	.close		= afs_vm_close,
 	.fault		= filemap_fault,
@@ -494,32 +497,45 @@ static void afs_drop_open_mmap(struct afs_vnode *vnode)
  */
 static int afs_file_mmap_prepare(struct vm_area_desc *desc)
 {
-	struct afs_vnode *vnode = AFS_FS_I(file_inode(desc->file));
 	int ret;
 
-	afs_add_open_mmap(vnode);
-
 	ret = generic_file_mmap_prepare(desc);
-	if (ret == 0)
-		desc->vm_ops = &afs_vm_ops;
-	else
-		afs_drop_open_mmap(vnode);
+	if (ret)
+		return ret;
+
+	desc->vm_ops = &afs_vm_ops;
 	return ret;
 }
 
+static int afs_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
+		      const struct file *file, void **vm_private_data)
+{
+	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
+
+	afs_add_open_mmap(vnode);
+	return 0;
+}
+
 static void afs_vm_open(struct vm_area_struct *vma)
 {
-	afs_add_open_mmap(AFS_FS_I(file_inode(vma->vm_file)));
+	struct file *file = vma->vm_file;
+	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
+
+	afs_add_open_mmap(vnode);
 }
 
 static void afs_vm_close(struct vm_area_struct *vma)
 {
-	afs_drop_open_mmap(AFS_FS_I(file_inode(vma->vm_file)));
+	struct file *file = vma->vm_file;
+	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
+
+	afs_drop_open_mmap(vnode);
 }
 
 static vm_fault_t afs_vm_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff)
 {
-	struct afs_vnode *vnode = AFS_FS_I(file_inode(vmf->vma->vm_file));
+	struct file *file = vmf->vma->vm_file;
+	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
 
 	if (afs_check_validity(vnode))
 		return filemap_map_pages(vmf, start_pgoff, end_pgoff);
-- 
2.53.0

[PATCH v3 06/16] mm: add mmap_action_simple_ioremap()

[Lorenzo Stoakes (Oracle)]

Currently drivers use vm_iomap_memory() as a simple helper function for
I/O remapping memory over a range starting at a specified physical address
over a specified length.

In order to utilise this from mmap_prepare, separate out the core logic
into __simple_ioremap_prep(), update vm_iomap_memory() to use it, and add
simple_ioremap_prepare() to do the same with a VMA descriptor object.

We also add MMAP_SIMPLE_IO_REMAP and relevant fields to the struct
mmap_action type to permit this operation also.

We use mmap_action_ioremap() to set up the actual I/O remap operation once
we have checked and figured out the parameters, which makes
simple_ioremap_prepare() easy to implement.

We then add mmap_action_simple_ioremap() to allow drivers to make use of
this mode.

We update the mmap_prepare documentation to describe this mode.  Finally,
we update the VMA tests to reflect this change.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 Documentation/filesystems/mmap_prepare.rst |  3 +
 include/linux/mm.h                         | 24 +++++-
 include/linux/mm_types.h                   |  6 +-
 mm/internal.h                              |  1 +
 mm/memory.c                                | 85 +++++++++++++++-------
 mm/util.c                                  |  5 ++
 tools/testing/vma/include/dup.h            |  6 +-
 7 files changed, 102 insertions(+), 28 deletions(-)

diff --git a/Documentation/filesystems/mmap_prepare.rst b/Documentation/filesystems/mmap_prepare.rst
index 20db474915da..be76ae475b9c 100644
--- a/Documentation/filesystems/mmap_prepare.rst
+++ b/Documentation/filesystems/mmap_prepare.rst
@@ -153,5 +153,8 @@ pointer. These are:
 * mmap_action_ioremap_full() - Same as mmap_action_ioremap(), only remaps
   the entire mapping from ``start_pfn`` onward.
 
+* mmap_action_simple_ioremap() - Sets up an I/O remap from a specified
+  physical address and over a specified length.
+
 **NOTE:** The ``action`` field should never normally be manipulated directly,
 rather you ought to use one of these helpers.
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 68dee1101313..ef2e4dccfe8e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4337,11 +4337,33 @@ static inline void mmap_action_ioremap(struct vm_area_desc *desc,
  * @start_pfn: The first PFN in the range to remap.
  */
 static inline void mmap_action_ioremap_full(struct vm_area_desc *desc,
-					  unsigned long start_pfn)
+					    unsigned long start_pfn)
 {
 	mmap_action_ioremap(desc, desc->start, start_pfn, vma_desc_size(desc));
 }
 
+/**
+ * mmap_action_simple_ioremap - helper for mmap_prepare hook to specify that the
+ * physical range in [start_phys_addr, start_phys_addr + size) should be I/O
+ * remapped.
+ * @desc: The VMA descriptor for the VMA requiring remap.
+ * @start_phys_addr: Start of the physical memory to be mapped.
+ * @size: Size of the area to map.
+ *
+ * NOTE: Some drivers might want to tweak desc->page_prot for purposes of
+ * write-combine or similar.
+ */
+static inline void mmap_action_simple_ioremap(struct vm_area_desc *desc,
+					      phys_addr_t start_phys_addr,
+					      unsigned long size)
+{
+	struct mmap_action *action = &desc->action;
+
+	action->simple_ioremap.start_phys_addr = start_phys_addr;
+	action->simple_ioremap.size = size;
+	action->type = MMAP_SIMPLE_IO_REMAP;
+}
+
 int mmap_action_prepare(struct vm_area_desc *desc);
 int mmap_action_complete(struct vm_area_struct *vma,
 			 struct mmap_action *action,
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 4a229cc0a06b..50685cf29792 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -814,6 +814,7 @@ enum mmap_action_type {
 	MMAP_NOTHING,		/* Mapping is complete, no further action. */
 	MMAP_REMAP_PFN,		/* Remap PFN range. */
 	MMAP_IO_REMAP_PFN,	/* I/O remap PFN range. */
+	MMAP_SIMPLE_IO_REMAP,	/* I/O remap with guardrails. */
 };
 
 /*
@@ -822,13 +823,16 @@ enum mmap_action_type {
  */
 struct mmap_action {
 	union {
-		/* Remap range. */
 		struct {
 			unsigned long start;
 			unsigned long start_pfn;
 			unsigned long size;
 			pgprot_t pgprot;
 		} remap;
+		struct {
+			phys_addr_t start_phys_addr;
+			unsigned long size;
+		} simple_ioremap;
 	};
 	enum mmap_action_type type;
 
diff --git a/mm/internal.h b/mm/internal.h
index e0f554178143..2aa04d87ac10 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1804,6 +1804,7 @@ int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm);
 int remap_pfn_range_prepare(struct vm_area_desc *desc);
 int remap_pfn_range_complete(struct vm_area_struct *vma,
 			     struct mmap_action *action);
+int simple_ioremap_prepare(struct vm_area_desc *desc);
 
 static inline int io_remap_pfn_range_prepare(struct vm_area_desc *desc)
 {
diff --git a/mm/memory.c b/mm/memory.c
index 9dec67a18116..b3bcc21af20a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3170,6 +3170,58 @@ int remap_pfn_range_complete(struct vm_area_struct *vma,
 	return do_remap_pfn_range(vma, start, pfn, size, prot);
 }
 
+static int __simple_ioremap_prep(unsigned long vm_len, pgoff_t vm_pgoff,
+				 phys_addr_t start_phys, unsigned long size,
+				 unsigned long *pfnp)
+{
+	unsigned long pfn, pages;
+
+	/* Check that the physical memory area passed in looks valid */
+	if (start_phys + size < start_phys)
+		return -EINVAL;
+	/*
+	 * You *really* shouldn't map things that aren't page-aligned,
+	 * but we've historically allowed it because IO memory might
+	 * just have smaller alignment.
+	 */
+	size += start_phys & ~PAGE_MASK;
+	pfn = start_phys >> PAGE_SHIFT;
+	pages = (size + ~PAGE_MASK) >> PAGE_SHIFT;
+	if (pfn + pages < pfn)
+		return -EINVAL;
+
+	/* We start the mapping 'vm_pgoff' pages into the area */
+	if (vm_pgoff > pages)
+		return -EINVAL;
+	pfn += vm_pgoff;
+	pages -= vm_pgoff;
+
+	/* Can we fit all of the mapping? */
+	if ((vm_len >> PAGE_SHIFT) > pages)
+		return -EINVAL;
+
+	*pfnp = pfn;
+	return 0;
+}
+
+int simple_ioremap_prepare(struct vm_area_desc *desc)
+{
+	struct mmap_action *action = &desc->action;
+	const phys_addr_t start = action->simple_ioremap.start_phys_addr;
+	const unsigned long size = action->simple_ioremap.size;
+	unsigned long pfn;
+	int err;
+
+	err = __simple_ioremap_prep(vma_desc_size(desc), desc->pgoff,
+				    start, size, &pfn);
+	if (err)
+		return err;
+
+	/* The I/O remap logic does the heavy lifting. */
+	mmap_action_ioremap_full(desc, pfn);
+	return io_remap_pfn_range_prepare(desc);
+}
+
 /**
  * vm_iomap_memory - remap memory to userspace
  * @vma: user vma to map to
@@ -3187,32 +3239,15 @@ int remap_pfn_range_complete(struct vm_area_struct *vma,
  */
 int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len)
 {
-	unsigned long vm_len, pfn, pages;
-
-	/* Check that the physical memory area passed in looks valid */
-	if (start + len < start)
-		return -EINVAL;
-	/*
-	 * You *really* shouldn't map things that aren't page-aligned,
-	 * but we've historically allowed it because IO memory might
-	 * just have smaller alignment.
-	 */
-	len += start & ~PAGE_MASK;
-	pfn = start >> PAGE_SHIFT;
-	pages = (len + ~PAGE_MASK) >> PAGE_SHIFT;
-	if (pfn + pages < pfn)
-		return -EINVAL;
-
-	/* We start the mapping 'vm_pgoff' pages into the area */
-	if (vma->vm_pgoff > pages)
-		return -EINVAL;
-	pfn += vma->vm_pgoff;
-	pages -= vma->vm_pgoff;
+	const unsigned long vm_start = vma->vm_start;
+	const unsigned long vm_end = vma->vm_end;
+	const unsigned long vm_len = vm_end - vm_start;
+	unsigned long pfn;
+	int err;
 
-	/* Can we fit all of the mapping? */
-	vm_len = vma->vm_end - vma->vm_start;
-	if (vm_len >> PAGE_SHIFT > pages)
-		return -EINVAL;
+	err = __simple_ioremap_prep(vm_len, vma->vm_pgoff, start, len, &pfn);
+	if (err)
+		return err;
 
 	/* Ok, let it rip */
 	return io_remap_pfn_range(vma, vma->vm_start, pfn, vm_len, vma->vm_page_prot);
diff --git a/mm/util.c b/mm/util.c
index fc1bd8a8f3ea..879ba62b5f0c 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1392,6 +1392,8 @@ int mmap_action_prepare(struct vm_area_desc *desc)
 		return remap_pfn_range_prepare(desc);
 	case MMAP_IO_REMAP_PFN:
 		return io_remap_pfn_range_prepare(desc);
+	case MMAP_SIMPLE_IO_REMAP:
+		return simple_ioremap_prepare(desc);
 	}
 
 	WARN_ON_ONCE(1);
@@ -1423,6 +1425,7 @@ int mmap_action_complete(struct vm_area_struct *vma,
 		err = remap_pfn_range_complete(vma, action);
 		break;
 	case MMAP_IO_REMAP_PFN:
+	case MMAP_SIMPLE_IO_REMAP:
 		/* Should have been delegated. */
 		WARN_ON_ONCE(1);
 		err = -EINVAL;
@@ -1441,6 +1444,7 @@ int mmap_action_prepare(struct vm_area_desc *desc)
 		break;
 	case MMAP_REMAP_PFN:
 	case MMAP_IO_REMAP_PFN:
+	case MMAP_SIMPLE_IO_REMAP:
 		WARN_ON_ONCE(1); /* nommu cannot handle these. */
 		break;
 	}
@@ -1460,6 +1464,7 @@ int mmap_action_complete(struct vm_area_struct *vma,
 		break;
 	case MMAP_REMAP_PFN:
 	case MMAP_IO_REMAP_PFN:
+	case MMAP_SIMPLE_IO_REMAP:
 		WARN_ON_ONCE(1); /* nommu cannot handle this. */
 
 		err = -EINVAL;
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index aa34966cbc62..1b86c34e1158 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -453,6 +453,7 @@ enum mmap_action_type {
 	MMAP_NOTHING,		/* Mapping is complete, no further action. */
 	MMAP_REMAP_PFN,		/* Remap PFN range. */
 	MMAP_IO_REMAP_PFN,	/* I/O remap PFN range. */
+	MMAP_SIMPLE_IO_REMAP,	/* I/O remap with guardrails. */
 };
 
 /*
@@ -461,13 +462,16 @@ enum mmap_action_type {
  */
 struct mmap_action {
 	union {
-		/* Remap range. */
 		struct {
 			unsigned long start;
 			unsigned long start_pfn;
 			unsigned long size;
 			pgprot_t pgprot;
 		} remap;
+		struct {
+			phys_addr_t start_phys_addr;
+			unsigned long size;
+		} simple_ioremap;
 	};
 	enum mmap_action_type type;
 
-- 
2.53.0

[PATCH v3 07/16] misc: open-dice: replace deprecated mmap hook with mmap_prepare

[Lorenzo Stoakes (Oracle)]

The f_op->mmap interface is deprecated, so update driver to use its
successor, mmap_prepare.

The driver previously used vm_iomap_memory(), so this change replaces it
with its mmap_prepare equivalent, mmap_action_simple_ioremap().

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 drivers/misc/open-dice.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/misc/open-dice.c b/drivers/misc/open-dice.c
index 24c29e0f00ef..45060fb4ea27 100644
--- a/drivers/misc/open-dice.c
+++ b/drivers/misc/open-dice.c
@@ -86,29 +86,32 @@ static ssize_t open_dice_write(struct file *filp, const char __user *ptr,
 /*
  * Creates a mapping of the reserved memory region in user address space.
  */
-static int open_dice_mmap(struct file *filp, struct vm_area_struct *vma)
+static int open_dice_mmap_prepare(struct vm_area_desc *desc)
 {
+	struct file *filp = desc->file;
 	struct open_dice_drvdata *drvdata = to_open_dice_drvdata(filp);
 
-	if (vma->vm_flags & VM_MAYSHARE) {
+	if (vma_desc_test(desc, VMA_MAYSHARE_BIT)) {
 		/* Do not allow userspace to modify the underlying data. */
-		if (vma->vm_flags & VM_WRITE)
+		if (vma_desc_test(desc, VMA_WRITE_BIT))
 			return -EPERM;
 		/* Ensure userspace cannot acquire VM_WRITE later. */
-		vm_flags_clear(vma, VM_MAYWRITE);
+		vma_desc_clear_flags(desc, VMA_MAYWRITE_BIT);
 	}
 
 	/* Create write-combine mapping so all clients observe a wipe. */
-	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
-	vm_flags_set(vma, VM_DONTCOPY | VM_DONTDUMP);
-	return vm_iomap_memory(vma, drvdata->rmem->base, drvdata->rmem->size);
+	desc->page_prot = pgprot_writecombine(desc->page_prot);
+	vma_desc_set_flags(desc, VMA_DONTCOPY_BIT, VMA_DONTDUMP_BIT);
+	mmap_action_simple_ioremap(desc, drvdata->rmem->base,
+				   drvdata->rmem->size);
+	return 0;
 }
 
 static const struct file_operations open_dice_fops = {
 	.owner = THIS_MODULE,
 	.read = open_dice_read,
 	.write = open_dice_write,
-	.mmap = open_dice_mmap,
+	.mmap_prepare = open_dice_mmap_prepare,
 };
 
 static int __init open_dice_probe(struct platform_device *pdev)
-- 
2.53.0

[PATCH v3 08/16] hpet: replace deprecated mmap hook with mmap_prepare

[Lorenzo Stoakes (Oracle)]

The f_op->mmap interface is deprecated, so update driver to use its
successor, mmap_prepare.

The driver previously used vm_iomap_memory(), so this change replaces it
with its mmap_prepare equivalent, mmap_action_simple_ioremap().

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 drivers/char/hpet.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 60dd09a56f50..8f128cc40147 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -354,8 +354,9 @@ static __init int hpet_mmap_enable(char *str)
 }
 __setup("hpet_mmap=", hpet_mmap_enable);
 
-static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
+static int hpet_mmap_prepare(struct vm_area_desc *desc)
 {
+	struct file *file = desc->file;
 	struct hpet_dev *devp;
 	unsigned long addr;
 
@@ -368,11 +369,12 @@ static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
 	if (addr & (PAGE_SIZE - 1))
 		return -ENOSYS;
 
-	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
-	return vm_iomap_memory(vma, addr, PAGE_SIZE);
+	desc->page_prot = pgprot_noncached(desc->page_prot);
+	mmap_action_simple_ioremap(desc, addr, PAGE_SIZE);
+	return 0;
 }
 #else
-static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
+static int hpet_mmap_prepare(struct vm_area_desc *desc)
 {
 	return -ENOSYS;
 }
@@ -710,7 +712,7 @@ static const struct file_operations hpet_fops = {
 	.open = hpet_open,
 	.release = hpet_release,
 	.fasync = hpet_fasync,
-	.mmap = hpet_mmap,
+	.mmap_prepare = hpet_mmap_prepare,
 };
 
 static int hpet_is_known(struct hpet_data *hdp)
-- 
2.53.0

[PATCH v3 09/16] mtdchar: replace deprecated mmap hook with mmap_prepare, clean up

[Lorenzo Stoakes (Oracle)]

Replace the deprecated mmap callback with mmap_prepare.

Commit f5cf8f07423b ("mtd: Disable mtdchar mmap on MMU systems") commented
out the CONFIG_MMU part of this function back in 2012, so after ~14 years
it's probably reasonable to remove this altogether rather than updating
dead code.

Acked-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 drivers/mtd/mtdchar.c | 21 +++------------------
 1 file changed, 3 insertions(+), 18 deletions(-)

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 55a43682c567..bf01e6ac7293 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -1376,27 +1376,12 @@ static unsigned mtdchar_mmap_capabilities(struct file *file)
 /*
  * set up a mapping for shared memory segments
  */
-static int mtdchar_mmap(struct file *file, struct vm_area_struct *vma)
+static int mtdchar_mmap_prepare(struct vm_area_desc *desc)
 {
 #ifdef CONFIG_MMU
-	struct mtd_file_info *mfi = file->private_data;
-	struct mtd_info *mtd = mfi->mtd;
-	struct map_info *map = mtd->priv;
-
-        /* This is broken because it assumes the MTD device is map-based
-	   and that mtd->priv is a valid struct map_info.  It should be
-	   replaced with something that uses the mtd_get_unmapped_area()
-	   operation properly. */
-	if (0 /*mtd->type == MTD_RAM || mtd->type == MTD_ROM*/) {
-#ifdef pgprot_noncached
-		if (file->f_flags & O_DSYNC || map->phys >= __pa(high_memory))
-			vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
-#endif
-		return vm_iomap_memory(vma, map->phys, map->size);
-	}
 	return -ENODEV;
 #else
-	return vma->vm_flags & VM_SHARED ? 0 : -EACCES;
+	return vma_desc_test(desc, VMA_SHARED_BIT) ? 0 : -EACCES;
 #endif
 }
 
@@ -1411,7 +1396,7 @@ static const struct file_operations mtd_fops = {
 #endif
 	.open		= mtdchar_open,
 	.release	= mtdchar_close,
-	.mmap		= mtdchar_mmap,
+	.mmap_prepare	= mtdchar_mmap_prepare,
 #ifndef CONFIG_MMU
 	.get_unmapped_area = mtdchar_get_unmapped_area,
 	.mmap_capabilities = mtdchar_mmap_capabilities,
-- 
2.53.0

[PATCH v3 10/16] stm: replace deprecated mmap hook with mmap_prepare

[Lorenzo Stoakes (Oracle)]

The f_op->mmap interface is deprecated, so update driver to use its
successor, mmap_prepare.

