[PATCH v28 0/6] Implement IOCTL to get and optionally clear info about PTEs

[PATCH v28 0/6] Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

*Changes in v28:*
- Fix walk_end and add 17 test cases in selftests patch

*Changes in v27:*
- Handle review comments and minor improvements
- Add performance improvement patch on top with test for easy review

*Changes in v26:*
- Code re-structurring and API changes in PAGEMAP_IOCTL

*Changes in v25*:
- Do proper filtering on hole as well (hole got missed earlier)

*Changes in v24*:
- Rebase on top of next-20230710
- Place WP markers in case of hole as well

*Changes in v23*:
- Set vec_buf_index in loop only when vec_buf_index is set
- Return -EFAULT instead of -EINVAL if vec is NULL
- Correctly return the walk ending address to the page granularity

*Changes in v22*:
- Interface change:
  - Replace [start start + len) with [start, end)
  - Return the ending address of the address walk in start

*Changes in v21*:
- Abort walk instead of returning error if WP is to be performed on
  partial hugetlb

*Changes in v20*
- Correct PAGE_IS_FILE and add PAGE_IS_PFNZERO

*Changes in v19*
- Minor changes and interface updates

*Changes in v18*
- Rebase on top of next-20230613
- Minor updates

*Changes in v17*
- Rebase on top of next-20230606
- Minor improvements in PAGEMAP_SCAN IOCTL patch

*Changes in v16*
- Fix a corner case
- Add exclusive PM_SCAN_OP_WP back

*Changes in v15*
- Build fix (Add missed build fix in RESEND)

*Changes in v14*
- Fix build error caused by #ifdef added at last minute in some configs

*Changes in v13*
- Rebase on top of next-20230414
- Give-up on using uffd_wp_range() and write new helpers, flush tlb only
  once

*Changes in v12*
- Update and other memory types to UFFD_FEATURE_WP_ASYNC
- Rebaase on top of next-20230406
- Review updates

*Changes in v11*
- Rebase on top of next-20230307
- Base patches on UFFD_FEATURE_WP_UNPOPULATED
- Do a lot of cosmetic changes and review updates
- Remove ENGAGE_WP + !GET operation as it can be performed with
  UFFDIO_WRITEPROTECT

*Changes in v10*
- Add specific condition to return error if hugetlb is used with wp
  async
- Move changes in tools/include/uapi/linux/fs.h to separate patch
- Add documentation

*Changes in v9:*
- Correct fault resolution for userfaultfd wp async
- Fix build warnings and errors which were happening on some configs
- Simplify pagemap ioctl's code

*Changes in v8:*
- Update uffd async wp implementation
- Improve PAGEMAP_IOCTL implementation

*Changes in v7:*
- Add uffd wp async
- Update the IOCTL to use uffd under the hood instead of soft-dirty
  flags

*Motivation*
The real motivation for adding PAGEMAP_SCAN IOCTL is to emulate Windows
GetWriteWatch() and ResetWriteWatch() syscalls [1]. The GetWriteWatch()
retrieves the addresses of the pages that are written to in a region of
virtual memory.

This syscall is used in Windows applications and games etc. This syscall is
being emulated in pretty slow manner in userspace. Our purpose is to
enhance the kernel such that we translate it efficiently in a better way.
Currently some out of tree hack patches are being used to efficiently
emulate it in some kernels. We intend to replace those with these patches.
So the whole gaming on Linux can effectively get benefit from this. It
means there would be tons of users of this code.

CRIU use case [2] was mentioned by Andrei and Danylo:
> Use cases for migrating sparse VMAs are binaries sanitized with ASAN,
> MSAN or TSAN [3]. All of these sanitizers produce sparse mappings of
> shadow memory [4]. Being able to migrate such binaries allows to highly
> reduce the amount of work needed to identify and fix post-migration
> crashes, which happen constantly.

Andrei's defines the following uses of this code:
* it is more granular and allows us to track changed pages more
  effectively. The current interface can clear dirty bits for the entire
  process only. In addition, reading info about pages is a separate
  operation. It means we must freeze the process to read information
  about all its pages, reset dirty bits, only then we can start dumping
  pages. The information about pages becomes more and more outdated,
  while we are processing pages. The new interface solves both these
  downsides. First, it allows us to read pte bits and clear the
  soft-dirty bit atomically. It means that CRIU will not need to freeze
  processes to pre-dump their memory. Second, it clears soft-dirty bits
  for a specified region of memory. It means CRIU will have actual info
  about pages to the moment of dumping them.
* The new interface has to be much faster because basic page filtering
  is happening in the kernel. With the old interface, we have to read
  pagemap for each page.

*Implementation Evolution (Short Summary)*
From the definition of GetWriteWatch(), we feel like kernel's soft-dirty
feature can be used under the hood with some additions like:
* reset soft-dirty flag for only a specific region of memory instead of
clearing the flag for the entire process
* get and clear soft-dirty flag for a specific region atomically

So we decided to use ioctl on pagemap file to read or/and reset soft-dirty
flag. But using soft-dirty flag, sometimes we get extra pages which weren't
even written. They had become soft-dirty because of VMA merging and
VM_SOFTDIRTY flag. This breaks the definition of GetWriteWatch(). We were
able to by-pass this short coming by ignoring VM_SOFTDIRTY until David
reported that mprotect etc messes up the soft-dirty flag while ignoring
VM_SOFTDIRTY [5]. This wasn't happening until [6] got introduced. We
discussed if we can revert these patches. But we could not reach to any
conclusion. So at this point, I made couple of tries to solve this whole
VM_SOFTDIRTY issue by correcting the soft-dirty implementation:
* [7] Correct the bug fixed wrongly back in 2014. It had potential to cause
regression. We left it behind.
* [8] Keep a list of soft-dirty part of a VMA across splits and merges. I
got the reply don't increase the size of the VMA by 8 bytes.

At this point, we left soft-dirty considering it is too much delicate and
userfaultfd [9] seemed like the only way forward. From there onward, we
have been basing soft-dirty emulation on userfaultfd wp feature where
kernel resolves the faults itself when WP_ASYNC feature is used. It was
straight forward to add WP_ASYNC feature in userfautlfd. Now we get only
those pages dirty or written-to which are really written in reality. (PS
There is another WP_UNPOPULATED userfautfd feature is required which is
needed to avoid pre-faulting memory before write-protecting [9].)

All the different masks were added on the request of CRIU devs to create
interface more generic and better.

[1] https://learn.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-getwritewatch
[2] https://lore.kernel.org/all/20221014134802.1361436-1-mdanylo@google.com
[3] https://github.com/google/sanitizers
[4] https://github.com/google/sanitizers/wiki/AddressSanitizerAlgorithm#64-bit
[5] https://lore.kernel.org/all/bfcae708-db21-04b4-0bbe-712badd03071@redhat.com
[6] https://lore.kernel.org/all/20220725142048.30450-1-peterx@redhat.com/
[7] https://lore.kernel.org/all/20221122115007.2787017-1-usama.anjum@collabora.com
[8] https://lore.kernel.org/all/20221220162606.1595355-1-usama.anjum@collabora.com
[9] https://lore.kernel.org/all/20230306213925.617814-1-peterx@redhat.com
[10] https://lore.kernel.org/all/20230125144529.1630917-1-mdanylo@google.com

* Original Cover letter from v8*
Hello,

Note:
Soft-dirty pages and pages which have been written-to are synonyms. As
kernel already has soft-dirty feature inside which we have given up to
use, we are using written-to terminology while using UFFD async WP under
the hood.

It is possible to find and clear soft-dirty pages entirely in userspace.
But it isn't efficient:
- The mprotect and SIGSEGV handler for bookkeeping
- The userfaultfd wp (synchronous) with the handler for bookkeeping

Some benchmarks can be seen here[1]. This series adds features that weren't
present earlier:
- There is no atomic get soft-dirty/Written-to status and clear present in
  the kernel.
- The pages which have been written-to can not be found in accurate way.
  (Kernel's soft-dirty PTE bit + sof_dirty VMA bit shows more soft-dirty
  pages than there actually are.)

Historically, soft-dirty PTE bit tracking has been used in the CRIU
project. The procfs interface is enough for finding the soft-dirty bit
status and clearing the soft-dirty bit of all the pages of a process.
We have the use case where we need to track the soft-dirty PTE bit for
only specific pages on-demand. We need this tracking and clear mechanism
of a region of memory while the process is running to emulate the
getWriteWatch() syscall of Windows.

*(Moved to using UFFD instead of soft-dirty feature to find pages which
have been written-to from v7 patch series)*:
Stop using the soft-dirty flags for finding which pages have been
written to. It is too delicate and wrong as it shows more soft-dirty
pages than the actual soft-dirty pages. There is no interest in
correcting it [2][3] as this is how the feature was written years ago.
It shouldn't be updated to changed behaviour. Peter Xu has suggested
using the async version of the UFFD WP [4] as it is based inherently
on the PTEs.

So in this patch series, I've added a new mode to the UFFD which is
asynchronous version of the write protect. When this variant of the
UFFD WP is used, the page faults are resolved automatically by the
kernel. The pages which have been written-to can be found by reading
pagemap file (!PM_UFFD_WP). This feature can be used successfully to
find which pages have been written to from the time the pages were
write protected. This works just like the soft-dirty flag without
showing any extra pages which aren't soft-dirty in reality.

The information related to pages if the page is file mapped, present and
swapped is required for the CRIU project [5][6]. The addition of the
required mask, any mask, excluded mask and return masks are also required
for the CRIU project [5].

The IOCTL returns the addresses of the pages which match the specific
masks. The page addresses are returned in struct page_region in a compact
form. The max_pages is needed to support a use case where user only wants
to get a specific number of pages. So there is no need to find all the
pages of interest in the range when max_pages is specified. The IOCTL
returns when the maximum number of the pages are found. The max_pages is
optional. If max_pages is specified, it must be equal or greater than the
vec_size. This restriction is needed to handle worse case when one
page_region only contains info of one page and it cannot be compacted.
This is needed to emulate the Windows getWriteWatch() syscall.

The patch series include the detailed selftest which can be used as an
example for the uffd async wp test and PAGEMAP_IOCTL. It shows the
interface usages as well.

[1] https://lore.kernel.org/lkml/54d4c322-cd6e-eefd-b161-2af2b56aae24@collabora.com/
[2] https://lore.kernel.org/all/20221220162606.1595355-1-usama.anjum@collabora.com
[3] https://lore.kernel.org/all/20221122115007.2787017-1-usama.anjum@collabora.com
[4] https://lore.kernel.org/all/Y6Hc2d+7eTKs7AiH@x1n
[5] https://lore.kernel.org/all/YyiDg79flhWoMDZB@gmail.com/
[6] https://lore.kernel.org/all/20221014134802.1361436-1-mdanylo@google.com/

Regards,
Muhammad Usama Anjum

Muhammad Usama Anjum (5):
  fs/proc/task_mmu: Implement IOCTL to get and optionally clear info
    about PTEs
  fs/proc/task_mmu: Add fast paths to get/clear PAGE_IS_WRITTEN flag
  tools headers UAPI: Update linux/fs.h with the kernel sources
  mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL
  selftests: mm: add pagemap ioctl tests

Peter Xu (1):
  userfaultfd: UFFD_FEATURE_WP_ASYNC

 Documentation/admin-guide/mm/pagemap.rst     |   64 +
 Documentation/admin-guide/mm/userfaultfd.rst |   35 +
 fs/proc/task_mmu.c                           |  716 ++++++++
 fs/userfaultfd.c                             |   26 +-
 include/linux/hugetlb.h                      |    1 +
 include/linux/userfaultfd_k.h                |   21 +-
 include/uapi/linux/fs.h                      |   59 +
 include/uapi/linux/userfaultfd.h             |    9 +-
 mm/hugetlb.c                                 |   34 +-
 mm/memory.c                                  |   27 +-
 tools/include/uapi/linux/fs.h                |   59 +
 tools/testing/selftests/mm/.gitignore        |    2 +
 tools/testing/selftests/mm/Makefile          |    3 +-
 tools/testing/selftests/mm/config            |    1 +
 tools/testing/selftests/mm/pagemap_ioctl.c   | 1658 ++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh    |    4 +
 16 files changed, 2695 insertions(+), 24 deletions(-)
 create mode 100644 tools/testing/selftests/mm/pagemap_ioctl.c

-- 
2.39.2

[PATCH v28 1/6] userfaultfd: UFFD_FEATURE_WP_ASYNC

[Muhammad Usama Anjum]

From: Peter Xu <peterx@redhat.com>

This patch adds a new userfaultfd-wp feature UFFD_FEATURE_WP_ASYNC, that
allows userfaultfd wr-protect faults to be resolved by the kernel directly.

It can be used like a high accuracy version of soft-dirty, without vma
modifications during tracking, and also with ranged support by default
rather than for a whole mm when reset the protections due to existence of
ioctl(UFFDIO_WRITEPROTECT).

Several goals of such a dirty tracking interface:

1. All types of memory should be supported and tracable. This is nature
   for soft-dirty but should mention when the context is userfaultfd,
   because it used to only support anon/shmem/hugetlb. The problem is for
   a dirty tracking purpose these three types may not be enough, and it's
   legal to track anything e.g. any page cache writes from mmap.

2. Protections can be applied to partial of a memory range, without vma
   split/merge fuss.  The hope is that the tracking itself should not
   affect any vma layout change.  It also helps when reset happens because
   the reset will not need mmap write lock which can block the tracee.

3. Accuracy needs to be maintained.  This means we need pte markers to work
   on any type of VMA.

One could question that, the whole concept of async dirty tracking is not
really close to fundamentally what userfaultfd used to be: it's not "a
fault to be serviced by userspace" anymore. However, using userfaultfd-wp
here as a framework is convenient for us in at least:

1. VM_UFFD_WP vma flag, which has a very good name to suite something like
   this, so we don't need VM_YET_ANOTHER_SOFT_DIRTY. Just use a new
   feature bit to identify from a sync version of uffd-wp registration.

2. PTE markers logic can be leveraged across the whole kernel to maintain
   the uffd-wp bit as long as an arch supports, this also applies to this
   case where uffd-wp bit will be a hint to dirty information and it will
   not go lost easily (e.g. when some page cache ptes got zapped).

3. Reuse ioctl(UFFDIO_WRITEPROTECT) interface for either starting or
   resetting a range of memory, while there's no counterpart in the old
   soft-dirty world, hence if this is wanted in a new design we'll need a
   new interface otherwise.

We can somehow understand that commonality because uffd-wp was
fundamentally a similar idea of write-protecting pages just like
soft-dirty.

This implementation allows WP_ASYNC to imply WP_UNPOPULATED, because so far
WP_ASYNC seems to not usable if without WP_UNPOPULATE.  This also gives us
chance to modify impl of WP_ASYNC just in case it could be not depending on
WP_UNPOPULATED anymore in the future kernels. It's also fine to imply that
because both features will rely on PTE_MARKER_UFFD_WP config option, so
they'll show up together (or both missing) in an UFFDIO_API probe.

vma_can_userfault() now allows any VMA if the userfaultfd registration is
only about async uffd-wp. So we can track dirty for all kinds of memory
including generic file systems (like XFS, EXT4 or BTRFS).

One trick worth mention in do_wp_page() is that we need to manually update
vmf->orig_pte here because it can be used later with a pte_same() check -
this path always has FAULT_FLAG_ORIG_PTE_VALID set in the flags.

The major defect of this approach of dirty tracking is we need to populate
the pgtables when tracking starts. Soft-dirty doesn't do it like that.
It's unwanted in the case where the range of memory to track is huge and
unpopulated (e.g., tracking updates on a 10G file with mmap() on top,
without having any page cache installed yet). One way to improve this is
to allow pte markers exist for larger than PTE level for PMD+. That will
not change the interface if to implemented, so we can leave that for later.

Co-developed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
Changes in v24:
- Rebase on top of next-20230710
- UFFD_FEATURE_WP_ASYNC has been defined to be (1 << 15) after the
  rebase

Changes in v18:
- Rebase on top of next-20230613 (use ptep_get)

Changes in v17:
- Rebase on top of next-20230525

Changes in v12:
- Peter added the hugetlb support and revamped some other implementation
- Transferred the authorship to Peter
- Merge documentation to this patch

Changes in v11:
- Fix return code in userfaultfd_register() and minor changes here and
  there
- Rebase on top of next-20230307
- Base patches on UFFD_FEATURE_WP_UNPOPULATED https://lore.kernel.org/all/20230306213925.617814-1-peterx@redhat.com
- UFFD_FEATURE_WP_ASYNC depends on UFFD_FEATURE_WP_UNPOPULATED to work
  (correctly)

Changes in v10:
- Build fix
- Update comments and add error condition to return error from uffd
  register if hugetlb pages are present when wp async flag is set

Changes in v9:
- Correct the fault resolution with code contributed by Peter

Changes in v7:
- Remove UFFDIO_WRITEPROTECT_MODE_ASYNC_WP and add UFFD_FEATURE_WP_ASYNC
- Handle automatic page fault resolution in better way (thanks to Peter)
---
 Documentation/admin-guide/mm/userfaultfd.rst | 35 ++++++++++++++++++++
 fs/userfaultfd.c                             | 26 ++++++++++++---
 include/linux/userfaultfd_k.h                | 21 +++++++++++-
 include/uapi/linux/userfaultfd.h             |  9 ++++-
 mm/hugetlb.c                                 | 32 ++++++++++--------
 mm/memory.c                                  | 27 +++++++++++++--
 6 files changed, 128 insertions(+), 22 deletions(-)

diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
index 4349a8c2b9783..203e26da5f920 100644
--- a/Documentation/admin-guide/mm/userfaultfd.rst
+++ b/Documentation/admin-guide/mm/userfaultfd.rst
@@ -244,6 +244,41 @@ write-protected (so future writes will also result in a WP fault). These ioctls
 support a mode flag (``UFFDIO_COPY_MODE_WP`` or ``UFFDIO_CONTINUE_MODE_WP``
 respectively) to configure the mapping this way.
 
+If the userfaultfd context has ``UFFD_FEATURE_WP_ASYNC`` feature bit set,
+any vma registered with write-protection will work in async mode rather
+than the default sync mode.
+
+In async mode, there will be no message generated when a write operation
+happens, meanwhile the write-protection will be resolved automatically by
+the kernel.  It can be seen as a more accurate version of soft-dirty
+tracking and it can be different in a few ways:
+
+  - The dirty result will not be affected by vma changes (e.g. vma
+    merging) because the dirty is only tracked by the pte.
+
+  - It supports range operations by default, so one can enable tracking on
+    any range of memory as long as page aligned.
+
+  - Dirty information will not get lost if the pte was zapped due to
+    various reasons (e.g. during split of a shmem transparent huge page).
+
+  - Due to a reverted meaning of soft-dirty (page clean when uffd-wp bit
+    set; dirty when uffd-wp bit cleared), it has different semantics on
+    some of the memory operations.  For example: ``MADV_DONTNEED`` on
+    anonymous (or ``MADV_REMOVE`` on a file mapping) will be treated as
+    dirtying of memory by dropping uffd-wp bit during the procedure.
+
+The user app can collect the "written/dirty" status by looking up the
+uffd-wp bit for the pages being interested in /proc/pagemap.
+
+The page will not be under track of uffd-wp async mode until the page is
+explicitly write-protected by ``ioctl(UFFDIO_WRITEPROTECT)`` with the mode
+flag ``UFFDIO_WRITEPROTECT_MODE_WP`` set.  Trying to resolve a page fault
+that was tracked by async mode userfaultfd-wp is invalid.
+
+When userfaultfd-wp async mode is used alone, it can be applied to all
+kinds of memory.
+
 Memory Poisioning Emulation
 ---------------------------
 
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index bbfaf5837a08a..938f29be55422 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -123,6 +123,11 @@ static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
 	return ctx->features & UFFD_FEATURE_INITIALIZED;
 }
 
+static bool userfaultfd_wp_async_ctx(struct userfaultfd_ctx *ctx)
+{
+	return ctx && (ctx->features & UFFD_FEATURE_WP_ASYNC);
+}
+
 /*
  * Whether WP_UNPOPULATED is enabled on the uffd context.  It is only
  * meaningful when userfaultfd_wp()==true on the vma and when it's
@@ -1318,6 +1323,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 	bool basic_ioctls;
 	unsigned long start, end, vma_end;
 	struct vma_iterator vmi;
+	bool wp_async = userfaultfd_wp_async_ctx(ctx);
 	pgoff_t pgoff;
 
 	user_uffdio_register = (struct uffdio_register __user *) arg;
@@ -1392,7 +1398,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 
 		/* check not compatible vmas */
 		ret = -EINVAL;
-		if (!vma_can_userfault(cur, vm_flags))
+		if (!vma_can_userfault(cur, vm_flags, wp_async))
 			goto out_unlock;
 
 		/*
@@ -1453,7 +1459,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 	for_each_vma_range(vmi, vma, end) {
 		cond_resched();
 
-		BUG_ON(!vma_can_userfault(vma, vm_flags));
+		BUG_ON(!vma_can_userfault(vma, vm_flags, wp_async));
 		BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
 		       vma->vm_userfaultfd_ctx.ctx != ctx);
 		WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
@@ -1553,6 +1559,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 	unsigned long start, end, vma_end;
 	const void __user *buf = (void __user *)arg;
 	struct vma_iterator vmi;
+	bool wp_async = userfaultfd_wp_async_ctx(ctx);
 	pgoff_t pgoff;
 
 	ret = -EFAULT;
@@ -1607,7 +1614,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 		 * provides for more strict behavior to notice
 		 * unregistration errors.
 		 */
-		if (!vma_can_userfault(cur, cur->vm_flags))
+		if (!vma_can_userfault(cur, cur->vm_flags, wp_async))
 			goto out_unlock;
 
 		found = true;
@@ -1623,7 +1630,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 	for_each_vma_range(vmi, vma, end) {
 		cond_resched();
 
-		BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
+		BUG_ON(!vma_can_userfault(vma, vma->vm_flags, wp_async));
 
 		/*
 		 * Nothing to do: this vma is already registered into this
@@ -2008,6 +2015,11 @@ static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long
 	return ret;
 }
 
+bool userfaultfd_wp_async(struct vm_area_struct *vma)
+{
+	return userfaultfd_wp_async_ctx(vma->vm_userfaultfd_ctx.ctx);
+}
+
 static inline unsigned int uffd_ctx_features(__u64 user_features)
 {
 	/*
@@ -2041,6 +2053,11 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 	ret = -EPERM;
 	if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
 		goto err_out;
+
+	/* WP_ASYNC relies on WP_UNPOPULATED, choose it unconditionally */
+	if (features & UFFD_FEATURE_WP_ASYNC)
+		features |= UFFD_FEATURE_WP_UNPOPULATED;
+
 	/* report all available features and ioctls to userland */
 	uffdio_api.features = UFFD_API_FEATURES;
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
@@ -2053,6 +2070,7 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 #ifndef CONFIG_PTE_MARKER_UFFD_WP
 	uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
 	uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
+	uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
 #endif
 	uffdio_api.ioctls = UFFD_API_IOCTLS;
 	ret = -EFAULT;
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index ac8c6854097cd..c98df391bfd8f 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -161,11 +161,22 @@ static inline bool userfaultfd_armed(struct vm_area_struct *vma)
 }
 
 static inline bool vma_can_userfault(struct vm_area_struct *vma,
-				     unsigned long vm_flags)
+				     unsigned long vm_flags,
+				     bool wp_async)
 {
+	vm_flags &= __VM_UFFD_FLAGS;
+
 	if ((vm_flags & VM_UFFD_MINOR) &&
 	    (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma)))
 		return false;
+
+	/*
+	 * If wp async enabled, and WP is the only mode enabled, allow any
+	 * memory type.
+	 */
+	if (wp_async && (vm_flags == VM_UFFD_WP))
+		return true;
+
 #ifndef CONFIG_PTE_MARKER_UFFD_WP
 	/*
 	 * If user requested uffd-wp but not enabled pte markers for
@@ -175,6 +186,8 @@ static inline bool vma_can_userfault(struct vm_area_struct *vma,
 	if ((vm_flags & VM_UFFD_WP) && !vma_is_anonymous(vma))
 		return false;
 #endif
+
+	/* By default, allow any of anon|shmem|hugetlb */
 	return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
 	    vma_is_shmem(vma);
 }
@@ -197,6 +210,7 @@ extern int userfaultfd_unmap_prep(struct vm_area_struct *vma,
 extern void userfaultfd_unmap_complete(struct mm_struct *mm,
 				       struct list_head *uf);
 extern bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma);
+extern bool userfaultfd_wp_async(struct vm_area_struct *vma);
 
 #else /* CONFIG_USERFAULTFD */
 
@@ -297,6 +311,11 @@ static inline bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)
 	return false;
 }
 
+static inline bool userfaultfd_wp_async(struct vm_area_struct *vma)
+{
+	return false;
+}
+
 #endif /* CONFIG_USERFAULTFD */
 
 static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma)
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 62151706c5a38..0dbc81015018b 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -40,7 +40,8 @@
 			   UFFD_FEATURE_EXACT_ADDRESS |		\
 			   UFFD_FEATURE_WP_HUGETLBFS_SHMEM |	\
 			   UFFD_FEATURE_WP_UNPOPULATED |	\
-			   UFFD_FEATURE_POISON)
+			   UFFD_FEATURE_POISON |		\
+			   UFFD_FEATURE_WP_ASYNC)
 #define UFFD_API_IOCTLS				\
 	((__u64)1 << _UFFDIO_REGISTER |		\
 	 (__u64)1 << _UFFDIO_UNREGISTER |	\
@@ -216,6 +217,11 @@ struct uffdio_api {
 	 * (i.e. empty ptes).  This will be the default behavior for shmem
 	 * & hugetlbfs, so this flag only affects anonymous memory behavior
 	 * when userfault write-protection mode is registered.
+	 *
+	 * UFFD_FEATURE_WP_ASYNC indicates that userfaultfd write-protection
+	 * asynchronous mode is supported in which the write fault is
+	 * automatically resolved and write-protection is un-set.
+	 * It implies UFFD_FEATURE_WP_UNPOPULATED.
 	 */
 #define UFFD_FEATURE_PAGEFAULT_FLAG_WP		(1<<0)
 #define UFFD_FEATURE_EVENT_FORK			(1<<1)
@@ -232,6 +238,7 @@ struct uffdio_api {
 #define UFFD_FEATURE_WP_HUGETLBFS_SHMEM		(1<<12)
 #define UFFD_FEATURE_WP_UNPOPULATED		(1<<13)
 #define UFFD_FEATURE_POISON			(1<<14)
+#define UFFD_FEATURE_WP_ASYNC			(1<<15)
 	__u64 features;
 
 	__u64 ioctls;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 154cc5b315727..a073e6ed8900b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6191,21 +6191,27 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	/* Handle userfault-wp first, before trying to lock more pages */
 	if (userfaultfd_wp(vma) && huge_pte_uffd_wp(huge_ptep_get(ptep)) &&
 	    (flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
-		struct vm_fault vmf = {
-			.vma = vma,
-			.address = haddr,
-			.real_address = address,
-			.flags = flags,
-		};
+		if (!userfaultfd_wp_async(vma)) {
+			struct vm_fault vmf = {
+				.vma = vma,
+				.address = haddr,
+				.real_address = address,
+				.flags = flags,
+			};
 
-		spin_unlock(ptl);
-		if (pagecache_folio) {
-			folio_unlock(pagecache_folio);
-			folio_put(pagecache_folio);
+			spin_unlock(ptl);
+			if (pagecache_folio) {
+				folio_unlock(pagecache_folio);
+				folio_put(pagecache_folio);
+			}
+			hugetlb_vma_unlock_read(vma);
+			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+			return handle_userfault(&vmf, VM_UFFD_WP);
 		}
-		hugetlb_vma_unlock_read(vma);
-		mutex_unlock(&hugetlb_fault_mutex_table[hash]);
-		return handle_userfault(&vmf, VM_UFFD_WP);
+
+		entry = huge_pte_clear_uffd_wp(entry);
+		set_huge_pte_at(mm, haddr, ptep, entry);
+		/* Fallthrough to CoW */
 	}
 
 	/*
diff --git a/mm/memory.c b/mm/memory.c
index 7ff73a197cced..94a24ac2270b2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3466,11 +3466,28 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
 	const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
 	struct vm_area_struct *vma = vmf->vma;
 	struct folio *folio = NULL;
+	pte_t pte;
 
 	if (likely(!unshare)) {
 		if (userfaultfd_pte_wp(vma, ptep_get(vmf->pte))) {
-			pte_unmap_unlock(vmf->pte, vmf->ptl);
-			return handle_userfault(vmf, VM_UFFD_WP);
+			if (!userfaultfd_wp_async(vma)) {
+				pte_unmap_unlock(vmf->pte, vmf->ptl);
+				return handle_userfault(vmf, VM_UFFD_WP);
+			}
+
+			/*
+			 * Nothing needed (cache flush, TLB invalidations,
+			 * etc.) because we're only removing the uffd-wp bit,
+			 * which is completely invisible to the user.
+			 */
+			pte = pte_clear_uffd_wp(ptep_get(vmf->pte));
+
+			set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
+			/*
+			 * Update this to be prepared for following up CoW
+			 * handling
+			 */
+			vmf->orig_pte = pte;
 		}
 
 		/*
@@ -4965,8 +4982,11 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
 
 	if (vma_is_anonymous(vmf->vma)) {
 		if (likely(!unshare) &&
-		    userfaultfd_huge_pmd_wp(vmf->vma, vmf->orig_pmd))
+		    userfaultfd_huge_pmd_wp(vmf->vma, vmf->orig_pmd)) {
+			if (userfaultfd_wp_async(vmf->vma))
+				goto split;
 			return handle_userfault(vmf, VM_UFFD_WP);
+		}
 		return do_huge_pmd_wp_page(vmf);
 	}
 
@@ -4978,6 +4998,7 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
 		}
 	}
 
+split:
 	/* COW or write-notify handled on pte level: split pmd. */
 	__split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
 
-- 
2.39.2

[PATCH v28 2/6] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

This IOCTL, PAGEMAP_SCAN on pagemap file can be used to get and/or clear
the info about page table entries. The following operations are supported
in this ioctl:
- Get the information if the pages have Async Write-Protection enabled
  (``PAGE_IS_WPALLOWED``), have been written to (``PAGE_IS_WRITTEN``), file
  mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``), swapped
  (``PAGE_IS_SWAPPED``) or page has pfn zero (``PAGE_IS_PFNZERO``).
- Find pages which have been written to and/or write protect
  (atomic ``PM_SCAN_WP_MATCHING + PM_SCAN_CHECK_WPASYNC``) the pages
  atomically. The (``PM_SCAN_WP_MATCHING``) is used to WP the matched
  pages. The (``PM_SCAN_CHECK_WPASYNC``) aborts the operation if
  non-Async-Write-Protected pages are found. Get is automatically performed
  if output buffer is specified.