The driver previously used vm_iomap_memory(), so this change replaces it
with its mmap_prepare equivalent, mmap_action_simple_ioremap().

Also, in order to correctly maintain reference counting, add a
vm_ops->mapped callback to increment the reference count when successfully
mapped.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 drivers/hwtracing/stm/core.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index 37584e786bb5..f48c6a8a0654 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -666,6 +666,16 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
 	return count;
 }
 
+static int stm_mmap_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
+			   const struct file *file, void **vm_private_data)
+{
+	struct stm_file *stmf = file->private_data;
+	struct stm_device *stm = stmf->stm;
+
+	pm_runtime_get_sync(&stm->dev);
+	return 0;
+}
+
 static void stm_mmap_open(struct vm_area_struct *vma)
 {
 	struct stm_file *stmf = vma->vm_file->private_data;
@@ -684,12 +694,14 @@ static void stm_mmap_close(struct vm_area_struct *vma)
 }
 
 static const struct vm_operations_struct stm_mmap_vmops = {
+	.mapped = stm_mmap_mapped,
 	.open	= stm_mmap_open,
 	.close	= stm_mmap_close,
 };
 
-static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
+static int stm_char_mmap_prepare(struct vm_area_desc *desc)
 {
+	struct file *file = desc->file;
 	struct stm_file *stmf = file->private_data;
 	struct stm_device *stm = stmf->stm;
 	unsigned long size, phys;
@@ -697,10 +709,10 @@ static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
 	if (!stm->data->mmio_addr)
 		return -EOPNOTSUPP;
 
-	if (vma->vm_pgoff)
+	if (desc->pgoff)
 		return -EINVAL;
 
-	size = vma->vm_end - vma->vm_start;
+	size = vma_desc_size(desc);
 
 	if (stmf->output.nr_chans * stm->data->sw_mmiosz != size)
 		return -EINVAL;
@@ -712,13 +724,12 @@ static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
 	if (!phys)
 		return -EINVAL;
 
-	pm_runtime_get_sync(&stm->dev);
-
-	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
-	vm_flags_set(vma, VM_IO | VM_DONTEXPAND | VM_DONTDUMP);
-	vma->vm_ops = &stm_mmap_vmops;
-	vm_iomap_memory(vma, phys, size);
+	desc->page_prot = pgprot_noncached(desc->page_prot);
+	vma_desc_set_flags(desc, VMA_IO_BIT, VMA_DONTEXPAND_BIT,
+			   VMA_DONTDUMP_BIT);
+	desc->vm_ops = &stm_mmap_vmops;
 
+	mmap_action_simple_ioremap(desc, phys, size);
 	return 0;
 }
 
@@ -836,7 +847,7 @@ static const struct file_operations stm_fops = {
 	.open		= stm_char_open,
 	.release	= stm_char_release,
 	.write		= stm_char_write,
-	.mmap		= stm_char_mmap,
+	.mmap_prepare	= stm_char_mmap_prepare,
 	.unlocked_ioctl	= stm_char_ioctl,
 	.compat_ioctl	= compat_ptr_ioctl,
 };
-- 
2.53.0

[PATCH v3 11/16] staging: vme_user: replace deprecated mmap hook with mmap_prepare

[Lorenzo Stoakes (Oracle)]

The f_op->mmap interface is deprecated, so update driver to use its
successor, mmap_prepare.

The driver previously used vm_iomap_memory(), so this change replaces it
with its mmap_prepare equivalent, mmap_action_simple_ioremap().

Functions that wrap mmap() are also converted to wrap mmap_prepare()
instead.

Also update the documentation accordingly.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 Documentation/driver-api/vme.rst    |  2 +-
 drivers/staging/vme_user/vme.c      | 20 +++++------
 drivers/staging/vme_user/vme.h      |  2 +-
 drivers/staging/vme_user/vme_user.c | 51 +++++++++++++++++------------
 4 files changed, 42 insertions(+), 33 deletions(-)

diff --git a/Documentation/driver-api/vme.rst b/Documentation/driver-api/vme.rst
index c0b475369de0..7111999abc14 100644
--- a/Documentation/driver-api/vme.rst
+++ b/Documentation/driver-api/vme.rst
@@ -107,7 +107,7 @@ The function :c:func:`vme_master_read` can be used to read from and
 
 In addition to simple reads and writes, :c:func:`vme_master_rmw` is provided to
 do a read-modify-write transaction. Parts of a VME window can also be mapped
-into user space memory using :c:func:`vme_master_mmap`.
+into user space memory using :c:func:`vme_master_mmap_prepare`.
 
 
 Slave windows
diff --git a/drivers/staging/vme_user/vme.c b/drivers/staging/vme_user/vme.c
index f10a00c05f12..7220aba7b919 100644
--- a/drivers/staging/vme_user/vme.c
+++ b/drivers/staging/vme_user/vme.c
@@ -735,9 +735,9 @@ unsigned int vme_master_rmw(struct vme_resource *resource, unsigned int mask,
 EXPORT_SYMBOL(vme_master_rmw);
 
 /**
- * vme_master_mmap - Mmap region of VME master window.
+ * vme_master_mmap_prepare - Mmap region of VME master window.
  * @resource: Pointer to VME master resource.
- * @vma: Pointer to definition of user mapping.
+ * @desc: Pointer to descriptor of user mapping.
  *
  * Memory map a region of the VME master window into user space.
  *
@@ -745,12 +745,13 @@ EXPORT_SYMBOL(vme_master_rmw);
  *         resource or -EFAULT if map exceeds window size. Other generic mmap
  *         errors may also be returned.
  */
-int vme_master_mmap(struct vme_resource *resource, struct vm_area_struct *vma)
+int vme_master_mmap_prepare(struct vme_resource *resource,
+			    struct vm_area_desc *desc)
 {
+	const unsigned long vma_size = vma_desc_size(desc);
 	struct vme_bridge *bridge = find_bridge(resource);
 	struct vme_master_resource *image;
 	phys_addr_t phys_addr;
-	unsigned long vma_size;
 
 	if (resource->type != VME_MASTER) {
 		dev_err(bridge->parent, "Not a master resource\n");
@@ -758,19 +759,18 @@ int vme_master_mmap(struct vme_resource *resource, struct vm_area_struct *vma)
 	}
 
 	image = list_entry(resource->entry, struct vme_master_resource, list);
-	phys_addr = image->bus_resource.start + (vma->vm_pgoff << PAGE_SHIFT);
-	vma_size = vma->vm_end - vma->vm_start;
+	phys_addr = image->bus_resource.start + (desc->pgoff << PAGE_SHIFT);
 
 	if (phys_addr + vma_size > image->bus_resource.end + 1) {
 		dev_err(bridge->parent, "Map size cannot exceed the window size\n");
 		return -EFAULT;
 	}
 
-	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
-
-	return vm_iomap_memory(vma, phys_addr, vma->vm_end - vma->vm_start);
+	desc->page_prot = pgprot_noncached(desc->page_prot);
+	mmap_action_simple_ioremap(desc, phys_addr, vma_size);
+	return 0;
 }
-EXPORT_SYMBOL(vme_master_mmap);
+EXPORT_SYMBOL(vme_master_mmap_prepare);
 
 /**
  * vme_master_free - Free VME master window
diff --git a/drivers/staging/vme_user/vme.h b/drivers/staging/vme_user/vme.h
index 797e9940fdd1..b6413605ea49 100644
--- a/drivers/staging/vme_user/vme.h
+++ b/drivers/staging/vme_user/vme.h
@@ -151,7 +151,7 @@ ssize_t vme_master_read(struct vme_resource *resource, void *buf, size_t count,
 ssize_t vme_master_write(struct vme_resource *resource, void *buf, size_t count, loff_t offset);
 unsigned int vme_master_rmw(struct vme_resource *resource, unsigned int mask, unsigned int compare,
 			    unsigned int swap, loff_t offset);
-int vme_master_mmap(struct vme_resource *resource, struct vm_area_struct *vma);
+int vme_master_mmap_prepare(struct vme_resource *resource, struct vm_area_desc *desc);
 void vme_master_free(struct vme_resource *resource);
 
 struct vme_resource *vme_dma_request(struct vme_dev *vdev, u32 route);
diff --git a/drivers/staging/vme_user/vme_user.c b/drivers/staging/vme_user/vme_user.c
index d95dd7d9190a..11e25c2f6b0a 100644
--- a/drivers/staging/vme_user/vme_user.c
+++ b/drivers/staging/vme_user/vme_user.c
@@ -446,24 +446,14 @@ static void vme_user_vm_close(struct vm_area_struct *vma)
 	kfree(vma_priv);
 }
 
-static const struct vm_operations_struct vme_user_vm_ops = {
-	.open = vme_user_vm_open,
-	.close = vme_user_vm_close,
-};
-
-static int vme_user_master_mmap(unsigned int minor, struct vm_area_struct *vma)
+static int vme_user_vm_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
+			      const struct file *file, void **vm_private_data)
 {
-	int err;
+	const unsigned int minor = iminor(file_inode(file));
 	struct vme_user_vma_priv *vma_priv;
 
 	mutex_lock(&image[minor].mutex);
 
-	err = vme_master_mmap(image[minor].resource, vma);
-	if (err) {
-		mutex_unlock(&image[minor].mutex);
-		return err;
-	}
-
 	vma_priv = kmalloc_obj(*vma_priv);
 	if (!vma_priv) {
 		mutex_unlock(&image[minor].mutex);
@@ -472,22 +462,41 @@ static int vme_user_master_mmap(unsigned int minor, struct vm_area_struct *vma)
 
 	vma_priv->minor = minor;
 	refcount_set(&vma_priv->refcnt, 1);
-	vma->vm_ops = &vme_user_vm_ops;
-	vma->vm_private_data = vma_priv;
-
+	*vm_private_data = vma_priv;
 	image[minor].mmap_count++;
 
 	mutex_unlock(&image[minor].mutex);
-
 	return 0;
 }
 
-static int vme_user_mmap(struct file *file, struct vm_area_struct *vma)
+static const struct vm_operations_struct vme_user_vm_ops = {
+	.mapped = vme_user_vm_mapped,
+	.open = vme_user_vm_open,
+	.close = vme_user_vm_close,
+};
+
+static int vme_user_master_mmap_prepare(unsigned int minor,
+					struct vm_area_desc *desc)
+{
+	int err;
+
+	mutex_lock(&image[minor].mutex);
+
+	err = vme_master_mmap_prepare(image[minor].resource, desc);
+	if (!err)
+		desc->vm_ops = &vme_user_vm_ops;
+
+	mutex_unlock(&image[minor].mutex);
+	return err;
+}
+
+static int vme_user_mmap_prepare(struct vm_area_desc *desc)
 {
-	unsigned int minor = iminor(file_inode(file));
+	const struct file *file = desc->file;
+	const unsigned int minor = iminor(file_inode(file));
 
 	if (type[minor] == MASTER_MINOR)
-		return vme_user_master_mmap(minor, vma);
+		return vme_user_master_mmap_prepare(minor, desc);
 
 	return -ENODEV;
 }
@@ -498,7 +507,7 @@ static const struct file_operations vme_user_fops = {
 	.llseek = vme_user_llseek,
 	.unlocked_ioctl = vme_user_unlocked_ioctl,
 	.compat_ioctl = compat_ptr_ioctl,
-	.mmap = vme_user_mmap,
+	.mmap_prepare = vme_user_mmap_prepare,
 };
 
 static int vme_user_match(struct vme_dev *vdev)
-- 
2.53.0

[PATCH v3 12/16] mm: allow handling of stacked mmap_prepare hooks in more drivers

[Lorenzo Stoakes (Oracle)]

While the conversion of mmap hooks to mmap_prepare is underway, we will
encounter situations where mmap hooks need to invoke nested mmap_prepare
hooks.

The nesting of mmap hooks is termed 'stacking'.  In order to flexibly
facilitate the conversion of custom mmap hooks in drivers which stack, we
must split up the existing __compat_vma_mmap() function into two separate
functions:

* compat_set_desc_from_vma() - This allows the setting of a vm_area_desc
  object's fields to the relevant fields of a VMA.

* __compat_vma_mmap() - Once an mmap_prepare hook has been executed upon a
  vm_area_desc object, this function performs any mmap actions specified by
  the mmap_prepare hook and then invokes its vm_ops->mapped() hook if any
  were specified.

In ordinary cases, where a file's f_op->mmap_prepare() hook simply needs
to be invoked in a stacked mmap() hook, compat_vma_mmap() can be used.

However some drivers define their own nested hooks, which are invoked in
turn by another hook.

A concrete example is vmbus_channel->mmap_ring_buffer(), which is invoked
in turn by bin_attribute->mmap():

vmbus_channel->mmap_ring_buffer() has a signature of:

int (*mmap_ring_buffer)(struct vmbus_channel *channel,
			struct vm_area_struct *vma);

And bin_attribute->mmap() has a signature of:

	int (*mmap)(struct file *, struct kobject *,
		    const struct bin_attribute *attr,
		    struct vm_area_struct *vma);

And so compat_vma_mmap() cannot be used here for incremental conversion of
hooks from mmap() to mmap_prepare().

There are many such instances like this, where conversion to mmap_prepare
would otherwise cascade to a huge change set due to nesting of this kind.

The changes in this patch mean we could now instead convert
vmbus_channel->mmap_ring_buffer() to
vmbus_channel->mmap_prepare_ring_buffer(), and implement something like:

	struct vm_area_desc desc;
	int err;

	compat_set_desc_from_vma(&desc, file, vma);
	err = channel->mmap_prepare_ring_buffer(channel, &desc);
	if (err)
		return err;

	return __compat_vma_mmap(&desc, vma);

Allowing us to incrementally update this logic, and other logic like it.

Unfortunately, as part of this change, we need to be able to flexibly
assign to the VMA descriptor, so have to remove some of the const
declarations within the structure.

Also update the VMA tests to reflect the changes.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 include/linux/fs.h              |   3 +
 include/linux/mm_types.h        |   4 +-
 mm/util.c                       | 112 ++++++++++++++++++++++---------
 mm/vma.h                        |   2 +-
 tools/testing/vma/include/dup.h | 114 +++++++++++++++++++++-----------
 5 files changed, 162 insertions(+), 73 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index c390f5c667e3..0bdccfa70b44 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2058,6 +2058,9 @@ static inline bool can_mmap_file(struct file *file)
 	return true;
 }
 
+void compat_set_desc_from_vma(struct vm_area_desc *desc, const struct file *file,
+			      const struct vm_area_struct *vma);
+int __compat_vma_mmap(struct vm_area_desc *desc, struct vm_area_struct *vma);
 int compat_vma_mmap(struct file *file, struct vm_area_struct *vma);
 int __vma_check_mmap_hook(struct vm_area_struct *vma);
 
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 50685cf29792..7538d64f8848 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -891,8 +891,8 @@ static __always_inline bool vma_flags_empty(vma_flags_t *flags)
  */
 struct vm_area_desc {
 	/* Immutable state. */
-	const struct mm_struct *const mm;
-	struct file *const file; /* May vary from vm_file in stacked callers. */
+	struct mm_struct *mm;
+	struct file *file; /* May vary from vm_file in stacked callers. */
 	unsigned long start;
 	unsigned long end;
 
diff --git a/mm/util.c b/mm/util.c
index 879ba62b5f0c..8cf59267a9ac 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1163,34 +1163,40 @@ void flush_dcache_folio(struct folio *folio)
 EXPORT_SYMBOL(flush_dcache_folio);
 #endif
 
-static int __compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
+/**
+ * compat_set_desc_from_vma() - assigns VMA descriptor @desc fields from a VMA.
+ * @desc: A VMA descriptor whose fields need to be set.
+ * @file: The file object describing the file being mmap()'d.
+ * @vma: The VMA whose fields we wish to assign to @desc.
+ *
+ * This is a compatibility function to allow an mmap() hook to call
+ * mmap_prepare() hooks when drivers nest these. This function specifically
+ * allows the construction of a vm_area_desc value, @desc, from a VMA @vma for
+ * the purposes of doing this.
+ *
+ * Once the conversion of drivers is complete this function will no longer be
+ * required and will be removed.
+ */
+void compat_set_desc_from_vma(struct vm_area_desc *desc,
+			      const struct file *file,
+			      const struct vm_area_struct *vma)
 {
-	struct vm_area_desc desc = {
-		.mm = vma->vm_mm,
-		.file = file,
-		.start = vma->vm_start,
-		.end = vma->vm_end,
+	memset(desc, 0, sizeof(*desc));
 
-		.pgoff = vma->vm_pgoff,
-		.vm_file = vma->vm_file,
-		.vma_flags = vma->flags,
-		.page_prot = vma->vm_page_prot,
-
-		.action.type = MMAP_NOTHING, /* Default */
-	};
-	int err;
+	desc->mm = vma->vm_mm;
+	desc->file = (struct file *)file;
+	desc->start = vma->vm_start;
+	desc->end = vma->vm_end;
 
-	err = vfs_mmap_prepare(file, &desc);
-	if (err)
-		return err;
+	desc->pgoff = vma->vm_pgoff;
+	desc->vm_file = vma->vm_file;
+	desc->vma_flags = vma->flags;
+	desc->page_prot = vma->vm_page_prot;
 
-	err = mmap_action_prepare(&desc);
-	if (err)
-		return err;
-
-	set_vma_from_desc(vma, &desc);
-	return mmap_action_complete(vma, &desc.action, /*rmap_lock_held=*/false);
+	/* Default. */
+	desc->action.type = MMAP_NOTHING;
 }
+EXPORT_SYMBOL(compat_set_desc_from_vma);
 
 static int __compat_vma_mapped(struct file *file, struct vm_area_struct *vma)
 {
@@ -1211,6 +1217,50 @@ static int __compat_vma_mapped(struct file *file, struct vm_area_struct *vma)
 	return err;
 }
 
+/**
+ * __compat_vma_mmap() - Similar to compat_vma_mmap(), only it allows
+ * flexibility as to how the mmap_prepare callback is invoked, which is useful
+ * for drivers which invoke nested mmap_prepare callbacks in an mmap() hook.
+ * @desc: A VMA descriptor upon which an mmap_prepare() hook has already been
+ * executed.
+ * @vma: The VMA to which @desc should be applied.
+ *
+ * The function assumes that you have obtained a VMA descriptor @desc from
+ * compat_set_desc_from_vma(), and already executed the mmap_prepare() hook upon
+ * it.
+ *
+ * It then performs any specified mmap actions, and invokes the vm_ops->mapped()
+ * hook if one is present.
+ *
+ * See the description of compat_vma_mmap() for more details.
+ *
+ * Once the conversion of drivers is complete this function will no longer be
+ * required and will be removed.
+ *
+ * Returns: 0 on success or error.
+ */
+int __compat_vma_mmap(struct vm_area_desc *desc,
+		      struct vm_area_struct *vma)
+{
+	int err;
+
+	/* Perform any preparatory tasks for mmap action. */
+	err = mmap_action_prepare(desc);
+	if (err)
+		return err;
+	/* Update the VMA from the descriptor. */
+	compat_set_vma_from_desc(vma, desc);
+	/* Complete any specified mmap actions. */
+	err = mmap_action_complete(vma, &desc->action,
+				   /*rmap_lock_held=*/false);
+	if (err)
+		return err;
+
+	/* Invoke vm_ops->mapped callback. */
+	return __compat_vma_mapped(desc->file, vma);
+}
+EXPORT_SYMBOL(__compat_vma_mmap);
+
 /**
  * compat_vma_mmap() - Apply the file's .mmap_prepare() hook to an
  * existing VMA and execute any requested actions.
@@ -1218,10 +1268,10 @@ static int __compat_vma_mapped(struct file *file, struct vm_area_struct *vma)
  * @vma: The VMA to apply the .mmap_prepare() hook to.
  *
  * Ordinarily, .mmap_prepare() is invoked directly upon mmap(). However, certain
- * stacked filesystems invoke a nested mmap hook of an underlying file.
+ * stacked drivers invoke a nested mmap hook of an underlying file.
  *
- * Until all filesystems are converted to use .mmap_prepare(), we must be
- * conservative and continue to invoke these stacked filesystems using the
+ * Until all drivers are converted to use .mmap_prepare(), we must be
+ * conservative and continue to invoke these stacked drivers using the
  * deprecated .mmap() hook.
  *
  * However we have a problem if the underlying file system possesses an
@@ -1232,20 +1282,22 @@ static int __compat_vma_mapped(struct file *file, struct vm_area_struct *vma)
  * establishes a struct vm_area_desc descriptor, passes to the underlying
  * .mmap_prepare() hook and applies any changes performed by it.
  *
- * Once the conversion of filesystems is complete this function will no longer
- * be required and will be removed.
+ * Once the conversion of drivers is complete this function will no longer be
+ * required and will be removed.
  *
  * Returns: 0 on success or error.
  */
 int compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
 {
+	struct vm_area_desc desc;
 	int err;
 
-	err = __compat_vma_mmap(file, vma);
+	compat_set_desc_from_vma(&desc, file, vma);
+	err = vfs_mmap_prepare(file, &desc);
 	if (err)
 		return err;
 
-	return __compat_vma_mapped(file, vma);
+	return __compat_vma_mmap(&desc, vma);
 }
 EXPORT_SYMBOL(compat_vma_mmap);
 
diff --git a/mm/vma.h b/mm/vma.h
index adc18f7dd9f1..a76046c39b14 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -300,7 +300,7 @@ static inline int vma_iter_store_gfp(struct vma_iterator *vmi,
  * f_op->mmap() but which might have an underlying file system which implements
  * f_op->mmap_prepare().
  */
-static inline void set_vma_from_desc(struct vm_area_struct *vma,
+static inline void compat_set_vma_from_desc(struct vm_area_struct *vma,
 		struct vm_area_desc *desc)
 {
 	/*
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 1b86c34e1158..1f123704078e 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -519,8 +519,8 @@ enum vma_operation {
  */
 struct vm_area_desc {
 	/* Immutable state. */
-	const struct mm_struct *const mm;
-	struct file *const file; /* May vary from vm_file in stacked callers. */
+	struct mm_struct *mm;
+	struct file *file; /* May vary from vm_file in stacked callers. */
 	unsigned long start;
 	unsigned long end;
 
@@ -1272,43 +1272,95 @@ static inline void vma_set_anonymous(struct vm_area_struct *vma)
 }
 
 /* Declared in vma.h. */
-static inline void set_vma_from_desc(struct vm_area_struct *vma,
+static inline void compat_set_vma_from_desc(struct vm_area_struct *vma,
 		struct vm_area_desc *desc);
 
-static inline int __compat_vma_mmap(const struct file_operations *f_op,
-		struct file *file, struct vm_area_struct *vma)
+static inline void compat_set_desc_from_vma(struct vm_area_desc *desc,
+			      const struct file *file,
+			      const struct vm_area_struct *vma)
 {
-	struct vm_area_desc desc = {
-		.mm = vma->vm_mm,
-		.file = file,
-		.start = vma->vm_start,
-		.end = vma->vm_end,
+	memset(desc, 0, sizeof(*desc));
 
-		.pgoff = vma->vm_pgoff,
-		.vm_file = vma->vm_file,
-		.vma_flags = vma->flags,
-		.page_prot = vma->vm_page_prot,
+	desc->mm = vma->vm_mm;
+	desc->file = (struct file *)file;
+	desc->start = vma->vm_start;
+	desc->end = vma->vm_end;
 
-		.action.type = MMAP_NOTHING, /* Default */
-	};
+	desc->pgoff = vma->vm_pgoff;
+	desc->vm_file = vma->vm_file;
+	desc->vma_flags = vma->flags;
+	desc->page_prot = vma->vm_page_prot;
+
+	/* Default. */
+	desc->action.type = MMAP_NOTHING;
+}
+
+static inline unsigned long vma_pages(const struct vm_area_struct *vma)
+{
+	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+}
+
+static inline void unmap_vma_locked(struct vm_area_struct *vma)
+{
+	const size_t len = vma_pages(vma) << PAGE_SHIFT;
+
+	mmap_assert_write_locked(vma->vm_mm);
+	do_munmap(vma->vm_mm, vma->vm_start, len, NULL);
+}
+
+static inline int __compat_vma_mapped(struct file *file, struct vm_area_struct *vma)
+{
+	const struct vm_operations_struct *vm_ops = vma->vm_ops;
 	int err;
 
-	err = f_op->mmap_prepare(&desc);
+	if (!vm_ops->mapped)
+		return 0;
+
+	err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff, file,
+			     &vma->vm_private_data);
 	if (err)
-		return err;
+		unmap_vma_locked(vma);
+	return err;
+}
 
-	err = mmap_action_prepare(&desc);
+static inline int __compat_vma_mmap(struct vm_area_desc *desc,
+		struct vm_area_struct *vma)
+{
+	int err;
+
+	/* Perform any preparatory tasks for mmap action. */
+	err = mmap_action_prepare(desc);
+	if (err)
+		return err;
+	/* Update the VMA from the descriptor. */
+	compat_set_vma_from_desc(vma, desc);
+	/* Complete any specified mmap actions. */
+	err = mmap_action_complete(vma, &desc->action,
+				   /*rmap_lock_held=*/false);
 	if (err)
 		return err;
 
-	set_vma_from_desc(vma, &desc);
-	return mmap_action_complete(vma, &desc.action, /*rmap_lock_held=*/false);
+	/* Invoke vm_ops->mapped callback. */
+	return __compat_vma_mapped(desc->file, vma);
+}
+
+static inline int vfs_mmap_prepare(struct file *file, struct vm_area_desc *desc)
+{
+	return file->f_op->mmap_prepare(desc);
 }
 
 static inline int compat_vma_mmap(struct file *file,
 		struct vm_area_struct *vma)
 {
-	return __compat_vma_mmap(file->f_op, file, vma);
+	struct vm_area_desc desc;
+	int err;
+
+	compat_set_desc_from_vma(&desc, file, vma);
+	err = vfs_mmap_prepare(file, &desc);
+	if (err)
+		return err;
+
+	return __compat_vma_mmap(&desc, vma);
 }
 
 
@@ -1318,11 +1370,6 @@ static inline void vma_iter_init(struct vma_iterator *vmi,
 	mas_init(&vmi->mas, &mm->mm_mt, addr);
 }
 
-static inline unsigned long vma_pages(struct vm_area_struct *vma)
-{
-	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
-}
-
 static inline void mmap_assert_locked(struct mm_struct *);
 static inline struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
 						unsigned long start_addr,
@@ -1492,11 +1539,6 @@ static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma)
 	return file->f_op->mmap(file, vma);
 }
 
-static inline int vfs_mmap_prepare(struct file *file, struct vm_area_desc *desc)
-{
-	return file->f_op->mmap_prepare(desc);
-}
-
 static inline void vma_set_file(struct vm_area_struct *vma, struct file *file)
 {
 	/* Changing an anonymous vma with this is illegal */
@@ -1521,11 +1563,3 @@ static inline pgprot_t vma_get_page_prot(vma_flags_t vma_flags)
 
 	return vm_get_page_prot(vm_flags);
 }
-
-static inline void unmap_vma_locked(struct vm_area_struct *vma)
-{
-	const size_t len = vma_pages(vma) << PAGE_SHIFT;
-
-	mmap_assert_write_locked(vma->vm_mm);
-	do_munmap(vma->vm_mm, vma->vm_start, len, NULL);
-}
-- 
2.53.0

[PATCH v3 13/16] drivers: hv: vmbus: replace deprecated mmap hook with mmap_prepare

[Lorenzo Stoakes (Oracle)]

The f_op->mmap interface is deprecated, so update the vmbus driver to use
its successor, mmap_prepare.

This updates all callbacks which referenced the function pointer
hv_mmap_ring_buffer to instead reference hv_mmap_prepare_ring_buffer,
utilising the newly introduced compat_set_desc_from_vma() and
__compat_vma_mmap() to be able to implement this change.

The UIO HV generic driver is the only user of hv_create_ring_sysfs(),
which is the only function which references
vmbus_channel->mmap_prepare_ring_buffer which, in turn, is the only
external interface to hv_mmap_prepare_ring_buffer.

This patch therefore updates this caller to use mmap_prepare instead,
which also previously used vm_iomap_memory(), so this change replaces it
with its mmap_prepare equivalent, mmap_action_simple_ioremap().

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 drivers/hv/hyperv_vmbus.h    |  4 ++--
 drivers/hv/vmbus_drv.c       | 31 +++++++++++++++++++------------
 drivers/uio/uio_hv_generic.c | 11 ++++++-----
 include/linux/hyperv.h       |  4 ++--
 4 files changed, 29 insertions(+), 21 deletions(-)

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 7bd8f8486e85..31f576464f18 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -545,8 +545,8 @@ static inline int hv_debug_add_dev_dir(struct hv_device *dev)
 
 /* Create and remove sysfs entry for memory mapped ring buffers for a channel */
 int hv_create_ring_sysfs(struct vmbus_channel *channel,
-			 int (*hv_mmap_ring_buffer)(struct vmbus_channel *channel,
-						    struct vm_area_struct *vma));
+			 int (*hv_mmap_prepare_ring_buffer)(struct vmbus_channel *channel,
+							    struct vm_area_desc *desc));
 int hv_remove_ring_sysfs(struct vmbus_channel *channel);
 
 #endif /* _HYPERV_VMBUS_H */
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index bc4fc1951ae1..45625487ba36 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1951,12 +1951,19 @@ static int hv_mmap_ring_buffer_wrapper(struct file *filp, struct kobject *kobj,
 				       struct vm_area_struct *vma)
 {
 	struct vmbus_channel *channel = container_of(kobj, struct vmbus_channel, kobj);
+	struct vm_area_desc desc;
+	int err;
 
 	/*
-	 * hv_(create|remove)_ring_sysfs implementation ensures that mmap_ring_buffer
-	 * is not NULL.
+	 * hv_(create|remove)_ring_sysfs implementation ensures that
+	 * mmap_prepare_ring_buffer is not NULL.
 	 */
-	return channel->mmap_ring_buffer(channel, vma);
+	compat_set_desc_from_vma(&desc, filp, vma);
+	err = channel->mmap_prepare_ring_buffer(channel, &desc);
+	if (err)
+		return err;
+
+	return __compat_vma_mmap(&desc, vma);
 }
 
 static struct bin_attribute chan_attr_ring_buffer = {
@@ -2048,13 +2055,13 @@ static const struct kobj_type vmbus_chan_ktype = {
 /**
  * hv_create_ring_sysfs() - create "ring" sysfs entry corresponding to ring buffers for a channel.
  * @channel: Pointer to vmbus_channel structure
- * @hv_mmap_ring_buffer: function pointer for initializing the function to be called on mmap of
+ * @hv_mmap_prepare_ring_buffer: function pointer for initializing the function to be called on mmap
  *                       channel's "ring" sysfs node, which is for the ring buffer of that channel.
  *                       Function pointer is of below type:
- *                       int (*hv_mmap_ring_buffer)(struct vmbus_channel *channel,
- *                                                  struct vm_area_struct *vma))
- *                       This has a pointer to the channel and a pointer to vm_area_struct,
- *                       used for mmap, as arguments.
+ *                       int (*hv_mmap_prepare_ring_buffer)(struct vmbus_channel *channel,
+ *                                                          struct vm_area_desc *desc))
+ *                       This has a pointer to the channel and a pointer to vm_area_desc,
+ *                       used for mmap_prepare, as arguments.
  *
  * Sysfs node for ring buffer of a channel is created along with other fields, however its
  * visibility is disabled by default. Sysfs creation needs to be controlled when the use-case
@@ -2071,12 +2078,12 @@ static const struct kobj_type vmbus_chan_ktype = {
  * Returns 0 on success or error code on failure.
  */
 int hv_create_ring_sysfs(struct vmbus_channel *channel,
-			 int (*hv_mmap_ring_buffer)(struct vmbus_channel *channel,
-						    struct vm_area_struct *vma))
+			 int (*hv_mmap_prepare_ring_buffer)(struct vmbus_channel *channel,
+							    struct vm_area_desc *desc))
 {
 	struct kobject *kobj = &channel->kobj;
 
-	channel->mmap_ring_buffer = hv_mmap_ring_buffer;
+	channel->mmap_prepare_ring_buffer = hv_mmap_prepare_ring_buffer;
 	channel->ring_sysfs_visible = true;
 
 	return sysfs_update_group(kobj, &vmbus_chan_group);
@@ -2098,7 +2105,7 @@ int hv_remove_ring_sysfs(struct vmbus_channel *channel)
 
 	channel->ring_sysfs_visible = false;
 	ret = sysfs_update_group(kobj, &vmbus_chan_group);
-	channel->mmap_ring_buffer = NULL;
+	channel->mmap_prepare_ring_buffer = NULL;
 	return ret;
 }
 EXPORT_SYMBOL_GPL(hv_remove_ring_sysfs);
diff --git a/drivers/uio/uio_hv_generic.c b/drivers/uio/uio_hv_generic.c
index 3f8e2e27697f..29ec2d15ada8 100644
--- a/drivers/uio/uio_hv_generic.c
+++ b/drivers/uio/uio_hv_generic.c
@@ -154,15 +154,16 @@ static void hv_uio_rescind(struct vmbus_channel *channel)
  * The ring buffer is allocated as contiguous memory by vmbus_open
  */
 static int
-hv_uio_ring_mmap(struct vmbus_channel *channel, struct vm_area_struct *vma)
+hv_uio_ring_mmap_prepare(struct vmbus_channel *channel, struct vm_area_desc *desc)
 {
 	void *ring_buffer = page_address(channel->ringbuffer_page);
 
 	if (channel->state != CHANNEL_OPENED_STATE)
 		return -ENODEV;
 
-	return vm_iomap_memory(vma, virt_to_phys(ring_buffer),
-			       channel->ringbuffer_pagecount << PAGE_SHIFT);
+	mmap_action_simple_ioremap(desc, virt_to_phys(ring_buffer),
+			channel->ringbuffer_pagecount << PAGE_SHIFT);
+	return 0;
 }
 
 /* Callback from VMBUS subsystem when new channel created. */
@@ -183,7 +184,7 @@ hv_uio_new_channel(struct vmbus_channel *new_sc)
 	}
 
 	set_channel_read_mode(new_sc, HV_CALL_ISR);
-	ret = hv_create_ring_sysfs(new_sc, hv_uio_ring_mmap);
+	ret = hv_create_ring_sysfs(new_sc, hv_uio_ring_mmap_prepare);
 	if (ret) {
 		dev_err(device, "sysfs create ring bin file failed; %d\n", ret);
 		vmbus_close(new_sc);
@@ -366,7 +367,7 @@ hv_uio_probe(struct hv_device *dev,
 	 * or decoupled from uio_hv_generic probe. Userspace programs can make use of inotify
 	 * APIs to make sure that ring is created.
 	 */
-	hv_create_ring_sysfs(channel, hv_uio_ring_mmap);
+	hv_create_ring_sysfs(channel, hv_uio_ring_mmap_prepare);
 
 	hv_set_drvdata(dev, pdata);
 
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index dfc516c1c719..3a721b1853a4 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1015,8 +1015,8 @@ struct vmbus_channel {
 	/* The max size of a packet on this channel */
 	u32 max_pkt_size;
 
-	/* function to mmap ring buffer memory to the channel's sysfs ring attribute */
-	int (*mmap_ring_buffer)(struct vmbus_channel *channel, struct vm_area_struct *vma);
+	/* function to mmap_prepare ring buffer memory to the channel's sysfs ring attribute */
+	int (*mmap_prepare_ring_buffer)(struct vmbus_channel *channel, struct vm_area_desc *desc);
 
 	/* boolean to control visibility of sysfs for ring buffer */
 	bool ring_sysfs_visible;
-- 
2.53.0

[PATCH v3 14/16] uio: replace deprecated mmap hook with mmap_prepare in uio_info

[Lorenzo Stoakes (Oracle)]

The f_op->mmap interface is deprecated, so update uio_info to use its
successor, mmap_prepare.

Therefore, replace the uio_info->mmap hook with a new
uio_info->mmap_prepare hook, and update its one user, target_core_user,
to both specify this new mmap_prepare hook and also to use the new
vm_ops->mapped() hook to continue to maintain a correct udev->kref
refcount.