This IOCTL can be extended to get information about more PTE bits. The
entire address range passed by user [start, end) is scanned until either
the user provided buffer is full or max_pages have been found.

Reviewed-by: Andrei Vagin <avagin@gmail.com>
Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
---
Changes in v28:
- Fix walk_end one last time after doing through testing

Changes in v27:
- Add PAGE_IS_HUGE
- Iterate until temporary buffer is full to do less iterations
- Don't check if PAGE_IS_FILE if no mask needs it as it is very
  expensive to check per pte
- bring is_interesting_page() outside pagemap_scan_output() to remove
  the horrible return value check
- Replace memcpy() with direct copy
- rename end_addr to walk_end_addr in pagemap_scan_private
- Abort walk if fatal_signal_pending()

Changes in v26:
Changes made by Usama:
- Fix the wrong breaking of loop if page isn't interesting, skip intsead
- Untag the address and save them into struct
- Round off the end address to next page
- Correct the partial hugetlb page handling and returning the error
- Rename PAGE_IS_WPASYNC to PAGE_IS_WPALLOWED
- Return walk ending address in walk_end instead of returning in start
  as there is potential of replacing the memory tag

Changes by Michał:
1. the API:
  a. return ranges as {begin, end} instead of {begin + len};
  b. rename match "flags" to 'page categories' everywhere - this makes
	it easier to differentiate the ioctl()s categorisation of pages
	from struct page flags;
  c. change {required + excluded} to {inverted + required}. This was
	rejected before, but I'd like to illustrate the difference.
	Old interface can be translated to the new by:
		categories_inverted = excluded_mask
		categories_mask = required_mask | excluded_mask
		categories_anyof_mask = anyof_mask
	The new way allows filtering by: A & (B | !C)
		categories_inverted = C
		categories_mask = A
		categories_anyof_mask = B | C
  e. allow no-op calls
2. the implementation:
  a. gather the page-categorising and write-protecting code in one place;
  b. optimization: add whole-vma skipping for WP usecase;
  c. extracted output limiting code to pagemap_scan_output();
  d. extracted range coalescing to pagemap_scan_push_range();
  e. extracted THP entry handling to pagemap_scan_thp_entry();
  f. added a shortcut for non-WP hugetlb scan; avoids conditional
	locking;
  g. extracted scan buffer handling code out of do_pagemap_scan();
  h. rework output code to always try to write pending ranges; if EFAULT
	is generated it always overwrites the original error code;
	(the case of SIGKILL is needlessly trying to write the output
	now, but this should be rare case and ignoring it makes the code
	not needing a goto)
3.Change no-GET operation condition from `arg.return_mask == 0` to
  `arg.vec == NULL`. This will allow issuing the ioctl with
  return_mask == 0 to gather matching ranges when the exact category
  is not interesting. (Anticipated for CRIU scanning a large sparse
  anonymous mapping).

Changes in v25:
- Do proper filtering on hole as well (hole got missed earlier)

Changes in v24:
- Place WP markers in case of hole as well

Changes in v23:
- Set vec_buf_index to 0 only when vec_buf_index is set
- Return -EFAULT instead of -EINVAL if vec is NULL
- Correctly return the walk ending address to the page granularity

Changes in v22:
- Interface change to return walk ending address to user:
  - Replace [start start + len) with [start, end)
  - Return the ending address of the address walk in start

Changes in v21:
- Abort walk instead of returning error if WP is to be performed on
  partial hugetlb
- Changed the data types of some variables in pagemap_scan_private to
  long

Changes in v20:
- Correct PAGE_IS_FILE and add PAGE_IS_PFNZERO

Changes in v19:
- Interface changes such as renaming, return mask and WP can be used
  with any flags specified in masks
- Internal code changes

Changes in v18:
- Rebased on top of next-20230613
  - ptep_get() updates
  - remove pmd_trans_unstable() and add ACTION_AGAIN
- Review updates (Micheal)

Changes in v17:
- Rebased on next-20230606
- Made make_uffd_wp_*_pte() better and minor changes

Changes in v16:
- Fixed a corner case where kernel writes beyond user buffer by one
  element
- Bring back exclusive PM_SCAN_OP_WP
- Cosmetic changes

Changes in v15:
- Build fix:
  - Use generic tlb flush function in pagemap_scan_pmd_entry() instead of
    using x86 specific flush function in do_pagemap_scan()
  - Remove #ifdef from pagemap_scan_hugetlb_entry()
  - Use mm instead of undefined vma->vm_mm

Changes in v14:
- Fix build error caused by #ifdef added at last minute in some configs

Changes in v13:
- Review updates
- mmap_read_lock_killable() instead of mmap_read_lock()
- Replace uffd_wp_range() with helpers which increases performance
  drastically for OP_WP operations by reducing the number of tlb
  flushing etc
- Add MMU_NOTIFY_PROTECTION_VMA notification for the memory range

Changes in v12:
- Add hugetlb support to cover all memory types
- Merge "userfaultfd: Define dummy uffd_wp_range()" with this patch
- Review updates to the code

Changes in v11:
- Find written pages in a better way
- Fix a corner case (thanks Paul)
- Improve the code/comments
- remove ENGAGE_WP + ! GET operation
- shorten the commit message in favour of moving documentation to
  pagemap.rst

Changes in v10:
- move changes in tools/include/uapi/linux/fs.h to separate patch
- update commit message

Change in v8:
- Correct is_pte_uffd_wp()
- Improve readability and error checks
- Remove some un-needed code

Changes in v7:
- Rebase on top of latest next
- Fix some corner cases
- Base soft-dirty on the uffd wp async
- Update the terminologies
- Optimize the memory usage inside the ioctl
---
 fs/proc/task_mmu.c      | 678 ++++++++++++++++++++++++++++++++++++++++
 include/linux/hugetlb.h |   1 +
 include/uapi/linux/fs.h |  59 ++++
 mm/hugetlb.c            |   2 +-
 4 files changed, 739 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index c1e6531cb02ae..0e219a44e97cd 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -19,6 +19,8 @@
 #include <linux/shmem_fs.h>
 #include <linux/uaccess.h>
 #include <linux/pkeys.h>
+#include <linux/minmax.h>
+#include <linux/overflow.h>
 
 #include <asm/elf.h>
 #include <asm/tlb.h>
@@ -1749,11 +1751,687 @@ static int pagemap_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
+#define PM_SCAN_CATEGORIES	(PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN |	\
+				 PAGE_IS_FILE |	PAGE_IS_PRESENT |	\
+				 PAGE_IS_SWAPPED | PAGE_IS_PFNZERO |	\
+				 PAGE_IS_HUGE)
+#define PM_SCAN_FLAGS		(PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
+
+#define MASKS_OF_INTEREST(a)	(a.category_inverted | a.category_mask | \
+				 a.category_anyof_mask | a.return_mask)
+
+struct pagemap_scan_private {
+	struct pm_scan_arg arg;
+	unsigned long masks_of_interest, cur_vma_category;
+	struct page_region *vec_buf, cur_buf;
+	unsigned long vec_buf_len, vec_buf_index, found_pages, walk_end_addr;
+	struct page_region __user *vec_out;
+};
+
+static unsigned long pagemap_page_category(struct pagemap_scan_private *p,
+					   struct vm_area_struct *vma,
+					   unsigned long addr, pte_t pte)
+{
+	unsigned long categories = 0;
+
+	if (pte_present(pte)) {
+		struct page *page;
+
+		categories |= PAGE_IS_PRESENT;
+		if (!pte_uffd_wp(pte))
+			categories |= PAGE_IS_WRITTEN;
+
+		if (p->masks_of_interest & PAGE_IS_FILE) {
+			page = vm_normal_page(vma, addr, pte);
+			if (page && !PageAnon(page))
+				categories |= PAGE_IS_FILE;
+		}
+
+		if (is_zero_pfn(pte_pfn(pte)))
+			categories |= PAGE_IS_PFNZERO;
+	} else if (is_swap_pte(pte)) {
+		swp_entry_t swp;
+
+		categories |= PAGE_IS_SWAPPED;
+		if (!pte_swp_uffd_wp_any(pte))
+			categories |= PAGE_IS_WRITTEN;
+
+		if (p->masks_of_interest & PAGE_IS_FILE) {
+			swp = pte_to_swp_entry(pte);
+			if (is_pfn_swap_entry(swp) &&
+			    !PageAnon(pfn_swap_entry_to_page(swp)))
+				categories |= PAGE_IS_FILE;
+		}
+	}
+
+	return categories;
+}
+
+static void make_uffd_wp_pte(struct vm_area_struct *vma,
+			     unsigned long addr, pte_t *pte)
+{
+	pte_t ptent = ptep_get(pte);
+
+	if (pte_present(ptent)) {
+		pte_t old_pte;
+
+		old_pte = ptep_modify_prot_start(vma, addr, pte);
+		ptent = pte_mkuffd_wp(ptent);
+		ptep_modify_prot_commit(vma, addr, pte, old_pte, ptent);
+	} else if (is_swap_pte(ptent)) {
+		ptent = pte_swp_mkuffd_wp(ptent);
+		set_pte_at(vma->vm_mm, addr, pte, ptent);
+	} else {
+		set_pte_at(vma->vm_mm, addr, pte,
+			   make_pte_marker(PTE_MARKER_UFFD_WP));
+	}
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static unsigned long pagemap_thp_category(pmd_t pmd)
+{
+	unsigned long categories = PAGE_IS_HUGE;
+
+	if (pmd_present(pmd)) {
+		categories |= PAGE_IS_PRESENT;
+		if (!pmd_uffd_wp(pmd))
+			categories |= PAGE_IS_WRITTEN;
+		if (is_zero_pfn(pmd_pfn(pmd)))
+			categories |= PAGE_IS_PFNZERO;
+	} else if (is_swap_pmd(pmd)) {
+		categories |= PAGE_IS_SWAPPED;
+		if (!pmd_swp_uffd_wp(pmd))
+			categories |= PAGE_IS_WRITTEN;
+	}
+
+	return categories;
+}
+
+static void make_uffd_wp_pmd(struct vm_area_struct *vma,
+			     unsigned long addr, pmd_t *pmdp)
+{
+	pmd_t old, pmd = *pmdp;
+
+	if (pmd_present(pmd)) {
+		old = pmdp_invalidate_ad(vma, addr, pmdp);
+		pmd = pmd_mkuffd_wp(old);
+		set_pmd_at(vma->vm_mm, addr, pmdp, pmd);
+	} else if (is_migration_entry(pmd_to_swp_entry(pmd))) {
+		pmd = pmd_swp_mkuffd_wp(pmd);
+		set_pmd_at(vma->vm_mm, addr, pmdp, pmd);
+	}
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+#ifdef CONFIG_HUGETLB_PAGE
+static unsigned long pagemap_hugetlb_category(pte_t pte)
+{
+	unsigned long categories = PAGE_IS_HUGE;
+
+	if (pte_present(pte)) {
+		categories |= PAGE_IS_PRESENT;
+		if (!huge_pte_uffd_wp(pte))
+			categories |= PAGE_IS_WRITTEN;
+		if (!PageAnon(pte_page(pte)))
+			categories |= PAGE_IS_FILE;
+		if (is_zero_pfn(pte_pfn(pte)))
+			categories |= PAGE_IS_PFNZERO;
+	} else if (is_swap_pte(pte)) {
+		categories |= PAGE_IS_SWAPPED;
+		if (!pte_swp_uffd_wp_any(pte))
+			categories |= PAGE_IS_WRITTEN;
+	}
+
+	return categories;
+}
+
+static void make_uffd_wp_huge_pte(struct vm_area_struct *vma,
+				  unsigned long addr, pte_t *ptep,
+				  pte_t ptent)
+{
+	if (is_hugetlb_entry_hwpoisoned(ptent) || is_pte_marker(ptent))
+		return;
+
+	if (is_hugetlb_entry_migration(ptent))
+		set_huge_pte_at(vma->vm_mm, addr, ptep,
+				pte_swp_mkuffd_wp(ptent));
+	else if (!huge_pte_none(ptent))
+		huge_ptep_modify_prot_commit(vma, addr, ptep, ptent,
+					     huge_pte_mkuffd_wp(ptent));
+	else
+		set_huge_pte_at(vma->vm_mm, addr, ptep,
+				make_pte_marker(PTE_MARKER_UFFD_WP));
+}
+#endif /* CONFIG_HUGETLB_PAGE */
+
+static bool pagemap_scan_is_interesting_page(unsigned long categories,
+					     const struct pagemap_scan_private *p)
+{
+	categories ^= p->arg.category_inverted;
+	if ((categories & p->arg.category_mask) != p->arg.category_mask)
+		return false;
+	if (p->arg.category_anyof_mask && !(categories & p->arg.category_anyof_mask))
+		return false;
+
+	return true;
+}
+
+static bool pagemap_scan_is_interesting_vma(unsigned long categories,
+					    const struct pagemap_scan_private *p)
+{
+	unsigned long required = p->arg.category_mask & PAGE_IS_WPALLOWED;
+
+	categories ^= p->arg.category_inverted;
+	if ((categories & required) != required)
+		return false;
+
+	return true;
+}
+
+static int pagemap_scan_test_walk(unsigned long start, unsigned long end,
+				  struct mm_walk *walk)
+{
+	struct pagemap_scan_private *p = walk->private;
+	struct vm_area_struct *vma = walk->vma;
+	unsigned long vma_category = 0;
+
+	if (userfaultfd_wp_async(vma) && userfaultfd_wp_use_markers(vma))
+		vma_category |= PAGE_IS_WPALLOWED;
+	else if (p->arg.flags & PM_SCAN_CHECK_WPASYNC)
+		return -EPERM;
+
+	if (vma->vm_flags & VM_PFNMAP)
+		return 1;
+
+	if (!pagemap_scan_is_interesting_vma(vma_category, p))
+		return 1;
+
+	p->cur_vma_category = vma_category;
+
+	return 0;
+}
+
+static bool pagemap_scan_push_range(unsigned long categories,
+				    struct pagemap_scan_private *p,
+				    unsigned long addr, unsigned long end)
+{
+	struct page_region *cur_buf = &p->cur_buf;
+
+	/*
+	 * When there is no output buffer provided at all, the sentinel values
+	 * won't match here. There is no other way for `cur_buf->end` to be
+	 * non-zero other than it being non-empty.
+	 */
+	if (addr == cur_buf->end && categories == cur_buf->categories) {
+		cur_buf->end = end;
+		return true;
+	}
+
+	if (cur_buf->end) {
+		if (p->vec_buf_index >= p->vec_buf_len)
+			return false;
+
+		p->vec_buf[p->vec_buf_index++] = *cur_buf;
+	}
+
+	cur_buf->start = addr;
+	cur_buf->end = end;
+	cur_buf->categories = categories;
+
+	return true;
+}
+
+static void pagemap_scan_backout_range(struct pagemap_scan_private *p,
+				       unsigned long addr, unsigned long end,
+				       unsigned long walk_end_addr)
+{
+	struct page_region *cur_buf = &p->cur_buf;
+
+	if (cur_buf->start != addr)
+		cur_buf->end = addr;
+	else
+		cur_buf->start = cur_buf->end = 0;
+
+	p->walk_end_addr = walk_end_addr;
+	p->found_pages -= (end - addr) / PAGE_SIZE;
+}
+
+static int pagemap_scan_output(unsigned long categories,
+			       struct pagemap_scan_private *p,
+			       unsigned long addr, unsigned long *end)
+{
+	unsigned long n_pages, total_pages;
+	int ret = 0;
+
+	if (!p->vec_buf)
+		return 0;
+
+	categories &= p->arg.return_mask;
+
+	n_pages = (*end - addr) / PAGE_SIZE;
+	if (check_add_overflow(p->found_pages, n_pages, &total_pages) || //TODO
+	    total_pages > p->arg.max_pages) {
+		size_t n_too_much = total_pages - p->arg.max_pages;
+		*end -= n_too_much * PAGE_SIZE;
+		n_pages -= n_too_much;
+		ret = -ENOSPC;
+	}
+
+	if (!pagemap_scan_push_range(categories, p, addr, *end)) {
+		*end = addr;
+		n_pages = 0;
+		ret = -ENOSPC;
+	}
+
+	p->found_pages += n_pages;
+	if (ret)
+		p->walk_end_addr = *end;
+
+	return ret;
+}
+
+static int pagemap_scan_thp_entry(pmd_t *pmd, unsigned long start,
+				  unsigned long end, struct mm_walk *walk)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	struct pagemap_scan_private *p = walk->private;
+	struct vm_area_struct *vma = walk->vma;
+	unsigned long categories;
+	spinlock_t *ptl;
+	int ret = 0;
+
+	ptl = pmd_trans_huge_lock(pmd, vma);
+	if (!ptl)
+		return -ENOENT;
+
+	categories = p->cur_vma_category | pagemap_thp_category(*pmd);
+
+	if (!pagemap_scan_is_interesting_page(categories, p))
+		goto out_unlock;
+
+	ret = pagemap_scan_output(categories, p, start, &end);
+	if (start == end)
+		goto out_unlock;
+
+	if (~p->arg.flags & PM_SCAN_WP_MATCHING)
+		goto out_unlock;
+	if (~categories & PAGE_IS_WRITTEN)
+		goto out_unlock;
+
+	/*
+	 * Break huge page into small pages if the WP operation
+	 * need to be performed is on a portion of the huge page.
+	 */
+	if (end != start + HPAGE_SIZE) {
+		spin_unlock(ptl);
+		split_huge_pmd(vma, pmd, start);
+		pagemap_scan_backout_range(p, start, end, 0);
+		/* Indicate to caller for processing these as normal pages */
+		return -ENOENT;
+	}
+
+	make_uffd_wp_pmd(vma, start, pmd);
+	flush_tlb_range(vma, start, end);
+out_unlock:
+	spin_unlock(ptl);
+	return ret;
+#else /* !CONFIG_TRANSPARENT_HUGEPAGE */
+	return -ENOENT;
+#endif
+}
+
+static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
+				  unsigned long end, struct mm_walk *walk)
+{
+	struct pagemap_scan_private *p = walk->private;
+	struct vm_area_struct *vma = walk->vma;
+	pte_t *pte, *start_pte;
+	unsigned long addr;
+	bool flush = false;
+	spinlock_t *ptl;
+	int ret;
+
+	arch_enter_lazy_mmu_mode();
+
+	ret = pagemap_scan_thp_entry(pmd, start, end, walk);
+	if (ret != -ENOENT) {
+		arch_leave_lazy_mmu_mode();
+		return ret;
+	}
+
+	ret = 0;
+	start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
+	if (!pte) {
+		arch_leave_lazy_mmu_mode();
+		walk->action = ACTION_AGAIN;
+		return 0;
+	}
+
+	for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
+		unsigned long categories = p->cur_vma_category |
+					   pagemap_page_category(p, vma, addr, ptep_get(pte));
+		unsigned long next = addr + PAGE_SIZE;
+
+		if (!pagemap_scan_is_interesting_page(categories, p))
+			continue;
+
+		ret = pagemap_scan_output(categories, p, addr, &next);
+		if (next == addr)
+			break;
+
+		if (~p->arg.flags & PM_SCAN_WP_MATCHING)
+			continue;
+		if (~categories & PAGE_IS_WRITTEN)
+			continue;
+
+		make_uffd_wp_pte(vma, addr, pte);
+		if (!flush) {
+			start = addr;
+			flush = true;
+		}
+	}
+
+	if (flush)
+		flush_tlb_range(vma, start, addr);
+
+	pte_unmap_unlock(start_pte, ptl);
+	arch_leave_lazy_mmu_mode();
+
+	cond_resched();
+	return ret;
+}
+
+#ifdef CONFIG_HUGETLB_PAGE
+static int pagemap_scan_hugetlb_entry(pte_t *ptep, unsigned long hmask,
+				      unsigned long start, unsigned long end,
+				      struct mm_walk *walk)
+{
+	struct pagemap_scan_private *p = walk->private;
+	struct vm_area_struct *vma = walk->vma;
+	unsigned long categories;
+	spinlock_t *ptl;
+	int ret = 0;
+	pte_t pte;
+
+	if (~p->arg.flags & PM_SCAN_WP_MATCHING) {
+		/* Go the short route when not write-protecting pages. */
+
+		pte = huge_ptep_get(ptep);
+		categories = p->cur_vma_category | pagemap_hugetlb_category(pte);
+
+		if (!pagemap_scan_is_interesting_page(categories, p))
+			return 0;
+
+		return pagemap_scan_output(categories, p, start, &end);
+	}
+
+	i_mmap_lock_write(vma->vm_file->f_mapping);
+	ptl = huge_pte_lock(hstate_vma(vma), vma->vm_mm, ptep);
+
+	pte = huge_ptep_get(ptep);
+	categories = p->cur_vma_category | pagemap_hugetlb_category(pte);
+
+	if (!pagemap_scan_is_interesting_page(categories, p))
+		goto out_unlock;
+
+	ret = pagemap_scan_output(categories, p, start, &end);
+	if (start == end)
+		goto out_unlock;
+
+	if (~categories & PAGE_IS_WRITTEN)
+		goto out_unlock;
+
+	if (end != start + HPAGE_SIZE) {
+		/* Partial HugeTLB page WP isn't possible. */
+		pagemap_scan_backout_range(p, start, end, start);
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	make_uffd_wp_huge_pte(vma, start, ptep, pte);
+	flush_hugetlb_tlb_range(vma, start, end);
+
+out_unlock:
+	spin_unlock(ptl);
+	i_mmap_unlock_write(vma->vm_file->f_mapping);
+
+	return ret;
+}
+#else
+#define pagemap_scan_hugetlb_entry NULL
+#endif
+
+static int pagemap_scan_pte_hole(unsigned long addr, unsigned long end,
+				 int depth, struct mm_walk *walk)
+{
+	struct pagemap_scan_private *p = walk->private;
+	struct vm_area_struct *vma = walk->vma;
+	int ret, err;
+
+	if (!vma || !pagemap_scan_is_interesting_page(p->cur_vma_category, p))
+		return 0;
+
+	ret = pagemap_scan_output(p->cur_vma_category, p, addr, &end);
+	if (addr == end)
+		return ret;
+
+	if (~p->arg.flags & PM_SCAN_WP_MATCHING)
+		return ret;
+
+	err = uffd_wp_range(vma, addr, end - addr, true);
+	if (err < 0)
+		ret = err;
+
+	return ret;
+}
+
+static const struct mm_walk_ops pagemap_scan_ops = {
+	.test_walk = pagemap_scan_test_walk,
+	.pmd_entry = pagemap_scan_pmd_entry,
+	.pte_hole = pagemap_scan_pte_hole,
+	.hugetlb_entry = pagemap_scan_hugetlb_entry,
+};
+
+static int pagemap_scan_get_args(struct pm_scan_arg *arg,
+				 unsigned long uarg)
+{
+	if (copy_from_user(arg, (void __user *)uarg, sizeof(*arg)))
+		return -EFAULT;
+
+	if (arg->size != sizeof(struct pm_scan_arg))
+		return -EINVAL;
+
+	/* Validate requested features */
+	if (arg->flags & ~PM_SCAN_FLAGS)
+		return -EINVAL;
+	if ((arg->category_inverted | arg->category_mask |
+	     arg->category_anyof_mask | arg->return_mask) & ~PM_SCAN_CATEGORIES)
+		return -EINVAL;
+
+	arg->start = untagged_addr((unsigned long)arg->start);
+	arg->end = untagged_addr((unsigned long)arg->end);
+	arg->vec = untagged_addr((unsigned long)arg->vec);
+
+	/* Validate memory pointers */
+	if (!IS_ALIGNED(arg->start, PAGE_SIZE))
+		return -EINVAL;
+	if (!access_ok((void __user *)arg->start, arg->end - arg->start))
+		return -EFAULT;
+	if (!arg->vec && arg->vec_len)
+		return -EFAULT;
+	if (arg->vec && !access_ok((void __user *)arg->vec,
+			      arg->vec_len * sizeof(struct page_region)))
+		return -EFAULT;
+
+	/* Fixup default values */
+	arg->end = ALIGN(arg->end, PAGE_SIZE);
+	if (!arg->max_pages)
+		arg->max_pages = ULONG_MAX;
+
+	return 0;
+}
+
+static int pagemap_scan_writeback_args(struct pm_scan_arg *arg,
+				       unsigned long uargl)
+{
+	struct pm_scan_arg __user *uarg	= (void __user *)uargl;
+
+	if (copy_to_user(&uarg->walk_end, &arg->walk_end, sizeof(arg->walk_end)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int pagemap_scan_init_bounce_buffer(struct pagemap_scan_private *p)
+{
+	if (!p->arg.vec_len) {
+		/*
+		 * An arbitrary non-page-aligned sentinel value for
+		 * pagemap_scan_push_range().
+		 */
+		p->cur_buf.start = p->cur_buf.end = ULLONG_MAX;
+		if (p->arg.vec)
+			p->vec_buf = ZERO_SIZE_PTR;
+		return 0;
+	}
+
+	/*
+	 * Allocate a smaller buffer to get output from inside the page
+	 * walk functions and walk the range in PAGEMAP_WALK_SIZE chunks.
+	 * The last range is always stored in p.cur_buf to allow coalescing
+	 * consecutive ranges that have the same categories returned across
+	 * walk_page_range() calls.
+	 */
+	p->vec_buf_len = min_t(size_t, PAGEMAP_WALK_SIZE >> PAGE_SHIFT,
+			       p->arg.vec_len - 1);
+	p->vec_buf = kmalloc_array(p->vec_buf_len, sizeof(*p->vec_buf),
+				   GFP_KERNEL);
+	if (!p->vec_buf)
+		return -ENOMEM;
+
+	p->vec_out = (struct page_region __user *)p->arg.vec;
+
+	return 0;
+}
+
+static int pagemap_scan_flush_buffer(struct pagemap_scan_private *p)
+{
+	const struct page_region *buf = p->vec_buf;
+	int n = (int)p->vec_buf_index;
+
+	if (!n)
+		return 0;
+
+	if (copy_to_user(p->vec_out, buf, n * sizeof(*buf)))
+		return -EFAULT;
+
+	p->arg.vec_len -= n;
+	p->vec_out += n;
+
+	p->vec_buf_index = 0;
+	p->vec_buf_len = min_t(size_t, p->vec_buf_len, p->arg.vec_len - 1);
+
+	return n;
+}
+
+static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg)
+{
+	struct mmu_notifier_range range;
+	struct pagemap_scan_private p;
+	unsigned long walk_start;
+	size_t n_ranges_out = 0;
+	int ret;
+
+	memset(&p, 0, sizeof(p));
+	ret = pagemap_scan_get_args(&p.arg, uarg);
+	if (ret)
+		return ret;
+
+	p.masks_of_interest = MASKS_OF_INTEREST(p.arg);
+	ret = pagemap_scan_init_bounce_buffer(&p);
+	if (ret)
+		return ret;
+
+	/* Protection change for the range is going to happen. */
+	if (p.arg.flags & PM_SCAN_WP_MATCHING) {
+		mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0,
+					mm, p.arg.start, p.arg.end);
+		mmu_notifier_invalidate_range_start(&range);
+	}
+
+	walk_start = p.arg.start;
+	for (; walk_start < p.arg.end; walk_start = p.arg.walk_end) {
+		int n_out;
+
+		if (fatal_signal_pending(current)) {
+			ret = -EINTR;
+			break;
+		}
+
+		ret = mmap_read_lock_killable(mm);
+		if (ret)
+			break;
+		ret = walk_page_range(mm, walk_start, p.arg.end,
+				      &pagemap_scan_ops, &p);
+		mmap_read_unlock(mm);
+
+		n_out = pagemap_scan_flush_buffer(&p);
+		if (n_out < 0)
+			ret = n_out;
+		else
+			n_ranges_out += n_out;
+
+		if (!ret)
+			p.walk_end_addr = p.arg.end;
+
+		if (ret != -ENOSPC || p.arg.vec_len - 1 == 0 ||
+		    p.found_pages == p.arg.max_pages)
+			break;
+	}
+
+	if (p.cur_buf.start != p.cur_buf.end) {
+		if (copy_to_user(p.vec_out, &p.cur_buf, sizeof(p.cur_buf)))
+			ret = -EFAULT;
+		else
+			++n_ranges_out;
+	}
+
+	/* ENOSPC signifies early stop (buffer full) from the walk. */
+	if (!ret || ret == -ENOSPC)
+		ret = n_ranges_out;
+
+	p.arg.walk_end = p.walk_end_addr ? p.walk_end_addr : walk_start;
+	if (pagemap_scan_writeback_args(&p.arg, uarg))
+		ret = -EFAULT;
+
+	if (p.arg.flags & PM_SCAN_WP_MATCHING)
+		mmu_notifier_invalidate_range_end(&range);
+
+	kfree(p.vec_buf);
+	return ret;
+}
+
+static long do_pagemap_cmd(struct file *file, unsigned int cmd,
+			   unsigned long arg)
+{
+	struct mm_struct *mm = file->private_data;
+
+	switch (cmd) {
+	case PAGEMAP_SCAN:
+		return do_pagemap_scan(mm, arg);
+
+	default:
+		return -EINVAL;
+	}
+}
+
 const struct file_operations proc_pagemap_operations = {
 	.llseek		= mem_lseek, /* borrow this */
 	.read		= pagemap_read,
 	.open		= pagemap_open,
 	.release	= pagemap_release,
+	.unlocked_ioctl = do_pagemap_cmd,
+	.compat_ioctl	= do_pagemap_cmd,
 };
 #endif /* CONFIG_PROC_PAGE_MONITOR */
 