Then update uio_mmap() to utilise the mmap_prepare compatibility layer to
invoke this callback from the uio mmap invocation.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 drivers/target/target_core_user.c | 26 ++++++++++++++++++--------
 drivers/uio/uio.c                 | 10 ++++++++--
 include/linux/uio_driver.h        |  4 ++--
 3 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index af95531ddd35..edc2afd5f4ee 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1860,6 +1860,17 @@ static struct page *tcmu_try_get_data_page(struct tcmu_dev *udev, uint32_t dpi)
 	return NULL;
 }
 
+static int tcmu_vma_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
+			   const struct file *file, void **vm_private_data)
+{
+	struct tcmu_dev *udev = *vm_private_data;
+
+	pr_debug("vma_mapped\n");
+
+	kref_get(&udev->kref);
+	return 0;
+}
+
 static void tcmu_vma_open(struct vm_area_struct *vma)
 {
 	struct tcmu_dev *udev = vma->vm_private_data;
@@ -1919,26 +1930,25 @@ static vm_fault_t tcmu_vma_fault(struct vm_fault *vmf)
 }
 
 static const struct vm_operations_struct tcmu_vm_ops = {
+	.mapped = tcmu_vma_mapped,
 	.open = tcmu_vma_open,
 	.close = tcmu_vma_close,
 	.fault = tcmu_vma_fault,
 };
 
-static int tcmu_mmap(struct uio_info *info, struct vm_area_struct *vma)
+static int tcmu_mmap_prepare(struct uio_info *info, struct vm_area_desc *desc)
 {
 	struct tcmu_dev *udev = container_of(info, struct tcmu_dev, uio_info);
 
-	vm_flags_set(vma, VM_DONTEXPAND | VM_DONTDUMP);
-	vma->vm_ops = &tcmu_vm_ops;
+	vma_desc_set_flags(desc, VMA_DONTEXPAND_BIT, VMA_DONTDUMP_BIT);
+	desc->vm_ops = &tcmu_vm_ops;
 
-	vma->vm_private_data = udev;
+	desc->private_data = udev;
 
 	/* Ensure the mmap is exactly the right size */
-	if (vma_pages(vma) != udev->mmap_pages)
+	if (vma_desc_pages(desc) != udev->mmap_pages)
 		return -EINVAL;
 
-	tcmu_vma_open(vma);
-
 	return 0;
 }
 
@@ -2253,7 +2263,7 @@ static int tcmu_configure_device(struct se_device *dev)
 	info->irqcontrol = tcmu_irqcontrol;
 	info->irq = UIO_IRQ_CUSTOM;
 
-	info->mmap = tcmu_mmap;
+	info->mmap_prepare = tcmu_mmap_prepare;
 	info->open = tcmu_open;
 	info->release = tcmu_release;
 
diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 5a4998e2caf8..1e4ade78ed84 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -850,8 +850,14 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
 		goto out;
 	}
 
-	if (idev->info->mmap) {
-		ret = idev->info->mmap(idev->info, vma);
+	if (idev->info->mmap_prepare) {
+		struct vm_area_desc desc;
+
+		compat_set_desc_from_vma(&desc, filep, vma);
+		ret = idev->info->mmap_prepare(idev->info, &desc);
+		if (ret)
+			goto out;
+		ret = __compat_vma_mmap(&desc, vma);
 		goto out;
 	}
 
diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index 334641e20fb1..02eaac47ac44 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -97,7 +97,7 @@ struct uio_device {
  * @irq_flags:		flags for request_irq()
  * @priv:		optional private data
  * @handler:		the device's irq handler
- * @mmap:		mmap operation for this uio device
+ * @mmap_prepare:	mmap_prepare operation for this uio device
  * @open:		open operation for this uio device
  * @release:		release operation for this uio device
  * @irqcontrol:		disable/enable irqs when 0/1 is written to /dev/uioX
@@ -112,7 +112,7 @@ struct uio_info {
 	unsigned long		irq_flags;
 	void			*priv;
 	irqreturn_t (*handler)(int irq, struct uio_info *dev_info);
-	int (*mmap)(struct uio_info *info, struct vm_area_struct *vma);
+	int (*mmap_prepare)(struct uio_info *info, struct vm_area_desc *desc);
 	int (*open)(struct uio_info *info, struct inode *inode);
 	int (*release)(struct uio_info *info, struct inode *inode);
 	int (*irqcontrol)(struct uio_info *info, s32 irq_on);
-- 
2.53.0

[PATCH v3 15/16] mm: add mmap_action_map_kernel_pages[_full]()

[Lorenzo Stoakes (Oracle)]

A user can invoke mmap_action_map_kernel_pages() to specify that the
mapping should map kernel pages starting from desc->start of a specified
number of pages specified in an array.

In order to implement this, adjust mmap_action_prepare() to be able to
return an error code, as it makes sense to assert that the specified
parameters are valid as quickly as possible as well as updating the VMA
flags to include VMA_MIXEDMAP_BIT as necessary.

This provides an mmap_prepare equivalent of vm_insert_pages().  We
additionally update the existing vm_insert_pages() code to use
range_in_vma() and add a new range_in_vma_desc() helper function for the
mmap_prepare case, sharing the code between the two in range_is_subset().

We add both mmap_action_map_kernel_pages() and
mmap_action_map_kernel_pages_full() to allow for both partial and full VMA
mappings.

We update the documentation to reflect the new features.

Finally, we update the VMA tests accordingly to reflect the changes.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 Documentation/filesystems/mmap_prepare.rst |  8 ++
 include/linux/mm.h                         | 95 +++++++++++++++++++++-
 include/linux/mm_types.h                   |  7 ++
 mm/memory.c                                | 42 +++++++++-
 mm/util.c                                  |  6 ++
 tools/testing/vma/include/dup.h            |  7 ++
 6 files changed, 159 insertions(+), 6 deletions(-)

diff --git a/Documentation/filesystems/mmap_prepare.rst b/Documentation/filesystems/mmap_prepare.rst
index be76ae475b9c..e810aa4134eb 100644
--- a/Documentation/filesystems/mmap_prepare.rst
+++ b/Documentation/filesystems/mmap_prepare.rst
@@ -156,5 +156,13 @@ pointer. These are:
 * mmap_action_simple_ioremap() - Sets up an I/O remap from a specified
   physical address and over a specified length.
 
+* mmap_action_map_kernel_pages() - Maps a specified array of `struct page`
+  pointers in the VMA from a specific offset.
+
+* mmap_action_map_kernel_pages_full() - Maps a specified array of `struct
+  page` pointers over the entire VMA. The caller must ensure there are
+  sufficient entries in the page array to cover the entire range of the
+  described VMA.
+
 **NOTE:** The ``action`` field should never normally be manipulated directly,
 rather you ought to use one of these helpers.
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ef2e4dccfe8e..8aadf115278e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2912,7 +2912,7 @@ static inline bool folio_maybe_mapped_shared(struct folio *folio)
  * The caller must add any reference (e.g., from folio_try_get()) it might be
  * holding itself to the result.
  *
- * Returns the expected folio refcount.
+ * Returns: the expected folio refcount.
  */
 static inline int folio_expected_ref_count(const struct folio *folio)
 {
@@ -4364,6 +4364,45 @@ static inline void mmap_action_simple_ioremap(struct vm_area_desc *desc,
 	action->type = MMAP_SIMPLE_IO_REMAP;
 }
 
+/**
+ * mmap_action_map_kernel_pages - helper for mmap_prepare hook to specify that
+ * @num kernel pages contained in the @pages array should be mapped to userland
+ * starting at virtual address @start.
+ * @desc: The VMA descriptor for the VMA requiring kernel pags to be mapped.
+ * @start: The virtual address from which to map them.
+ * @pages: An array of struct page pointers describing the memory to map.
+ * @nr_pages: The number of entries in the @pages aray.
+ */
+static inline void mmap_action_map_kernel_pages(struct vm_area_desc *desc,
+		unsigned long start, struct page **pages,
+		unsigned long nr_pages)
+{
+	struct mmap_action *action = &desc->action;
+
+	action->type = MMAP_MAP_KERNEL_PAGES;
+	action->map_kernel.start = start;
+	action->map_kernel.pages = pages;
+	action->map_kernel.nr_pages = nr_pages;
+	action->map_kernel.pgoff = desc->pgoff;
+}
+
+/**
+ * mmap_action_map_kernel_pages_full - helper for mmap_prepare hook to specify that
+ * kernel pages contained in the @pages array should be mapped to userland
+ * from @desc->start to @desc->end.
+ * @desc: The VMA descriptor for the VMA requiring kernel pags to be mapped.
+ * @pages: An array of struct page pointers describing the memory to map.
+ *
+ * The caller must ensure that @pages contains sufficient entries to cover the
+ * entire range described by @desc.
+ */
+static inline void mmap_action_map_kernel_pages_full(struct vm_area_desc *desc,
+		struct page **pages)
+{
+	mmap_action_map_kernel_pages(desc, desc->start, pages,
+				     vma_desc_pages(desc));
+}
+
 int mmap_action_prepare(struct vm_area_desc *desc);
 int mmap_action_complete(struct vm_area_struct *vma,
 			 struct mmap_action *action,
@@ -4381,10 +4420,59 @@ static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
 	return vma;
 }
 
+/**
+ * range_is_subset - Is the specified inner range a subset of the outer range?
+ * @outer_start: The start of the outer range.
+ * @outer_end: The exclusive end of the outer range.
+ * @inner_start: The start of the inner range.
+ * @inner_end: The exclusive end of the inner range.
+ *
+ * Returns: %true if [inner_start, inner_end) is a subset of [outer_start,
+ * outer_end), otherwise %false.
+ */
+static inline bool range_is_subset(unsigned long outer_start,
+				   unsigned long outer_end,
+				   unsigned long inner_start,
+				   unsigned long inner_end)
+{
+	return outer_start <= inner_start && inner_end <= outer_end;
+}
+
+/**
+ * range_in_vma - is the specified [@start, @end) range a subset of the VMA?
+ * @vma: The VMA against which we want to check [@start, @end).
+ * @start: The start of the range we wish to check.
+ * @end: The exclusive end of the range we wish to check.
+ *
+ * Returns: %true if [@start, @end) is a subset of [@vma->vm_start,
+ * @vma->vm_end), %false otherwise.
+ */
 static inline bool range_in_vma(const struct vm_area_struct *vma,
 				unsigned long start, unsigned long end)
 {
-	return (vma && vma->vm_start <= start && end <= vma->vm_end);
+	if (!vma)
+		return false;
+
+	return range_is_subset(vma->vm_start, vma->vm_end, start, end);
+}
+
+/**
+ * range_in_vma_desc - is the specified [@start, @end) range a subset of the VMA
+ * described by @desc, a VMA descriptor?
+ * @desc: The VMA descriptor against which we want to check [@start, @end).
+ * @start: The start of the range we wish to check.
+ * @end: The exclusive end of the range we wish to check.
+ *
+ * Returns: %true if [@start, @end) is a subset of [@desc->start, @desc->end),
+ * %false otherwise.
+ */
+static inline bool range_in_vma_desc(const struct vm_area_desc *desc,
+				     unsigned long start, unsigned long end)
+{
+	if (!desc)
+		return false;
+
+	return range_is_subset(desc->start, desc->end, start, end);
 }
 
 #ifdef CONFIG_MMU
@@ -4428,6 +4516,9 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
 int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
 int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
 			struct page **pages, unsigned long *num);
+int map_kernel_pages_prepare(struct vm_area_desc *desc);
+int map_kernel_pages_complete(struct vm_area_struct *vma,
+			      struct mmap_action *action);
 int vm_map_pages(struct vm_area_struct *vma, struct page **pages,
 				unsigned long num);
 int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages,
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 7538d64f8848..c46224020a46 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -815,6 +815,7 @@ enum mmap_action_type {
 	MMAP_REMAP_PFN,		/* Remap PFN range. */
 	MMAP_IO_REMAP_PFN,	/* I/O remap PFN range. */
 	MMAP_SIMPLE_IO_REMAP,	/* I/O remap with guardrails. */
+	MMAP_MAP_KERNEL_PAGES,	/* Map kernel page range from array. */
 };
 
 /*
@@ -833,6 +834,12 @@ struct mmap_action {
 			phys_addr_t start_phys_addr;
 			unsigned long size;
 		} simple_ioremap;
+		struct {
+			unsigned long start;
+			struct page **pages;
+			unsigned long nr_pages;
+			pgoff_t pgoff;
+		} map_kernel;
 	};
 	enum mmap_action_type type;
 
diff --git a/mm/memory.c b/mm/memory.c
index b3bcc21af20a..53ef8ef3d04a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2484,13 +2484,14 @@ static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
 int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
 			struct page **pages, unsigned long *num)
 {
-	const unsigned long end_addr = addr + (*num * PAGE_SIZE) - 1;
+	const unsigned long nr_pages = *num;
+	const unsigned long end = addr + PAGE_SIZE * nr_pages;
 
-	if (addr < vma->vm_start || end_addr >= vma->vm_end)
+	if (!range_in_vma(vma, addr, end))
 		return -EFAULT;
 	if (!(vma->vm_flags & VM_MIXEDMAP)) {
-		BUG_ON(mmap_read_trylock(vma->vm_mm));
-		BUG_ON(vma->vm_flags & VM_PFNMAP);
+		VM_WARN_ON_ONCE(mmap_read_trylock(vma->vm_mm));
+		VM_WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP);
 		vm_flags_set(vma, VM_MIXEDMAP);
 	}
 	/* Defer page refcount checking till we're about to map that page. */
@@ -2498,6 +2499,39 @@ int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
 }
 EXPORT_SYMBOL(vm_insert_pages);
 
+int map_kernel_pages_prepare(struct vm_area_desc *desc)
+{
+	const struct mmap_action *action = &desc->action;
+	const unsigned long addr = action->map_kernel.start;
+	unsigned long nr_pages, end;
+
+	if (!vma_desc_test(desc, VMA_MIXEDMAP_BIT)) {
+		VM_WARN_ON_ONCE(mmap_read_trylock(desc->mm));
+		VM_WARN_ON_ONCE(vma_desc_test(desc, VMA_PFNMAP_BIT));
+		vma_desc_set_flags(desc, VMA_MIXEDMAP_BIT);
+	}
+
+	nr_pages = action->map_kernel.nr_pages;
+	end = addr + PAGE_SIZE * nr_pages;
+	if (!range_in_vma_desc(desc, addr, end))
+		return -EFAULT;
+
+	return 0;
+}
+EXPORT_SYMBOL(map_kernel_pages_prepare);
+
+int map_kernel_pages_complete(struct vm_area_struct *vma,
+			      struct mmap_action *action)
+{
+	unsigned long nr_pages;
+
+	nr_pages = action->map_kernel.nr_pages;
+	return insert_pages(vma, action->map_kernel.start,
+			    action->map_kernel.pages,
+			    &nr_pages, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(map_kernel_pages_complete);
+
 /**
  * vm_insert_page - insert single page into user vma
  * @vma: user vma to map to
diff --git a/mm/util.c b/mm/util.c
index 8cf59267a9ac..682d0d24e1c6 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1446,6 +1446,8 @@ int mmap_action_prepare(struct vm_area_desc *desc)
 		return io_remap_pfn_range_prepare(desc);
 	case MMAP_SIMPLE_IO_REMAP:
 		return simple_ioremap_prepare(desc);
+	case MMAP_MAP_KERNEL_PAGES:
+		return map_kernel_pages_prepare(desc);
 	}
 
 	WARN_ON_ONCE(1);
@@ -1476,6 +1478,9 @@ int mmap_action_complete(struct vm_area_struct *vma,
 	case MMAP_REMAP_PFN:
 		err = remap_pfn_range_complete(vma, action);
 		break;
+	case MMAP_MAP_KERNEL_PAGES:
+		err = map_kernel_pages_complete(vma, action);
+		break;
 	case MMAP_IO_REMAP_PFN:
 	case MMAP_SIMPLE_IO_REMAP:
 		/* Should have been delegated. */
@@ -1497,6 +1502,7 @@ int mmap_action_prepare(struct vm_area_desc *desc)
 	case MMAP_REMAP_PFN:
 	case MMAP_IO_REMAP_PFN:
 	case MMAP_SIMPLE_IO_REMAP:
+	case MMAP_MAP_KERNEL_PAGES:
 		WARN_ON_ONCE(1); /* nommu cannot handle these. */
 		break;
 	}
diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 1f123704078e..6392e7835f89 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -454,6 +454,7 @@ enum mmap_action_type {
 	MMAP_REMAP_PFN,		/* Remap PFN range. */
 	MMAP_IO_REMAP_PFN,	/* I/O remap PFN range. */
 	MMAP_SIMPLE_IO_REMAP,	/* I/O remap with guardrails. */
+	MMAP_MAP_KERNEL_PAGES,	/* Map kernel page range from an array. */
 };
 
 /*
@@ -472,6 +473,12 @@ struct mmap_action {
 			phys_addr_t start_phys_addr;
 			unsigned long size;
 		} simple_ioremap;
+		struct {
+			unsigned long start;
+			struct page **pages;
+			unsigned long nr_pages;
+			pgoff_t pgoff;
+		} map_kernel;
 	};
 	enum mmap_action_type type;
 
-- 
2.53.0

[PATCH v3 16/16] mm: on remap assert that input range within the proposed VMA

[Lorenzo Stoakes (Oracle)]

Now we have range_in_vma_desc(), update remap_pfn_range_prepare() to check
whether the input range in contained within the specified VMA, so we can
fail at prepare time if an invalid range is specified.

This covers the I/O remap mmap actions also which ultimately call into
this function, and other mmap action types either already span the full
VMA or check this already.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
 mm/memory.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 53ef8ef3d04a..68cc592ff0ba 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3142,6 +3142,9 @@ int remap_pfn_range_prepare(struct vm_area_desc *desc)
 	const bool is_cow = vma_desc_is_cow_mapping(desc);
 	int err;
 
+	if (!range_in_vma_desc(desc, start, end))
+		return -EFAULT;
+
 	err = get_remap_pgoff(is_cow, start, end, desc->start, desc->end, pfn,
 			      &desc->pgoff);
 	if (err)
-- 
2.53.0

Re: [PATCH v3 00/16] mm: expand mmap_prepare functionality and usage

[Andrew Morton]

On Thu, 19 Mar 2026 18:23:24 +0000 "Lorenzo Stoakes (Oracle)" <ljs@kernel.org> wrote:

> This series expands the mmap_prepare functionality, which is intended to
> replace the deprecated f_op->mmap hook which has been the source of bugs
> and security issues for some time.
> 

Thanks, I updated mm.git's mm-new branch to this version.
> 
> v3:
> * Propagated tags (thanks Suren, Richard!)
> * Updated 12/16 to correctly clear the vm_area_desc data structure in
>   set_desc_from_vma() as per Joshua Hahn (thanks! :)
> * Fixed type in 12/16 as per Suren (cheers!)
> * Fixed up 6/16 to use mmap_action_ioremap_full() in simple_ioremap_prepare() as
>   suggested by Suren.
> * Also fixed up 6/16 to call io_remap_pfn_range_prepare() direct rather than
>   mmap_action_prepare() as per Suren.
> * Also fixed up 6/16 to pass vm_len rather than vm_[start, end] to
>   __simple_ioremap_prep() as per Suren (thanks for all the above! :)
> * Fixed issue in rmap lock being held - we were referencing a vma->vm_file after
>   the VMA was unmapped, so UAF. Avoid that. Also do_munmap() relies on rmap lock
>   NOT being held or may deadlock, so extend functionality to ensure we drop it
>   when it is held on error paths.
> * Updated 'area' -> 'vma' variable in 3/16 in VMA test dup.h.
> * Fixed up reference to __compat_vma_mmap() in 12/16 commit message.
> * Updated 1/16 to no longer duplicatively apply io_remap_pfn_range_pfn().
> * Updated 1/16 to delegate I/O remap complete to remap complete logic.
> * Fixed various typos in 12/16.
> * Fixed stale comment typos in 13/16.
> * Fixed commit msg and comment typos in 14/16.
> * Removed accidental sneak peak to future functionality in 15/16 commit message
>   :).
> * Fixed up field names to be identical in VMA tests + mm_types.h in 6/16,
>   15/16.