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 0a393bc02f25b..8f8ff07453f22 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -259,6 +259,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma,
 		unsigned long cp_flags);
 
 bool is_hugetlb_entry_migration(pte_t pte);
+bool is_hugetlb_entry_hwpoisoned(pte_t pte);
 void hugetlb_unshare_all_pmds(struct vm_area_struct *vma);
 
 #else /* !CONFIG_HUGETLB_PAGE */
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index b7b56871029c5..1c9d38af1015e 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -305,4 +305,63 @@ typedef int __bitwise __kernel_rwf_t;
 #define RWF_SUPPORTED	(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
 			 RWF_APPEND)
 
+/* Pagemap ioctl */
+#define PAGEMAP_SCAN	_IOWR('f', 16, struct pm_scan_arg)
+
+/* Bits are set in flags of the page_region and masks in pm_scan_args */
+#define PAGE_IS_WPALLOWED	(1 << 0)
+#define PAGE_IS_WRITTEN		(1 << 1)
+#define PAGE_IS_FILE		(1 << 2)
+#define PAGE_IS_PRESENT		(1 << 3)
+#define PAGE_IS_SWAPPED		(1 << 4)
+#define PAGE_IS_PFNZERO		(1 << 5)
+#define PAGE_IS_HUGE		(1 << 6)
+
+/*
+ * struct page_region - Page region with flags
+ * @start:	Start of the region
+ * @end:	End of the region (exclusive)
+ * @categories:	PAGE_IS_* category bitmask for the region
+ */
+struct page_region {
+	__u64 start;
+	__u64 end;
+	__u64 categories;
+};
+
+/* Flags for PAGEMAP_SCAN ioctl */
+#define PM_SCAN_WP_MATCHING	(1 << 0)	/* Write protect the pages matched. */
+#define PM_SCAN_CHECK_WPASYNC	(1 << 1)	/* Abort the scan when a non-WP-enabled page is found. */
+
+/*
+ * struct pm_scan_arg - Pagemap ioctl argument
+ * @size:		Size of the structure
+ * @flags:		Flags for the IOCTL
+ * @start:		Starting address of the region
+ * @end:		Ending address of the region
+ * @walk_end		Address where the scan stopped (written by kernel).
+ *			walk_end == end informs that the scan completed on entire range.
+ * @vec:		Address of page_region struct array for output
+ * @vec_len:		Length of the page_region struct array
+ * @max_pages:		Optional limit for number of returned pages (0 = disabled)
+ * @category_inverted:	PAGE_IS_* categories which values match if 0 instead of 1
+ * @category_mask:	Skip pages for which any category doesn't match
+ * @category_anyof_mask: Skip pages for which no category matches
+ * @return_mask:	PAGE_IS_* categories that are to be reported in `page_region`s returned
+ */
+struct pm_scan_arg {
+	__u64 size;
+	__u64 flags;
+	__u64 start;
+	__u64 end;
+	__u64 walk_end;
+	__u64 vec;
+	__u64 vec_len;
+	__u64 max_pages;
+	__u64 category_inverted;
+	__u64 category_mask;
+	__u64 category_anyof_mask;
+	__u64 return_mask;
+};
+
 #endif /* _UAPI_LINUX_FS_H */
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a073e6ed8900b..3b07db0a4f2d9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5008,7 +5008,7 @@ bool is_hugetlb_entry_migration(pte_t pte)
 		return false;
 }
 
-static bool is_hugetlb_entry_hwpoisoned(pte_t pte)
+bool is_hugetlb_entry_hwpoisoned(pte_t pte)
 {
 	swp_entry_t swp;
 
-- 
2.39.2

[PATCH v28 3/6] fs/proc/task_mmu: Add fast paths to get/clear PAGE_IS_WRITTEN flag

[Muhammad Usama Anjum]

Adding fast code paths to handle specifically only get and/or clear
operation of PAGE_IS_WRITTEN, increases its performance by 0-35%.
The results of some test cases are given below:

Test-case-1
t1 = (Get + WP) time
t2 = WP time
                       t1            t2
Without this patch:    140-170mcs    90-115mcs
With this patch:       110mcs        80mcs
Worst case diff:       35% faster    30% faster

Test-case-2
t3 = atomic Get and WP
                      t3
Without this patch:   120-140mcs
With this patch:      100-110mcs
Worst case diff:      21% faster

Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
---
The test to measure the performance can be found: https://is.gd/FtSKcD
8 8192 3 1 0 and 8 8192 3 1 1 arguments have been used to produce the
above mentioned results.
---
 fs/proc/task_mmu.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 0e219a44e97cd..e336ec0151185 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -2107,6 +2107,43 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
 		return 0;
 	}
 
+	if (!p->vec_out) {
+		/* Fast path for performing exclusive WP */
+		for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
+			if (pte_uffd_wp(ptep_get(pte)))
+				continue;
+			make_uffd_wp_pte(vma, addr, pte);
+			if (!flush) {
+				start = addr;
+				flush = true;
+			}
+		}
+		goto flush_and_return;
+	}
+
+	if (!p->arg.category_anyof_mask && !p->arg.category_inverted &&
+	    p->arg.category_mask == PAGE_IS_WRITTEN &&
+	    p->arg.return_mask == PAGE_IS_WRITTEN) {
+		for (addr = start; addr < end; pte++, addr += PAGE_SIZE) {
+			unsigned long next = addr + PAGE_SIZE;
+
+			if (pte_uffd_wp(ptep_get(pte)))
+				continue;
+			ret = pagemap_scan_output(p->cur_vma_category | PAGE_IS_WRITTEN,
+						  p, addr, &next);
+			if (next == addr)
+				break;
+			if (~p->arg.flags & PM_SCAN_WP_MATCHING)
+				continue;
+			make_uffd_wp_pte(vma, addr, pte);
+			if (!flush) {
+				start = addr;
+				flush = true;
+			}
+		}
+		goto flush_and_return;
+	}
+
 	for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
 		unsigned long categories = p->cur_vma_category |
 					   pagemap_page_category(p, vma, addr, ptep_get(pte));
@@ -2131,6 +2168,7 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
 		}
 	}
 
+flush_and_return:
 	if (flush)
 		flush_tlb_range(vma, start, addr);
 
-- 
2.39.2

[PATCH v28 4/6] tools headers UAPI: Update linux/fs.h with the kernel sources

[Muhammad Usama Anjum]

New IOCTL and macros has been added in the kernel sources. Update the
tools header file as well.

Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
---
Changes in v27:
- Comment updates in fs.h

Changes in v26:
- Update according to tools/include/uapi/linux/fs.h

Changes in v21:
- Update tools/include/uapi/linux/fs.h

Changes in v19:
- Update fs.h according to precious patch
---
 tools/include/uapi/linux/fs.h | 59 +++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/tools/include/uapi/linux/fs.h b/tools/include/uapi/linux/fs.h
index b7b56871029c5..1c9d38af1015e 100644
--- a/tools/include/uapi/linux/fs.h
+++ b/tools/include/uapi/linux/fs.h
@@ -305,4 +305,63 @@ typedef int __bitwise __kernel_rwf_t;
 #define RWF_SUPPORTED	(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
 			 RWF_APPEND)
 
+/* Pagemap ioctl */
+#define PAGEMAP_SCAN	_IOWR('f', 16, struct pm_scan_arg)
+
+/* Bits are set in flags of the page_region and masks in pm_scan_args */
+#define PAGE_IS_WPALLOWED	(1 << 0)
+#define PAGE_IS_WRITTEN		(1 << 1)
+#define PAGE_IS_FILE		(1 << 2)
+#define PAGE_IS_PRESENT		(1 << 3)
+#define PAGE_IS_SWAPPED		(1 << 4)
+#define PAGE_IS_PFNZERO		(1 << 5)
+#define PAGE_IS_HUGE		(1 << 6)
+
+/*
+ * struct page_region - Page region with flags
+ * @start:	Start of the region
+ * @end:	End of the region (exclusive)
+ * @categories:	PAGE_IS_* category bitmask for the region
+ */
+struct page_region {
+	__u64 start;
+	__u64 end;
+	__u64 categories;
+};
+
+/* Flags for PAGEMAP_SCAN ioctl */
+#define PM_SCAN_WP_MATCHING	(1 << 0)	/* Write protect the pages matched. */
+#define PM_SCAN_CHECK_WPASYNC	(1 << 1)	/* Abort the scan when a non-WP-enabled page is found. */
+
+/*
+ * struct pm_scan_arg - Pagemap ioctl argument
+ * @size:		Size of the structure
+ * @flags:		Flags for the IOCTL
+ * @start:		Starting address of the region
+ * @end:		Ending address of the region
+ * @walk_end		Address where the scan stopped (written by kernel).
+ *			walk_end == end informs that the scan completed on entire range.
+ * @vec:		Address of page_region struct array for output
+ * @vec_len:		Length of the page_region struct array
+ * @max_pages:		Optional limit for number of returned pages (0 = disabled)
+ * @category_inverted:	PAGE_IS_* categories which values match if 0 instead of 1
+ * @category_mask:	Skip pages for which any category doesn't match
+ * @category_anyof_mask: Skip pages for which no category matches
+ * @return_mask:	PAGE_IS_* categories that are to be reported in `page_region`s returned
+ */
+struct pm_scan_arg {
+	__u64 size;
+	__u64 flags;
+	__u64 start;
+	__u64 end;
+	__u64 walk_end;
+	__u64 vec;
+	__u64 vec_len;
+	__u64 max_pages;
+	__u64 category_inverted;
+	__u64 category_mask;
+	__u64 category_anyof_mask;
+	__u64 return_mask;
+};
+
 #endif /* _UAPI_LINUX_FS_H */
-- 
2.39.2

[PATCH v28 5/6] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL

[Muhammad Usama Anjum]

Add some explanation and method to use write-protection and written-to
on memory range.

Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
---
Changes in v26:
- Update documentation according to latest revision

Changes in v21:
- Update according to changed interface

Changes in v20:
- Add new flag in documentation

Changes in v19:
- Improved documentatiom with punctuation marks

Changes in v16:
- Update the documentation

Changes in v11:
- Add more documentation
---
 Documentation/admin-guide/mm/pagemap.rst | 64 ++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index c8f380271cad8..ea18e4575902a 100644
--- a/Documentation/admin-guide/mm/pagemap.rst
+++ b/Documentation/admin-guide/mm/pagemap.rst
@@ -227,3 +227,67 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is
 always 12 at most architectures). Since Linux 3.11 their meaning changes
 after first clear of soft-dirty bits. Since Linux 4.2 they are used for
 flags unconditionally.
+
+Pagemap Scan IOCTL
+==================
+
+The ``PAGEMAP_SCAN`` IOCTL on the pagemap file can be used to get or optionally
+clear the info about page table entries. The following operations are supported
+in this IOCTL:
+- Get the information if the pages have Async Write-Protection enabled
+  (``PAGE_IS_WPALLOWED``), have been written to (``PAGE_IS_WRITTEN``), file mapped
+  (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``), swapped (``PAGE_IS_SWAPPED``)
+  or page has pfn zero (``PAGE_IS_PFNZERO``).
+- Find pages which have been written to and/or write protect
+  (atomic ``PM_SCAN_WP_MATCHING + PM_SCAN_CHECK_WPASYNC``) the pages atomically.
+  The (``PM_SCAN_WP_MATCHING``) is used to WP the matched pages. The
+  (``PM_SCAN_CHECK_WPASYNC``) aborts the operation if non-Async-Write-Protected
+  pages are found.
+
+The ``struct pm_scan_arg`` is used as the argument of the IOCTL.
+ 1. The size of the ``struct pm_scan_arg`` must be specified in the ``size``
+    field. This field will be helpful in recognizing the structure if extensions
+    are done later.
+ 2. The flags can be specified in the ``flags`` field. The ``PM_SCAN_WP_MATCHING``
+    and ``PM_SCAN_CHECK_WPASYNC`` are the only added flags at this time. The get
+    operation is optionally performed depending upon if the output buffer is
+    provided or not.
+ 3. The range is specified through ``start`` and ``end``.
+ 4. The output buffer of ``struct page_region`` array and size is specified in
+    ``vec`` and ``vec_len``.
+ 5. The optional maximum requested pages are specified in the ``max_pages``.
+ 6. The masks are specified in ``category_mask``, ``category_anyof_mask``,
+    ``category_inverted`` and ``return_mask``.
+    1.  To find if ``PAGE_IS_WRITTEN`` flag is set for pages which have
+        ``PAGE_IS_FILE`` set and ``PAGE_IS_SWAPPED`` unset, ``category_mask``
+        is set to ``PAGE_IS_FILE | PAGE_IS_SWAPPED``, ``category_inverted`` is
+        set to ``PAGE_IS_SWAPPED`` and ``return_mask`` is set to ``PAGE_IS_WRITTEN``.
+        The output buffer in ``vec`` and length must be specified in ``vec_len``.
+    2. To find pages which have either ``PAGE_IS_FILE`` or ``PAGE_IS_SWAPPED``
+       set, ``category_anyof_mask`` is set to  ``PAGE_IS_FILE | PAGE_IS_SWAPPED``.
+    3. To find written pages and engage write protect, ``PAGE_IS_WRITTEN`` is
+       specified in ``category_mask`` and ``return_mask``. In addition to
+       specifying the output buffer in ``vec`` and length in ``vec_len``, the
+       ``PM_SCAN_WP_MATCHING`` is specified in ``flags`` to perform write protect
+       on the range as well.
+
+The ``PAGE_IS_WRITTEN`` flag can be considered as the better and correct
+alternative of soft-dirty flag. It doesn't get affected by housekeeping chores
+(VMA merging) of the kernel and hence the user can find the true soft-dirty pages
+only. This IOCTL adds the atomic way to find which pages have been written and
+write protect those pages again. This kind of operation is needed to efficiently
+find out which pages have changed in the memory.
+
+To get information about which pages have been written to or optionally write
+protect the pages, following must be performed first in order:
+ 1. The userfaultfd file descriptor is created with ``userfaultfd`` syscall.
+ 2. The ``UFFD_FEATURE_WP_UNPOPULATED`` and ``UFFD_FEATURE_WP_ASYNC`` features
+    are set by ``UFFDIO_API`` IOCTL.
+ 3. The memory range is registered with ``UFFDIO_REGISTER_MODE_WP`` mode
+    through ``UFFDIO_REGISTER`` IOCTL.
+ 4. Then any part of the registered memory or the whole memory region must
+    be write protected using ``PAGEMAP_SCAN`` IOCTL with flag ``PM_SCAN_OP_WP``
+    or the ``UFFDIO_WRITEPROTECT`` IOCTL can be used. Both of these perform the
+    same operation. The former is better in terms of performance.
+ 5. Now the ``PAGEMAP_SCAN`` IOCTL can be used to either just find pages which
+    have been written to and/or optionally write protect the pages as well.
-- 
2.39.2

[PATCH v28 6/6] selftests: mm: add pagemap ioctl tests

[Muhammad Usama Anjum]

Add pagemap ioctl tests. Add several different types of tests to judge
the correction of the interface.

Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
---
Changes in v28:
- Add walk_end tests

Changes in v27:
- Open the pagemap file with O_RDONLY
- Use UFFD_USER_MODE_ONLY flag for userfaultfd() syscall

Changes in v26:
- Updates

Changes in v19:
- Incorporated interface changes and update tests

Changes in v18:
- Rebase on top of 20230613 (Resolve conflict in Makefile)
- Add temp files to .gitignore

Changes in v17:
- Rebase on top of next-20230525

Changes in v16:
- Added yet more tests which is a randomization test case to catch the
  corner cases
- Add reset by exclusive PM_SCAN_OP_WP as well

Changes in v13:
- Update tests and rebase Makefile

Changes in v12:
- Updates and add more memory type tests

Changes in v11:
- Rebase on top of next-20230216 and update tests

Chages in v7:
- Add and update all test cases

Changes in v6:
- Rename variables

Changes in v4:
- Updated all the tests to conform to new IOCTL

Changes in v3:
- Add another test to do sanity of flags

Changes in v2:
- Update the tests to use the ioctl interface instead of syscall
---
TAP version 13
1..108
ok 1 sanity_tests_sd Zero range size is valid
ok 2 sanity_tests_sd output buffer must be specified with size
ok 3 sanity_tests_sd output buffer can be 0
ok 4 sanity_tests_sd wrong flag specified
ok 5 sanity_tests_sd flag has extra bits specified
ok 6 sanity_tests_sd no selection mask is specified
ok 7 sanity_tests_sd no return mask is specified
ok 8 sanity_tests_sd wrong return mask specified
ok 9 sanity_tests_sd mixture of correct and wrong flag
ok 10 sanity_tests_sd PAGEMAP_BITS_ALL can be specified with PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC
ok 11 sanity_tests_sd Clear area with larger vec size
ok 12 sanity_tests_sd Repeated pattern of written and non-written pages
ok 13 sanity_tests_sd Repeated pattern of written and non-written pages in parts 3 2 2
ok 14 sanity_tests_sd Repeated pattern of written and non-written pages max_pages
ok 15 sanity_tests_sd only get 2 written pages and clear them as well
ok 16 sanity_tests_sd Two regions
ok 17 sanity_tests_sd Smaller max_pages
ok 18 Smaller vec
ok 19 Walk_end: Same start and end address
ok 20 Walk_end: Same start and end with WP
ok 21 Walk_end: Same start and end with 0 output buffer
ok 22 Walk_end: Big vec
ok 23 Walk_end: vec of minimum length
ok 24 Walk_end: Max pages specified
ok 25 Walk_end: Half max pages
ok 26 Walk_end: 1 max page
ok 27 Walk_end: max pages
ok 28 Walk_end sparse: Big vec
ok 29 Walk_end sparse: vec of minimum length
ok 30 Walk_end sparse: Max pages specified
ok 31 Walk_end sparse: Max pages specified
ok 32 Walk_end sparse: Max pages specified
ok 33 Walk_endsparse : Half max pages
ok 34 Walk_end: 1 max page
ok 35 Page testing: all new pages must not be written (dirty)
ok 36 Page testing: all pages must be written (dirty)
ok 37 Page testing: all pages dirty other than first and the last one
ok 38 Page testing: PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC
ok 39 Page testing: only middle page dirty
ok 40 Page testing: only two middle pages dirty
ok 41 Large Page testing: all new pages must not be written (dirty)
ok 42 Large Page testing: all pages must be written (dirty)
ok 43 Large Page testing: all pages dirty other than first and the last one
ok 44 Large Page testing: PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC
ok 45 Large Page testing: only middle page dirty
ok 46 Large Page testing: only two middle pages dirty
ok 47 Huge page testing: all new pages must not be written (dirty)
ok 48 Huge page testing: all pages must be written (dirty)
ok 49 Huge page testing: all pages dirty other than first and the last one
ok 50 Huge page testing: PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC
ok 51 Huge page testing: only middle page dirty
ok 52 Huge page testing: only two middle pages dirty
ok 53 Hugetlb shmem testing: all new pages must not be written (dirty)
ok 54 Hugetlb shmem testing: all pages must be written (dirty)
ok 55 Hugetlb shmem testing: all pages dirty other than first and the last one
ok 56 Hugetlb shmem testing: PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC
ok 57 Hugetlb shmem testing: only middle page dirty
ok 58 Hugetlb shmem testing: only two middle pages dirty
ok 59 Hugetlb mem testing: all new pages must not be written (dirty)
ok 60 Hugetlb mem testing: all pages must be written (dirty)
ok 61 Hugetlb mem testing: all pages dirty other than first and the last one
ok 62 Hugetlb mem testing: PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC
ok 63 Hugetlb mem testing: only middle page dirty
ok 64 Hugetlb mem testing: only two middle pages dirty
ok 65 File memory testing: all new pages must not be written (dirty)
ok 66 File memory testing: all pages must be written (dirty)
ok 67 File memory testing: all pages dirty other than first and the last one
ok 68 File memory testing: PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC
ok 69 File memory testing: only middle page dirty
ok 70 File memory testing: only two middle pages dirty
ok 71 File anonymous memory testing: all new pages must not be written (dirty)
ok 72 File anonymous memory testing: all pages must be written (dirty)
ok 73 File anonymous memory testing: all pages dirty other than first and the last one
ok 74 File anonymous memory testing: PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC
ok 75 File anonymous memory testing: only middle page dirty
ok 76 File anonymous memory testing: only two middle pages dirty
ok 77 hpage_unit_tests all new huge page must not be written (dirty)
ok 78 hpage_unit_tests all the huge page must not be written
ok 79 hpage_unit_tests all the huge page must be written and clear
ok 80 hpage_unit_tests only middle page written
ok 81 hpage_unit_tests clear first half of huge page
ok 82 hpage_unit_tests clear first half of huge page with limited buffer
ok 83 hpage_unit_tests clear second half huge page
ok 84 hpage_unit_tests get half huge page
ok 85 hpage_unit_tests get half huge page
ok 86 Test test_simple
ok 87 mprotect_tests Both pages written
ok 88 mprotect_tests Both pages are not written (dirty)
ok 89 mprotect_tests Both pages written after remap and mprotect
ok 90 mprotect_tests Clear and make the pages written
ok 91 transact_test count 192
ok 92 transact_test count 0
ok 93 transact_test Extra pages 1 (0.0%), extra thread faults 1.
ok 94 sanity_tests WP op can be specified with !PAGE_IS_WRITTEN
ok 95 sanity_tests required_mask specified
ok 96 sanity_tests anyof_mask specified
ok 97 sanity_tests excluded_mask specified
ok 98 sanity_tests required_mask and anyof_mask specified
ok 99 sanity_tests Get sd and present pages with anyof_mask
ok 100 sanity_tests Get all the pages with required_mask
ok 101 sanity_tests Get sd and present pages with required_mask and anyof_mask
ok 102 sanity_tests Don't get sd pages
ok 103 sanity_tests Don't get present pages
ok 104 sanity_tests Find written present pages with return mask
ok 105 sanity_tests Memory mapped file
ok 106 sanity_tests Read/write to memory
ok 107 unmapped_region_tests Get status of pages
ok 108 userfaultfd_tests all new pages must not be written (dirty)
 # Totals: pass:108 fail:0 xfail:0 xpass:0 skip:0 error:0
---
 tools/testing/selftests/mm/.gitignore      |    2 +
 tools/testing/selftests/mm/Makefile        |    3 +-
 tools/testing/selftests/mm/config          |    1 +
 tools/testing/selftests/mm/pagemap_ioctl.c | 1658 ++++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh  |    4 +
 5 files changed, 1667 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/mm/pagemap_ioctl.c

diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
index cdc9ce4426b95..cc920c79ff1c3 100644
--- a/tools/testing/selftests/mm/.gitignore
+++ b/tools/testing/selftests/mm/.gitignore
@@ -18,6 +18,8 @@ mremap_dontunmap
 mremap_test
 on-fault-limit
 transhuge-stress
+pagemap_ioctl
+*.tmp*
 protection_keys
 protection_keys_32
 protection_keys_64
diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index b7fce9073279e..1dac4e8477e48 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -33,7 +33,7 @@ endif
 MAKEFLAGS += --no-builtin-rules
 
 CFLAGS = -Wall -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
-LDLIBS = -lrt -lpthread
+LDLIBS = -lrt -lpthread -lm
 
 TEST_GEN_PROGS = cow
 TEST_GEN_PROGS += compaction_test
@@ -60,6 +60,7 @@ TEST_GEN_PROGS += mrelease_test
 TEST_GEN_PROGS += mremap_dontunmap
 TEST_GEN_PROGS += mremap_test
 TEST_GEN_PROGS += on-fault-limit
+TEST_GEN_PROGS += pagemap_ioctl
 TEST_GEN_PROGS += thuge-gen
 TEST_GEN_PROGS += transhuge-stress
 TEST_GEN_PROGS += uffd-stress
diff --git a/tools/testing/selftests/mm/config b/tools/testing/selftests/mm/config
index be087c4bc3961..4309916f629e3 100644
--- a/tools/testing/selftests/mm/config
+++ b/tools/testing/selftests/mm/config
@@ -1,5 +1,6 @@
 CONFIG_SYSVIPC=y
 CONFIG_USERFAULTFD=y
+CONFIG_PTE_MARKER_UFFD_WP=y
 CONFIG_TEST_VMALLOC=m
 CONFIG_DEVICE_PRIVATE=y
 CONFIG_TEST_HMM=m
diff --git a/tools/testing/selftests/mm/pagemap_ioctl.c b/tools/testing/selftests/mm/pagemap_ioctl.c
new file mode 100644
index 0000000000000..9313beddb23d9
--- /dev/null
+++ b/tools/testing/selftests/mm/pagemap_ioctl.c
@@ -0,0 +1,1658 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <errno.h>
+#include <malloc.h>
+#include "vm_util.h"
+#include "../kselftest.h"
+#include <linux/types.h>
+#include <linux/memfd.h>
+#include <linux/userfaultfd.h>
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <math.h>
+#include <asm/unistd.h>
+#include <pthread.h>
+#include <sys/resource.h>
+#include <assert.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+
+#define PAGEMAP_BITS_ALL		(PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN |	\
+					 PAGE_IS_FILE | PAGE_IS_PRESENT |	\
+					 PAGE_IS_SWAPPED | PAGE_IS_PFNZERO |	\
+					 PAGE_IS_HUGE)
+#define PAGEMAP_NON_WRITTEN_BITS	(PAGE_IS_WPALLOWED | PAGE_IS_FILE |	\
+					 PAGE_IS_PRESENT | PAGE_IS_SWAPPED |	\
+					 PAGE_IS_PFNZERO | PAGE_IS_HUGE)
+
+#define TEST_ITERATIONS 100
+#define PAGEMAP "/proc/self/pagemap"
+int pagemap_fd;
+int uffd;
+int page_size;
+int hpage_size;
+
+#define LEN(region)	((region.end - region.start)/page_size)
+
+static long pagemap_ioctl(void *start, int len, void *vec, int vec_len, int flag,
+			  int max_pages, long required_mask, long anyof_mask, long excluded_mask,
+			  long return_mask)
+{
+	struct pm_scan_arg arg;
+
+	arg.start = (uintptr_t)start;
+	arg.end = (uintptr_t)(start + len);
+	arg.vec = (uintptr_t)vec;
+	arg.vec_len = vec_len;
+	arg.flags = flag;
+	arg.size = sizeof(struct pm_scan_arg);
+	arg.max_pages = max_pages;
+	arg.category_mask = required_mask;
+	arg.category_anyof_mask = anyof_mask;
+	arg.category_inverted = excluded_mask;
+	arg.return_mask = return_mask;
+
+	return ioctl(pagemap_fd, PAGEMAP_SCAN, &arg);
+}
+
+static long pagemap_ioc(void *start, int len, void *vec, int vec_len, int flag,
+			int max_pages, long required_mask, long anyof_mask, long excluded_mask,
+			long return_mask, long *walk_end)
+{
+	struct pm_scan_arg arg;
+	int ret;
+
+	arg.start = (uintptr_t)start;
+	arg.end = (uintptr_t)(start + len);
+	arg.vec = (uintptr_t)vec;
+	arg.vec_len = vec_len;
+	arg.flags = flag;
+	arg.size = sizeof(struct pm_scan_arg);
+	arg.max_pages = max_pages;
+	arg.category_mask = required_mask;
+	arg.category_anyof_mask = anyof_mask;
+	arg.category_inverted = excluded_mask;
+	arg.return_mask = return_mask;
+
+	ret = ioctl(pagemap_fd, PAGEMAP_SCAN, &arg);
+
+	if (walk_end)
+		*walk_end = arg.walk_end;
+
+	return ret;
+}
+
+
+int init_uffd(void)
+{
+	struct uffdio_api uffdio_api;
+
+	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
+	if (uffd == -1)
+		ksft_exit_fail_msg("uffd syscall failed\n");
+
+	uffdio_api.api = UFFD_API;
+	uffdio_api.features = UFFD_FEATURE_WP_UNPOPULATED | UFFD_FEATURE_WP_ASYNC |
+			      UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
+	if (ioctl(uffd, UFFDIO_API, &uffdio_api))
+		ksft_exit_fail_msg("UFFDIO_API\n");
+
+	if (!(uffdio_api.api & UFFDIO_REGISTER_MODE_WP) ||
+	    !(uffdio_api.features & UFFD_FEATURE_WP_UNPOPULATED) ||
+	    !(uffdio_api.features & UFFD_FEATURE_WP_ASYNC) ||
+	    !(uffdio_api.features & UFFD_FEATURE_WP_HUGETLBFS_SHMEM))
+		ksft_exit_fail_msg("UFFDIO_API error %llu\n", uffdio_api.api);
+
+	return 0;
+}
+
+int wp_init(void *lpBaseAddress, int dwRegionSize)
+{
+	struct uffdio_register uffdio_register;
+	struct uffdio_writeprotect wp;
+
+	uffdio_register.range.start = (unsigned long)lpBaseAddress;
+	uffdio_register.range.len = dwRegionSize;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_WP;
+	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
+		ksft_exit_fail_msg("ioctl(UFFDIO_REGISTER) %d %s\n", errno, strerror(errno));
+
+	if (!(uffdio_register.ioctls & UFFDIO_WRITEPROTECT))
+		ksft_exit_fail_msg("ioctl set is incorrect\n");
+
+	wp.range.start = (unsigned long)lpBaseAddress;
+	wp.range.len = dwRegionSize;
+	wp.mode = UFFDIO_WRITEPROTECT_MODE_WP;
+
+	if (ioctl(uffd, UFFDIO_WRITEPROTECT, &wp))
+		ksft_exit_fail_msg("ioctl(UFFDIO_WRITEPROTECT)\n");
+
+	return 0;
+}
+
+int wp_free(void *lpBaseAddress, int dwRegionSize)
+{
+	struct uffdio_register uffdio_register;
+
+	uffdio_register.range.start = (unsigned long)lpBaseAddress;
+	uffdio_register.range.len = dwRegionSize;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_WP;
+	if (ioctl(uffd, UFFDIO_UNREGISTER, &uffdio_register.range))
+		ksft_exit_fail_msg("ioctl unregister failure\n");
+	return 0;
+}
+
+int wp_addr_range(void *lpBaseAddress, int dwRegionSize)
+{
+	struct uffdio_writeprotect wp;
+
+	if (rand() % 2) {
+		wp.range.start = (unsigned long)lpBaseAddress;
+		wp.range.len = dwRegionSize;
+		wp.mode = UFFDIO_WRITEPROTECT_MODE_WP;
+
+		if (ioctl(uffd, UFFDIO_WRITEPROTECT, &wp))
+			ksft_exit_fail_msg("ioctl(UFFDIO_WRITEPROTECT)\n");
+	} else {
+		if (pagemap_ioctl(lpBaseAddress, dwRegionSize, NULL, 0,
+				  PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				  0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN) < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", 1, errno, strerror(errno));
+	}
+
+	return 0;
+}
+
+void *gethugetlb_mem(int size, int *shmid)
+{
+	char *mem;
+
+	if (shmid) {
+		*shmid = shmget(2, size, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
+		if (*shmid < 0)
+			return NULL;
+
+		mem = shmat(*shmid, 0, 0);
+		if (mem == (char *)-1) {
+			shmctl(*shmid, IPC_RMID, NULL);
+			ksft_exit_fail_msg("Shared memory attach failure\n");
+		}
+	} else {
+		mem = mmap(NULL, size, PROT_READ | PROT_WRITE,
+			   MAP_ANONYMOUS | MAP_HUGETLB | MAP_PRIVATE, -1, 0);
+		if (mem == MAP_FAILED)
+			return NULL;
+	}
+
+	return mem;
+}
+
+int userfaultfd_tests(void)
+{
+	int mem_size, vec_size, written, num_pages = 16;
+	char *mem, *vec;
+
+	mem_size = num_pages * page_size;
+	mem = mmap(NULL, mem_size, PROT_NONE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+
+	wp_init(mem, mem_size);
+
+	/* Change protection of pages differently */
+	mprotect(mem, mem_size/8, PROT_READ|PROT_WRITE);
+	mprotect(mem + 1 * mem_size/8, mem_size/8, PROT_READ);
+	mprotect(mem + 2 * mem_size/8, mem_size/8, PROT_READ|PROT_WRITE);
+	mprotect(mem + 3 * mem_size/8, mem_size/8, PROT_READ);
+	mprotect(mem + 4 * mem_size/8, mem_size/8, PROT_READ|PROT_WRITE);
+	mprotect(mem + 5 * mem_size/8, mem_size/8, PROT_NONE);
+	mprotect(mem + 6 * mem_size/8, mem_size/8, PROT_READ|PROT_WRITE);
+	mprotect(mem + 7 * mem_size/8, mem_size/8, PROT_READ);
+
+	wp_addr_range(mem + (mem_size/16), mem_size - 2 * (mem_size/8));
+	wp_addr_range(mem, mem_size);
+
+	vec_size = mem_size/page_size;
+	vec = malloc(sizeof(struct page_region) * vec_size);
+
+	written = pagemap_ioctl(mem, mem_size, vec, 1, PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				vec_size - 2, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	ksft_test_result(written == 0, "%s all new pages must not be written (dirty)\n", __func__);
+
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+	free(vec);
+	return 0;
+}
+
+int get_reads(struct page_region *vec, int vec_size)
+{
+	int i, sum = 0;
+
+	for (i = 0; i < vec_size; i++)
+		sum += LEN(vec[i]);
+
+	return sum;
+}
+
+int sanity_tests_sd(void)
+{
+	int mem_size, vec_size, ret, ret2, ret3, i, num_pages = 10, total_pages = 0;
+	int total_writes, total_reads, reads, count;
+	struct page_region *vec, *vec2;
+	char *mem, *m[2];
+	long walk_end;
+
+	vec_size = 100;
+	mem_size = num_pages * page_size;
+
+	vec = malloc(sizeof(struct page_region) * vec_size);
+	if (!vec)
+		ksft_exit_fail_msg("error nomem\n");
+
+	vec2 = malloc(sizeof(struct page_region) * vec_size);
+	if (!vec2)
+		ksft_exit_fail_msg("error nomem\n");
+
+	mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+
+	wp_init(mem, mem_size);
+	wp_addr_range(mem, mem_size);
+
+	/* 1. wrong operation */
+	ksft_test_result(pagemap_ioctl(mem, 0, vec, vec_size, 0,
+				       0, PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL) == 0,
+			 "%s Zero range size is valid\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, NULL, vec_size, 0,
+				       0, PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL) < 0,
+			 "%s output buffer must be specified with size\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, 0, 0,
+				       0, PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL) == 0,
+			 "%s output buffer can be 0\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size, -1,
+				       0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN) < 0,
+			 "%s wrong flag specified\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size,
+				       PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC | 0xFF,
+				       0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN) < 0,
+			 "%s flag has extra bits specified\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size, 0,
+				       0, 0, 0, 0, PAGE_IS_WRITTEN) >= 0,
+			 "%s no selection mask is specified\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size, 0,
+				       0, PAGE_IS_WRITTEN, PAGE_IS_WRITTEN, 0, 0) == 0,
+			 "%s no return mask is specified\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size, 0,
+				       0, PAGE_IS_WRITTEN, 0, 0, 0x1000) < 0,
+			 "%s wrong return mask specified\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size,
+				       PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				       0, 0xFFF, PAGE_IS_WRITTEN, 0, PAGE_IS_WRITTEN) < 0,
+			 "%s mixture of correct and wrong flag\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size,
+				       PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				       0, 0, 0, PAGEMAP_BITS_ALL, PAGE_IS_WRITTEN) >= 0,
+			 "%s PAGEMAP_BITS_ALL can be specified with PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC\n",
+			 __func__);
+
+	/* 2. Clear area with larger vec size */
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC, 0,
+			    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	ksft_test_result(ret >= 0, "%s Clear area with larger vec size\n", __func__);
+
+	/* 3. Repeated pattern of written and non-written pages */
+	for (i = 0; i < mem_size; i += 2 * page_size)
+		mem[i]++;
+
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0, PAGE_IS_WRITTEN, 0,
+			    0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	ksft_test_result(ret == mem_size/(page_size * 2),
+			 "%s Repeated pattern of written and non-written pages\n", __func__);
+
+	/* 4. Repeated pattern of written and non-written pages in parts */
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			    num_pages/2 - 2, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	ret2 = pagemap_ioctl(mem, mem_size, vec, 2, 0, 0, PAGE_IS_WRITTEN, 0, 0,
+			     PAGE_IS_WRITTEN);
+	if (ret2 < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret2, errno, strerror(errno));
+
+	ret3 = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			     PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			     0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret3 < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret3, errno, strerror(errno));
+
+	ksft_test_result((ret + ret3) == num_pages/2 && ret2 == 2,
+			 "%s Repeated pattern of written and non-written pages in parts %d %d %d\n",
+			 __func__, ret, ret3, ret2);
+
+	/* 5. Repeated pattern of written and non-written pages max_pages */
+	for (i = 0; i < mem_size; i += 2 * page_size)
+		mem[i]++;
+	mem[(mem_size/page_size - 1) * page_size]++;
+
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			    num_pages/2, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	ret2 = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			     PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			     0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret2 < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret2, errno, strerror(errno));
+
+	ksft_test_result(ret == num_pages/2 && ret2 == 1,
+			 "%s Repeated pattern of written and non-written pages max_pages\n",
+			 __func__);
+
+	/* 6. only get 2 dirty pages and clear them as well */
+	vec_size = mem_size/page_size;
+	memset(mem, -1, mem_size);
+
+	/* get and clear second and third pages */
+	ret = pagemap_ioctl(mem + page_size, 2 * page_size, vec, 1,
+			    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			    2, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	ret2 = pagemap_ioctl(mem, mem_size, vec2, vec_size, 0, 0,
+			      PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret2 < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret2, errno, strerror(errno));
+
+	ksft_test_result(ret == 1 && LEN(vec[0]) == 2 &&
+			 vec[0].start == (uintptr_t)(mem + page_size) &&
+			 ret2 == 2 && LEN(vec2[0]) == 1 && vec2[0].start == (uintptr_t)mem &&
+			 LEN(vec2[1]) == vec_size - 3 &&
+			 vec2[1].start == (uintptr_t)(mem + 3 * page_size),
+			 "%s only get 2 written pages and clear them as well\n", __func__);
+
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+
+	/* 7. Two regions */
+	m[0] = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (m[0] == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+	m[1] = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (m[1] == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+
+	wp_init(m[0], mem_size);
+	wp_init(m[1], mem_size);
+	wp_addr_range(m[0], mem_size);
+	wp_addr_range(m[1], mem_size);
+
+	memset(m[0], 'a', mem_size);
+	memset(m[1], 'b', mem_size);
+
+	wp_addr_range(m[0], mem_size);
+
+	ret = pagemap_ioctl(m[1], mem_size, vec, 1, 0, 0, PAGE_IS_WRITTEN, 0, 0,
+			    PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	ksft_test_result(ret == 1 && LEN(vec[0]) == mem_size/page_size,
+			 "%s Two regions\n", __func__);
+
+	wp_free(m[0], mem_size);
+	wp_free(m[1], mem_size);
+	munmap(m[0], mem_size);
+	munmap(m[1], mem_size);
+
+	free(vec);
+	free(vec2);
+
+	/* 8. Smaller vec */
+	mem_size = 1050 * page_size;
+	vec_size = mem_size/(page_size*2);
+
+	vec = malloc(sizeof(struct page_region) * vec_size);
+	if (!vec)
+		ksft_exit_fail_msg("error nomem\n");
+
+	mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+
+	wp_init(mem, mem_size);
+	wp_addr_range(mem, mem_size);
+
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC, 0,
+			    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	for (i = 0; i < mem_size/page_size; i += 2)
+		mem[i * page_size]++;
+
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			    mem_size/(page_size*5), PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	total_pages += ret;
+
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			    mem_size/(page_size*5), PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	total_pages += ret;
+
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			    mem_size/(page_size*5), PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	total_pages += ret;
+
+	ksft_test_result(total_pages == mem_size/(page_size*2), "%s Smaller max_pages\n", __func__);
+
+	free(vec);
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+	total_pages = 0;
+
+	/* 9. Smaller vec */
+	mem_size = 10000 * page_size;
+	vec_size = 50;
+
+	vec = malloc(sizeof(struct page_region) * vec_size);
+	if (!vec)
+		ksft_exit_fail_msg("error nomem\n");
+
+	mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+
+	wp_init(mem, mem_size);
+	wp_addr_range(mem, mem_size);
+
+	for (count = 0; count < TEST_ITERATIONS; count++) {
+		total_writes = total_reads = 0;
+		walk_end = (long)mem;
+
+		for (i = 0; i < mem_size; i += page_size) {
+			if (rand() % 2) {
+				mem[i]++;
+				total_writes++;
+			}
+		}
+
+		while (total_reads < total_writes) {
+			ret = pagemap_ioc((void *)walk_end, mem_size-(walk_end - (long)mem), vec,
+					  vec_size, PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+					  0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+			if (ret < 0)
+				ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+			if (ret > vec_size)
+				break;
+
+			reads = get_reads(vec, ret);
+			total_reads += reads;
+		}
+
+		if (total_reads != total_writes)
+			break;
+	}
+
+	ksft_test_result(count == TEST_ITERATIONS, "Smaller vec\n");
+
+	free(vec);
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+
+	/* 10. Walk_end tester */
+	vec_size = 1000;
+	mem_size = vec_size * page_size;
+
+	vec = malloc(sizeof(struct page_region) * vec_size);
+	if (!vec)
+		ksft_exit_fail_msg("error nomem\n");
+
+	mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+
+	wp_init(mem, mem_size);
+	wp_addr_range(mem, mem_size);
+
+	memset(mem, 0, mem_size);
+
+	ret = pagemap_ioc(mem, 0, vec, vec_size, 0,
+			  0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 0 && walk_end == (long)mem,
+			 "Walk_end: Same start and end address\n");
+
+	ret = pagemap_ioc(mem, 0, vec, vec_size, PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			  0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 0 && walk_end == (long)mem,
+			 "Walk_end: Same start and end with WP\n");
+
+	ret = pagemap_ioc(mem, 0, vec, 0, PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+			  0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 0 && walk_end == (long)mem,
+			 "Walk_end: Same start and end with 0 output buffer \n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, vec_size, 0,
+			  0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 1 && walk_end == (long)(mem + mem_size),
+			 "Walk_end: Big vec\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, 1, 0,
+			  0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 1 && walk_end == (long)(mem + mem_size),
+			 "Walk_end: vec of minimum length\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, 1, 0,
+			  vec_size, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 1 && walk_end == (long)(mem + mem_size),
+			 "Walk_end: Max pages specified\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, vec_size, 0,
+			  vec_size/2, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 1 && walk_end == (long)(mem + mem_size/2),
+			 "Walk_end: Half max pages\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, vec_size, 0,
+			  1, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 1 && walk_end == (long)(mem + page_size),
+			 "Walk_end: 1 max page\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, vec_size, 0,
+			  -1, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 1 && walk_end == (long)(mem + mem_size),
+			 "Walk_end: max pages\n");
+
+	wp_addr_range(mem, mem_size);
+	for (i = 0; i < mem_size; i += 2 * page_size)
+		mem[i]++;
+
+	ret = pagemap_ioc(mem, mem_size, vec, vec_size, 0,
+			  0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == vec_size/2 && walk_end == (long)(mem + mem_size),
+			 "Walk_end sparse: Big vec\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, 1, 0,
+			  0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 1 && walk_end == (long)(mem + page_size * 2),
+			 "Walk_end sparse: vec of minimum length\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, 1, 0,
+			  vec_size, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 1 && walk_end == (long)(mem + page_size * 2),
+			 "Walk_end sparse: Max pages specified\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, vec_size/2, 0,
+			  vec_size, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == vec_size/2 && walk_end == (long)(mem + mem_size),
+			 "Walk_end sparse: Max pages specified\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, vec_size, 0,
+			  vec_size, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == vec_size/2 && walk_end == (long)(mem + mem_size),
+			 "Walk_end sparse: Max pages specified\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, vec_size, 0,
+			  vec_size/2, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == vec_size/2 && walk_end == (long)(mem + mem_size),
+			 "Walk_endsparse : Half max pages\n");
+
+	ret = pagemap_ioc(mem, mem_size, vec, vec_size, 0,
+			  1, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN, &walk_end);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+	ksft_test_result(ret == 1 && walk_end == (long)(mem + page_size * 2),
+			 "Walk_end: 1 max page\n");
+
+	free(vec);
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+
+	return 0;
+}
+
+int base_tests(char *prefix, char *mem, int mem_size, int skip)
+{
+	int vec_size, written;
+	struct page_region *vec, *vec2;
+
+	if (skip) {
+		ksft_test_result_skip("%s all new pages must not be written (dirty)\n", prefix);
+		ksft_test_result_skip("%s all pages must be written (dirty)\n", prefix);
+		ksft_test_result_skip("%s all pages dirty other than first and the last one\n",
+				      prefix);
+		ksft_test_result_skip("%s PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC\n", prefix);
+		ksft_test_result_skip("%s only middle page dirty\n", prefix);
+		ksft_test_result_skip("%s only two middle pages dirty\n", prefix);
+		return 0;
+	}
+
+	vec_size = mem_size/page_size;
+	vec = malloc(sizeof(struct page_region) * vec_size);
+	vec2 = malloc(sizeof(struct page_region) * vec_size);
+
+	/* 1. all new pages must be not be written (dirty) */
+	written = pagemap_ioctl(mem, mem_size, vec, 1, PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				vec_size - 2, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	ksft_test_result(written == 0, "%s all new pages must not be written (dirty)\n", prefix);
+
+	/* 2. all pages must be written */
+	memset(mem, -1, mem_size);
+
+	written = pagemap_ioctl(mem, mem_size, vec, 1, 0, 0, PAGE_IS_WRITTEN, 0, 0,
+			      PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	ksft_test_result(written == 1 && LEN(vec[0]) == mem_size/page_size,
+			 "%s all pages must be written (dirty)\n", prefix);
+
+	/* 3. all pages dirty other than first and the last one */
+	written = pagemap_ioctl(mem, mem_size, vec, 1, PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	memset(mem + page_size, 0, mem_size - (2 * page_size));
+
+	written = pagemap_ioctl(mem, mem_size, vec, 1, PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	ksft_test_result(written == 1 && LEN(vec[0]) >= vec_size - 2 && LEN(vec[0]) <= vec_size,
+			 "%s all pages dirty other than first and the last one\n", prefix);
+
+	written = pagemap_ioctl(mem, mem_size, vec, 1, 0, 0,
+				PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	ksft_test_result(written == 0,
+			 "%s PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC\n", prefix);
+
+	/* 4. only middle page dirty */
+	written = pagemap_ioctl(mem, mem_size, vec, 1, PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	mem[vec_size/2 * page_size]++;
+
+	written = pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0, PAGE_IS_WRITTEN,
+				0, 0, PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	ksft_test_result(written == 1 && LEN(vec[0]) >= 1,
+			 "%s only middle page dirty\n", prefix);
+
+	/* 5. only two middle pages dirty and walk over only middle pages */
+	written = pagemap_ioctl(mem, mem_size, vec, 1, PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	mem[vec_size/2 * page_size]++;
+	mem[(vec_size/2 + 1) * page_size]++;
+
+	written = pagemap_ioctl(&mem[vec_size/2 * page_size], 2 * page_size, vec, 1, 0,
+				0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	ksft_test_result(written == 1 && vec[0].start == (uintptr_t)(&mem[vec_size/2 * page_size])
+			 && LEN(vec[0]) == 2,
+			 "%s only two middle pages dirty\n", prefix);
+
+	free(vec);
+	free(vec2);
+	return 0;
+}
+
+void *gethugepage(int map_size)
+{
+	int ret;
+	char *map;
+
+	map = memalign(hpage_size, map_size);
+	if (!map)
+		ksft_exit_fail_msg("memalign failed %d %s\n", errno, strerror(errno));
+
+	ret = madvise(map, map_size, MADV_HUGEPAGE);
+	if (ret)
+		return NULL;
+
+	memset(map, 0, map_size);
+
+	return map;
+}
+
+int hpage_unit_tests(void)
+{
+	char *map;
+	int ret, ret2;
+	size_t num_pages = 10;
+	int map_size = hpage_size * num_pages;
+	int vec_size = map_size/page_size;
+	struct page_region *vec, *vec2;
+
+	vec = malloc(sizeof(struct page_region) * vec_size);
+	vec2 = malloc(sizeof(struct page_region) * vec_size);
+	if (!vec || !vec2)
+		ksft_exit_fail_msg("malloc failed\n");
+
+	map = gethugepage(map_size);
+	if (map) {
+		wp_init(map, map_size);
+		wp_addr_range(map, map_size);
+
+		/* 1. all new huge page must not be written (dirty) */
+		ret = pagemap_ioctl(map, map_size, vec, vec_size,
+				    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC, 0,
+				    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ksft_test_result(ret == 0, "%s all new huge page must not be written (dirty)\n",
+				 __func__);
+
+		/* 2. all the huge page must not be written */
+		ret = pagemap_ioctl(map, map_size, vec, vec_size, 0, 0,
+				    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ksft_test_result(ret == 0, "%s all the huge page must not be written\n", __func__);
+
+		/* 3. all the huge page must be written and clear dirty as well */
+		memset(map, -1, map_size);
+		ret = pagemap_ioctl(map, map_size, vec, vec_size,
+				    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				    0, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ksft_test_result(ret == 1 && vec[0].start == (uintptr_t)map &&
+				 LEN(vec[0]) == vec_size && vec[0].categories == PAGE_IS_WRITTEN,