Here's how v3 altered mm.git:


 drivers/hv/vmbus_drv.c            |    6 +-
 drivers/target/target_core_user.c |    2 
 include/linux/mm.h                |    3 -
 include/linux/uio_driver.h        |    2 
 mm/internal.h                     |   22 ++++-----
 mm/memory.c                       |   16 +++----
 mm/util.c                         |   62 ++++++++++++++--------------
 mm/vma.c                          |   24 +++-------
 tools/testing/vma/include/dup.h   |   19 ++++----
 tools/testing/vma/include/stubs.h |    3 -
 10 files changed, 77 insertions(+), 82 deletions(-)

--- a/drivers/hv/vmbus_drv.c~b
+++ a/drivers/hv/vmbus_drv.c
@@ -1955,8 +1955,8 @@ static int hv_mmap_ring_buffer_wrapper(s
 	int err;
 
 	/*
-	 * hv_(create|remove)_ring_sysfs implementation ensures that mmap_ring_buffer
-	 * is not NULL.
+	 * hv_(create|remove)_ring_sysfs implementation ensures that
+	 * mmap_prepare_ring_buffer is not NULL.
 	 */
 	compat_set_desc_from_vma(&desc, filp, vma);
 	err = channel->mmap_prepare_ring_buffer(channel, &desc);
@@ -2055,7 +2055,7 @@ static const struct kobj_type vmbus_chan
 /**
  * hv_create_ring_sysfs() - create "ring" sysfs entry corresponding to ring buffers for a channel.
  * @channel: Pointer to vmbus_channel structure
- * @hv_mmap_ring_buffer: function pointer for initializing the function to be called on mmap
+ * @hv_mmap_prepare_ring_buffer: function pointer for initializing the function to be called on mmap
  *                       channel's "ring" sysfs node, which is for the ring buffer of that channel.
  *                       Function pointer is of below type:
  *                       int (*hv_mmap_prepare_ring_buffer)(struct vmbus_channel *channel,
--- a/drivers/target/target_core_user.c~b
+++ a/drivers/target/target_core_user.c
@@ -1865,7 +1865,7 @@ static int tcmu_vma_mapped(unsigned long
 {
 	struct tcmu_dev *udev = *vm_private_data;
 
-	pr_debug("vma_open\n");
+	pr_debug("vma_mapped\n");
 
 	kref_get(&udev->kref);
 	return 0;
--- a/include/linux/mm.h~b
+++ a/include/linux/mm.h
@@ -4405,7 +4405,8 @@ static inline void mmap_action_map_kerne
 
 int mmap_action_prepare(struct vm_area_desc *desc);
 int mmap_action_complete(struct vm_area_struct *vma,
-			 struct mmap_action *action);
+			 struct mmap_action *action,
+			 bool rmap_lock_held);
 
 /* Look up the first VMA which exactly match the interval vm_start ... vm_end */
 static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
--- a/include/linux/uio_driver.h~b
+++ a/include/linux/uio_driver.h
@@ -97,7 +97,7 @@ struct uio_device {
  * @irq_flags:		flags for request_irq()
  * @priv:		optional private data
  * @handler:		the device's irq handler
- * @mmap_prepare:	mmap_pepare operation for this uio device
+ * @mmap_prepare:	mmap_prepare operation for this uio device
  * @open:		open operation for this uio device
  * @release:		release operation for this uio device
  * @irqcontrol:		disable/enable irqs when 0/1 is written to /dev/uioX
--- a/mm/internal.h~b
+++ a/mm/internal.h
@@ -1805,29 +1805,25 @@ int remap_pfn_range_prepare(struct vm_ar
 int remap_pfn_range_complete(struct vm_area_struct *vma,
 			     struct mmap_action *action);
 int simple_ioremap_prepare(struct vm_area_desc *desc);
-/* No simple_ioremap_complete, is ultimately handled by remap complete. */
 
 static inline int io_remap_pfn_range_prepare(struct vm_area_desc *desc)
 {
 	struct mmap_action *action = &desc->action;
 	const unsigned long orig_pfn = action->remap.start_pfn;
+	const pgprot_t orig_pgprot = action->remap.pgprot;
 	const unsigned long size = action->remap.size;
 	const unsigned long pfn = io_remap_pfn_range_pfn(orig_pfn, size);
+	int err;
 
 	action->remap.start_pfn = pfn;
-	return remap_pfn_range_prepare(desc);
-}
-
-static inline int io_remap_pfn_range_complete(struct vm_area_struct *vma,
-					      struct mmap_action *action)
-{
-	const unsigned long size = action->remap.size;
-	const unsigned long orig_pfn = action->remap.start_pfn;
-	const pgprot_t orig_prot = vma->vm_page_prot;
+	action->remap.pgprot = pgprot_decrypted(orig_pgprot);
+	err = remap_pfn_range_prepare(desc);
+	if (err)
+		return err;
 
-	action->remap.pgprot = pgprot_decrypted(orig_prot);
-	action->remap.start_pfn  = io_remap_pfn_range_pfn(orig_pfn, size);
-	return remap_pfn_range_complete(vma, action);
+	/* Remap does the actual work. */
+	action->type = MMAP_REMAP_PFN;
+	return 0;
 }
 
 #ifdef CONFIG_MMU_NOTIFIER
--- a/mm/memory.c~b
+++ a/mm/memory.c
@@ -3207,11 +3207,10 @@ int remap_pfn_range_complete(struct vm_a
 	return do_remap_pfn_range(vma, start, pfn, size, prot);
 }
 
-static int __simple_ioremap_prep(unsigned long vm_start, unsigned long vm_end,
-				 pgoff_t vm_pgoff, phys_addr_t start_phys,
-				 unsigned long size, unsigned long *pfnp)
+static int __simple_ioremap_prep(unsigned long vm_len, pgoff_t vm_pgoff,
+				 phys_addr_t start_phys, unsigned long size,
+				 unsigned long *pfnp)
 {
-	const unsigned long vm_len = vm_end - vm_start;
 	unsigned long pfn, pages;
 
 	/* Check that the physical memory area passed in looks valid */
@@ -3250,14 +3249,14 @@ int simple_ioremap_prepare(struct vm_are
 	unsigned long pfn;
 	int err;
 
-	err = __simple_ioremap_prep(desc->start, desc->end, desc->pgoff,
+	err = __simple_ioremap_prep(vma_desc_size(desc), desc->pgoff,
 				    start, size, &pfn);
 	if (err)
 		return err;
 
 	/* The I/O remap logic does the heavy lifting. */
-	mmap_action_ioremap(desc, desc->start, pfn, vma_desc_size(desc));
-	return mmap_action_prepare(desc);
+	mmap_action_ioremap_full(desc, pfn);
+	return io_remap_pfn_range_prepare(desc);
 }
 
 /**
@@ -3283,8 +3282,7 @@ int vm_iomap_memory(struct vm_area_struc
 	unsigned long pfn;
 	int err;
 
-	err = __simple_ioremap_prep(vm_start, vm_end, vma->vm_pgoff, start,
-				    len, &pfn);
+	err = __simple_ioremap_prep(vm_len, vma->vm_pgoff, start, len, &pfn);
 	if (err)
 		return err;
 
--- a/mm/util.c~b
+++ a/mm/util.c
@@ -1181,6 +1181,8 @@ void compat_set_desc_from_vma(struct vm_
 			      const struct file *file,
 			      const struct vm_area_struct *vma)
 {
+	memset(desc, 0, sizeof(*desc));
+
 	desc->mm = vma->vm_mm;
 	desc->file = (struct file *)file;
 	desc->start = vma->vm_start;
@@ -1224,7 +1226,7 @@ static int __compat_vma_mapped(struct fi
  * @vma: The VMA to which @desc should be applied.
  *
  * The function assumes that you have obtained a VMA descriptor @desc from
- * compt_set_desc_from_vma(), and already executed the mmap_prepare() hook upon
+ * compat_set_desc_from_vma(), and already executed the mmap_prepare() hook upon
  * it.
  *
  * It then performs any specified mmap actions, and invokes the vm_ops->mapped()
@@ -1249,7 +1251,8 @@ int __compat_vma_mmap(struct vm_area_des
 	/* Update the VMA from the descriptor. */
 	compat_set_vma_from_desc(vma, desc);
 	/* Complete any specified mmap actions. */
-	err = mmap_action_complete(vma, &desc->action);
+	err = mmap_action_complete(vma, &desc->action,
+				   /*rmap_lock_held=*/false);
 	if (err)
 		return err;
 
@@ -1397,29 +1400,31 @@ again:
 }
 
 static int mmap_action_finish(struct vm_area_struct *vma,
-			      struct mmap_action *action, int err)
+			      struct mmap_action *action, int err,
+			      bool rmap_lock_held)
 {
+	if (rmap_lock_held)
+		i_mmap_unlock_write(vma->vm_file->f_mapping);
+
+	if (!err) {
+		if (action->success_hook)
+			return action->success_hook(vma);
+		return 0;
+	}
+
 	/*
 	 * If an error occurs, unmap the VMA altogether and return an error. We
 	 * only clear the newly allocated VMA, since this function is only
 	 * invoked if we do NOT merge, so we only clean up the VMA we created.
 	 */
-	if (err) {
-		unmap_vma_locked(vma);
-		if (action->error_hook) {
-			/* We may want to filter the error. */
-			err = action->error_hook(err);
-
-			/* The caller should not clear the error. */
-			VM_WARN_ON_ONCE(!err);
-		}
-		return err;
+	unmap_vma_locked(vma);
+	if (action->error_hook) {
+		/* We may want to filter the error. */
+		err = action->error_hook(err);
+		/* The caller should not clear the error. */
+		VM_WARN_ON_ONCE(!err);
 	}
-
-	if (action->success_hook)
-		return action->success_hook(vma);
-
-	return 0;
+	return err;
 }
 
 #ifdef CONFIG_MMU
@@ -1454,13 +1459,15 @@ EXPORT_SYMBOL(mmap_action_prepare);
  * mmap_action_complete - Execute VMA descriptor action.
  * @vma: The VMA to perform the action upon.
  * @action: The action to perform.
+ * @rmap_lock_held: Is the file rmap lock held?
  *
  * Similar to mmap_action_prepare().
  *
  * Return: 0 on success, or error, at which point the VMA will be unmapped.
  */
 int mmap_action_complete(struct vm_area_struct *vma,
-			 struct mmap_action *action)
+			 struct mmap_action *action,
+			 bool rmap_lock_held)
 
 {
 	int err = 0;
@@ -1471,23 +1478,19 @@ int mmap_action_complete(struct vm_area_
 	case MMAP_REMAP_PFN:
 		err = remap_pfn_range_complete(vma, action);
 		break;
-	case MMAP_IO_REMAP_PFN:
-		err = io_remap_pfn_range_complete(vma, action);
-		break;
 	case MMAP_MAP_KERNEL_PAGES:
 		err = map_kernel_pages_complete(vma, action);
 		break;
+	case MMAP_IO_REMAP_PFN:
 	case MMAP_SIMPLE_IO_REMAP:
-		/*
-		 * The simple I/O remap should have been delegated to an I/O
-		 * remap.
-		 */
+		/* Should have been delegated. */
 		WARN_ON_ONCE(1);
 		err = -EINVAL;
 		break;
 	}
 
-	return mmap_action_finish(vma, action, err);
+	return mmap_action_finish(vma, action, err,
+				  rmap_lock_held);
 }
 EXPORT_SYMBOL(mmap_action_complete);
 #else
@@ -1509,7 +1512,8 @@ int mmap_action_prepare(struct vm_area_d
 EXPORT_SYMBOL(mmap_action_prepare);
 
 int mmap_action_complete(struct vm_area_struct *vma,
-			 struct mmap_action *action)
+			 struct mmap_action *action,
+			 bool rmap_lock_held)
 {
 	int err = 0;
 
@@ -1525,7 +1529,7 @@ int mmap_action_complete(struct vm_area_
 		break;
 	}
 
-	return mmap_action_finish(vma, action, err);
+	return mmap_action_finish(vma, action, err, rmap_lock_held);
 }
 EXPORT_SYMBOL(mmap_action_complete);
 #endif
--- a/mm/vma.c~b
+++ a/mm/vma.c
@@ -2732,7 +2732,8 @@ static bool can_set_ksm_flags_early(stru
 	return false;
 }
 
-static int call_mapped_hook(struct vm_area_struct *vma)
+static int call_mapped_hook(struct mmap_state *map,
+			    struct vm_area_struct *vma)
 {
 	const struct vm_operations_struct *vm_ops = vma->vm_ops;
 	void *vm_private_data = vma->vm_private_data;
@@ -2743,6 +2744,9 @@ static int call_mapped_hook(struct vm_ar
 	err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff,
 			     vma->vm_file, &vm_private_data);
 	if (err) {
+		if (map->hold_file_rmap_lock)
+			i_mmap_unlock_write(vma->vm_file->f_mapping);
+
 		unmap_vma_locked(vma);
 		return err;
 	}
@@ -2752,17 +2756,6 @@ static int call_mapped_hook(struct vm_ar
 	return 0;
 }
 
-static void maybe_drop_file_rmap_lock(struct mmap_state *map,
-				      struct vm_area_struct *vma)
-{
-	struct file *file;
-
-	if (!map->hold_file_rmap_lock)
-		return;
-	file = vma->vm_file;
-	i_mmap_unlock_write(file->f_mapping);
-}
-
 static unsigned long __mmap_region(struct file *file, unsigned long addr,
 		unsigned long len, vma_flags_t vma_flags,
 		unsigned long pgoff, struct list_head *uf)
@@ -2814,11 +2807,10 @@ static unsigned long __mmap_region(struc
 	__mmap_complete(&map, vma);
 
 	if (have_mmap_prepare && allocated_new) {
-		error = mmap_action_complete(vma, &desc.action);
+		error = mmap_action_complete(vma, &desc.action,
+					     map.hold_file_rmap_lock);
 		if (!error)
-			error = call_mapped_hook(vma);
-
-		maybe_drop_file_rmap_lock(&map, vma);
+			error = call_mapped_hook(&map, vma);
 		if (error)
 			return error;
 	}
--- a/tools/testing/vma/include/dup.h~b
+++ a/tools/testing/vma/include/dup.h
@@ -470,13 +470,13 @@ struct mmap_action {
 			pgprot_t pgprot;
 		} remap;
 		struct {
-			phys_addr_t start;
-			unsigned long len;
+			phys_addr_t start_phys_addr;
+			unsigned long size;
 		} simple_ioremap;
 		struct {
 			unsigned long start;
 			struct page **pages;
-			unsigned long num;
+			unsigned long nr_pages;
 			pgoff_t pgoff;
 		} map_kernel;
 	};
@@ -648,7 +648,7 @@ struct vm_operations_struct {
 	 * upon first mapping a VMA.
 	 * Context: User context.  May sleep.  Caller holds mmap_lock.
 	 */
-	void (*open)(struct vm_area_struct * area);
+	void (*open)(struct vm_area_struct *vma);
 	/**
 	 * @close: Called when the VMA is being removed from the MM.
 	 * Context: User context.  May sleep.  Caller holds mmap_lock.
@@ -672,8 +672,8 @@ struct vm_operations_struct {
 	int (*mapped)(unsigned long start, unsigned long end, pgoff_t pgoff,
 		      const struct file *file, void **vm_private_data);
 	/* Called any time before splitting to check if it's allowed */
-	int (*may_split)(struct vm_area_struct *area, unsigned long addr);
-	int (*mremap)(struct vm_area_struct *area);
+	int (*may_split)(struct vm_area_struct *vma, unsigned long addr);
+	int (*mremap)(struct vm_area_struct *vma);
 	/*
 	 * Called by mprotect() to make driver-specific permission
 	 * checks before mprotect() is finalised.   The VMA must not
@@ -685,7 +685,7 @@ struct vm_operations_struct {
 	vm_fault_t (*huge_fault)(struct vm_fault *vmf, unsigned int order);
 	vm_fault_t (*map_pages)(struct vm_fault *vmf,
 			pgoff_t start_pgoff, pgoff_t end_pgoff);
-	unsigned long (*pagesize)(struct vm_area_struct * area);
+	unsigned long (*pagesize)(struct vm_area_struct *vma);
 
 	/* notification that a previously read-only page is about to become
 	 * writable, if an error is returned it will cause a SIGBUS */
@@ -1288,6 +1288,8 @@ static inline void compat_set_desc_from_
 			      const struct file *file,
 			      const struct vm_area_struct *vma)
 {
+	memset(desc, 0, sizeof(*desc));
+
 	desc->mm = vma->vm_mm;
 	desc->file = (struct file *)file;
 	desc->start = vma->vm_start;
@@ -1342,7 +1344,8 @@ static inline int __compat_vma_mmap(stru
 	/* Update the VMA from the descriptor. */
 	compat_set_vma_from_desc(vma, desc);
 	/* Complete any specified mmap actions. */
-	err = mmap_action_complete(vma, &desc->action);
+	err = mmap_action_complete(vma, &desc->action,
+				   /*rmap_lock_held=*/false);
 	if (err)
 		return err;
 
--- a/tools/testing/vma/include/stubs.h~b
+++ a/tools/testing/vma/include/stubs.h
@@ -87,7 +87,8 @@ static inline int mmap_action_prepare(st
 }
 
 static inline int mmap_action_complete(struct vm_area_struct *vma,
-				       struct mmap_action *action)
+				       struct mmap_action *action,
+				       bool rmap_lock_held)
 {
 	return 0;
 }
_

Re: [PATCH v3 01/16] mm: various small mmap_prepare cleanups

[Vlastimil Babka (SUSE)]

On 3/19/26 19:23, Lorenzo Stoakes (Oracle) wrote:
> Rather than passing arbitrary fields, pass a vm_area_desc pointer to mmap
> prepare functions to mmap prepare, and an action and vma pointer to mmap
> complete in order to put all the action-specific logic in the function
> actually doing the work.
> 
> Additionally, allow mmap prepare functions to return an error so we can
> error out as soon as possible if there is something logically incorrect in
> the input.
> 
> Update remap_pfn_range_prepare() to properly check the input range for the
> CoW case.
> 
> Also remove io_remap_pfn_range_complete(), as we can simply set up the
> fields correctly in io_remap_pfn_range_prepare() and use
> remap_pfn_range_complete() for this.
> 
> While we're here, make remap_pfn_range_prepare_vma() a little neater, and
> pass mmap_action directly to call_action_complete().
> 
> Then, update compat_vma_mmap() to perform its logic directly, as
> __compat_vma_map() is not used by anything so we don't need to export it.
> 
> Also update compat_vma_mmap() to use vfs_mmap_prepare() rather than
> calling the mmap_prepare op directly.
> 
> Finally, update the VMA userland tests to reflect the changes.
> 
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Re: [PATCH v3 02/16] mm: add documentation for the mmap_prepare file operation callback

[Vlastimil Babka (SUSE)]

On 3/19/26 19:23, Lorenzo Stoakes (Oracle) wrote:
> This documentation makes it easier for a driver/file system implementer to
> correctly use this callback.
> 
> It covers the fundamentals, whilst intentionally leaving the less lovely
> possible actions one might take undocumented (for instance - the
> success_hook, error_hook fields in mmap_action).
> 
> The document also covers the new VMA flags implementation which is the
> only one which will work correctly with mmap_prepare.
> 
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Re: [PATCH v3 03/16] mm: document vm_operations_struct->open the same as close()

[Vlastimil Babka (SUSE)]

On 3/19/26 19:23, Lorenzo Stoakes (Oracle) wrote:
> Describe when the operation is invoked and the context in which it is
> invoked, matching the description already added for vm_op->close().
> 
> While we're here, update all outdated references to an 'area' field for
> VMAs to the more consistent 'vma'.
> 
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Re: [PATCH v3 04/16] mm: add vm_ops->mapped hook

[Vlastimil Babka (SUSE)]

On 3/19/26 19:23, Lorenzo Stoakes (Oracle) wrote:
> Previously, when a driver needed to do something like establish a
> reference count, it could do so in the mmap hook in the knowledge that the
> mapping would succeed.
> 
> With the introduction of f_op->mmap_prepare this is no longer the case, as
> it is invoked prior to actually establishing the mapping.
> 
> mmap_prepare is not appropriate for this kind of thing as it is called
> before any merge might take place, and after which an error might occur
> meaning resources could be leaked.
> 
> To take this into account, introduce a new vm_ops->mapped callback which
> is invoked when the VMA is first mapped (though notably - not when it is
> merged - which is correct and mirrors existing mmap/open/close behaviour).
> 
> We do better that vm_ops->open() here, as this callback can return an
> error, at which point the VMA will be unmapped.
> 
> Note that vm_ops->mapped() is invoked after any mmap action is complete
> (such as I/O remapping).
> 
> We intentionally do not expose the VMA at this point, exposing only the
> fields that could be used, and an output parameter in case the operation
> needs to update the vma->vm_private_data field.
> 
> In order to deal with stacked filesystems which invoke inner filesystem's
> mmap() invocations, add __compat_vma_mapped() and invoke it on vfs_mmap()
> (via compat_vma_mmap()) to ensure that the mapped callback is handled when
> an mmap() caller invokes a nested filesystem's mmap_prepare() callback.
> 
> We can now also remove call_action_complete() and invoke
> mmap_action_complete() directly, as we separate out the rmap lock logic.
> 
> The rmap lock logic, which was added in order to keep hugetlb working (!)
> to allow for the rmap lock to be held longer, needs to be propagated to the
> error paths on mmap complete and mapped hook error paths.
> 
> This is because do_munmap() might otherwise deadlock with the rmap being
> held, so instead we unlock at the point of unmap.