+				 "%s all the huge page must be written and clear\n", __func__);
+
+		/* 4. only middle page written */
+		wp_free(map, map_size);
+		free(map);
+		map = gethugepage(map_size);
+		wp_init(map, map_size);
+		wp_addr_range(map, map_size);
+		map[vec_size/2 * page_size]++;
+
+		ret = pagemap_ioctl(map, map_size, vec, vec_size, 0, 0,
+				    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ksft_test_result(ret == 1 && LEN(vec[0]) > 0,
+				 "%s only middle page written\n", __func__);
+
+		wp_free(map, map_size);
+		free(map);
+	} else {
+		ksft_test_result_skip("%s all new huge page must be written\n", __func__);
+		ksft_test_result_skip("%s all the huge page must not be written\n", __func__);
+		ksft_test_result_skip("%s all the huge page must be written and clear\n", __func__);
+		ksft_test_result_skip("%s only middle page written\n", __func__);
+	}
+
+	/* 5. clear first half of huge page */
+	map = gethugepage(map_size);
+	if (map) {
+		wp_init(map, map_size);
+		wp_addr_range(map, map_size);
+
+		memset(map, 0, map_size);
+
+		wp_addr_range(map, map_size/2);
+
+		ret = pagemap_ioctl(map, map_size, vec, vec_size, 0, 0,
+				    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ksft_test_result(ret == 1 && LEN(vec[0]) == vec_size/2 &&
+				 vec[0].start == (uintptr_t)(map + map_size/2),
+				 "%s clear first half of huge page\n", __func__);
+		wp_free(map, map_size);
+		free(map);
+	} else {
+		ksft_test_result_skip("%s clear first half of huge page\n", __func__);
+	}
+
+	/* 6. clear first half of huge page with limited buffer */
+	map = gethugepage(map_size);
+	if (map) {
+		wp_init(map, map_size);
+		wp_addr_range(map, map_size);
+
+		memset(map, 0, map_size);
+
+		ret = pagemap_ioctl(map, map_size, vec, vec_size,
+				    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				    vec_size/2, PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ret = pagemap_ioctl(map, map_size, vec, vec_size, 0, 0,
+				    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ksft_test_result(ret == 1 && LEN(vec[0]) == vec_size/2 &&
+				 vec[0].start == (uintptr_t)(map + map_size/2),
+				 "%s clear first half of huge page with limited buffer\n",
+				 __func__);
+		wp_free(map, map_size);
+		free(map);
+	} else {
+		ksft_test_result_skip("%s clear first half of huge page with limited buffer\n",
+				      __func__);
+	}
+
+	/* 7. clear second half of huge page */
+	map = gethugepage(map_size);
+	if (map) {
+		wp_init(map, map_size);
+		wp_addr_range(map, map_size);
+
+		memset(map, -1, map_size);
+
+		ret = pagemap_ioctl(map + map_size/2, map_size/2, vec, vec_size,
+				    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC, vec_size/2,
+				    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ret = pagemap_ioctl(map, map_size, vec, vec_size, 0, 0,
+				    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ksft_test_result(ret == 1 && LEN(vec[0]) == vec_size/2,
+				 "%s clear second half huge page\n", __func__);
+		wp_free(map, map_size);
+		free(map);
+	} else {
+		ksft_test_result_skip("%s clear second half huge page\n", __func__);
+	}
+
+	/* 8. get half huge page */
+	map = gethugepage(map_size);
+	if (map) {
+		wp_init(map, map_size);
+		wp_addr_range(map, map_size);
+
+		memset(map, -1, map_size);
+		usleep(100);
+
+		ret = pagemap_ioctl(map, map_size, vec, 1,
+				    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				    hpage_size/(2*page_size), PAGE_IS_WRITTEN, 0, 0,
+				    PAGE_IS_WRITTEN);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ksft_test_result(ret == 1 && LEN(vec[0]) == hpage_size/(2*page_size),
+				 "%s get half huge page\n", __func__);
+
+		ret2 = pagemap_ioctl(map, map_size, vec, vec_size, 0, 0,
+				    PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN);
+		if (ret2 < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret2, errno, strerror(errno));
+
+		ksft_test_result(ret2 == 1 && LEN(vec[0]) == (map_size - hpage_size/2)/page_size,
+				 "%s get half huge page\n", __func__);
+
+		wp_free(map, map_size);
+		free(map);
+	} else {
+		ksft_test_result_skip("%s get half huge page\n", __func__);
+		ksft_test_result_skip("%s get half huge page\n", __func__);
+	}
+
+	free(vec);
+	free(vec2);
+	return 0;
+}
+
+int unmapped_region_tests(void)
+{
+	void *start = (void *)0x10000000;
+	int written, len = 0x00040000;
+	int vec_size = len / page_size;
+	struct page_region *vec = malloc(sizeof(struct page_region) * vec_size);
+
+	/* 1. Get written pages */
+	written = pagemap_ioctl(start, len, vec, vec_size, 0, 0,
+				PAGEMAP_NON_WRITTEN_BITS, 0, 0, PAGEMAP_NON_WRITTEN_BITS);
+	if (written < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", written, errno, strerror(errno));
+
+	ksft_test_result(written >= 0, "%s Get status of pages\n", __func__);
+
+	free(vec);
+	return 0;
+}
+
+static void test_simple(void)
+{
+	int i;
+	char *map;
+	struct page_region vec;
+
+	map = aligned_alloc(page_size, page_size);
+	if (!map)
+		ksft_exit_fail_msg("aligned_alloc failed\n");
+
+	wp_init(map, page_size);
+	wp_addr_range(map, page_size);
+
+	for (i = 0 ; i < TEST_ITERATIONS; i++) {
+		if (pagemap_ioctl(map, page_size, &vec, 1, 0, 0,
+				  PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN) == 1) {
+			ksft_print_msg("written bit was 1, but should be 0 (i=%d)\n", i);
+			break;
+		}
+
+		wp_addr_range(map, page_size);
+		/* Write something to the page to get the written bit enabled on the page */
+		map[0]++;
+
+		if (pagemap_ioctl(map, page_size, &vec, 1, 0, 0,
+				  PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN) == 0) {
+			ksft_print_msg("written bit was 0, but should be 1 (i=%d)\n", i);
+			break;
+		}
+
+		wp_addr_range(map, page_size);
+	}
+	wp_free(map, page_size);
+	free(map);
+
+	ksft_test_result(i == TEST_ITERATIONS, "Test %s\n", __func__);
+}
+
+int sanity_tests(void)
+{
+	int mem_size, vec_size, ret, fd, i, buf_size;
+	struct page_region *vec;
+	char *mem, *fmem;
+	struct stat sbuf;
+	char *tmp_buf;
+
+	/* 1. wrong operation */
+	mem_size = 10 * page_size;
+	vec_size = mem_size / page_size;
+
+	vec = malloc(sizeof(struct page_region) * vec_size);
+	mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED || vec == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+
+	wp_init(mem, mem_size);
+	wp_addr_range(mem, mem_size);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size,
+				       PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
+				       0, PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL) >= 0,
+			 "%s WP op can be specified with !PAGE_IS_WRITTEN\n", __func__);
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0,
+				       PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL) >= 0,
+			 "%s required_mask specified\n", __func__);
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0,
+				       0, PAGEMAP_BITS_ALL, 0, PAGEMAP_BITS_ALL) >= 0,
+			 "%s anyof_mask specified\n", __func__);
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0,
+				       0, 0, PAGEMAP_BITS_ALL, PAGEMAP_BITS_ALL) >= 0,
+			 "%s excluded_mask specified\n", __func__);
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0,
+				       PAGEMAP_BITS_ALL, PAGEMAP_BITS_ALL, 0,
+				       PAGEMAP_BITS_ALL) >= 0,
+			 "%s required_mask and anyof_mask specified\n", __func__);
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+
+	/* 2. Get sd and present pages with anyof_mask */
+	mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+	wp_init(mem, mem_size);
+	wp_addr_range(mem, mem_size);
+
+	memset(mem, 0, mem_size);
+
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0,
+			    0, PAGEMAP_BITS_ALL, 0, PAGEMAP_BITS_ALL);
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)mem && LEN(vec[0]) == vec_size &&
+			 (vec[0].categories & (PAGE_IS_WRITTEN | PAGE_IS_PRESENT)) ==
+			 (PAGE_IS_WRITTEN | PAGE_IS_PRESENT),
+			 "%s Get sd and present pages with anyof_mask\n", __func__);
+
+	/* 3. Get sd and present pages with required_mask */
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0,
+			    PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL);
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)mem && LEN(vec[0]) == vec_size &&
+			 (vec[0].categories & (PAGE_IS_WRITTEN | PAGE_IS_PRESENT)) ==
+			 (PAGE_IS_WRITTEN | PAGE_IS_PRESENT),
+			 "%s Get all the pages with required_mask\n", __func__);
+
+	/* 4. Get sd and present pages with required_mask and anyof_mask */
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0,
+			    PAGE_IS_WRITTEN, PAGE_IS_PRESENT, 0, PAGEMAP_BITS_ALL);
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)mem && LEN(vec[0]) == vec_size &&
+			 (vec[0].categories & (PAGE_IS_WRITTEN | PAGE_IS_PRESENT)) ==
+			 (PAGE_IS_WRITTEN | PAGE_IS_PRESENT),
+			 "%s Get sd and present pages with required_mask and anyof_mask\n",
+			 __func__);
+
+	/* 5. Don't get sd pages */
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0,
+			    PAGE_IS_WRITTEN, 0, PAGE_IS_WRITTEN, PAGEMAP_BITS_ALL);
+	ksft_test_result(ret == 0, "%s Don't get sd pages\n", __func__);
+
+	/* 6. Don't get present pages */
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size, 0, 0,
+			    PAGE_IS_PRESENT, 0, PAGE_IS_PRESENT, PAGEMAP_BITS_ALL);
+	ksft_test_result(ret == 0, "%s Don't get present pages\n", __func__);
+
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+
+	/* 8. Find written present pages with return mask */
+	mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+	wp_init(mem, mem_size);
+	wp_addr_range(mem, mem_size);
+
+	memset(mem, 0, mem_size);
+
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size,
+			    PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC, 0,
+			    0, PAGEMAP_BITS_ALL, 0, PAGE_IS_WRITTEN);
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)mem && LEN(vec[0]) == vec_size &&
+			 vec[0].categories == PAGE_IS_WRITTEN,
+			 "%s Find written present pages with return mask\n", __func__);
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+
+	/* 9. Memory mapped file */
+	fd = open(__FILE__, O_RDONLY);
+	if (fd < 0)
+		ksft_exit_fail_msg("%s Memory mapped file\n");
+
+	ret = stat(__FILE__, &sbuf);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	fmem = mmap(NULL, sbuf.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (fmem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem %ld %s\n", errno, strerror(errno));
+
+	tmp_buf = malloc(sbuf.st_size);
+	memcpy(tmp_buf, fmem, sbuf.st_size);
+
+	ret = pagemap_ioctl(fmem, sbuf.st_size, vec, vec_size, 0, 0,
+			    0, PAGEMAP_NON_WRITTEN_BITS, 0, PAGEMAP_NON_WRITTEN_BITS);
+
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)fmem &&
+			 LEN(vec[0]) == ceilf((float)sbuf.st_size/page_size) &&
+			 (vec[0].categories & PAGE_IS_FILE),
+			 "%s Memory mapped file\n", __func__);
+
+	munmap(fmem, sbuf.st_size);
+	close(fd);
+
+	/* 10. Create and read/write to a memory mapped file */
+	buf_size = page_size * 10;
+
+	fd = open(__FILE__".tmp2", O_RDWR | O_CREAT, 0666);
+	if (fd < 0)
+		ksft_exit_fail_msg("Read/write to memory: %s\n",
+				   strerror(errno));
+
+	for (i = 0; i < buf_size; i++)
+		if (write(fd, "c", 1) < 0)
+			ksft_exit_fail_msg("Create and read/write to a memory mapped file\n");
+
+	fmem = mmap(NULL, buf_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+	if (fmem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem %ld %s\n", errno, strerror(errno));
+
+	wp_init(fmem, buf_size);
+	wp_addr_range(fmem, buf_size);
+
+	for (i = 0; i < buf_size; i++)
+		fmem[i] = 'z';
+
+	msync(fmem, buf_size, MS_SYNC);
+
+	ret = pagemap_ioctl(fmem, buf_size, vec, vec_size, 0, 0,
+			    PAGE_IS_WRITTEN, PAGE_IS_PRESENT | PAGE_IS_SWAPPED | PAGE_IS_FILE, 0,
+			    PAGEMAP_BITS_ALL);
+
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)fmem &&
+			 LEN(vec[0]) == (buf_size/page_size) &&
+			 (vec[0].categories & PAGE_IS_WRITTEN),
+			 "%s Read/write to memory\n", __func__);
+
+	wp_free(fmem, buf_size);
+	munmap(fmem, buf_size);
+	close(fd);
+
+	free(vec);
+	return 0;
+}
+
+int mprotect_tests(void)
+{
+	int ret;
+	char *mem, *mem2;
+	struct page_region vec;
+	int pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+
+	if (pagemap_fd < 0) {
+		fprintf(stderr, "open() failed\n");
+		exit(1);
+	}
+
+	/* 1. Map two pages */
+	mem = mmap(0, 2 * page_size, PROT_READ|PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+	wp_init(mem, 2 * page_size);
+	wp_addr_range(mem, 2 * page_size);
+
+	/* Populate both pages. */
+	memset(mem, 1, 2 * page_size);
+
+	ret = pagemap_ioctl(mem, 2 * page_size, &vec, 1, 0, 0, PAGE_IS_WRITTEN,
+			    0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	ksft_test_result(ret == 1 && LEN(vec) == 2, "%s Both pages written\n", __func__);
+
+	/* 2. Start tracking */
+	wp_addr_range(mem, 2 * page_size);
+
+	ksft_test_result(pagemap_ioctl(mem, 2 * page_size, &vec, 1, 0, 0,
+				       PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN) == 0,
+			 "%s Both pages are not written (dirty)\n", __func__);
+
+	/* 3. Remap the second page */
+	mem2 = mmap(mem + page_size, page_size, PROT_READ|PROT_WRITE,
+		    MAP_PRIVATE|MAP_ANON|MAP_FIXED, -1, 0);
+	if (mem2 == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+	wp_init(mem2, page_size);
+	wp_addr_range(mem2, page_size);
+
+	/* Protect + unprotect. */
+	mprotect(mem, page_size, PROT_NONE);
+	mprotect(mem, 2 * page_size, PROT_READ);
+	mprotect(mem, 2 * page_size, PROT_READ|PROT_WRITE);
+
+	/* Modify both pages. */
+	memset(mem, 2, 2 * page_size);
+
+	/* Protect + unprotect. */
+	mprotect(mem, page_size, PROT_NONE);
+	mprotect(mem, page_size, PROT_READ);
+	mprotect(mem, page_size, PROT_READ|PROT_WRITE);
+
+	ret = pagemap_ioctl(mem, 2 * page_size, &vec, 1, 0, 0, PAGE_IS_WRITTEN,
+			    0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	ksft_test_result(ret == 1 && LEN(vec) == 2,
+			 "%s Both pages written after remap and mprotect\n", __func__);
+
+	/* 4. Clear and make the pages written */
+	wp_addr_range(mem, 2 * page_size);
+
+	memset(mem, 'A', 2 * page_size);
+
+	ret = pagemap_ioctl(mem, 2 * page_size, &vec, 1, 0, 0, PAGE_IS_WRITTEN,
+			    0, 0, PAGE_IS_WRITTEN);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	ksft_test_result(ret == 1 && LEN(vec) == 2,
+			 "%s Clear and make the pages written\n", __func__);
+
+	wp_free(mem, 2 * page_size);
+	munmap(mem, 2 * page_size);
+	return 0;
+}
+
+/* transact test */
+static const unsigned int nthreads = 6, pages_per_thread = 32, access_per_thread = 8;
+static pthread_barrier_t start_barrier, end_barrier;
+static unsigned int extra_thread_faults;
+static unsigned int iter_count = 1000;
+static volatile int finish;
+
+static ssize_t get_dirty_pages_reset(char *mem, unsigned int count,
+				     int reset, int page_size)
+{
+	struct pm_scan_arg arg = {0};
+	struct page_region rgns[256];
+	int i, j, cnt, ret;
+
+	arg.size = sizeof(struct pm_scan_arg);
+	arg.start = (uintptr_t)mem;
+	arg.max_pages = count;
+	arg.end = (uintptr_t)(mem + count * page_size);
+	arg.vec = (uintptr_t)rgns;
+	arg.vec_len = sizeof(rgns) / sizeof(*rgns);
+	if (reset)
+		arg.flags |= PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC;
+	arg.category_mask = PAGE_IS_WRITTEN;
+	arg.return_mask = PAGE_IS_WRITTEN;
+
+	ret = ioctl(pagemap_fd, PAGEMAP_SCAN, &arg);
+	if (ret < 0)
+		ksft_exit_fail_msg("ioctl failed\n");
+
+	cnt = 0;
+	for (i = 0; i < ret; ++i) {
+		if (rgns[i].categories != PAGE_IS_WRITTEN)
+			ksft_exit_fail_msg("wrong flags\n");
+
+		for (j = 0; j < LEN(rgns[i]); ++j)
+			cnt++;
+	}
+
+	return cnt;
+}
+
+void *thread_proc(void *mem)
+{
+	int *m = mem;
+	long curr_faults, faults;
+	struct rusage r;
+	unsigned int i;
+	int ret;
+
+	if (getrusage(RUSAGE_THREAD, &r))
+		ksft_exit_fail_msg("getrusage\n");
+
+	curr_faults = r.ru_minflt;
+
+	while (!finish) {
+		ret = pthread_barrier_wait(&start_barrier);
+		if (ret && ret != PTHREAD_BARRIER_SERIAL_THREAD)
+			ksft_exit_fail_msg("pthread_barrier_wait\n");
+
+		for (i = 0; i < access_per_thread; ++i)
+			__atomic_add_fetch(m + i * (0x1000 / sizeof(*m)), 1, __ATOMIC_SEQ_CST);
+
+		ret = pthread_barrier_wait(&end_barrier);
+		if (ret && ret != PTHREAD_BARRIER_SERIAL_THREAD)
+			ksft_exit_fail_msg("pthread_barrier_wait\n");
+
+		if (getrusage(RUSAGE_THREAD, &r))
+			ksft_exit_fail_msg("getrusage\n");
+
+		faults = r.ru_minflt - curr_faults;
+		if (faults < access_per_thread)
+			ksft_exit_fail_msg("faults < access_per_thread");
+
+		__atomic_add_fetch(&extra_thread_faults, faults - access_per_thread,
+				   __ATOMIC_SEQ_CST);
+		curr_faults = r.ru_minflt;
+	}
+
+	return NULL;
+}
+
+static void transact_test(int page_size)
+{
+	unsigned int i, count, extra_pages;
+	pthread_t th;
+	char *mem;
+	int ret, c;
+
+	if (pthread_barrier_init(&start_barrier, NULL, nthreads + 1))
+		ksft_exit_fail_msg("pthread_barrier_init\n");
+
+	if (pthread_barrier_init(&end_barrier, NULL, nthreads + 1))
+		ksft_exit_fail_msg("pthread_barrier_init\n");
+
+	mem = mmap(NULL, 0x1000 * nthreads * pages_per_thread, PROT_READ | PROT_WRITE,
+		   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("Error mmap %s.\n", strerror(errno));
+
+	wp_init(mem, 0x1000 * nthreads * pages_per_thread);
+	wp_addr_range(mem, 0x1000 * nthreads * pages_per_thread);
+
+	memset(mem, 0, 0x1000 * nthreads * pages_per_thread);
+
+	count = get_dirty_pages_reset(mem, nthreads * pages_per_thread, 1, page_size);
+	ksft_test_result(count > 0, "%s count %d\n", __func__, count);
+	count = get_dirty_pages_reset(mem, nthreads * pages_per_thread, 1, page_size);
+	ksft_test_result(count == 0, "%s count %d\n", __func__, count);
+
+	finish = 0;
+	for (i = 0; i < nthreads; ++i)
+		pthread_create(&th, NULL, thread_proc, mem + 0x1000 * i * pages_per_thread);
+
+	extra_pages = 0;
+	for (i = 0; i < iter_count; ++i) {
+		count = 0;
+
+		ret = pthread_barrier_wait(&start_barrier);
+		if (ret && ret != PTHREAD_BARRIER_SERIAL_THREAD)
+			ksft_exit_fail_msg("pthread_barrier_wait\n");
+
+		count = get_dirty_pages_reset(mem, nthreads * pages_per_thread, 1,
+					      page_size);
+
+		ret = pthread_barrier_wait(&end_barrier);
+		if (ret && ret != PTHREAD_BARRIER_SERIAL_THREAD)
+			ksft_exit_fail_msg("pthread_barrier_wait\n");
+
+		if (count > nthreads * access_per_thread)
+			ksft_exit_fail_msg("Too big count %d expected %d, iter %d\n",
+					   count, nthreads * access_per_thread, i);
+
+		c = get_dirty_pages_reset(mem, nthreads * pages_per_thread, 1, page_size);
+		count += c;
+
+		if (c > nthreads * access_per_thread) {
+			ksft_test_result_fail(" %s count > nthreads\n", __func__);
+			return;
+		}
+
+		if (count != nthreads * access_per_thread) {
+			/*
+			 * The purpose of the test is to make sure that no page updates are lost
+			 * when the page updates and read-resetting soft dirty flags are performed
+			 * in parallel. However, it is possible that the application will get the
+			 * soft dirty flags twice on the two consecutive read-resets. This seems
+			 * unavoidable as soft dirty flag is handled in software through page faults
+			 * in kernel. While the updating the flags is supposed to be synchronized
+			 * between page fault handling and read-reset, it is possible that
+			 * read-reset happens after page fault PTE update but before the application
+			 * re-executes write instruction. So read-reset gets the flag, clears write
+			 * access and application gets page fault again for the same write.
+			 */
+			if (count < nthreads * access_per_thread) {
+				ksft_test_result_fail("Lost update, iter %d, %d vs %d.\n", i, count,
+						      nthreads * access_per_thread);
+				return;
+			}
+
+			extra_pages += count - nthreads * access_per_thread;
+		}
+	}
+
+	pthread_barrier_wait(&start_barrier);
+	finish = 1;
+	pthread_barrier_wait(&end_barrier);
+
+	ksft_test_result_pass("%s Extra pages %u (%.1lf%%), extra thread faults %d.\n", __func__,
+			      extra_pages,
+			      100.0 * extra_pages / (iter_count * nthreads * access_per_thread),
+			      extra_thread_faults);
+}
+
+int main(void)
+{
+	int mem_size, shmid, buf_size, fd, i, ret;
+	char *mem, *map, *fmem;
+	struct stat sbuf;
+
+	ksft_print_header();
+	ksft_set_plan(108);
+
+	page_size = getpagesize();
+	hpage_size = read_pmd_pagesize();
+
+	pagemap_fd = open(PAGEMAP, O_RDONLY);
+	if (pagemap_fd < 0)
+		return -EINVAL;
+
+	if (init_uffd())
+		ksft_exit_fail_msg("uffd init failed\n");
+
+	/*
+	 * Written (dirty) PTE bit tests
+	 */
+
+	/* 1. Sanity testing */
+	sanity_tests_sd();
+
+	/* 2. Normal page testing */
+	mem_size = 10 * page_size;
+	mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+	wp_init(mem, mem_size);
+	wp_addr_range(mem, mem_size);
+
+	base_tests("Page testing:", mem, mem_size, 0);
+
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+
+	/* 3. Large page testing */
+	mem_size = 512 * 10 * page_size;
+	mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+	wp_init(mem, mem_size);
+	wp_addr_range(mem, mem_size);
+
+	base_tests("Large Page testing:", mem, mem_size, 0);
+
+	wp_free(mem, mem_size);
+	munmap(mem, mem_size);
+
+	/* 4. Huge page testing */
+	map = gethugepage(hpage_size);
+	if (map) {
+		wp_init(map, hpage_size);
+		wp_addr_range(map, hpage_size);
+		base_tests("Huge page testing:", map, hpage_size, 0);
+		wp_free(map, hpage_size);
+		free(map);
+	} else {
+		base_tests("Huge page testing:", NULL, 0, 1);
+	}
+
+	/* 5. Hugetlb page testing */
+	mem_size = 2*1024*1024;
+	mem = gethugetlb_mem(mem_size, &shmid);
+	if (mem) {
+		wp_init(mem, mem_size);
+		wp_addr_range(mem, mem_size);
+
+		base_tests("Hugetlb shmem testing:", mem, mem_size, 0);
+
+		wp_free(mem, mem_size);
+		shmctl(shmid, IPC_RMID, NULL);
+	} else {
+		base_tests("Hugetlb shmem testing:", NULL, 0, 1);
+	}
+
+	/* 6. Hugetlb page testing */
+	mem = gethugetlb_mem(mem_size, NULL);
+	if (mem) {
+		wp_init(mem, mem_size);
+		wp_addr_range(mem, mem_size);
+
+		base_tests("Hugetlb mem testing:", mem, mem_size, 0);
+
+		wp_free(mem, mem_size);
+	} else {
+		base_tests("Hugetlb mem testing:", NULL, 0, 1);
+	}
+
+	/* 7. file memory testing */
+	buf_size = page_size * 10;
+
+	fd = open(__FILE__".tmp0", O_RDWR | O_CREAT, 0777);
+	if (fd < 0)
+		ksft_exit_fail_msg("Create and read/write to a memory mapped file: %s\n",
+				   strerror(errno));
+
+	for (i = 0; i < buf_size; i++)
+		if (write(fd, "c", 1) < 0)
+			ksft_exit_fail_msg("Create and read/write to a memory mapped file\n");
+
+	ret = stat(__FILE__".tmp0", &sbuf);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	fmem = mmap(NULL, sbuf.st_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+	if (fmem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem %ld %s\n", errno, strerror(errno));
+
+	wp_init(fmem, sbuf.st_size);
+	wp_addr_range(fmem, sbuf.st_size);
+
+	base_tests("File memory testing:", fmem, sbuf.st_size, 0);
+
+	wp_free(fmem, sbuf.st_size);
+	munmap(fmem, sbuf.st_size);
+	close(fd);
+
+	/* 8. file memory testing */
+	buf_size = page_size * 10;
+
+	fd = memfd_create(__FILE__".tmp00", MFD_NOEXEC_SEAL);
+	if (fd < 0)
+		ksft_exit_fail_msg("Create and read/write to a memory mapped file: %s\n",
+				   strerror(errno));
+
+	if (ftruncate(fd, buf_size))
+		ksft_exit_fail_msg("Error ftruncate\n");
+
+	for (i = 0; i < buf_size; i++)
+		if (write(fd, "c", 1) < 0)
+			ksft_exit_fail_msg("Create and read/write to a memory mapped file\n");
+
+	fmem = mmap(NULL, buf_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+	if (fmem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem %ld %s\n", errno, strerror(errno));
+
+	wp_init(fmem, buf_size);
+	wp_addr_range(fmem, buf_size);
+
+	base_tests("File anonymous memory testing:", fmem, buf_size, 0);
+
+	wp_free(fmem, buf_size);
+	munmap(fmem, buf_size);
+	close(fd);
+
+	/* 9. Huge page tests */
+	hpage_unit_tests();
+
+	/* 10. Iterative test */
+	test_simple();
+
+	/* 11. Mprotect test */
+	mprotect_tests();
+
+	/* 12. Transact test */
+	transact_test(page_size);
+
+	/*
+	 * Other PTE bit tests
+	 */
+
+	/* 1. Sanity testing */
+	sanity_tests();
+
+	/* 2. Unmapped address test */
+	unmapped_region_tests();
+
+	/* 3. Userfaultfd tests */
+	userfaultfd_tests();
+
+	close(pagemap_fd);
+	return ksft_exit_pass();
+}
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 9666c0c171ab8..cca4dd8ee45d3 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -56,6 +56,8 @@ separated by spaces:
 	memory protection key tests
 - soft_dirty
 	test soft dirty page bit semantics
+- pagemap
+	test pagemap_scan IOCTL
 - cow
 	test copy-on-write semantics
 example: ./run_vmtests.sh -t "hmm mmap ksm"
@@ -324,6 +326,8 @@ fi
 
 CATEGORY="soft_dirty" run_test ./soft-dirty
 
+CATEGORY="pagemap" run_test ./pagemap_ioctl
+
 # COW tests
 CATEGORY="cow" run_test ./cow
 
-- 
2.39.2

Re: [PATCH v28 2/6] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Michał Mirosław]

On Wed, 9 Aug 2023 at 08:16, Muhammad Usama Anjum
<usama.anjum@collabora.com> wrote:
> This IOCTL, PAGEMAP_SCAN on pagemap file can be used to get and/or clear
> the info about page table entries. The following operations are supported
> in this ioctl:
> - Get the information if the pages have Async Write-Protection enabled
>   (``PAGE_IS_WPALLOWED``), have been written to (``PAGE_IS_WRITTEN``), file
>   mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``), swapped
>   (``PAGE_IS_SWAPPED``) or page has pfn zero (``PAGE_IS_PFNZERO``).
> - Find pages which have been written to and/or write protect
>   (atomic ``PM_SCAN_WP_MATCHING + PM_SCAN_CHECK_WPASYNC``) the pages
>   atomically. The (``PM_SCAN_WP_MATCHING``) is used to WP the matched
>   pages. The (``PM_SCAN_CHECK_WPASYNC``) aborts the operation if
>   non-Async-Write-Protected pages are found. Get is automatically performed
>   if output buffer is specified.
>
> This IOCTL can be extended to get information about more PTE bits. The
> entire address range passed by user [start, end) is scanned until either
> the user provided buffer is full or max_pages have been found.
>
> Reviewed-by: Andrei Vagin <avagin@gmail.com>
> Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>

Still applies, thanks! Please find some mostly-polishing comments below.

> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>

> ---
> Changes in v28:
> - Fix walk_end one last time after doing through testing
>
> Changes in v27:
> - Add PAGE_IS_HUGE

It seems to be missing from the commitmsg, though. But maybe listing
all the flags there is redundant, since a doc is coming anyway and the
values are listed in the .h?

[...]
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
[...]
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static unsigned long pagemap_thp_category(pmd_t pmd)
> +{
> +       unsigned long categories = PAGE_IS_HUGE;
> +
> +       if (pmd_present(pmd)) {
> +               categories |= PAGE_IS_PRESENT;
> +               if (!pmd_uffd_wp(pmd))
> +                       categories |= PAGE_IS_WRITTEN;
> +               if (is_zero_pfn(pmd_pfn(pmd)))
> +                       categories |= PAGE_IS_PFNZERO;
> +       } else if (is_swap_pmd(pmd)) {
> +               categories |= PAGE_IS_SWAPPED;
> +               if (!pmd_swp_uffd_wp(pmd))
> +                       categories |= PAGE_IS_WRITTEN;
> +       }
> +
> +       return categories;
> +}

I guess THPs can't be file-backed currently, but can we somehow mark
this assumption so it can be easily found if the capability arrives?

> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> +
> +#ifdef CONFIG_HUGETLB_PAGE
> +static unsigned long pagemap_hugetlb_category(pte_t pte)
> +{
> +       unsigned long categories = PAGE_IS_HUGE;
> +
> +       if (pte_present(pte)) {
> +               categories |= PAGE_IS_PRESENT;
> +               if (!huge_pte_uffd_wp(pte))
> +                       categories |= PAGE_IS_WRITTEN;
> +               if (!PageAnon(pte_page(pte)))
> +                       categories |= PAGE_IS_FILE;
> +               if (is_zero_pfn(pte_pfn(pte)))
> +                       categories |= PAGE_IS_PFNZERO;
> +       } else if (is_swap_pte(pte)) {
> +               categories |= PAGE_IS_SWAPPED;
> +               if (!pte_swp_uffd_wp_any(pte))
> +                       categories |= PAGE_IS_WRITTEN;
> +       }

BTW, can a HugeTLB page be file-backed and swapped out?

> +static void pagemap_scan_backout_range(struct pagemap_scan_private *p,
> +                                      unsigned long addr, unsigned long end,
> +                                      unsigned long walk_end_addr)
> +{
> +       struct page_region *cur_buf = &p->cur_buf;
> +
> +       if (cur_buf->start != addr)
> +               cur_buf->end = addr;
> +       else
> +               cur_buf->start = cur_buf->end = 0;
> +
> +       p->walk_end_addr = walk_end_addr;
> +       p->found_pages -= (end - addr) / PAGE_SIZE;
> +}

When would `walk_end_addr` be different from `end`? Maybe it would be
easier to understand if the `p->walk_end_addr` update was pushed to
the callers? (Actually: the one that wants to change it.)

> +static int pagemap_scan_output(unsigned long categories,
> +                              struct pagemap_scan_private *p,
> +                              unsigned long addr, unsigned long *end)
> +{
> +       unsigned long n_pages, total_pages;
> +       int ret = 0;
> +
> +       if (!p->vec_buf)
> +               return 0;
> +
> +       categories &= p->arg.return_mask;
> +
> +       n_pages = (*end - addr) / PAGE_SIZE;
> +       if (check_add_overflow(p->found_pages, n_pages, &total_pages) || //TODO
> +           total_pages > p->arg.max_pages) {

Re: TODO: Is there anything left to change here?

> +               size_t n_too_much = total_pages - p->arg.max_pages;
> +               *end -= n_too_much * PAGE_SIZE;
> +               n_pages -= n_too_much;
> +               ret = -ENOSPC;
> +       }
[...]

> +static int pagemap_scan_thp_entry(pmd_t *pmd, unsigned long start,
> +                                 unsigned long end, struct mm_walk *walk)
> +{
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +       struct pagemap_scan_private *p = walk->private;
> +       struct vm_area_struct *vma = walk->vma;
> +       unsigned long categories;
> +       spinlock_t *ptl;
> +       int ret = 0;
> +
> +       ptl = pmd_trans_huge_lock(pmd, vma);
> +       if (!ptl)
> +               return -ENOENT;
> +
> +       categories = p->cur_vma_category | pagemap_thp_category(*pmd);
> +
> +       if (!pagemap_scan_is_interesting_page(categories, p))
> +               goto out_unlock;
> +
> +       ret = pagemap_scan_output(categories, p, start, &end);
> +       if (start == end)
> +               goto out_unlock;
> +
> +       if (~p->arg.flags & PM_SCAN_WP_MATCHING)
> +               goto out_unlock;
> +       if (~categories & PAGE_IS_WRITTEN)
> +               goto out_unlock;
> +
> +       /*
> +        * Break huge page into small pages if the WP operation
> +        * need to be performed is on a portion of the huge page.

"needs to be performed on ..."

> +        */
> +       if (end != start + HPAGE_SIZE) {
> +               spin_unlock(ptl);
> +               split_huge_pmd(vma, pmd, start);
> +               pagemap_scan_backout_range(p, start, end, 0);
> +               /* Indicate to caller for processing these as normal pages */

Nit: "Report as if there was no THP." ?

> +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
> +                                 unsigned long end, struct mm_walk *walk)
> +{
> +       struct pagemap_scan_private *p = walk->private;
> +       struct vm_area_struct *vma = walk->vma;
> +       pte_t *pte, *start_pte;
> +       unsigned long addr;
> +       bool flush = false;
> +       spinlock_t *ptl;
> +       int ret;
> +
> +       arch_enter_lazy_mmu_mode();
> +
> +       ret = pagemap_scan_thp_entry(pmd, start, end, walk);
> +       if (ret != -ENOENT) {
> +               arch_leave_lazy_mmu_mode();
> +               return ret;
> +       }
> +
> +       ret = 0;
> +       start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
> +       if (!pte) {
> +               arch_leave_lazy_mmu_mode();
> +               walk->action = ACTION_AGAIN;
> +               return 0;
> +       }
> +
> +       for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
> +               unsigned long categories = p->cur_vma_category |
> +                                          pagemap_page_category(p, vma, addr, ptep_get(pte));
> +               unsigned long next = addr + PAGE_SIZE;
> +
> +               if (!pagemap_scan_is_interesting_page(categories, p))
> +                       continue;
> +
> +               ret = pagemap_scan_output(categories, p, addr, &next);
> +               if (next == addr)
> +                       break;
> +
> +               if (~p->arg.flags & PM_SCAN_WP_MATCHING)
> +                       continue;
> +               if (~categories & PAGE_IS_WRITTEN)
> +                       continue;
> +
> +               make_uffd_wp_pte(vma, addr, pte);
> +               if (!flush) {
> +                       start = addr;
> +                       flush = true;
> +               }

A quick improvement:

/* instead of `flush` declaration */ unsigned long flush_end = 0;

if (!flush_end)
  start = addr;
flush_end = next;

> +       }
> +
> +       if (flush)
> +               flush_tlb_range(vma, start, addr);

And here:
if (flush_end)
  flush_tlb_range(vma, start, flush_end);

> +       pte_unmap_unlock(start_pte, ptl);
> +       arch_leave_lazy_mmu_mode();
> +
> +       cond_resched();
> +       return ret;
> +}

[...]
> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg)
> +{
> +       struct mmu_notifier_range range;
> +       struct pagemap_scan_private p;
> +       unsigned long walk_start;
> +       size_t n_ranges_out = 0;
> +       int ret;
> +
> +       memset(&p, 0, sizeof(p));
> +       ret = pagemap_scan_get_args(&p.arg, uarg);
> +       if (ret)
> +               return ret;
> +
> +       p.masks_of_interest = MASKS_OF_INTEREST(p.arg);

Please inline the macro as here is the only use of it.

[...]
> +       walk_start = p.arg.start;
> +       for (; walk_start < p.arg.end; walk_start = p.arg.walk_end) {

Nit: the initialization statement can now be part of the for().

> +               int n_out;
> +
> +               if (fatal_signal_pending(current)) {
> +                       ret = -EINTR;
> +                       break;
> +               }
> +
> +               ret = mmap_read_lock_killable(mm);
> +               if (ret)
> +                       break;
> +               ret = walk_page_range(mm, walk_start, p.arg.end,
> +                                     &pagemap_scan_ops, &p);
> +               mmap_read_unlock(mm);
> +
> +               n_out = pagemap_scan_flush_buffer(&p);
> +               if (n_out < 0)
> +                       ret = n_out;
> +               else
> +                       n_ranges_out += n_out;
> +
> +               if (!ret)
> +                       p.walk_end_addr = p.arg.end;
> +
> +               if (ret != -ENOSPC || p.arg.vec_len - 1 == 0 ||
> +                   p.found_pages == p.arg.max_pages)
> +                       break;

The second condition is equivalent to `p.arg.vec_len == 1`, but why is
that an ending condition? Isn't the last entry enough to gather one
more range? (The walk could have returned -ENOSPC due to buffer full
and after flushing it could continue with the last free entry.)

[...]
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -259,6 +259,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma,
>                 unsigned long cp_flags);
>
>  bool is_hugetlb_entry_migration(pte_t pte);
> +bool is_hugetlb_entry_hwpoisoned(pte_t pte);
>  void hugetlb_unshare_all_pmds(struct vm_area_struct *vma);
>
>  #else /* !CONFIG_HUGETLB_PAGE */
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index b7b56871029c5..1c9d38af1015e 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -305,4 +305,63 @@ typedef int __bitwise __kernel_rwf_t;
>  #define RWF_SUPPORTED  (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
>                          RWF_APPEND)
>
> +/* Pagemap ioctl */
> +#define PAGEMAP_SCAN   _IOWR('f', 16, struct pm_scan_arg)
> +
> +/* Bits are set in flags of the page_region and masks in pm_scan_args */

"Bitmasks provided in pm_scan_args masks and reported in
page_region.categories."

> +#define PAGE_IS_WPALLOWED      (1 << 0)
> +#define PAGE_IS_WRITTEN                (1 << 1)
> +#define PAGE_IS_FILE           (1 << 2)
> +#define PAGE_IS_PRESENT                (1 << 3)
> +#define PAGE_IS_SWAPPED                (1 << 4)
> +#define PAGE_IS_PFNZERO                (1 << 5)
> +#define PAGE_IS_HUGE           (1 << 6)
> +
> +/*
> + * struct page_region - Page region with flags
> + * @start:     Start of the region
> + * @end:       End of the region (exclusive)
> + * @categories:        PAGE_IS_* category bitmask for the region
> + */
> +struct page_region {
> +       __u64 start;
> +       __u64 end;
> +       __u64 categories;
> +};
> +
> +/* Flags for PAGEMAP_SCAN ioctl */
> +#define PM_SCAN_WP_MATCHING    (1 << 0)        /* Write protect the pages matched. */
> +#define PM_SCAN_CHECK_WPASYNC  (1 << 1)        /* Abort the scan when a non-WP-enabled page is found. */
> +
> +/*
> + * struct pm_scan_arg - Pagemap ioctl argument
> + * @size:              Size of the structure
> + * @flags:             Flags for the IOCTL
> + * @start:             Starting address of the region
> + * @end:               Ending address of the region
> + * @walk_end           Address where the scan stopped (written by kernel).
> + *                     walk_end == end informs that the scan completed on entire range.

Can we ensure this holds also for the tagged pointers?

> + * @vec:               Address of page_region struct array for output
> + * @vec_len:           Length of the page_region struct array
> + * @max_pages:         Optional limit for number of returned pages (0 = disabled)
> + * @category_inverted: PAGE_IS_* categories which values match if 0 instead of 1
> + * @category_mask:     Skip pages for which any category doesn't match
> + * @category_anyof_mask: Skip pages for which no category matches
> + * @return_mask:       PAGE_IS_* categories that are to be reported in `page_region`s returned
> + */
[...]

Best Regards
Michał Mirosław

Re: [PATCH v28 2/6] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Andrei Vagin]

On Tue, Aug 8, 2023 at 11:16 PM Muhammad Usama Anjum
<usama.anjum@collabora.com> wrote:
>
> This IOCTL, PAGEMAP_SCAN on pagemap file can be used to get and/or clear
> the info about page table entries. The following operations are supported
> in this ioctl:
> - Get the information if the pages have Async Write-Protection enabled
>   (``PAGE_IS_WPALLOWED``), have been written to (``PAGE_IS_WRITTEN``), file
>   mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``), swapped
>   (``PAGE_IS_SWAPPED``) or page has pfn zero (``PAGE_IS_PFNZERO``).
> - Find pages which have been written to and/or write protect
>   (atomic ``PM_SCAN_WP_MATCHING + PM_SCAN_CHECK_WPASYNC``) the pages
>   atomically. The (``PM_SCAN_WP_MATCHING``) is used to WP the matched
>   pages. The (``PM_SCAN_CHECK_WPASYNC``) aborts the operation if
>   non-Async-Write-Protected pages are found. Get is automatically performed
>   if output buffer is specified.
>
> This IOCTL can be extended to get information about more PTE bits. The
> entire address range passed by user [start, end) is scanned until either
> the user provided buffer is full or max_pages have been found.
>
> Reviewed-by: Andrei Vagin <avagin@gmail.com>
> Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
> ---
> Changes in v28:
> - Fix walk_end one last time after doing through testing
>
> Changes in v27:
> - Add PAGE_IS_HUGE
> - Iterate until temporary buffer is full to do less iterations
> - Don't check if PAGE_IS_FILE if no mask needs it as it is very
>   expensive to check per pte
> - bring is_interesting_page() outside pagemap_scan_output() to remove
>   the horrible return value check
> - Replace memcpy() with direct copy
> - rename end_addr to walk_end_addr in pagemap_scan_private
> - Abort walk if fatal_signal_pending()
>
> Changes in v26:
> Changes made by Usama:
> - Fix the wrong breaking of loop if page isn't interesting, skip intsead
> - Untag the address and save them into struct
> - Round off the end address to next page
> - Correct the partial hugetlb page handling and returning the error
> - Rename PAGE_IS_WPASYNC to PAGE_IS_WPALLOWED
> - Return walk ending address in walk_end instead of returning in start
>   as there is potential of replacing the memory tag
>
> Changes by Michał:
> 1. the API:
>   a. return ranges as {begin, end} instead of {begin + len};
>   b. rename match "flags" to 'page categories' everywhere - this makes
>         it easier to differentiate the ioctl()s categorisation of pages
>         from struct page flags;
>   c. change {required + excluded} to {inverted + required}. This was
>         rejected before, but I'd like to illustrate the difference.
>         Old interface can be translated to the new by:
>                 categories_inverted = excluded_mask
>                 categories_mask = required_mask | excluded_mask
>                 categories_anyof_mask = anyof_mask
>         The new way allows filtering by: A & (B | !C)
>                 categories_inverted = C
>                 categories_mask = A
>                 categories_anyof_mask = B | C
>   e. allow no-op calls
> 2. the implementation:
>   a. gather the page-categorising and write-protecting code in one place;
>   b. optimization: add whole-vma skipping for WP usecase;
>   c. extracted output limiting code to pagemap_scan_output();
>   d. extracted range coalescing to pagemap_scan_push_range();
>   e. extracted THP entry handling to pagemap_scan_thp_entry();
>   f. added a shortcut for non-WP hugetlb scan; avoids conditional
>         locking;
>   g. extracted scan buffer handling code out of do_pagemap_scan();
>   h. rework output code to always try to write pending ranges; if EFAULT
>         is generated it always overwrites the original error code;
>         (the case of SIGKILL is needlessly trying to write the output
>         now, but this should be rare case and ignoring it makes the code
>         not needing a goto)
> 3.Change no-GET operation condition from `arg.return_mask == 0` to
>   `arg.vec == NULL`. This will allow issuing the ioctl with
>   return_mask == 0 to gather matching ranges when the exact category
>   is not interesting. (Anticipated for CRIU scanning a large sparse
>   anonymous mapping).
>
> Changes in v25:
> - Do proper filtering on hole as well (hole got missed earlier)
>
> Changes in v24:
> - Place WP markers in case of hole as well
>
> Changes in v23:
> - Set vec_buf_index to 0 only when vec_buf_index is set
> - Return -EFAULT instead of -EINVAL if vec is NULL
> - Correctly return the walk ending address to the page granularity
>
> Changes in v22:
> - Interface change to return walk ending address to user:
>   - Replace [start start + len) with [start, end)
>   - Return the ending address of the address walk in start
>
> Changes in v21:
> - Abort walk instead of returning error if WP is to be performed on
>   partial hugetlb
> - Changed the data types of some variables in pagemap_scan_private to
>   long
>
> Changes in v20:
> - Correct PAGE_IS_FILE and add PAGE_IS_PFNZERO
>
> Changes in v19:
> - Interface changes such as renaming, return mask and WP can be used
>   with any flags specified in masks
> - Internal code changes
>
> Changes in v18:
> - Rebased on top of next-20230613
>   - ptep_get() updates
>   - remove pmd_trans_unstable() and add ACTION_AGAIN
> - Review updates (Micheal)
>
> Changes in v17:
> - Rebased on next-20230606
> - Made make_uffd_wp_*_pte() better and minor changes
>
> Changes in v16:
> - Fixed a corner case where kernel writes beyond user buffer by one
>   element
> - Bring back exclusive PM_SCAN_OP_WP
> - Cosmetic changes
>
> Changes in v15:
> - Build fix:
>   - Use generic tlb flush function in pagemap_scan_pmd_entry() instead of
>     using x86 specific flush function in do_pagemap_scan()
>   - Remove #ifdef from pagemap_scan_hugetlb_entry()
>   - Use mm instead of undefined vma->vm_mm
>
> Changes in v14:
> - Fix build error caused by #ifdef added at last minute in some configs
>
> Changes in v13:
> - Review updates
> - mmap_read_lock_killable() instead of mmap_read_lock()
> - Replace uffd_wp_range() with helpers which increases performance
>   drastically for OP_WP operations by reducing the number of tlb
>   flushing etc
> - Add MMU_NOTIFY_PROTECTION_VMA notification for the memory range
>
> Changes in v12:
> - Add hugetlb support to cover all memory types
> - Merge "userfaultfd: Define dummy uffd_wp_range()" with this patch
> - Review updates to the code
>
> Changes in v11:
> - Find written pages in a better way
> - Fix a corner case (thanks Paul)
> - Improve the code/comments
> - remove ENGAGE_WP + ! GET operation
> - shorten the commit message in favour of moving documentation to
>   pagemap.rst
>
> Changes in v10:
> - move changes in tools/include/uapi/linux/fs.h to separate patch
> - update commit message
>
> Change in v8:
> - Correct is_pte_uffd_wp()
> - Improve readability and error checks
> - Remove some un-needed code
>
> Changes in v7:
> - Rebase on top of latest next
> - Fix some corner cases
> - Base soft-dirty on the uffd wp async
> - Update the terminologies
> - Optimize the memory usage inside the ioctl
> ---
>  fs/proc/task_mmu.c      | 678 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/hugetlb.h |   1 +
>  include/uapi/linux/fs.h |  59 ++++
>  mm/hugetlb.c            |   2 +-
>  4 files changed, 739 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index c1e6531cb02ae..0e219a44e97cd 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -19,6 +19,8 @@
>  #include <linux/shmem_fs.h>
>  #include <linux/uaccess.h>
>  #include <linux/pkeys.h>
> +#include <linux/minmax.h>
> +#include <linux/overflow.h>
>
>  #include <asm/elf.h>
>  #include <asm/tlb.h>
> @@ -1749,11 +1751,687 @@ static int pagemap_release(struct inode *inode, struct file *file)
>         return 0;
>  }
>
> +#define PM_SCAN_CATEGORIES     (PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN |  \
> +                                PAGE_IS_FILE | PAGE_IS_PRESENT |       \
> +                                PAGE_IS_SWAPPED | PAGE_IS_PFNZERO |    \
> +                                PAGE_IS_HUGE)
> +#define PM_SCAN_FLAGS          (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
> +
> +#define MASKS_OF_INTEREST(a)   (a.category_inverted | a.category_mask | \
> +                                a.category_anyof_mask | a.return_mask)
> +
> +struct pagemap_scan_private {
> +       struct pm_scan_arg arg;
> +       unsigned long masks_of_interest, cur_vma_category;
> +       struct page_region *vec_buf, cur_buf;

I think we can remove cur_buf. Imho, it makes code a bit more readable.
Here is a quick poc patch:
https://gist.github.com/avagin/2e465e7c362c515ec84d72a201a28de4

> +       unsigned long vec_buf_len, vec_buf_index, found_pages, walk_end_addr;
> +       struct page_region __user *vec_out;
> +};

...

> +#ifdef CONFIG_HUGETLB_PAGE
> +static int pagemap_scan_hugetlb_entry(pte_t *ptep, unsigned long hmask,
> +                                     unsigned long start, unsigned long end,
> +                                     struct mm_walk *walk)
> +{
> +       struct pagemap_scan_private *p = walk->private;
> +       struct vm_area_struct *vma = walk->vma;
> +       unsigned long categories;
> +       spinlock_t *ptl;
> +       int ret = 0;
> +       pte_t pte;
> +
> +       if (~p->arg.flags & PM_SCAN_WP_MATCHING) {
> +               /* Go the short route when not write-protecting pages. */
> +
> +               pte = huge_ptep_get(ptep);
> +               categories = p->cur_vma_category | pagemap_hugetlb_category(pte);
> +
> +               if (!pagemap_scan_is_interesting_page(categories, p))
> +                       return 0;
> +
> +               return pagemap_scan_output(categories, p, start, &end);
> +       }
> +
> +       i_mmap_lock_write(vma->vm_file->f_mapping);
> +       ptl = huge_pte_lock(hstate_vma(vma), vma->vm_mm, ptep);
> +
> +       pte = huge_ptep_get(ptep);
> +       categories = p->cur_vma_category | pagemap_hugetlb_category(pte);
> +
> +       if (!pagemap_scan_is_interesting_page(categories, p))
> +               goto out_unlock;
> +
> +       ret = pagemap_scan_output(categories, p, start, &end);
> +       if (start == end)
> +               goto out_unlock;
> +
> +       if (~categories & PAGE_IS_WRITTEN)
> +               goto out_unlock;
> +
> +       if (end != start + HPAGE_SIZE) {
> +               /* Partial HugeTLB page WP isn't possible. */
> +               pagemap_scan_backout_range(p, start, end, start);
> +               ret = -EINVAL;

Will this error be returned from ioctl? If the answer is yet, it looks
wrong to me.

> +               goto out_unlock;
> +       }
> +
> +       make_uffd_wp_huge_pte(vma, start, ptep, pte);
> +       flush_hugetlb_tlb_range(vma, start, end);
> +
> +out_unlock:
> +       spin_unlock(ptl);
> +       i_mmap_unlock_write(vma->vm_file->f_mapping);
> +
> +       return ret;
> +}

....

> +static int pagemap_scan_get_args(struct pm_scan_arg *arg,
> +                                unsigned long uarg)
> +{
> +       if (copy_from_user(arg, (void __user *)uarg, sizeof(*arg)))
> +               return -EFAULT;
> +
> +       if (arg->size != sizeof(struct pm_scan_arg))
> +               return -EINVAL;
> +
> +       /* Validate requested features */
> +       if (arg->flags & ~PM_SCAN_FLAGS)
> +               return -EINVAL;
> +       if ((arg->category_inverted | arg->category_mask |
> +            arg->category_anyof_mask | arg->return_mask) & ~PM_SCAN_CATEGORIES)
> +               return -EINVAL;
> +
> +       arg->start = untagged_addr((unsigned long)arg->start);
> +       arg->end = untagged_addr((unsigned long)arg->end);
> +       arg->vec = untagged_addr((unsigned long)arg->vec);
> +
> +       /* Validate memory pointers */
> +       if (!IS_ALIGNED(arg->start, PAGE_SIZE))
> +               return -EINVAL;
> +       if (!access_ok((void __user *)arg->start, arg->end - arg->start))
> +               return -EFAULT;
> +       if (!arg->vec && arg->vec_len)
> +               return -EFAULT;

It looks more like EINVAL.

> +       if (arg->vec && !access_ok((void __user *)arg->vec,
> +                             arg->vec_len * sizeof(struct page_region)))
> +               return -EFAULT;
> +
> +       /* Fixup default values */
> +       arg->end = ALIGN(arg->end, PAGE_SIZE);
> +       if (!arg->max_pages)
> +               arg->max_pages = ULONG_MAX;
> +
> +       return 0;
> +}
> +

Thanks,
Andrei

Re: [PATCH v28 5/6] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL

[Michał Mirosław]

On Wed, 9 Aug 2023 at 08:16, Muhammad Usama Anjum
<usama.anjum@collabora.com> wrote:
> Add some explanation and method to use write-protection and written-to
> on memory range.
[...]
> --- a/Documentation/admin-guide/mm/pagemap.rst
> +++ b/Documentation/admin-guide/mm/pagemap.rst
> @@ -227,3 +227,67 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is
>  always 12 at most architectures). Since Linux 3.11 their meaning changes
>  after first clear of soft-dirty bits. Since Linux 4.2 they are used for
>  flags unconditionally.
> +
> +Pagemap Scan IOCTL
> +==================
> +
> +The ``PAGEMAP_SCAN`` IOCTL on the pagemap file can be used to get or optionally
> +clear the info about page table entries. The following operations are supported
> +in this IOCTL:
> +- Get the information if the pages have Async Write-Protection enabled
> +  (``PAGE_IS_WPALLOWED``), have been written to (``PAGE_IS_WRITTEN``), file mapped
> +  (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``), swapped (``PAGE_IS_SWAPPED``)
> +  or page has pfn zero (``PAGE_IS_PFNZERO``).

A recent addition -- PAGE_IS_HUGE -- is missing.

BTW, it could be easier to understand if the page categories were
separated from the operation description and listed so that each has
its own line and maybe a longer description where needed.

> +- Find pages which have been written to and/or write protect
> +  (atomic ``PM_SCAN_WP_MATCHING + PM_SCAN_CHECK_WPASYNC``) the pages atomically.
> +  The (``PM_SCAN_WP_MATCHING``) is used to WP the matched pages. The
> +  (``PM_SCAN_CHECK_WPASYNC``) aborts the operation if non-Async-Write-Protected
> +  pages are found.