Hmm but that was also true prior to this series? So is this a bugfix? Should
it be a stable hotfix done outside of the series before the refactoring?

> This is fine as any reliance on the rmap being held is irrelevant on error.
> 
> While we're here, refactor mmap_action_finish() to avoid a big if (err)
> branch.
> 
> We also abstract unmapping of a VMA on mmap action completion into its own
> helper function, unmap_vma_locked().
> 
> Update the mmap_prepare documentation to describe the mapped hook and make
> it clear what its intended use is.
> 
> Additionally, update VMA userland test headers to reflect the change.
> 
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> ---
>  Documentation/filesystems/mmap_prepare.rst |  15 +++
>  include/linux/fs.h                         |   9 +-
>  include/linux/mm.h                         |  20 +++-
>  mm/internal.h                              |   8 ++
>  mm/util.c                                  | 129 ++++++++++++++-------
>  mm/vma.c                                   |  35 +++---
>  tools/testing/vma/include/dup.h            |  27 ++++-
>  tools/testing/vma/include/stubs.h          |   3 +-
>  8 files changed, 186 insertions(+), 60 deletions(-)
> 
> diff --git a/Documentation/filesystems/mmap_prepare.rst b/Documentation/filesystems/mmap_prepare.rst
> index 65a1f094e469..20db474915da 100644
> --- a/Documentation/filesystems/mmap_prepare.rst
> +++ b/Documentation/filesystems/mmap_prepare.rst
> @@ -25,6 +25,21 @@ That is - no resources should be allocated nor state updated to reflect that a
>  mapping has been established, as the mapping may either be merged, or fail to be
>  mapped after the callback is complete.
>  
> +Mapped callback
> +---------------
> +
> +If resources need to be allocated per-mapping, or state such as a reference
> +count needs to be manipulated, this should be done using the ``vm_ops->mapped``
> +hook, which itself should be set by the >mmap_prepare hook.
> +
> +This callback is only invoked if a new mapping has been established and was not
> +merged with any other, and is invoked at a point where no error may occur before
> +the mapping is established.
> +
> +You may return an error to the callback itself, which will cause the mapping to
> +become unmapped and an error returned to the mmap() caller. This is useful if
> +resources need to be allocated, and that allocation might fail.
> +
>  How To Use
>  ==========
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index a2628a12bd2b..c390f5c667e3 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2059,13 +2059,20 @@ static inline bool can_mmap_file(struct file *file)
>  }
>  
>  int compat_vma_mmap(struct file *file, struct vm_area_struct *vma);
> +int __vma_check_mmap_hook(struct vm_area_struct *vma);
>  
>  static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma)
>  {
> +	int err;
> +
>  	if (file->f_op->mmap_prepare)
>  		return compat_vma_mmap(file, vma);
>  
> -	return file->f_op->mmap(file, vma);
> +	err = file->f_op->mmap(file, vma);
> +	if (err)
> +		return err;
> +
> +	return __vma_check_mmap_hook(vma);
>  }
>  
>  static inline int vfs_mmap_prepare(struct file *file, struct vm_area_desc *desc)
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index da94edb287cd..68dee1101313 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -777,6 +777,23 @@ struct vm_operations_struct {
>  	 * Context: User context.  May sleep.  Caller holds mmap_lock.
>  	 */
>  	void (*close)(struct vm_area_struct *vma);
> +	/**
> +	 * @mapped: Called when the VMA is first mapped in the MM. Not called if
> +	 * the new VMA is merged with an adjacent VMA.
> +	 *
> +	 * The @vm_private_data field is an output field allowing the user to
> +	 * modify vma->vm_private_data as necessary.
> +	 *
> +	 * ONLY valid if set from f_op->mmap_prepare. Will result in an error if
> +	 * set from f_op->mmap.
> +	 *
> +	 * Returns %0 on success, or an error otherwise. On error, the VMA will
> +	 * be unmapped.
> +	 *
> +	 * Context: User context.  May sleep.  Caller holds mmap_lock.
> +	 */
> +	int (*mapped)(unsigned long start, unsigned long end, pgoff_t pgoff,
> +		      const struct file *file, void **vm_private_data);
>  	/* Called any time before splitting to check if it's allowed */
>  	int (*may_split)(struct vm_area_struct *vma, unsigned long addr);
>  	int (*mremap)(struct vm_area_struct *vma);
> @@ -4327,7 +4344,8 @@ static inline void mmap_action_ioremap_full(struct vm_area_desc *desc,
>  
>  int mmap_action_prepare(struct vm_area_desc *desc);
>  int mmap_action_complete(struct vm_area_struct *vma,
> -			 struct mmap_action *action);
> +			 struct mmap_action *action,
> +			 bool rmap_lock_held);
>  
>  /* Look up the first VMA which exactly match the interval vm_start ... vm_end */
>  static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
> diff --git a/mm/internal.h b/mm/internal.h
> index 0256ca44115a..e0f554178143 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -202,6 +202,14 @@ static inline void vma_close(struct vm_area_struct *vma)
>  /* unmap_vmas is in mm/memory.c */
>  void unmap_vmas(struct mmu_gather *tlb, struct unmap_desc *unmap);
>  
> +static inline void unmap_vma_locked(struct vm_area_struct *vma)
> +{
> +	const size_t len = vma_pages(vma) << PAGE_SHIFT;
> +
> +	mmap_assert_write_locked(vma->vm_mm);
> +	do_munmap(vma->vm_mm, vma->vm_start, len, NULL);
> +}
> +
>  #ifdef CONFIG_MMU
>  
>  static inline void get_anon_vma(struct anon_vma *anon_vma)
> diff --git a/mm/util.c b/mm/util.c
> index 73c97a748d8e..fc1bd8a8f3ea 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1163,6 +1163,54 @@ void flush_dcache_folio(struct folio *folio)
>  EXPORT_SYMBOL(flush_dcache_folio);
>  #endif
>  
> +static int __compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> +	struct vm_area_desc desc = {
> +		.mm = vma->vm_mm,
> +		.file = file,
> +		.start = vma->vm_start,
> +		.end = vma->vm_end,
> +
> +		.pgoff = vma->vm_pgoff,
> +		.vm_file = vma->vm_file,
> +		.vma_flags = vma->flags,
> +		.page_prot = vma->vm_page_prot,
> +
> +		.action.type = MMAP_NOTHING, /* Default */
> +	};
> +	int err;
> +
> +	err = vfs_mmap_prepare(file, &desc);
> +	if (err)
> +		return err;
> +
> +	err = mmap_action_prepare(&desc);
> +	if (err)
> +		return err;
> +
> +	set_vma_from_desc(vma, &desc);
> +	return mmap_action_complete(vma, &desc.action, /*rmap_lock_held=*/false);

Patch 1 removed this function and this one reinstates it with some
modifications. Could patch 1 only remove the export and otherwise both do
only the necessary modifications?

> +}
> +
> +static int __compat_vma_mapped(struct file *file, struct vm_area_struct *vma)
> +{
> +	const struct vm_operations_struct *vm_ops = vma->vm_ops;
> +	void *vm_private_data = vma->vm_private_data;
> +	int err;
> +
> +	if (!vm_ops || !vm_ops->mapped)
> +		return 0;
> +
> +	err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff, file,
> +			     &vm_private_data);
> +	if (err)
> +		unmap_vma_locked(vma);
> +	else if (vm_private_data != vma->vm_private_data)
> +		vma->vm_private_data = vm_private_data;
> +
> +	return err;
> +}
> +
>  /**
>   * compat_vma_mmap() - Apply the file's .mmap_prepare() hook to an
>   * existing VMA and execute any requested actions.
> @@ -1191,34 +1239,26 @@ EXPORT_SYMBOL(flush_dcache_folio);
>   */
>  int compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
>  {
> -	struct vm_area_desc desc = {
> -		.mm = vma->vm_mm,
> -		.file = file,
> -		.start = vma->vm_start,
> -		.end = vma->vm_end,
> -
> -		.pgoff = vma->vm_pgoff,
> -		.vm_file = vma->vm_file,
> -		.vma_flags = vma->flags,
> -		.page_prot = vma->vm_page_prot,
> -
> -		.action.type = MMAP_NOTHING, /* Default */
> -	};
>  	int err;
>  
> -	err = vfs_mmap_prepare(file, &desc);
> +	err = __compat_vma_mmap(file, vma);
>  	if (err)
>  		return err;
>  
> -	err = mmap_action_prepare(&desc);
> -	if (err)
> -		return err;
> -
> -	set_vma_from_desc(vma, &desc);
> -	return mmap_action_complete(vma, &desc.action);
> +	return __compat_vma_mapped(file, vma);
>  }
>  EXPORT_SYMBOL(compat_vma_mmap);
>  
> +int __vma_check_mmap_hook(struct vm_area_struct *vma)
> +{
> +	/* vm_ops->mapped is not valid if mmap() is specified. */
> +	if (vma->vm_ops && WARN_ON_ONCE(vma->vm_ops->mapped))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(__vma_check_mmap_hook);
> +
>  static void set_ps_flags(struct page_snapshot *ps, const struct folio *folio,
>  			 const struct page *page)
>  {
> @@ -1308,32 +1348,31 @@ void snapshot_page(struct page_snapshot *ps, const struct page *page)
>  }
>  
>  static int mmap_action_finish(struct vm_area_struct *vma,
> -			      struct mmap_action *action, int err)
> +			      struct mmap_action *action, int err,
> +			      bool rmap_lock_held)
>  {
> +	if (rmap_lock_held)
> +		i_mmap_unlock_write(vma->vm_file->f_mapping);

Should this be moved below the if (!err) ?

Otherwise I think we unlock prematurely, and can even try to unlock twice -
here and in call_mapped_hook(). And we want to unlock only if we're about to
munmap, right?

> +
> +	if (!err) {
> +		if (action->success_hook)
> +			return action->success_hook(vma);
> +		return 0;
> +	}
> +
>  	/*
>  	 * If an error occurs, unmap the VMA altogether and return an error. We
>  	 * only clear the newly allocated VMA, since this function is only
>  	 * invoked if we do NOT merge, so we only clean up the VMA we created.
>  	 */
> -	if (err) {
> -		const size_t len = vma_pages(vma) << PAGE_SHIFT;
> -
> -		do_munmap(current->mm, vma->vm_start, len, NULL);
> -
> -		if (action->error_hook) {
> -			/* We may want to filter the error. */
> -			err = action->error_hook(err);
> -
> -			/* The caller should not clear the error. */
> -			VM_WARN_ON_ONCE(!err);
> -		}
> -		return err;
> +	unmap_vma_locked(vma);
> +	if (action->error_hook) {
> +		/* We may want to filter the error. */
> +		err = action->error_hook(err);
> +		/* The caller should not clear the error. */
> +		VM_WARN_ON_ONCE(!err);
>  	}
> -
> -	if (action->success_hook)
> -		return action->success_hook(vma);
> -
> -	return 0;
> +	return err;
>  }
>  
>  #ifdef CONFIG_MMU
> @@ -1364,13 +1403,15 @@ EXPORT_SYMBOL(mmap_action_prepare);
>   * mmap_action_complete - Execute VMA descriptor action.
>   * @vma: The VMA to perform the action upon.
>   * @action: The action to perform.
> + * @rmap_lock_held: Is the file rmap lock held?
>   *
>   * Similar to mmap_action_prepare().
>   *
>   * Return: 0 on success, or error, at which point the VMA will be unmapped.
>   */
>  int mmap_action_complete(struct vm_area_struct *vma,
> -			 struct mmap_action *action)
> +			 struct mmap_action *action,
> +			 bool rmap_lock_held)
>  
>  {
>  	int err = 0;
> @@ -1388,7 +1429,8 @@ int mmap_action_complete(struct vm_area_struct *vma,
>  		break;
>  	}
>  
> -	return mmap_action_finish(vma, action, err);
> +	return mmap_action_finish(vma, action, err,
> +				  rmap_lock_held);
>  }
>  EXPORT_SYMBOL(mmap_action_complete);
>  #else
> @@ -1408,7 +1450,8 @@ int mmap_action_prepare(struct vm_area_desc *desc)
>  EXPORT_SYMBOL(mmap_action_prepare);
>  
>  int mmap_action_complete(struct vm_area_struct *vma,
> -			 struct mmap_action *action)
> +			 struct mmap_action *action,
> +			 bool rmap_lock_held)
>  {
>  	int err = 0;
>  
> @@ -1423,7 +1466,7 @@ int mmap_action_complete(struct vm_area_struct *vma,
>  		break;
>  	}
>  
> -	return mmap_action_finish(vma, action, err);
> +	return mmap_action_finish(vma, action, err, rmap_lock_held);
>  }
>  EXPORT_SYMBOL(mmap_action_complete);
>  #endif
> diff --git a/mm/vma.c b/mm/vma.c
> index 2a86c7575000..a27d1278ea6d 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -2731,21 +2731,28 @@ static bool can_set_ksm_flags_early(struct mmap_state *map)
>  	return false;
>  }
>  
> -static int call_action_complete(struct mmap_state *map,
> -				struct mmap_action *action,
> -				struct vm_area_struct *vma)
> +static int call_mapped_hook(struct mmap_state *map,
> +			    struct vm_area_struct *vma)
>  {
> -	int ret;
> -
> -	ret = mmap_action_complete(vma, action);
> +	const struct vm_operations_struct *vm_ops = vma->vm_ops;
> +	void *vm_private_data = vma->vm_private_data;
> +	int err;
>  
> -	/* If we held the file rmap we need to release it. */
> -	if (map->hold_file_rmap_lock) {
> -		struct file *file = vma->vm_file;
> +	if (!vm_ops || !vm_ops->mapped)
> +		return 0;
> +	err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff,
> +			     vma->vm_file, &vm_private_data);
> +	if (err) {
> +		if (map->hold_file_rmap_lock)
> +			i_mmap_unlock_write(vma->vm_file->f_mapping);
>  
> -		i_mmap_unlock_write(file->f_mapping);
> +		unmap_vma_locked(vma);
> +		return err;
>  	}
> -	return ret;
> +	/* Update private data if changed. */
> +	if (vm_private_data != vma->vm_private_data)
> +		vma->vm_private_data = vm_private_data;
> +	return 0;
>  }
>  
>  static unsigned long __mmap_region(struct file *file, unsigned long addr,
> @@ -2799,8 +2806,10 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr,
>  	__mmap_complete(&map, vma);
>  
>  	if (have_mmap_prepare && allocated_new) {
> -		error = call_action_complete(&map, &desc.action, vma);
> -
> +		error = mmap_action_complete(vma, &desc.action,
> +					     map.hold_file_rmap_lock);
> +		if (!error)
> +			error = call_mapped_hook(&map, vma);

And if neither of those above end up doing i_mmap_unlock_write(), we should
do it here? I think currently the misplaced unlock in mmap_action_finish()
masks the lack of it here, otherwise bots would already notice. Loss of
locking coverage (due to premature unlock) or the risk of double unlock is
probably harder to trigger. Or maybe a later patch in the series happens to
fix the issues, so it's just a bisection hazard here. Or I'm completely wrong.

>  		if (error)
>  			return error;
>  	}
> diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
> index 8ae525ed1738..aa34966cbc62 100644
> --- a/tools/testing/vma/include/dup.h
> +++ b/tools/testing/vma/include/dup.h
> @@ -643,6 +643,23 @@ struct vm_operations_struct {
>  	 * Context: User context.  May sleep.  Caller holds mmap_lock.
>  	 */
>  	void (*close)(struct vm_area_struct *vma);
> +	/**
> +	 * @mapped: Called when the VMA is first mapped in the MM. Not called if
> +	 * the new VMA is merged with an adjacent VMA.
> +	 *
> +	 * The @vm_private_data field is an output field allowing the user to
> +	 * modify vma->vm_private_data as necessary.
> +	 *
> +	 * ONLY valid if set from f_op->mmap_prepare. Will result in an error if
> +	 * set from f_op->mmap.
> +	 *
> +	 * Returns %0 on success, or an error otherwise. On error, the VMA will
> +	 * be unmapped.
> +	 *
> +	 * Context: User context.  May sleep.  Caller holds mmap_lock.
> +	 */
> +	int (*mapped)(unsigned long start, unsigned long end, pgoff_t pgoff,
> +		      const struct file *file, void **vm_private_data);
>  	/* Called any time before splitting to check if it's allowed */
>  	int (*may_split)(struct vm_area_struct *vma, unsigned long addr);
>  	int (*mremap)(struct vm_area_struct *vma);
> @@ -1281,7 +1298,7 @@ static inline int __compat_vma_mmap(const struct file_operations *f_op,
>  		return err;
>  
>  	set_vma_from_desc(vma, &desc);
> -	return mmap_action_complete(vma, &desc.action);
> +	return mmap_action_complete(vma, &desc.action, /*rmap_lock_held=*/false);
>  }
>  
>  static inline int compat_vma_mmap(struct file *file,
> @@ -1500,3 +1517,11 @@ static inline pgprot_t vma_get_page_prot(vma_flags_t vma_flags)
>  
>  	return vm_get_page_prot(vm_flags);
>  }
> +
> +static inline void unmap_vma_locked(struct vm_area_struct *vma)
> +{
> +	const size_t len = vma_pages(vma) << PAGE_SHIFT;
> +
> +	mmap_assert_write_locked(vma->vm_mm);
> +	do_munmap(vma->vm_mm, vma->vm_start, len, NULL);
> +}
> diff --git a/tools/testing/vma/include/stubs.h b/tools/testing/vma/include/stubs.h
> index a30b8bc84955..d1c3d4ddb5e9 100644
> --- a/tools/testing/vma/include/stubs.h
> +++ b/tools/testing/vma/include/stubs.h
> @@ -87,7 +87,8 @@ static inline int mmap_action_prepare(struct vm_area_desc *desc)
>  }
>  
>  static inline int mmap_action_complete(struct vm_area_struct *vma,
> -				       struct mmap_action *action)
> +				       struct mmap_action *action,
> +				       bool rmap_lock_held)
>  {
>  	return 0;
>  }

Re: [PATCH v3 05/16] fs: afs: correctly drop reference count on mapping failure

[Vlastimil Babka (SUSE)]

On 3/19/26 19:23, Lorenzo Stoakes (Oracle) wrote:
> Commit 9d5403b1036c ("fs: convert most other generic_file_*mmap() users to
> .mmap_prepare()") updated AFS to use the mmap_prepare callback in favour
> of the deprecated mmap callback.
> 
> However, it did not account for the fact that mmap_prepare is called
> pre-merge, and may then be merged, nor that mmap_prepare can fail to map
> due to an out of memory error.