The operation the IOCTL does now is: "scan the process page tables and
report memory ranges matching provided criteria '.
Flags extend the operation: "PM_SCAN_WP_MATCHING write protects the
memory reported" (it does it atomically, but this is just an
optimization, isn't it? A process could gather the ranges, WP them,
and then copy.)
"PM_SCAN_CHECK_WPASYNC" aborts the scan early if a non-WP-able
matching page is found.

> +The ``struct pm_scan_arg`` is used as the argument of the IOCTL.
> + 1. The size of the ``struct pm_scan_arg`` must be specified in the ``size``
> +    field. This field will be helpful in recognizing the structure if extensions
> +    are done later.
> + 2. The flags can be specified in the ``flags`` field. The ``PM_SCAN_WP_MATCHING``
> +    and ``PM_SCAN_CHECK_WPASYNC`` are the only added flags at this time. The get
> +    operation is optionally performed depending upon if the output buffer is
> +    provided or not.
> + 3. The range is specified through ``start`` and ``end``.
> + 4. The output buffer of ``struct page_region`` array and size is specified in
> +    ``vec`` and ``vec_len``.
> + 5. The optional maximum requested pages are specified in the ``max_pages``.
> + 6. The masks are specified in ``category_mask``, ``category_anyof_mask``,
> +    ``category_inverted`` and ``return_mask``.
> +    1.  To find if ``PAGE_IS_WRITTEN`` flag is set for pages which have
> +        ``PAGE_IS_FILE`` set and ``PAGE_IS_SWAPPED`` unset, ``category_mask``
> +        is set to ``PAGE_IS_FILE | PAGE_IS_SWAPPED``, ``category_inverted`` is
> +        set to ``PAGE_IS_SWAPPED`` and ``return_mask`` is set to ``PAGE_IS_WRITTEN``.
> +        The output buffer in ``vec`` and length must be specified in ``vec_len``.
> +    2. To find pages which have either ``PAGE_IS_FILE`` or ``PAGE_IS_SWAPPED``
> +       set, ``category_anyof_mask`` is set to  ``PAGE_IS_FILE | PAGE_IS_SWAPPED``.
> +    3. To find written pages and engage write protect, ``PAGE_IS_WRITTEN`` is
> +       specified in ``category_mask`` and ``return_mask``. In addition to
> +       specifying the output buffer in ``vec`` and length in ``vec_len``, the
> +       ``PM_SCAN_WP_MATCHING`` is specified in ``flags`` to perform write protect
> +       on the range as well.

Could this be rewritten as examples? E.g.:

Finding dirty file-backed pages:

struct pm_scan_arg arg = {
 .size = sizeof(arg),
  .flags = 0,
 ...
   .category_mask = ...,
   .return_mask = ...
};
ssize_t n = ioctl(..., &arg);

Find dirty pages and write protect them in the same call:

arg = { ... };
do {
  ... ioctl(...)
} while(...);

(The code snippets heavily commented.)

> +The ``PAGE_IS_WRITTEN`` flag can be considered as the better and correct

"as a better-performing alternative"

> +alternative of soft-dirty flag. It doesn't get affected by housekeeping chores
> +(VMA merging) of the kernel and hence the user can find the true soft-dirty pages
> +only.

This is still an optimization, e.g. in THP case there might be too
many pages reported?

> + This IOCTL adds the atomic way to find which pages have been written and
> +write protect those pages again. This kind of operation is needed to efficiently
> +find out which pages have changed in the memory.

This repeats the description of PM_SCAN_WP_MATCHING -- I suggest
removing this part.

> +To get information about which pages have been written to or optionally write
> +protect the pages, following must be performed first in order:

"PAGE_IS_WRITTEN" category is used with uffd write protect-enabled
ranges to implement memory dirty tracking in userspace:

> + 1. The userfaultfd file descriptor is created with ``userfaultfd`` syscall.
> + 2. The ``UFFD_FEATURE_WP_UNPOPULATED`` and ``UFFD_FEATURE_WP_ASYNC`` features
> +    are set by ``UFFDIO_API`` IOCTL.
> + 3. The memory range is registered with ``UFFDIO_REGISTER_MODE_WP`` mode
> +    through ``UFFDIO_REGISTER`` IOCTL.
> + 4. Then any part of the registered memory or the whole memory region must
> +    be write protected using ``PAGEMAP_SCAN`` IOCTL with flag ``PM_SCAN_OP_WP``
> +    or the ``UFFDIO_WRITEPROTECT`` IOCTL can be used. Both of these perform the
> +    same operation. The former is better in terms of performance.

I guess that the UFFD performance could be fixed? But this part refers
to the old PM_SCAN_OP_WP, so an updated example is needed.

> + 5. Now the ``PAGEMAP_SCAN`` IOCTL can be used to either just find pages which
> +    have been written to and/or optionally write protect the pages as well.

"find the pages written to since they were last write protected", but
this sounds contradicting: we look for pages that were WP but written
anyway. (IOW: marking write-protected is an implementation detail -
the ioctl is to find pages that changed since they were last marked.)
Maybe we should call the operation "marking CLEAN" or alike?

Best Regards
Michał Mirosław

Re: [PATCH v28 2/6] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

On 8/10/23 10:32 PM, Michał Mirosław wrote:
> On Wed, 9 Aug 2023 at 08:16, Muhammad Usama Anjum
> <usama.anjum@collabora.com> wrote:
>> This IOCTL, PAGEMAP_SCAN on pagemap file can be used to get and/or clear
>> the info about page table entries. The following operations are supported
>> in this ioctl:
>> - Get the information if the pages have Async Write-Protection enabled
>>   (``PAGE_IS_WPALLOWED``), have been written to (``PAGE_IS_WRITTEN``), file
>>   mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``), swapped
>>   (``PAGE_IS_SWAPPED``) or page has pfn zero (``PAGE_IS_PFNZERO``).
>> - Find pages which have been written to and/or write protect
>>   (atomic ``PM_SCAN_WP_MATCHING + PM_SCAN_CHECK_WPASYNC``) the pages
>>   atomically. The (``PM_SCAN_WP_MATCHING``) is used to WP the matched
>>   pages. The (``PM_SCAN_CHECK_WPASYNC``) aborts the operation if
>>   non-Async-Write-Protected pages are found. Get is automatically performed
>>   if output buffer is specified.
>>
>> This IOCTL can be extended to get information about more PTE bits. The
>> entire address range passed by user [start, end) is scanned until either
>> the user provided buffer is full or max_pages have been found.
>>
>> Reviewed-by: Andrei Vagin <avagin@gmail.com>
>> Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
> 
> Still applies, thanks! Please find some mostly-polishing comments below.
> 
>> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
> 
>> ---
>> Changes in v28:
>> - Fix walk_end one last time after doing through testing
>>
>> Changes in v27:
>> - Add PAGE_IS_HUGE
> 
> It seems to be missing from the commitmsg, though. But maybe listing
> all the flags there is redundant, since a doc is coming anyway and the
> values are listed in the .h?
Yeah, fs.h and doc has all these mentioned.

> 
> [...]
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
> [...]
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> +static unsigned long pagemap_thp_category(pmd_t pmd)
>> +{
>> +       unsigned long categories = PAGE_IS_HUGE;
>> +
>> +       if (pmd_present(pmd)) {
>> +               categories |= PAGE_IS_PRESENT;
>> +               if (!pmd_uffd_wp(pmd))
>> +                       categories |= PAGE_IS_WRITTEN;
>> +               if (is_zero_pfn(pmd_pfn(pmd)))
>> +                       categories |= PAGE_IS_PFNZERO;
>> +       } else if (is_swap_pmd(pmd)) {
>> +               categories |= PAGE_IS_SWAPPED;
>> +               if (!pmd_swp_uffd_wp(pmd))
>> +                       categories |= PAGE_IS_WRITTEN;
>> +       }
>> +
>> +       return categories;
>> +}
> 
> I guess THPs can't be file-backed currently, but can we somehow mark
> this assumption so it can be easily found if the capability arrives?
Yeah, THPs cannot be file backed. Lets not care for some feature which may
not arrive in several years or eternity.

> 
>> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>> +
>> +#ifdef CONFIG_HUGETLB_PAGE
>> +static unsigned long pagemap_hugetlb_category(pte_t pte)
>> +{
>> +       unsigned long categories = PAGE_IS_HUGE;
>> +
>> +       if (pte_present(pte)) {
>> +               categories |= PAGE_IS_PRESENT;
>> +               if (!huge_pte_uffd_wp(pte))
>> +                       categories |= PAGE_IS_WRITTEN;
>> +               if (!PageAnon(pte_page(pte)))
>> +                       categories |= PAGE_IS_FILE;
>> +               if (is_zero_pfn(pte_pfn(pte)))
>> +                       categories |= PAGE_IS_PFNZERO;
>> +       } else if (is_swap_pte(pte)) {
>> +               categories |= PAGE_IS_SWAPPED;
>> +               if (!pte_swp_uffd_wp_any(pte))
>> +                       categories |= PAGE_IS_WRITTEN;
>> +       }
> 
> BTW, can a HugeTLB page be file-backed and swapped out?
Accourding to pagemap_hugetlb_range(), file-backed HugeTLB page cannot be
swapped.

> 
>> +static void pagemap_scan_backout_range(struct pagemap_scan_private *p,
>> +                                      unsigned long addr, unsigned long end,
>> +                                      unsigned long walk_end_addr)
>> +{
>> +       struct page_region *cur_buf = &p->cur_buf;
>> +
>> +       if (cur_buf->start != addr)
>> +               cur_buf->end = addr;
>> +       else
>> +               cur_buf->start = cur_buf->end = 0;
>> +
>> +       p->walk_end_addr = walk_end_addr;
>> +       p->found_pages -= (end - addr) / PAGE_SIZE;
>> +}
> 
> When would `walk_end_addr` be different from `end`? Maybe it would be
> easier to understand if the `p->walk_end_addr` update was pushed to
> the callers? (Actually: the one that wants to change it.)
Not very major thing, I've made the changes for next revision.

> 
>> +static int pagemap_scan_output(unsigned long categories,
>> +                              struct pagemap_scan_private *p,
>> +                              unsigned long addr, unsigned long *end)
>> +{
>> +       unsigned long n_pages, total_pages;
>> +       int ret = 0;
>> +
>> +       if (!p->vec_buf)
>> +               return 0;
>> +
>> +       categories &= p->arg.return_mask;
>> +
>> +       n_pages = (*end - addr) / PAGE_SIZE;
>> +       if (check_add_overflow(p->found_pages, n_pages, &total_pages) || //TODO
>> +           total_pages > p->arg.max_pages) {
> 
> Re: TODO: Is there anything left to change here?
No, I'll remove it.

> 
>> +               size_t n_too_much = total_pages - p->arg.max_pages;
>> +               *end -= n_too_much * PAGE_SIZE;
>> +               n_pages -= n_too_much;
>> +               ret = -ENOSPC;
>> +       }
> [...]
> 
>> +static int pagemap_scan_thp_entry(pmd_t *pmd, unsigned long start,
>> +                                 unsigned long end, struct mm_walk *walk)
>> +{
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> +       struct pagemap_scan_private *p = walk->private;
>> +       struct vm_area_struct *vma = walk->vma;
>> +       unsigned long categories;
>> +       spinlock_t *ptl;
>> +       int ret = 0;
>> +
>> +       ptl = pmd_trans_huge_lock(pmd, vma);
>> +       if (!ptl)
>> +               return -ENOENT;
>> +
>> +       categories = p->cur_vma_category | pagemap_thp_category(*pmd);
>> +
>> +       if (!pagemap_scan_is_interesting_page(categories, p))
>> +               goto out_unlock;
>> +
>> +       ret = pagemap_scan_output(categories, p, start, &end);
>> +       if (start == end)
>> +               goto out_unlock;
>> +
>> +       if (~p->arg.flags & PM_SCAN_WP_MATCHING)
>> +               goto out_unlock;
>> +       if (~categories & PAGE_IS_WRITTEN)
>> +               goto out_unlock;
>> +
>> +       /*
>> +        * Break huge page into small pages if the WP operation
>> +        * need to be performed is on a portion of the huge page.
> 
> "needs to be performed on ..."
Okay. I'll update.

> 
>> +        */
>> +       if (end != start + HPAGE_SIZE) {
>> +               spin_unlock(ptl);
>> +               split_huge_pmd(vma, pmd, start);
>> +               pagemap_scan_backout_range(p, start, end, 0);
>> +               /* Indicate to caller for processing these as normal pages */
> 
> Nit: "Report as if there was no THP." ?
Sure. I'll update.

> 
>> +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
>> +                                 unsigned long end, struct mm_walk *walk)
>> +{
>> +       struct pagemap_scan_private *p = walk->private;
>> +       struct vm_area_struct *vma = walk->vma;
>> +       pte_t *pte, *start_pte;
>> +       unsigned long addr;
>> +       bool flush = false;
>> +       spinlock_t *ptl;
>> +       int ret;
>> +
>> +       arch_enter_lazy_mmu_mode();
>> +
>> +       ret = pagemap_scan_thp_entry(pmd, start, end, walk);
>> +       if (ret != -ENOENT) {
>> +               arch_leave_lazy_mmu_mode();
>> +               return ret;
>> +       }
>> +
>> +       ret = 0;
>> +       start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
>> +       if (!pte) {
>> +               arch_leave_lazy_mmu_mode();
>> +               walk->action = ACTION_AGAIN;
>> +               return 0;
>> +       }
>> +
>> +       for (addr = start; addr != end; pte++, addr += PAGE_SIZE) {
>> +               unsigned long categories = p->cur_vma_category |
>> +                                          pagemap_page_category(p, vma, addr, ptep_get(pte));
>> +               unsigned long next = addr + PAGE_SIZE;
>> +
>> +               if (!pagemap_scan_is_interesting_page(categories, p))
>> +                       continue;
>> +
>> +               ret = pagemap_scan_output(categories, p, addr, &next);
>> +               if (next == addr)
>> +                       break;
>> +
>> +               if (~p->arg.flags & PM_SCAN_WP_MATCHING)
>> +                       continue;
>> +               if (~categories & PAGE_IS_WRITTEN)
>> +                       continue;
>> +
>> +               make_uffd_wp_pte(vma, addr, pte);
>> +               if (!flush) {
>> +                       start = addr;
>> +                       flush = true;
>> +               }
> 
> A quick improvement:
> 
> /* instead of `flush` declaration */ unsigned long flush_end = 0;
> 
> if (!flush_end)
>   start = addr;
> flush_end = next;
I'll update.

> 
>> +       }
>> +
>> +       if (flush)
>> +               flush_tlb_range(vma, start, addr);
> 
> And here:
> if (flush_end)
>   flush_tlb_range(vma, start, flush_end);
> 
>> +       pte_unmap_unlock(start_pte, ptl);
>> +       arch_leave_lazy_mmu_mode();
>> +
>> +       cond_resched();
>> +       return ret;
>> +}
> 
> [...]
>> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg)
>> +{
>> +       struct mmu_notifier_range range;
>> +       struct pagemap_scan_private p;
>> +       unsigned long walk_start;
>> +       size_t n_ranges_out = 0;
>> +       int ret;
>> +
>> +       memset(&p, 0, sizeof(p));
>> +       ret = pagemap_scan_get_args(&p.arg, uarg);
>> +       if (ret)
>> +               return ret;
>> +
>> +       p.masks_of_interest = MASKS_OF_INTEREST(p.arg);
> 
> Please inline the macro as here is the only use of it.
Got it.

> 
> [...]
>> +       walk_start = p.arg.start;
>> +       for (; walk_start < p.arg.end; walk_start = p.arg.walk_end) {
> 
> Nit: the initialization statement can now be part of the for().
Sure.

> 
>> +               int n_out;
>> +
>> +               if (fatal_signal_pending(current)) {
>> +                       ret = -EINTR;
>> +                       break;
>> +               }
>> +
>> +               ret = mmap_read_lock_killable(mm);
>> +               if (ret)
>> +                       break;
>> +               ret = walk_page_range(mm, walk_start, p.arg.end,
>> +                                     &pagemap_scan_ops, &p);
>> +               mmap_read_unlock(mm);
>> +
>> +               n_out = pagemap_scan_flush_buffer(&p);
>> +               if (n_out < 0)
>> +                       ret = n_out;
>> +               else
>> +                       n_ranges_out += n_out;
>> +
>> +               if (!ret)
>> +                       p.walk_end_addr = p.arg.end;
>> +
>> +               if (ret != -ENOSPC || p.arg.vec_len - 1 == 0 ||
>> +                   p.found_pages == p.arg.max_pages)
>> +                       break;
> 
> The second condition is equivalent to `p.arg.vec_len == 1`, but why is
> that an ending condition? Isn't the last entry enough to gather one
> more range? (The walk could have returned -ENOSPC due to buffer full
> and after flushing it could continue with the last free entry.)
Now we are walking the entire range walk_page_range(). We don't break loop
when we get -ENOSPC as this error may only mean that the temporary buffer
is full. So we need check if max pages have been found or output buffer is
full or ret is 0 or any other error. When p.arg.vec_len = 1 is end
condition as the last entry is in cur. As we have walked over the entire
range, cur must be full after which the walk returned.

So current condition is necessary. I've double checked it. I'll change it
to `p.arg.vec_len == 1`.

> 
> [...]
>> --- a/include/linux/hugetlb.h
>> +++ b/include/linux/hugetlb.h
>> @@ -259,6 +259,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma,
>>                 unsigned long cp_flags);
>>
>>  bool is_hugetlb_entry_migration(pte_t pte);
>> +bool is_hugetlb_entry_hwpoisoned(pte_t pte);
>>  void hugetlb_unshare_all_pmds(struct vm_area_struct *vma);
>>
>>  #else /* !CONFIG_HUGETLB_PAGE */
>> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
>> index b7b56871029c5..1c9d38af1015e 100644
>> --- a/include/uapi/linux/fs.h
>> +++ b/include/uapi/linux/fs.h
>> @@ -305,4 +305,63 @@ typedef int __bitwise __kernel_rwf_t;
>>  #define RWF_SUPPORTED  (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
>>                          RWF_APPEND)
>>
>> +/* Pagemap ioctl */
>> +#define PAGEMAP_SCAN   _IOWR('f', 16, struct pm_scan_arg)
>> +
>> +/* Bits are set in flags of the page_region and masks in pm_scan_args */
> 
> "Bitmasks provided in pm_scan_args masks and reported in
> page_region.categories."
Okay.

> 
>> +#define PAGE_IS_WPALLOWED      (1 << 0)
>> +#define PAGE_IS_WRITTEN                (1 << 1)
>> +#define PAGE_IS_FILE           (1 << 2)
>> +#define PAGE_IS_PRESENT                (1 << 3)
>> +#define PAGE_IS_SWAPPED                (1 << 4)
>> +#define PAGE_IS_PFNZERO                (1 << 5)
>> +#define PAGE_IS_HUGE           (1 << 6)
>> +
>> +/*
>> + * struct page_region - Page region with flags
>> + * @start:     Start of the region
>> + * @end:       End of the region (exclusive)
>> + * @categories:        PAGE_IS_* category bitmask for the region
>> + */
>> +struct page_region {
>> +       __u64 start;
>> +       __u64 end;
>> +       __u64 categories;
>> +};
>> +
>> +/* Flags for PAGEMAP_SCAN ioctl */
>> +#define PM_SCAN_WP_MATCHING    (1 << 0)        /* Write protect the pages matched. */
>> +#define PM_SCAN_CHECK_WPASYNC  (1 << 1)        /* Abort the scan when a non-WP-enabled page is found. */
>> +
>> +/*
>> + * struct pm_scan_arg - Pagemap ioctl argument
>> + * @size:              Size of the structure
>> + * @flags:             Flags for the IOCTL
>> + * @start:             Starting address of the region
>> + * @end:               Ending address of the region
>> + * @walk_end           Address where the scan stopped (written by kernel).
>> + *                     walk_end == end informs that the scan completed on entire range.
> 
> Can we ensure this holds also for the tagged pointers?
No, we cannot.

> 
>> + * @vec:               Address of page_region struct array for output
>> + * @vec_len:           Length of the page_region struct array
>> + * @max_pages:         Optional limit for number of returned pages (0 = disabled)
>> + * @category_inverted: PAGE_IS_* categories which values match if 0 instead of 1
>> + * @category_mask:     Skip pages for which any category doesn't match
>> + * @category_anyof_mask: Skip pages for which no category matches
>> + * @return_mask:       PAGE_IS_* categories that are to be reported in `page_region`s returned
>> + */
> [...]
> 
> Best Regards
> Michał Mirosław

-- 
BR,
Muhammad Usama Anjum

Re: [PATCH v28 2/6] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Michał Mirosław]

On Fri, Aug 11, 2023 at 05:02:44PM +0500, Muhammad Usama Anjum wrote:
> On 8/10/23 10:32 PM, Michał Mirosław wrote:
> > On Wed, 9 Aug 2023 at 08:16, Muhammad Usama Anjum
> > <usama.anjum@collabora.com> wrote:
[...]
> >> --- a/fs/proc/task_mmu.c
> >> +++ b/fs/proc/task_mmu.c
> > [...]
> >> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >> +static unsigned long pagemap_thp_category(pmd_t pmd)
> >> +{
> >> +       unsigned long categories = PAGE_IS_HUGE;
> >> +
> >> +       if (pmd_present(pmd)) {
> >> +               categories |= PAGE_IS_PRESENT;
> >> +               if (!pmd_uffd_wp(pmd))
> >> +                       categories |= PAGE_IS_WRITTEN;
> >> +               if (is_zero_pfn(pmd_pfn(pmd)))
> >> +                       categories |= PAGE_IS_PFNZERO;
> >> +       } else if (is_swap_pmd(pmd)) {
> >> +               categories |= PAGE_IS_SWAPPED;
> >> +               if (!pmd_swp_uffd_wp(pmd))
> >> +                       categories |= PAGE_IS_WRITTEN;
> >> +       }
> >> +
> >> +       return categories;
> >> +}
> > I guess THPs can't be file-backed currently, but can we somehow mark
> > this assumption so it can be easily found if the capability arrives?
> Yeah, THPs cannot be file backed. Lets not care for some feature which may
> not arrive in several years or eternity.

Yes, it might not arrive. But please add at least a comment, so that it
is clearly visible that lack if PAGE_IS_FILE here is intentional.

> >> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> >> +
> >> +#ifdef CONFIG_HUGETLB_PAGE
> >> +static unsigned long pagemap_hugetlb_category(pte_t pte)
> >> +{
> >> +       unsigned long categories = PAGE_IS_HUGE;
> >> +
> >> +       if (pte_present(pte)) {
> >> +               categories |= PAGE_IS_PRESENT;
> >> +               if (!huge_pte_uffd_wp(pte))
> >> +                       categories |= PAGE_IS_WRITTEN;
> >> +               if (!PageAnon(pte_page(pte)))
> >> +                       categories |= PAGE_IS_FILE;
> >> +               if (is_zero_pfn(pte_pfn(pte)))
> >> +                       categories |= PAGE_IS_PFNZERO;
> >> +       } else if (is_swap_pte(pte)) {
> >> +               categories |= PAGE_IS_SWAPPED;
> >> +               if (!pte_swp_uffd_wp_any(pte))
> >> +                       categories |= PAGE_IS_WRITTEN;
> >> +       }
> > 
> > BTW, can a HugeTLB page be file-backed and swapped out?
> Accourding to pagemap_hugetlb_range(), file-backed HugeTLB page cannot be
> swapped.

Here too a comment that leaving out this case is intentional would be useful.

> > [...]
> >> +       walk_start = p.arg.start;
> >> +       for (; walk_start < p.arg.end; walk_start = p.arg.walk_end) {
[...[
> >> +               ret = mmap_read_lock_killable(mm);
> >> +               if (ret)
> >> +                       break;
> >> +               ret = walk_page_range(mm, walk_start, p.arg.end,
> >> +                                     &pagemap_scan_ops, &p);
> >> +               mmap_read_unlock(mm);
[...]
> >> +               if (ret != -ENOSPC || p.arg.vec_len - 1 == 0 ||
> >> +                   p.found_pages == p.arg.max_pages)
> >> +                       break;
> > 
> > The second condition is equivalent to `p.arg.vec_len == 1`, but why is
> > that an ending condition? Isn't the last entry enough to gather one
> > more range? (The walk could have returned -ENOSPC due to buffer full
> > and after flushing it could continue with the last free entry.)
> Now we are walking the entire range walk_page_range(). We don't break loop
> when we get -ENOSPC as this error may only mean that the temporary buffer
> is full. So we need check if max pages have been found or output buffer is
> full or ret is 0 or any other error. When p.arg.vec_len = 1 is end
> condition as the last entry is in cur. As we have walked over the entire
> range, cur must be full after which the walk returned.
> 
> So current condition is necessary. I've double checked it. I'll change it
> to `p.arg.vec_len == 1`.

If we have walked the whole range, then the loop will end anyway due to
`walk_start < walk_end` not held in the `for()`'s condition.

[...]
> >> +/*
> >> + * struct pm_scan_arg - Pagemap ioctl argument
> >> + * @size:              Size of the structure
> >> + * @flags:             Flags for the IOCTL
> >> + * @start:             Starting address of the region
> >> + * @end:               Ending address of the region
> >> + * @walk_end           Address where the scan stopped (written by kernel).
> >> + *                     walk_end == end informs that the scan completed on entire range.
> > 
> > Can we ensure this holds also for the tagged pointers?
> No, we cannot.

So this need explanation in the comment here. (Though I'd still like to
know how the address tags are supposed to be used from someone that
knows them.)

Best Regards
Michał Mirosław

Re: [PATCH v28 2/6] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

On 8/11/23 12:07 AM, Andrei Vagin wrote:
> On Tue, Aug 8, 2023 at 11:16 PM Muhammad Usama Anjum
> <usama.anjum@collabora.com> wrote:
>>
>> This IOCTL, PAGEMAP_SCAN on pagemap file can be used to get and/or clear
>> the info about page table entries. The following operations are supported
>> in this ioctl:
>> - Get the information if the pages have Async Write-Protection enabled
>>   (``PAGE_IS_WPALLOWED``), have been written to (``PAGE_IS_WRITTEN``), file
>>   mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``), swapped
>>   (``PAGE_IS_SWAPPED``) or page has pfn zero (``PAGE_IS_PFNZERO``).
>> - Find pages which have been written to and/or write protect
>>   (atomic ``PM_SCAN_WP_MATCHING + PM_SCAN_CHECK_WPASYNC``) the pages
>>   atomically. The (``PM_SCAN_WP_MATCHING``) is used to WP the matched
>>   pages. The (``PM_SCAN_CHECK_WPASYNC``) aborts the operation if
>>   non-Async-Write-Protected pages are found. Get is automatically performed
>>   if output buffer is specified.
>>
>> This IOCTL can be extended to get information about more PTE bits. The
>> entire address range passed by user [start, end) is scanned until either
>> the user provided buffer is full or max_pages have been found.
>>
>> Reviewed-by: Andrei Vagin <avagin@gmail.com>
>> Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
>> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
>> ---
>> Changes in v28:
>> - Fix walk_end one last time after doing through testing
>>
>> Changes in v27:
>> - Add PAGE_IS_HUGE
>> - Iterate until temporary buffer is full to do less iterations
>> - Don't check if PAGE_IS_FILE if no mask needs it as it is very
>>   expensive to check per pte
>> - bring is_interesting_page() outside pagemap_scan_output() to remove
>>   the horrible return value check
>> - Replace memcpy() with direct copy
>> - rename end_addr to walk_end_addr in pagemap_scan_private
>> - Abort walk if fatal_signal_pending()
>>
>> Changes in v26:
>> Changes made by Usama:
>> - Fix the wrong breaking of loop if page isn't interesting, skip intsead
>> - Untag the address and save them into struct
>> - Round off the end address to next page
>> - Correct the partial hugetlb page handling and returning the error
>> - Rename PAGE_IS_WPASYNC to PAGE_IS_WPALLOWED
>> - Return walk ending address in walk_end instead of returning in start
>>   as there is potential of replacing the memory tag
>>
>> Changes by Michał:
>> 1. the API:
>>   a. return ranges as {begin, end} instead of {begin + len};
>>   b. rename match "flags" to 'page categories' everywhere - this makes
>>         it easier to differentiate the ioctl()s categorisation of pages
>>         from struct page flags;
>>   c. change {required + excluded} to {inverted + required}. This was
>>         rejected before, but I'd like to illustrate the difference.
>>         Old interface can be translated to the new by:
>>                 categories_inverted = excluded_mask
>>                 categories_mask = required_mask | excluded_mask
>>                 categories_anyof_mask = anyof_mask
>>         The new way allows filtering by: A & (B | !C)
>>                 categories_inverted = C
>>                 categories_mask = A
>>                 categories_anyof_mask = B | C
>>   e. allow no-op calls
>> 2. the implementation:
>>   a. gather the page-categorising and write-protecting code in one place;
>>   b. optimization: add whole-vma skipping for WP usecase;
>>   c. extracted output limiting code to pagemap_scan_output();
>>   d. extracted range coalescing to pagemap_scan_push_range();
>>   e. extracted THP entry handling to pagemap_scan_thp_entry();
>>   f. added a shortcut for non-WP hugetlb scan; avoids conditional
>>         locking;
>>   g. extracted scan buffer handling code out of do_pagemap_scan();
>>   h. rework output code to always try to write pending ranges; if EFAULT
>>         is generated it always overwrites the original error code;
>>         (the case of SIGKILL is needlessly trying to write the output
>>         now, but this should be rare case and ignoring it makes the code
>>         not needing a goto)
>> 3.Change no-GET operation condition from `arg.return_mask == 0` to
>>   `arg.vec == NULL`. This will allow issuing the ioctl with
>>   return_mask == 0 to gather matching ranges when the exact category
>>   is not interesting. (Anticipated for CRIU scanning a large sparse
>>   anonymous mapping).
>>
>> Changes in v25:
>> - Do proper filtering on hole as well (hole got missed earlier)
>>
>> Changes in v24:
>> - Place WP markers in case of hole as well
>>
>> Changes in v23:
>> - Set vec_buf_index to 0 only when vec_buf_index is set
>> - Return -EFAULT instead of -EINVAL if vec is NULL
>> - Correctly return the walk ending address to the page granularity
>>
>> Changes in v22:
>> - Interface change to return walk ending address to user:
>>   - Replace [start start + len) with [start, end)
>>   - Return the ending address of the address walk in start
>>
>> Changes in v21:
>> - Abort walk instead of returning error if WP is to be performed on
>>   partial hugetlb
>> - Changed the data types of some variables in pagemap_scan_private to
>>   long
>>
>> Changes in v20:
>> - Correct PAGE_IS_FILE and add PAGE_IS_PFNZERO
>>
>> Changes in v19:
>> - Interface changes such as renaming, return mask and WP can be used
>>   with any flags specified in masks
>> - Internal code changes
>>
>> Changes in v18:
>> - Rebased on top of next-20230613
>>   - ptep_get() updates
>>   - remove pmd_trans_unstable() and add ACTION_AGAIN
>> - Review updates (Micheal)
>>
>> Changes in v17:
>> - Rebased on next-20230606
>> - Made make_uffd_wp_*_pte() better and minor changes
>>
>> Changes in v16:
>> - Fixed a corner case where kernel writes beyond user buffer by one
>>   element
>> - Bring back exclusive PM_SCAN_OP_WP
>> - Cosmetic changes
>>
>> Changes in v15:
>> - Build fix:
>>   - Use generic tlb flush function in pagemap_scan_pmd_entry() instead of
>>     using x86 specific flush function in do_pagemap_scan()
>>   - Remove #ifdef from pagemap_scan_hugetlb_entry()
>>   - Use mm instead of undefined vma->vm_mm
>>
>> Changes in v14:
>> - Fix build error caused by #ifdef added at last minute in some configs
>>
>> Changes in v13:
>> - Review updates
>> - mmap_read_lock_killable() instead of mmap_read_lock()
>> - Replace uffd_wp_range() with helpers which increases performance
>>   drastically for OP_WP operations by reducing the number of tlb
>>   flushing etc
>> - Add MMU_NOTIFY_PROTECTION_VMA notification for the memory range
>>
>> Changes in v12:
>> - Add hugetlb support to cover all memory types
>> - Merge "userfaultfd: Define dummy uffd_wp_range()" with this patch
>> - Review updates to the code
>>
>> Changes in v11:
>> - Find written pages in a better way
>> - Fix a corner case (thanks Paul)
>> - Improve the code/comments
>> - remove ENGAGE_WP + ! GET operation
>> - shorten the commit message in favour of moving documentation to
>>   pagemap.rst
>>
>> Changes in v10:
>> - move changes in tools/include/uapi/linux/fs.h to separate patch
>> - update commit message
>>
>> Change in v8:
>> - Correct is_pte_uffd_wp()
>> - Improve readability and error checks
>> - Remove some un-needed code
>>
>> Changes in v7:
>> - Rebase on top of latest next
>> - Fix some corner cases
>> - Base soft-dirty on the uffd wp async
>> - Update the terminologies
>> - Optimize the memory usage inside the ioctl
>> ---
>>  fs/proc/task_mmu.c      | 678 ++++++++++++++++++++++++++++++++++++++++
>>  include/linux/hugetlb.h |   1 +
>>  include/uapi/linux/fs.h |  59 ++++
>>  mm/hugetlb.c            |   2 +-
>>  4 files changed, 739 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>> index c1e6531cb02ae..0e219a44e97cd 100644
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
>> @@ -19,6 +19,8 @@
>>  #include <linux/shmem_fs.h>
>>  #include <linux/uaccess.h>
>>  #include <linux/pkeys.h>
>> +#include <linux/minmax.h>
>> +#include <linux/overflow.h>
>>
>>  #include <asm/elf.h>
>>  #include <asm/tlb.h>
>> @@ -1749,11 +1751,687 @@ static int pagemap_release(struct inode *inode, struct file *file)
>>         return 0;
>>  }
>>
>> +#define PM_SCAN_CATEGORIES     (PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN |  \
>> +                                PAGE_IS_FILE | PAGE_IS_PRESENT |       \
>> +                                PAGE_IS_SWAPPED | PAGE_IS_PFNZERO |    \
>> +                                PAGE_IS_HUGE)
>> +#define PM_SCAN_FLAGS          (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
>> +
>> +#define MASKS_OF_INTEREST(a)   (a.category_inverted | a.category_mask | \
>> +                                a.category_anyof_mask | a.return_mask)
>> +
>> +struct pagemap_scan_private {
>> +       struct pm_scan_arg arg;
>> +       unsigned long masks_of_interest, cur_vma_category;
>> +       struct page_region *vec_buf, cur_buf;
> 
> I think we can remove cur_buf. Imho, it makes code a bit more readable.
> Here is a quick poc patch:
> https://gist.github.com/avagin/2e465e7c362c515ec84d72a201a28de4
I thought ohhh how can this be removed initially. But considering that we
have moved to walking full range until temporary buffer is full, removing
cur_buf is possible. You have proved with your POC as well. Thank you for
doing it. I've updated it after testing and simplified it further.

> 
>> +       unsigned long vec_buf_len, vec_buf_index, found_pages, walk_end_addr;
>> +       struct page_region __user *vec_out;
>> +};
> 
> ...
> 
>> +#ifdef CONFIG_HUGETLB_PAGE
>> +static int pagemap_scan_hugetlb_entry(pte_t *ptep, unsigned long hmask,
>> +                                     unsigned long start, unsigned long end,
>> +                                     struct mm_walk *walk)
>> +{
>> +       struct pagemap_scan_private *p = walk->private;
>> +       struct vm_area_struct *vma = walk->vma;
>> +       unsigned long categories;
>> +       spinlock_t *ptl;
>> +       int ret = 0;
>> +       pte_t pte;
>> +
>> +       if (~p->arg.flags & PM_SCAN_WP_MATCHING) {
>> +               /* Go the short route when not write-protecting pages. */
>> +
>> +               pte = huge_ptep_get(ptep);
>> +               categories = p->cur_vma_category | pagemap_hugetlb_category(pte);
>> +
>> +               if (!pagemap_scan_is_interesting_page(categories, p))
>> +                       return 0;
>> +
>> +               return pagemap_scan_output(categories, p, start, &end);
>> +       }
>> +
>> +       i_mmap_lock_write(vma->vm_file->f_mapping);
>> +       ptl = huge_pte_lock(hstate_vma(vma), vma->vm_mm, ptep);
>> +
>> +       pte = huge_ptep_get(ptep);
>> +       categories = p->cur_vma_category | pagemap_hugetlb_category(pte);
>> +
>> +       if (!pagemap_scan_is_interesting_page(categories, p))
>> +               goto out_unlock;
>> +
>> +       ret = pagemap_scan_output(categories, p, start, &end);
>> +       if (start == end)
>> +               goto out_unlock;
>> +
>> +       if (~categories & PAGE_IS_WRITTEN)
>> +               goto out_unlock;
>> +
>> +       if (end != start + HPAGE_SIZE) {
>> +               /* Partial HugeTLB page WP isn't possible. */
>> +               pagemap_scan_backout_range(p, start, end, start);
>> +               ret = -EINVAL;
> 
> Will this error be returned from ioctl? If the answer is yet, it looks
> wrong to me.
Sorry, we missed it in previous revisions. I'll return 0 here and walk_end
will indicate to user that we have not walked the entire range.

> 
>> +               goto out_unlock;
>> +       }
>> +
>> +       make_uffd_wp_huge_pte(vma, start, ptep, pte);
>> +       flush_hugetlb_tlb_range(vma, start, end);
>> +
>> +out_unlock:
>> +       spin_unlock(ptl);
>> +       i_mmap_unlock_write(vma->vm_file->f_mapping);
>> +
>> +       return ret;
>> +}
> 
> ....
> 
>> +static int pagemap_scan_get_args(struct pm_scan_arg *arg,
>> +                                unsigned long uarg)
>> +{
>> +       if (copy_from_user(arg, (void __user *)uarg, sizeof(*arg)))
>> +               return -EFAULT;
>> +
>> +       if (arg->size != sizeof(struct pm_scan_arg))
>> +               return -EINVAL;
>> +
>> +       /* Validate requested features */
>> +       if (arg->flags & ~PM_SCAN_FLAGS)
>> +               return -EINVAL;
>> +       if ((arg->category_inverted | arg->category_mask |
>> +            arg->category_anyof_mask | arg->return_mask) & ~PM_SCAN_CATEGORIES)
>> +               return -EINVAL;
>> +
>> +       arg->start = untagged_addr((unsigned long)arg->start);
>> +       arg->end = untagged_addr((unsigned long)arg->end);
>> +       arg->vec = untagged_addr((unsigned long)arg->vec);
>> +
>> +       /* Validate memory pointers */
>> +       if (!IS_ALIGNED(arg->start, PAGE_SIZE))
>> +               return -EINVAL;
>> +       if (!access_ok((void __user *)arg->start, arg->end - arg->start))
>> +               return -EFAULT;
>> +       if (!arg->vec && arg->vec_len)
>> +               return -EFAULT;
> 
> It looks more like EINVAL.
Updated for next revision.

> 
>> +       if (arg->vec && !access_ok((void __user *)arg->vec,
>> +                             arg->vec_len * sizeof(struct page_region)))
>> +               return -EFAULT;
>> +
>> +       /* Fixup default values */
>> +       arg->end = ALIGN(arg->end, PAGE_SIZE);
>> +       if (!arg->max_pages)
>> +               arg->max_pages = ULONG_MAX;
>> +
>> +       return 0;
>> +}
>> +
> 
> Thanks,
> Andrei

-- 
BR,
Muhammad Usama Anjum

Re: [PATCH v28 2/6] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

On 8/11/23 6:32 PM, Michał Mirosław wrote:
> On Fri, Aug 11, 2023 at 05:02:44PM +0500, Muhammad Usama Anjum wrote:
>> On 8/10/23 10:32 PM, Michał Mirosław wrote:
>>> On Wed, 9 Aug 2023 at 08:16, Muhammad Usama Anjum
>>> <usama.anjum@collabora.com> wrote:
> [...]
>>>> --- a/fs/proc/task_mmu.c
>>>> +++ b/fs/proc/task_mmu.c
>>> [...]
>>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>>> +static unsigned long pagemap_thp_category(pmd_t pmd)
>>>> +{
>>>> +       unsigned long categories = PAGE_IS_HUGE;
>>>> +
>>>> +       if (pmd_present(pmd)) {
>>>> +               categories |= PAGE_IS_PRESENT;
>>>> +               if (!pmd_uffd_wp(pmd))
>>>> +                       categories |= PAGE_IS_WRITTEN;
>>>> +               if (is_zero_pfn(pmd_pfn(pmd)))
>>>> +                       categories |= PAGE_IS_PFNZERO;
>>>> +       } else if (is_swap_pmd(pmd)) {
>>>> +               categories |= PAGE_IS_SWAPPED;
>>>> +               if (!pmd_swp_uffd_wp(pmd))
>>>> +                       categories |= PAGE_IS_WRITTEN;
>>>> +       }
>>>> +
>>>> +       return categories;
>>>> +}
>>> I guess THPs can't be file-backed currently, but can we somehow mark
>>> this assumption so it can be easily found if the capability arrives?
>> Yeah, THPs cannot be file backed. Lets not care for some feature which may
>> not arrive in several years or eternity.
> 
> Yes, it might not arrive. But please add at least a comment, so that it
> is clearly visible that lack if PAGE_IS_FILE here is intentional.
I'll add a comment.

> 
>>>> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>>>> +
>>>> +#ifdef CONFIG_HUGETLB_PAGE
>>>> +static unsigned long pagemap_hugetlb_category(pte_t pte)
>>>> +{
>>>> +       unsigned long categories = PAGE_IS_HUGE;
>>>> +
>>>> +       if (pte_present(pte)) {
>>>> +               categories |= PAGE_IS_PRESENT;
>>>> +               if (!huge_pte_uffd_wp(pte))
>>>> +                       categories |= PAGE_IS_WRITTEN;
>>>> +               if (!PageAnon(pte_page(pte)))
>>>> +                       categories |= PAGE_IS_FILE;
>>>> +               if (is_zero_pfn(pte_pfn(pte)))
>>>> +                       categories |= PAGE_IS_PFNZERO;
>>>> +       } else if (is_swap_pte(pte)) {
>>>> +               categories |= PAGE_IS_SWAPPED;
>>>> +               if (!pte_swp_uffd_wp_any(pte))
>>>> +                       categories |= PAGE_IS_WRITTEN;
>>>> +       }
>>>
>>> BTW, can a HugeTLB page be file-backed and swapped out?
>> Accourding to pagemap_hugetlb_range(), file-backed HugeTLB page cannot be
>> swapped.
> 
> Here too a comment that leaving out this case is intentional would be useful.
Sure.

> 
>>> [...]
>>>> +       walk_start = p.arg.start;
>>>> +       for (; walk_start < p.arg.end; walk_start = p.arg.walk_end) {
> [...[
>>>> +               ret = mmap_read_lock_killable(mm);
>>>> +               if (ret)
>>>> +                       break;
>>>> +               ret = walk_page_range(mm, walk_start, p.arg.end,
>>>> +                                     &pagemap_scan_ops, &p);
>>>> +               mmap_read_unlock(mm);
> [...]
>>>> +               if (ret != -ENOSPC || p.arg.vec_len - 1 == 0 ||
>>>> +                   p.found_pages == p.arg.max_pages)
>>>> +                       break;
>>>
>>> The second condition is equivalent to `p.arg.vec_len == 1`, but why is
>>> that an ending condition? Isn't the last entry enough to gather one
>>> more range? (The walk could have returned -ENOSPC due to buffer full
>>> and after flushing it could continue with the last free entry.)
>> Now we are walking the entire range walk_page_range(). We don't break loop
>> when we get -ENOSPC as this error may only mean that the temporary buffer
>> is full. So we need check if max pages have been found or output buffer is
>> full or ret is 0 or any other error. When p.arg.vec_len = 1 is end
>> condition as the last entry is in cur. As we have walked over the entire
>> range, cur must be full after which the walk returned.
>>
>> So current condition is necessary. I've double checked it. I'll change it
>> to `p.arg.vec_len == 1`.
> 
> If we have walked the whole range, then the loop will end anyway due to
> `walk_start < walk_end` not held in the `for()`'s condition.
Sorry, for not explaining to-the-point.
Why would we walk the entire range when we should recognize that the output
buffer is full and break the loop?

I've test cases written for this case. If I remove `p.arg.vec_len == 1`
check, there is infinite loop for walking. So we are doing correct thing here.

> 
> [...]
>>>> +/*
>>>> + * struct pm_scan_arg - Pagemap ioctl argument
>>>> + * @size:              Size of the structure
>>>> + * @flags:             Flags for the IOCTL
>>>> + * @start:             Starting address of the region
>>>> + * @end:               Ending address of the region
>>>> + * @walk_end           Address where the scan stopped (written by kernel).
>>>> + *                     walk_end == end informs that the scan completed on entire range.
>>>
>>> Can we ensure this holds also for the tagged pointers?
>> No, we cannot.
> 
> So this need explanation in the comment here. (Though I'd still like to
> know how the address tags are supposed to be used from someone that
> knows them.)
I've looked at some documentations (presentations/talks) about tags. Tags
is more like userspace feature. Kernel should just ignore them for our use
case. I'll add comment.

> 
> Best Regards
> Michał Mirosław

-- 
BR,
Muhammad Usama Anjum

Re: [PATCH v28 5/6] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL

[Muhammad Usama Anjum]

On 8/11/23 12:26 AM, Michał Mirosław wrote:
> On Wed, 9 Aug 2023 at 08:16, Muhammad Usama Anjum
> <usama.anjum@collabora.com> wrote:
>> Add some explanation and method to use write-protection and written-to
>> on memory range.
> [...]
>> --- a/Documentation/admin-guide/mm/pagemap.rst
>> +++ b/Documentation/admin-guide/mm/pagemap.rst
>> @@ -227,3 +227,67 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is
>>  always 12 at most architectures). Since Linux 3.11 their meaning changes
>>  after first clear of soft-dirty bits. Since Linux 4.2 they are used for
>>  flags unconditionally.
>> +
>> +Pagemap Scan IOCTL
>> +==================
>> +
>> +The ``PAGEMAP_SCAN`` IOCTL on the pagemap file can be used to get or optionally
>> +clear the info about page table entries. The following operations are supported
>> +in this IOCTL:
>> +- Get the information if the pages have Async Write-Protection enabled
>> +  (``PAGE_IS_WPALLOWED``), have been written to (``PAGE_IS_WRITTEN``), file mapped
>> +  (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``), swapped (``PAGE_IS_SWAPPED``)
>> +  or page has pfn zero (``PAGE_IS_PFNZERO``).
> 
> A recent addition -- PAGE_IS_HUGE -- is missing.
> 
> BTW, it could be easier to understand if the page categories were
> separated from the operation description and listed so that each has
> its own line and maybe a longer description where needed.
I've made 90% of changes you have asked in documentation.

> 
>> +- Find pages which have been written to and/or write protect
>> +  (atomic ``PM_SCAN_WP_MATCHING + PM_SCAN_CHECK_WPASYNC``) the pages atomically.
>> +  The (``PM_SCAN_WP_MATCHING``) is used to WP the matched pages. The
>> +  (``PM_SCAN_CHECK_WPASYNC``) aborts the operation if non-Async-Write-Protected
>> +  pages are found.
> 
> The operation the IOCTL does now is: "scan the process page tables and
> report memory ranges matching provided criteria '.
> Flags extend the operation: "PM_SCAN_WP_MATCHING write protects the
> memory reported" (it does it atomically, but this is just an
> optimization, isn't it? A process could gather the ranges, WP them,
> and then copy.)
> "PM_SCAN_CHECK_WPASYNC" aborts the scan early if a non-WP-able
> matching page is found.
> 
>> +The ``struct pm_scan_arg`` is used as the argument of the IOCTL.
>> + 1. The size of the ``struct pm_scan_arg`` must be specified in the ``size``
>> +    field. This field will be helpful in recognizing the structure if extensions
>> +    are done later.
>> + 2. The flags can be specified in the ``flags`` field. The ``PM_SCAN_WP_MATCHING``
>> +    and ``PM_SCAN_CHECK_WPASYNC`` are the only added flags at this time. The get
>> +    operation is optionally performed depending upon if the output buffer is
>> +    provided or not.
>> + 3. The range is specified through ``start`` and ``end``.
>> + 4. The output buffer of ``struct page_region`` array and size is specified in
>> +    ``vec`` and ``vec_len``.
>> + 5. The optional maximum requested pages are specified in the ``max_pages``.
>> + 6. The masks are specified in ``category_mask``, ``category_anyof_mask``,
>> +    ``category_inverted`` and ``return_mask``.
>> +    1.  To find if ``PAGE_IS_WRITTEN`` flag is set for pages which have
>> +        ``PAGE_IS_FILE`` set and ``PAGE_IS_SWAPPED`` unset, ``category_mask``
>> +        is set to ``PAGE_IS_FILE | PAGE_IS_SWAPPED``, ``category_inverted`` is
>> +        set to ``PAGE_IS_SWAPPED`` and ``return_mask`` is set to ``PAGE_IS_WRITTEN``.
>> +        The output buffer in ``vec`` and length must be specified in ``vec_len``.
>> +    2. To find pages which have either ``PAGE_IS_FILE`` or ``PAGE_IS_SWAPPED``
>> +       set, ``category_anyof_mask`` is set to  ``PAGE_IS_FILE | PAGE_IS_SWAPPED``.
>> +    3. To find written pages and engage write protect, ``PAGE_IS_WRITTEN`` is
>> +       specified in ``category_mask`` and ``return_mask``. In addition to
>> +       specifying the output buffer in ``vec`` and length in ``vec_len``, the
>> +       ``PM_SCAN_WP_MATCHING`` is specified in ``flags`` to perform write protect
>> +       on the range as well.
> 
> Could this be rewritten as examples? E.g.:
> 
> Finding dirty file-backed pages:
> 
> struct pm_scan_arg arg = {
>  .size = sizeof(arg),
>   .flags = 0,
>  ...
>    .category_mask = ...,
>    .return_mask = ...
> };
> ssize_t n = ioctl(..., &arg);
> 
> Find dirty pages and write protect them in the same call:
> 
> arg = { ... };
> do {
>   ... ioctl(...)
> } while(...);
> 
> (The code snippets heavily commented.)
> 
>> +The ``PAGE_IS_WRITTEN`` flag can be considered as the better and correct
> 
> "as a better-performing alternative"
> 
>> +alternative of soft-dirty flag. It doesn't get affected by housekeeping chores
>> +(VMA merging) of the kernel and hence the user can find the true soft-dirty pages
>> +only.
> 
> This is still an optimization, e.g. in THP case there might be too
> many pages reported?
> 
>> + This IOCTL adds the atomic way to find which pages have been written and
>> +write protect those pages again. This kind of operation is needed to efficiently
>> +find out which pages have changed in the memory.
> 
> This repeats the description of PM_SCAN_WP_MATCHING -- I suggest
> removing this part.
> 
>> +To get information about which pages have been written to or optionally write
>> +protect the pages, following must be performed first in order:
> 
> "PAGE_IS_WRITTEN" category is used with uffd write protect-enabled
> ranges to implement memory dirty tracking in userspace:
> 
>> + 1. The userfaultfd file descriptor is created with ``userfaultfd`` syscall.
>> + 2. The ``UFFD_FEATURE_WP_UNPOPULATED`` and ``UFFD_FEATURE_WP_ASYNC`` features
>> +    are set by ``UFFDIO_API`` IOCTL.
>> + 3. The memory range is registered with ``UFFDIO_REGISTER_MODE_WP`` mode
>> +    through ``UFFDIO_REGISTER`` IOCTL.
>> + 4. Then any part of the registered memory or the whole memory region must
>> +    be write protected using ``PAGEMAP_SCAN`` IOCTL with flag ``PM_SCAN_OP_WP``
>> +    or the ``UFFDIO_WRITEPROTECT`` IOCTL can be used. Both of these perform the
>> +    same operation. The former is better in terms of performance.
> 
> I guess that the UFFD performance could be fixed? But this part refers
> to the old PM_SCAN_OP_WP, so an updated example is needed.
> 
>> + 5. Now the ``PAGEMAP_SCAN`` IOCTL can be used to either just find pages which
>> +    have been written to and/or optionally write protect the pages as well.
> 
> "find the pages written to since they were last write protected", but
> this sounds contradicting: we look for pages that were WP but written
> anyway. (IOW: marking write-protected is an implementation detail -
> the ioctl is to find pages that changed since they were last marked.)
> Maybe we should call the operation "marking CLEAN" or alike?
> 
> Best Regards
> Michał Mirosław

-- 
BR,
Muhammad Usama Anjum

Re: [PATCH v28 2/6] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Michał Mirosław]

On Fri, Aug 11, 2023 at 08:30:16PM +0500, Muhammad Usama Anjum wrote:
> On 8/11/23 6:32 PM, Michał Mirosław wrote:
> > On Fri, Aug 11, 2023 at 05:02:44PM +0500, Muhammad Usama Anjum wrote:
> >> Now we are walking the entire range walk_page_range(). We don't break loop
> >> when we get -ENOSPC as this error may only mean that the temporary buffer
> >> is full. So we need check if max pages have been found or output buffer is
> >> full or ret is 0 or any other error. When p.arg.vec_len = 1 is end
> >> condition as the last entry is in cur. As we have walked over the entire
> >> range, cur must be full after which the walk returned.
> >>
> >> So current condition is necessary. I've double checked it. I'll change it
> >> to `p.arg.vec_len == 1`.
> > If we have walked the whole range, then the loop will end anyway due to
> > `walk_start < walk_end` not held in the `for()`'s condition.
> Sorry, for not explaining to-the-point.
> Why would we walk the entire range when we should recognize that the output
> buffer is full and break the loop?
> 
> I've test cases written for this case. If I remove `p.arg.vec_len == 1`
> check, there is infinite loop for walking. So we are doing correct thing here.

It seems there is a bug somewhere then. I'll take a look at v29.

> > [...]
> >>>> +/*
> >>>> + * struct pm_scan_arg - Pagemap ioctl argument
> >>>> + * @size:              Size of the structure
> >>>> + * @flags:             Flags for the IOCTL
> >>>> + * @start:             Starting address of the region
> >>>> + * @end:               Ending address of the region
> >>>> + * @walk_end           Address where the scan stopped (written by kernel).
> >>>> + *                     walk_end == end informs that the scan completed on entire range.
> >>>
> >>> Can we ensure this holds also for the tagged pointers?
> >> No, we cannot.
> > So this need explanation in the comment here. (Though I'd still like to
> > know how the address tags are supposed to be used from someone that
> > knows them.)
> I've looked at some documentations (presentations/talks) about tags. Tags
> is more like userspace feature. Kernel should just ignore them for our use
> case. I'll add comment.

Kernel does ignore them when reading, but what about returning a tagged
pointer? How that should work? In case of `walk_end` we can safely copy
the tag from `end` or `start` when we return exactly on of those. But what
about other addresses? When fed back as `start` any tag will work, so
the question is only what to do with pointers in the middle? We can clear
those of course - this should be mentioned in the doc - so userspace always
gets a predictable value (note: 'predictable' does not require treating
`start` and `end` the same way as addresses between them, just that what
happens is well defined). (I think making `walk_end` == `end` work
regardless of pointer tagging will make userspace happier, but I guess
doc will also make it workable. And I'm repeating myself. ;-)

Best Regards
Michał Mirosław