So that means a file can become pinned forever? OOM is probably only a
problem with fault injection in practice, but the merge case can happen. And
9d5403b1036c is pre-6.18 LTS. Are we going to need Fixes: and Cc: stable then?

> Both of those are cases in which we should not be incrementing a reference
> count.
> 
> With the newly added vm_ops->mapped callback available, we can simply
> defer this operation to that callback which is only invoked once the
> mapping is successfully in place (but not yet visible to userspace as the
> mmap and VMA write locks are held).
> 
> Therefore add afs_mapped() to implement this callback for AFS, and remove
> the code doing so in afs_mmap_prepare().
> 
> Also update afs_vm_open(), afs_vm_close() and afs_vm_map_pages() to be
> consistent in how the vnode is accessed.
> 
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> ---
>  fs/afs/file.c | 36 ++++++++++++++++++++++++++----------
>  1 file changed, 26 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/afs/file.c b/fs/afs/file.c
> index f609366fd2ac..85696ac984cc 100644
> --- a/fs/afs/file.c
> +++ b/fs/afs/file.c
> @@ -28,6 +28,8 @@ static ssize_t afs_file_splice_read(struct file *in, loff_t *ppos,
>  static void afs_vm_open(struct vm_area_struct *area);
>  static void afs_vm_close(struct vm_area_struct *area);
>  static vm_fault_t afs_vm_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff);
> +static int afs_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
> +		      const struct file *file, void **vm_private_data);
>  
>  const struct file_operations afs_file_operations = {
>  	.open		= afs_open,
> @@ -61,6 +63,7 @@ const struct address_space_operations afs_file_aops = {
>  };
>  
>  static const struct vm_operations_struct afs_vm_ops = {
> +	.mapped		= afs_mapped,
>  	.open		= afs_vm_open,
>  	.close		= afs_vm_close,
>  	.fault		= filemap_fault,
> @@ -494,32 +497,45 @@ static void afs_drop_open_mmap(struct afs_vnode *vnode)
>   */
>  static int afs_file_mmap_prepare(struct vm_area_desc *desc)
>  {
> -	struct afs_vnode *vnode = AFS_FS_I(file_inode(desc->file));
>  	int ret;
>  
> -	afs_add_open_mmap(vnode);
> -
>  	ret = generic_file_mmap_prepare(desc);
> -	if (ret == 0)
> -		desc->vm_ops = &afs_vm_ops;
> -	else
> -		afs_drop_open_mmap(vnode);
> +	if (ret)
> +		return ret;
> +
> +	desc->vm_ops = &afs_vm_ops;
>  	return ret;
>  }
>  
> +static int afs_mapped(unsigned long start, unsigned long end, pgoff_t pgoff,
> +		      const struct file *file, void **vm_private_data)
> +{
> +	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
> +
> +	afs_add_open_mmap(vnode);
> +	return 0;
> +}
> +
>  static void afs_vm_open(struct vm_area_struct *vma)
>  {
> -	afs_add_open_mmap(AFS_FS_I(file_inode(vma->vm_file)));
> +	struct file *file = vma->vm_file;
> +	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
> +
> +	afs_add_open_mmap(vnode);
>  }
>  
>  static void afs_vm_close(struct vm_area_struct *vma)
>  {
> -	afs_drop_open_mmap(AFS_FS_I(file_inode(vma->vm_file)));
> +	struct file *file = vma->vm_file;
> +	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
> +
> +	afs_drop_open_mmap(vnode);
>  }
>  
>  static vm_fault_t afs_vm_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff)
>  {
> -	struct afs_vnode *vnode = AFS_FS_I(file_inode(vmf->vma->vm_file));
> +	struct file *file = vmf->vma->vm_file;
> +	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
>  
>  	if (afs_check_validity(vnode))
>  		return filemap_map_pages(vmf, start_pgoff, end_pgoff);

Re: [PATCH v3 05/16] fs: afs: correctly drop reference count on mapping failure

[Lorenzo Stoakes (Oracle)]

On Fri, Mar 20, 2026 at 07:57:29PM +0100, Vlastimil Babka (SUSE) wrote:
> On 3/19/26 19:23, Lorenzo Stoakes (Oracle) wrote:
> > Commit 9d5403b1036c ("fs: convert most other generic_file_*mmap() users to
> > .mmap_prepare()") updated AFS to use the mmap_prepare callback in favour
> > of the deprecated mmap callback.
> >
> > However, it did not account for the fact that mmap_prepare is called
> > pre-merge, and may then be merged, nor that mmap_prepare can fail to map
> > due to an out of memory error.
>
> So that means a file can become pinned forever? OOM is probably only a
> problem with fault injection in practice, but the merge case can happen. And
> 9d5403b1036c is pre-6.18 LTS. Are we going to need Fixes: and Cc: stable then?

That'd require backporting all of the .mapped functionality and half of this
series, I don't think that's really practical.

I guess I can do a manual backport of a partial revert.

Thanks, Lorenzo

Re: [PATCH v3 04/16] mm: add vm_ops->mapped hook

[Lorenzo Stoakes (Oracle)]

On Fri, Mar 20, 2026 at 07:26:37PM +0100, Vlastimil Babka (SUSE) wrote:
> On 3/19/26 19:23, Lorenzo Stoakes (Oracle) wrote:
> > Previously, when a driver needed to do something like establish a
> > reference count, it could do so in the mmap hook in the knowledge that the
> > mapping would succeed.
> >
> > With the introduction of f_op->mmap_prepare this is no longer the case, as
> > it is invoked prior to actually establishing the mapping.
> >
> > mmap_prepare is not appropriate for this kind of thing as it is called
> > before any merge might take place, and after which an error might occur
> > meaning resources could be leaked.
> >
> > To take this into account, introduce a new vm_ops->mapped callback which
> > is invoked when the VMA is first mapped (though notably - not when it is
> > merged - which is correct and mirrors existing mmap/open/close behaviour).
> >
> > We do better that vm_ops->open() here, as this callback can return an
> > error, at which point the VMA will be unmapped.
> >
> > Note that vm_ops->mapped() is invoked after any mmap action is complete
> > (such as I/O remapping).
> >
> > We intentionally do not expose the VMA at this point, exposing only the
> > fields that could be used, and an output parameter in case the operation
> > needs to update the vma->vm_private_data field.
> >
> > In order to deal with stacked filesystems which invoke inner filesystem's
> > mmap() invocations, add __compat_vma_mapped() and invoke it on vfs_mmap()
> > (via compat_vma_mmap()) to ensure that the mapped callback is handled when
> > an mmap() caller invokes a nested filesystem's mmap_prepare() callback.
> >
> > We can now also remove call_action_complete() and invoke
> > mmap_action_complete() directly, as we separate out the rmap lock logic.
> >
> > The rmap lock logic, which was added in order to keep hugetlb working (!)
> > to allow for the rmap lock to be held longer, needs to be propagated to the
> > error paths on mmap complete and mapped hook error paths.
> >
> > This is because do_munmap() might otherwise deadlock with the rmap being
> > held, so instead we unlock at the point of unmap.
>
> Hmm but that was also true prior to this series? So is this a bugfix? Should
> it be a stable hotfix done outside of the series before the refactoring?
>
> > This is fine as any reliance on the rmap being held is irrelevant on error.
> >
> > While we're here, refactor mmap_action_finish() to avoid a big if (err)
> > branch.
> >
> > We also abstract unmapping of a VMA on mmap action completion into its own
> > helper function, unmap_vma_locked().
> >
> > Update the mmap_prepare documentation to describe the mapped hook and make
> > it clear what its intended use is.
> >
> > Additionally, update VMA userland test headers to reflect the change.
> >
> > Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> > ---
> >  Documentation/filesystems/mmap_prepare.rst |  15 +++
> >  include/linux/fs.h                         |   9 +-
> >  include/linux/mm.h                         |  20 +++-
> >  mm/internal.h                              |   8 ++
> >  mm/util.c                                  | 129 ++++++++++++++-------
> >  mm/vma.c                                   |  35 +++---
> >  tools/testing/vma/include/dup.h            |  27 ++++-
> >  tools/testing/vma/include/stubs.h          |   3 +-
> >  8 files changed, 186 insertions(+), 60 deletions(-)
> >
> > diff --git a/Documentation/filesystems/mmap_prepare.rst b/Documentation/filesystems/mmap_prepare.rst
> > index 65a1f094e469..20db474915da 100644
> > --- a/Documentation/filesystems/mmap_prepare.rst
> > +++ b/Documentation/filesystems/mmap_prepare.rst
> > @@ -25,6 +25,21 @@ That is - no resources should be allocated nor state updated to reflect that a
> >  mapping has been established, as the mapping may either be merged, or fail to be
> >  mapped after the callback is complete.
> >
> > +Mapped callback
> > +---------------
> > +
> > +If resources need to be allocated per-mapping, or state such as a reference
> > +count needs to be manipulated, this should be done using the ``vm_ops->mapped``
> > +hook, which itself should be set by the >mmap_prepare hook.
> > +
> > +This callback is only invoked if a new mapping has been established and was not
> > +merged with any other, and is invoked at a point where no error may occur before
> > +the mapping is established.
> > +
> > +You may return an error to the callback itself, which will cause the mapping to
> > +become unmapped and an error returned to the mmap() caller. This is useful if
> > +resources need to be allocated, and that allocation might fail.
> > +
> >  How To Use
> >  ==========
> >
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index a2628a12bd2b..c390f5c667e3 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -2059,13 +2059,20 @@ static inline bool can_mmap_file(struct file *file)
> >  }
> >
> >  int compat_vma_mmap(struct file *file, struct vm_area_struct *vma);
> > +int __vma_check_mmap_hook(struct vm_area_struct *vma);
> >
> >  static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma)
> >  {
> > +	int err;
> > +
> >  	if (file->f_op->mmap_prepare)
> >  		return compat_vma_mmap(file, vma);
> >
> > -	return file->f_op->mmap(file, vma);
> > +	err = file->f_op->mmap(file, vma);
> > +	if (err)
> > +		return err;
> > +
> > +	return __vma_check_mmap_hook(vma);
> >  }
> >
> >  static inline int vfs_mmap_prepare(struct file *file, struct vm_area_desc *desc)
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index da94edb287cd..68dee1101313 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -777,6 +777,23 @@ struct vm_operations_struct {
> >  	 * Context: User context.  May sleep.  Caller holds mmap_lock.
> >  	 */
> >  	void (*close)(struct vm_area_struct *vma);
> > +	/**
> > +	 * @mapped: Called when the VMA is first mapped in the MM. Not called if
> > +	 * the new VMA is merged with an adjacent VMA.
> > +	 *
> > +	 * The @vm_private_data field is an output field allowing the user to
> > +	 * modify vma->vm_private_data as necessary.
> > +	 *
> > +	 * ONLY valid if set from f_op->mmap_prepare. Will result in an error if
> > +	 * set from f_op->mmap.
> > +	 *
> > +	 * Returns %0 on success, or an error otherwise. On error, the VMA will
> > +	 * be unmapped.
> > +	 *
> > +	 * Context: User context.  May sleep.  Caller holds mmap_lock.
> > +	 */
> > +	int (*mapped)(unsigned long start, unsigned long end, pgoff_t pgoff,
> > +		      const struct file *file, void **vm_private_data);
> >  	/* Called any time before splitting to check if it's allowed */
> >  	int (*may_split)(struct vm_area_struct *vma, unsigned long addr);
> >  	int (*mremap)(struct vm_area_struct *vma);
> > @@ -4327,7 +4344,8 @@ static inline void mmap_action_ioremap_full(struct vm_area_desc *desc,
> >
> >  int mmap_action_prepare(struct vm_area_desc *desc);
> >  int mmap_action_complete(struct vm_area_struct *vma,
> > -			 struct mmap_action *action);
> > +			 struct mmap_action *action,
> > +			 bool rmap_lock_held);
> >
> >  /* Look up the first VMA which exactly match the interval vm_start ... vm_end */
> >  static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
> > diff --git a/mm/internal.h b/mm/internal.h
> > index 0256ca44115a..e0f554178143 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -202,6 +202,14 @@ static inline void vma_close(struct vm_area_struct *vma)
> >  /* unmap_vmas is in mm/memory.c */
> >  void unmap_vmas(struct mmu_gather *tlb, struct unmap_desc *unmap);
> >
> > +static inline void unmap_vma_locked(struct vm_area_struct *vma)
> > +{
> > +	const size_t len = vma_pages(vma) << PAGE_SHIFT;
> > +
> > +	mmap_assert_write_locked(vma->vm_mm);
> > +	do_munmap(vma->vm_mm, vma->vm_start, len, NULL);
> > +}
> > +
> >  #ifdef CONFIG_MMU
> >
> >  static inline void get_anon_vma(struct anon_vma *anon_vma)
> > diff --git a/mm/util.c b/mm/util.c
> > index 73c97a748d8e..fc1bd8a8f3ea 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -1163,6 +1163,54 @@ void flush_dcache_folio(struct folio *folio)
> >  EXPORT_SYMBOL(flush_dcache_folio);
> >  #endif
> >
> > +static int __compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
> > +{
> > +	struct vm_area_desc desc = {
> > +		.mm = vma->vm_mm,
> > +		.file = file,
> > +		.start = vma->vm_start,
> > +		.end = vma->vm_end,
> > +
> > +		.pgoff = vma->vm_pgoff,
> > +		.vm_file = vma->vm_file,
> > +		.vma_flags = vma->flags,
> > +		.page_prot = vma->vm_page_prot,
> > +
> > +		.action.type = MMAP_NOTHING, /* Default */
> > +	};
> > +	int err;
> > +
> > +	err = vfs_mmap_prepare(file, &desc);
> > +	if (err)
> > +		return err;
> > +
> > +	err = mmap_action_prepare(&desc);
> > +	if (err)
> > +		return err;
> > +
> > +	set_vma_from_desc(vma, &desc);
> > +	return mmap_action_complete(vma, &desc.action, /*rmap_lock_held=*/false);
>
> Patch 1 removed this function and this one reinstates it with some
> modifications. Could patch 1 only remove the export and otherwise both do
> only the necessary modifications?

No, I'd rather do it this way because the function is now doing something
different and for different reasons.

Let's not just churn respins for no reason. If it's not breaking anything
let's just leave it as is please.

>
> > +}
> > +
> > +static int __compat_vma_mapped(struct file *file, struct vm_area_struct *vma)
> > +{
> > +	const struct vm_operations_struct *vm_ops = vma->vm_ops;
> > +	void *vm_private_data = vma->vm_private_data;
> > +	int err;
> > +
> > +	if (!vm_ops || !vm_ops->mapped)
> > +		return 0;
> > +
> > +	err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff, file,
> > +			     &vm_private_data);
> > +	if (err)
> > +		unmap_vma_locked(vma);
> > +	else if (vm_private_data != vma->vm_private_data)
> > +		vma->vm_private_data = vm_private_data;
> > +
> > +	return err;
> > +}
> > +
> >  /**
> >   * compat_vma_mmap() - Apply the file's .mmap_prepare() hook to an
> >   * existing VMA and execute any requested actions.
> > @@ -1191,34 +1239,26 @@ EXPORT_SYMBOL(flush_dcache_folio);
> >   */
> >  int compat_vma_mmap(struct file *file, struct vm_area_struct *vma)
> >  {
> > -	struct vm_area_desc desc = {
> > -		.mm = vma->vm_mm,
> > -		.file = file,
> > -		.start = vma->vm_start,
> > -		.end = vma->vm_end,
> > -
> > -		.pgoff = vma->vm_pgoff,
> > -		.vm_file = vma->vm_file,
> > -		.vma_flags = vma->flags,
> > -		.page_prot = vma->vm_page_prot,
> > -
> > -		.action.type = MMAP_NOTHING, /* Default */
> > -	};
> >  	int err;
> >
> > -	err = vfs_mmap_prepare(file, &desc);
> > +	err = __compat_vma_mmap(file, vma);
> >  	if (err)
> >  		return err;
> >
> > -	err = mmap_action_prepare(&desc);
> > -	if (err)
> > -		return err;
> > -
> > -	set_vma_from_desc(vma, &desc);
> > -	return mmap_action_complete(vma, &desc.action);
> > +	return __compat_vma_mapped(file, vma);
> >  }
> >  EXPORT_SYMBOL(compat_vma_mmap);
> >
> > +int __vma_check_mmap_hook(struct vm_area_struct *vma)
> > +{
> > +	/* vm_ops->mapped is not valid if mmap() is specified. */
> > +	if (vma->vm_ops && WARN_ON_ONCE(vma->vm_ops->mapped))
> > +		return -EINVAL;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(__vma_check_mmap_hook);
> > +
> >  static void set_ps_flags(struct page_snapshot *ps, const struct folio *folio,
> >  			 const struct page *page)
> >  {
> > @@ -1308,32 +1348,31 @@ void snapshot_page(struct page_snapshot *ps, const struct page *page)
> >  }
> >
> >  static int mmap_action_finish(struct vm_area_struct *vma,
> > -			      struct mmap_action *action, int err)
> > +			      struct mmap_action *action, int err,
> > +			      bool rmap_lock_held)
> >  {
> > +	if (rmap_lock_held)
> > +		i_mmap_unlock_write(vma->vm_file->f_mapping);
>
> Should this be moved below the if (!err) ?

Yup sigh, the success hook needs this hack to be held.

This is all because hugetlb does stupid things.

The one case in which it uses generic hooks rather than stupid 'if
(hugetlb) { ... }' branches, and it does stuff it shouldn't (of course! :)

>
> Otherwise I think we unlock prematurely, and can even try to unlock twice -
> here and in call_mapped_hook(). And we want to unlock only if we're about to
> munmap, right?

No, we want to unlock at the end of the operation regardless. But this can
unlock twice because I'm not threading this crap through enough clearly.

Let me rethink this I guess. I hate hugetlb.

>
> > +
> > +	if (!err) {
> > +		if (action->success_hook)
> > +			return action->success_hook(vma);
> > +		return 0;
> > +	}
> > +
> >  	/*
> >  	 * If an error occurs, unmap the VMA altogether and return an error. We
> >  	 * only clear the newly allocated VMA, since this function is only
> >  	 * invoked if we do NOT merge, so we only clean up the VMA we created.
> >  	 */
> > -	if (err) {
> > -		const size_t len = vma_pages(vma) << PAGE_SHIFT;
> > -
> > -		do_munmap(current->mm, vma->vm_start, len, NULL);
> > -
> > -		if (action->error_hook) {
> > -			/* We may want to filter the error. */
> > -			err = action->error_hook(err);
> > -
> > -			/* The caller should not clear the error. */
> > -			VM_WARN_ON_ONCE(!err);
> > -		}
> > -		return err;
> > +	unmap_vma_locked(vma);
> > +	if (action->error_hook) {
> > +		/* We may want to filter the error. */
> > +		err = action->error_hook(err);
> > +		/* The caller should not clear the error. */
> > +		VM_WARN_ON_ONCE(!err);
> >  	}
> > -
> > -	if (action->success_hook)
> > -		return action->success_hook(vma);
> > -
> > -	return 0;
> > +	return err;
> >  }
> >
> >  #ifdef CONFIG_MMU
> > @@ -1364,13 +1403,15 @@ EXPORT_SYMBOL(mmap_action_prepare);
> >   * mmap_action_complete - Execute VMA descriptor action.
> >   * @vma: The VMA to perform the action upon.
> >   * @action: The action to perform.
> > + * @rmap_lock_held: Is the file rmap lock held?
> >   *
> >   * Similar to mmap_action_prepare().
> >   *
> >   * Return: 0 on success, or error, at which point the VMA will be unmapped.
> >   */
> >  int mmap_action_complete(struct vm_area_struct *vma,
> > -			 struct mmap_action *action)
> > +			 struct mmap_action *action,
> > +			 bool rmap_lock_held)
> >
> >  {
> >  	int err = 0;
> > @@ -1388,7 +1429,8 @@ int mmap_action_complete(struct vm_area_struct *vma,
> >  		break;
> >  	}
> >
> > -	return mmap_action_finish(vma, action, err);
> > +	return mmap_action_finish(vma, action, err,
> > +				  rmap_lock_held);
> >  }
> >  EXPORT_SYMBOL(mmap_action_complete);
> >  #else
> > @@ -1408,7 +1450,8 @@ int mmap_action_prepare(struct vm_area_desc *desc)
> >  EXPORT_SYMBOL(mmap_action_prepare);
> >
> >  int mmap_action_complete(struct vm_area_struct *vma,
> > -			 struct mmap_action *action)
> > +			 struct mmap_action *action,
> > +			 bool rmap_lock_held)
> >  {
> >  	int err = 0;
> >
> > @@ -1423,7 +1466,7 @@ int mmap_action_complete(struct vm_area_struct *vma,
> >  		break;
> >  	}
> >
> > -	return mmap_action_finish(vma, action, err);
> > +	return mmap_action_finish(vma, action, err, rmap_lock_held);
> >  }
> >  EXPORT_SYMBOL(mmap_action_complete);
> >  #endif
> > diff --git a/mm/vma.c b/mm/vma.c
> > index 2a86c7575000..a27d1278ea6d 100644
> > --- a/mm/vma.c
> > +++ b/mm/vma.c
> > @@ -2731,21 +2731,28 @@ static bool can_set_ksm_flags_early(struct mmap_state *map)
> >  	return false;
> >  }
> >
> > -static int call_action_complete(struct mmap_state *map,
> > -				struct mmap_action *action,
> > -				struct vm_area_struct *vma)
> > +static int call_mapped_hook(struct mmap_state *map,
> > +			    struct vm_area_struct *vma)
> >  {
> > -	int ret;
> > -
> > -	ret = mmap_action_complete(vma, action);
> > +	const struct vm_operations_struct *vm_ops = vma->vm_ops;
> > +	void *vm_private_data = vma->vm_private_data;
> > +	int err;
> >
> > -	/* If we held the file rmap we need to release it. */
> > -	if (map->hold_file_rmap_lock) {
> > -		struct file *file = vma->vm_file;
> > +	if (!vm_ops || !vm_ops->mapped)
> > +		return 0;
> > +	err = vm_ops->mapped(vma->vm_start, vma->vm_end, vma->vm_pgoff,
> > +			     vma->vm_file, &vm_private_data);
> > +	if (err) {
> > +		if (map->hold_file_rmap_lock)
> > +			i_mmap_unlock_write(vma->vm_file->f_mapping);
> >
> > -		i_mmap_unlock_write(file->f_mapping);
> > +		unmap_vma_locked(vma);
> > +		return err;
> >  	}
> > -	return ret;
> > +	/* Update private data if changed. */
> > +	if (vm_private_data != vma->vm_private_data)
> > +		vma->vm_private_data = vm_private_data;
> > +	return 0;
> >  }
> >
> >  static unsigned long __mmap_region(struct file *file, unsigned long addr,
> > @@ -2799,8 +2806,10 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr,
> >  	__mmap_complete(&map, vma);
> >
> >  	if (have_mmap_prepare && allocated_new) {
> > -		error = call_action_complete(&map, &desc.action, vma);
> > -
> > +		error = mmap_action_complete(vma, &desc.action,
> > +					     map.hold_file_rmap_lock);
> > +		if (!error)
> > +			error = call_mapped_hook(&map, vma);
>
> And if neither of those above end up doing i_mmap_unlock_write(), we should
> do it here? I think currently the misplaced unlock in mmap_action_finish()

I don't think it's misplaced, I think it's a much better place for it than
here, and otherwise we have yet more hacks upon hacks threaded throughout
the code.

We don't actually need the hugetlb hack to hold the lock over .mapped but I
guess we should do that anyway just for the sake of consistency.

But obviously call_mapped_hook() is trying to unlock anyway.

> masks the lack of it here, otherwise bots would already notice. Loss of

And AI... it would require hitting a .mapped error I guess.

> locking coverage (due to premature unlock) or the risk of double unlock is
> probably harder to trigger. Or maybe a later patch in the series happens to
> fix the issues, so it's just a bisection hazard here. Or I'm completely wrong.

Nope I messed it up, will fix.

>
> >  		if (error)
> >  			return error;
> >  	}
> > diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
> > index 8ae525ed1738..aa34966cbc62 100644
> > --- a/tools/testing/vma/include/dup.h
> > +++ b/tools/testing/vma/include/dup.h
> > @@ -643,6 +643,23 @@ struct vm_operations_struct {
> >  	 * Context: User context.  May sleep.  Caller holds mmap_lock.
> >  	 */
> >  	void (*close)(struct vm_area_struct *vma);
> > +	/**
> > +	 * @mapped: Called when the VMA is first mapped in the MM. Not called if
> > +	 * the new VMA is merged with an adjacent VMA.
> > +	 *
> > +	 * The @vm_private_data field is an output field allowing the user to
> > +	 * modify vma->vm_private_data as necessary.
> > +	 *
> > +	 * ONLY valid if set from f_op->mmap_prepare. Will result in an error if
> > +	 * set from f_op->mmap.
> > +	 *
> > +	 * Returns %0 on success, or an error otherwise. On error, the VMA will
> > +	 * be unmapped.
> > +	 *
> > +	 * Context: User context.  May sleep.  Caller holds mmap_lock.
> > +	 */
> > +	int (*mapped)(unsigned long start, unsigned long end, pgoff_t pgoff,
> > +		      const struct file *file, void **vm_private_data);
> >  	/* Called any time before splitting to check if it's allowed */
> >  	int (*may_split)(struct vm_area_struct *vma, unsigned long addr);
> >  	int (*mremap)(struct vm_area_struct *vma);
> > @@ -1281,7 +1298,7 @@ static inline int __compat_vma_mmap(const struct file_operations *f_op,
> >  		return err;
> >
> >  	set_vma_from_desc(vma, &desc);
> > -	return mmap_action_complete(vma, &desc.action);
> > +	return mmap_action_complete(vma, &desc.action, /*rmap_lock_held=*/false);
> >  }
> >
> >  static inline int compat_vma_mmap(struct file *file,
> > @@ -1500,3 +1517,11 @@ static inline pgprot_t vma_get_page_prot(vma_flags_t vma_flags)
> >
> >  	return vm_get_page_prot(vm_flags);
> >  }
> > +
> > +static inline void unmap_vma_locked(struct vm_area_struct *vma)
> > +{
> > +	const size_t len = vma_pages(vma) << PAGE_SHIFT;
> > +
> > +	mmap_assert_write_locked(vma->vm_mm);
> > +	do_munmap(vma->vm_mm, vma->vm_start, len, NULL);
> > +}
> > diff --git a/tools/testing/vma/include/stubs.h b/tools/testing/vma/include/stubs.h
> > index a30b8bc84955..d1c3d4ddb5e9 100644
> > --- a/tools/testing/vma/include/stubs.h
> > +++ b/tools/testing/vma/include/stubs.h
> > @@ -87,7 +87,8 @@ static inline int mmap_action_prepare(struct vm_area_desc *desc)
> >  }
> >
> >  static inline int mmap_action_complete(struct vm_area_struct *vma,
> > -				       struct mmap_action *action)
> > +				       struct mmap_action *action,
> > +				       bool rmap_lock_held)
> >  {
> >  	return 0;
> >  }
>

Thanks, Lorenzo

Re: [PATCH v3 04/16] mm: add vm_ops->mapped hook

[Lorenzo Stoakes (Oracle)]

On Fri, Mar 20, 2026 at 07:26:37PM +0100, Vlastimil Babka (SUSE) wrote:
> On 3/19/26 19:23, Lorenzo Stoakes (Oracle) wrote:
> > Previously, when a driver needed to do something like establish a
> > reference count, it could do so in the mmap hook in the knowledge that the
> > mapping would succeed.
> >
> > With the introduction of f_op->mmap_prepare this is no longer the case, as
> > it is invoked prior to actually establishing the mapping.
> >
> > mmap_prepare is not appropriate for this kind of thing as it is called
> > before any merge might take place, and after which an error might occur
> > meaning resources could be leaked.
> >
> > To take this into account, introduce a new vm_ops->mapped callback which
> > is invoked when the VMA is first mapped (though notably - not when it is
> > merged - which is correct and mirrors existing mmap/open/close behaviour).
> >
> > We do better that vm_ops->open() here, as this callback can return an
> > error, at which point the VMA will be unmapped.
> >
> > Note that vm_ops->mapped() is invoked after any mmap action is complete
> > (such as I/O remapping).
> >
> > We intentionally do not expose the VMA at this point, exposing only the
> > fields that could be used, and an output parameter in case the operation
> > needs to update the vma->vm_private_data field.
> >
> > In order to deal with stacked filesystems which invoke inner filesystem's
> > mmap() invocations, add __compat_vma_mapped() and invoke it on vfs_mmap()
> > (via compat_vma_mmap()) to ensure that the mapped callback is handled when
> > an mmap() caller invokes a nested filesystem's mmap_prepare() callback.
> >
> > We can now also remove call_action_complete() and invoke
> > mmap_action_complete() directly, as we separate out the rmap lock logic.
> >
> > The rmap lock logic, which was added in order to keep hugetlb working (!)
> > to allow for the rmap lock to be held longer, needs to be propagated to the
> > error paths on mmap complete and mapped hook error paths.
> >
> > This is because do_munmap() might otherwise deadlock with the rmap being
> > held, so instead we unlock at the point of unmap.
>
> Hmm but that was also true prior to this series? So is this a bugfix? Should
> it be a stable hotfix done outside of the series before the refactoring?

Yup, will send a hotfix.

Thanks, Lorenzo

Re: [PATCH v3 15/16] mm: add mmap_action_map_kernel_pages[_full]()

[Nathan Chancellor]

Hi Lorenzo,

On Thu, Mar 19, 2026 at 06:23:39PM +0000, Lorenzo Stoakes (Oracle) wrote:
> A user can invoke mmap_action_map_kernel_pages() to specify that the
> mapping should map kernel pages starting from desc->start of a specified
> number of pages specified in an array.
> 
> In order to implement this, adjust mmap_action_prepare() to be able to
> return an error code, as it makes sense to assert that the specified
> parameters are valid as quickly as possible as well as updating the VMA
> flags to include VMA_MIXEDMAP_BIT as necessary.
> 
> This provides an mmap_prepare equivalent of vm_insert_pages().  We
> additionally update the existing vm_insert_pages() code to use
> range_in_vma() and add a new range_in_vma_desc() helper function for the
> mmap_prepare case, sharing the code between the two in range_is_subset().
> 
> We add both mmap_action_map_kernel_pages() and
> mmap_action_map_kernel_pages_full() to allow for both partial and full VMA
> mappings.
> 
> We update the documentation to reflect the new features.
> 
> Finally, we update the VMA tests accordingly to reflect the changes.
> 
> Reviewed-by: Suren Baghdasaryan <surenb@google.com>
> Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
...
> diff --git a/mm/util.c b/mm/util.c
> index 8cf59267a9ac..682d0d24e1c6 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1446,6 +1446,8 @@ int mmap_action_prepare(struct vm_area_desc *desc)
>  		return io_remap_pfn_range_prepare(desc);
>  	case MMAP_SIMPLE_IO_REMAP:
>  		return simple_ioremap_prepare(desc);
> +	case MMAP_MAP_KERNEL_PAGES:
> +		return map_kernel_pages_prepare(desc);
>  	}
>  
>  	WARN_ON_ONCE(1);
> @@ -1476,6 +1478,9 @@ int mmap_action_complete(struct vm_area_struct *vma,
>  	case MMAP_REMAP_PFN:
>  		err = remap_pfn_range_complete(vma, action);
>  		break;
> +	case MMAP_MAP_KERNEL_PAGES:
> +		err = map_kernel_pages_complete(vma, action);
> +		break;
>  	case MMAP_IO_REMAP_PFN:
>  	case MMAP_SIMPLE_IO_REMAP:
>  		/* Should have been delegated. */
> @@ -1497,6 +1502,7 @@ int mmap_action_prepare(struct vm_area_desc *desc)
>  	case MMAP_REMAP_PFN:
>  	case MMAP_IO_REMAP_PFN:
>  	case MMAP_SIMPLE_IO_REMAP:
> +	case MMAP_MAP_KERNEL_PAGES:
>  		WARN_ON_ONCE(1); /* nommu cannot handle these. */
>  		break;
>  	}

Not sure if it has been reported/addressed yet but it looks like
mmap_action_complete() was missed here, as pointed out by clang:

  $ make -skj"$(nproc)" ARCH=arm LLVM=1 mrproper allnoconfig mm/util.o
  mm/util.c:1520:10: warning: enumeration value 'MMAP_MAP_KERNEL_PAGES' not handled in switch [-Wswitch]
   1520 |         switch (action->type) {
        |                 ^~~~~~~~~~~~

I assume

diff --git a/mm/util.c b/mm/util.c
index 682d0d24e1c6..c41c119a5a74 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1523,6 +1523,7 @@ int mmap_action_complete(struct vm_area_struct *vma,
 	case MMAP_REMAP_PFN:
 	case MMAP_IO_REMAP_PFN:
 	case MMAP_SIMPLE_IO_REMAP:
+	case MMAP_MAP_KERNEL_PAGES:
 		WARN_ON_ONCE(1); /* nommu cannot handle this. */
 
 		err = -EINVAL;
--

should be the fix?

Cheers,
Nathan

Re: [PATCH v3 15/16] mm: add mmap_action_map_kernel_pages[_full]()

[Lorenzo Stoakes (Oracle)]

On Fri, Mar 20, 2026 at 02:08:12PM -0700, Nathan Chancellor wrote:
> Hi Lorenzo,
>
> On Thu, Mar 19, 2026 at 06:23:39PM +0000, Lorenzo Stoakes (Oracle) wrote:
> > A user can invoke mmap_action_map_kernel_pages() to specify that the
> > mapping should map kernel pages starting from desc->start of a specified
> > number of pages specified in an array.
> >
> > In order to implement this, adjust mmap_action_prepare() to be able to
> > return an error code, as it makes sense to assert that the specified
> > parameters are valid as quickly as possible as well as updating the VMA
> > flags to include VMA_MIXEDMAP_BIT as necessary.
> >
> > This provides an mmap_prepare equivalent of vm_insert_pages().  We
> > additionally update the existing vm_insert_pages() code to use
> > range_in_vma() and add a new range_in_vma_desc() helper function for the
> > mmap_prepare case, sharing the code between the two in range_is_subset().
> >
> > We add both mmap_action_map_kernel_pages() and
> > mmap_action_map_kernel_pages_full() to allow for both partial and full VMA
> > mappings.
> >
> > We update the documentation to reflect the new features.
> >
> > Finally, we update the VMA tests accordingly to reflect the changes.
> >
> > Reviewed-by: Suren Baghdasaryan <surenb@google.com>
> > Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> ...
> > diff --git a/mm/util.c b/mm/util.c
> > index 8cf59267a9ac..682d0d24e1c6 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -1446,6 +1446,8 @@ int mmap_action_prepare(struct vm_area_desc *desc)
> >  		return io_remap_pfn_range_prepare(desc);
> >  	case MMAP_SIMPLE_IO_REMAP:
> >  		return simple_ioremap_prepare(desc);
> > +	case MMAP_MAP_KERNEL_PAGES:
> > +		return map_kernel_pages_prepare(desc);
> >  	}
> >
> >  	WARN_ON_ONCE(1);
> > @@ -1476,6 +1478,9 @@ int mmap_action_complete(struct vm_area_struct *vma,
> >  	case MMAP_REMAP_PFN:
> >  		err = remap_pfn_range_complete(vma, action);
> >  		break;
> > +	case MMAP_MAP_KERNEL_PAGES:
> > +		err = map_kernel_pages_complete(vma, action);
> > +		break;
> >  	case MMAP_IO_REMAP_PFN:
> >  	case MMAP_SIMPLE_IO_REMAP:
> >  		/* Should have been delegated. */
> > @@ -1497,6 +1502,7 @@ int mmap_action_prepare(struct vm_area_desc *desc)
> >  	case MMAP_REMAP_PFN:
> >  	case MMAP_IO_REMAP_PFN:
> >  	case MMAP_SIMPLE_IO_REMAP:
> > +	case MMAP_MAP_KERNEL_PAGES:
> >  		WARN_ON_ONCE(1); /* nommu cannot handle these. */
> >  		break;
> >  	}
>
> Not sure if it has been reported/addressed yet but it looks like
> mmap_action_complete() was missed here, as pointed out by clang:
>
>   $ make -skj"$(nproc)" ARCH=arm LLVM=1 mrproper allnoconfig mm/util.o
>   mm/util.c:1520:10: warning: enumeration value 'MMAP_MAP_KERNEL_PAGES' not handled in switch [-Wswitch]
>    1520 |         switch (action->type) {
>         |                 ^~~~~~~~~~~~
>
> I assume
>
> diff --git a/mm/util.c b/mm/util.c
> index 682d0d24e1c6..c41c119a5a74 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1523,6 +1523,7 @@ int mmap_action_complete(struct vm_area_struct *vma,
>  	case MMAP_REMAP_PFN:
>  	case MMAP_IO_REMAP_PFN:
>  	case MMAP_SIMPLE_IO_REMAP:
> +	case MMAP_MAP_KERNEL_PAGES:
>  		WARN_ON_ONCE(1); /* nommu cannot handle this. */
>
>  		err = -EINVAL;
> --
>
> should be the fix?
>
> Cheers,
> Nathan

Thanks, will fix, working on a respin now anyway :)

Cheers, Lorenzo