[PATCH v16 0/5] Implement IOCTL to get and optionally clear info about PTEs

[PATCH v16 0/5] Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

*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() syscall [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.

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 been written-to (PAGE_IS_WRITTEN),
  file mapped (PAGE_IS_FILE), present (PAGE_IS_PRESENT) or swapped
  (PAGE_IS_SWAPPED).
- Write-protect the pages (PAGEMAP_WP_ENGAGE) to start finding which
  pages have been written-to.
- Find pages which have been written-to and write protect the pages
  (atomic PAGE_IS_WRITTEN + PAGEMAP_WP_ENGAGE)

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-dirtyi 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 (4):
  fs/proc/task_mmu: Implement IOCTL to get and optionally clear info
    about PTEs
  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     |   58 +
 Documentation/admin-guide/mm/userfaultfd.rst |   35 +
 fs/proc/task_mmu.c                           |  503 ++++++
 fs/userfaultfd.c                             |   26 +-
 include/linux/userfaultfd_k.h                |   21 +-
 include/uapi/linux/fs.h                      |   53 +
 include/uapi/linux/userfaultfd.h             |    9 +-
 mm/hugetlb.c                                 |   32 +-
 mm/memory.c                                  |   27 +-
 tools/include/uapi/linux/fs.h                |   53 +
 tools/testing/selftests/mm/.gitignore        |    1 +
 tools/testing/selftests/mm/Makefile          |    3 +-
 tools/testing/selftests/mm/config            |    1 +
 tools/testing/selftests/mm/pagemap_ioctl.c   | 1459 ++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh    |    4 +
 15 files changed, 2262 insertions(+), 23 deletions(-)
 create mode 100644 tools/testing/selftests/mm/pagemap_ioctl.c
 mode change 100644 => 100755 tools/testing/selftests/mm/run_vmtests.sh

-- 
2.39.2

[PATCH v16 1/5] 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 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 7c304e432205..4b7f43fbbe18 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.
+
 QEMU/KVM
 ========
 
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 0fd96d6e39ce..3ab021521a96 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
@@ -1332,6 +1337,7 @@ 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);
 
 	user_uffdio_register = (struct uffdio_register __user *) arg;
 
@@ -1405,7 +1411,7 @@ 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;
 
 		/*
@@ -1464,7 +1470,7 @@ 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));
@@ -1563,6 +1569,7 @@ 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);
 
 	ret = -EFAULT;
 	if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
@@ -1616,7 +1623,7 @@ 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;
@@ -1629,7 +1636,7 @@ 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
@@ -1966,6 +1973,11 @@ static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
 	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)
 {
 	/*
@@ -1999,6 +2011,11 @@ 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
@@ -2011,6 +2028,7 @@ 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 d78b01524349..ce4f9d18de3e 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -157,11 +157,22 @@ 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
@@ -171,6 +182,8 @@ 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);
 }
@@ -193,6 +206,7 @@ extern int userfaultfd_unmap_prep(struct mm_struct *mm, unsigned long start,
 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 */
 
@@ -293,6 +307,11 @@ 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 66dd4cd277bd..cfb87a112a9f 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -39,7 +39,8 @@
 			   UFFD_FEATURE_MINOR_SHMEM |		\
 			   UFFD_FEATURE_EXACT_ADDRESS |		\
 			   UFFD_FEATURE_WP_HUGETLBFS_SHMEM |	\
-			   UFFD_FEATURE_WP_UNPOPULATED)
+			   UFFD_FEATURE_WP_UNPOPULATED |	\
+			   UFFD_FEATURE_WP_ASYNC)
 #define UFFD_API_IOCTLS				\
 	((__u64)1 << _UFFDIO_REGISTER |		\
 	 (__u64)1 << _UFFDIO_UNREGISTER |	\
@@ -210,6 +211,11 @@ 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)
@@ -225,6 +231,7 @@ struct uffdio_api {
 #define UFFD_FEATURE_EXACT_ADDRESS		(1<<11)
 #define UFFD_FEATURE_WP_HUGETLBFS_SHMEM		(1<<12)
 #define UFFD_FEATURE_WP_UNPOPULATED		(1<<13)
+#define UFFD_FEATURE_WP_ASYNC			(1<<14)
 	__u64 features;
 
 	__u64 ioctls;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 155bb6712be1..0d0efd96449e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6150,21 +6150,27 @@ 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 1c5b231fe6e3..60f1a4e348b5 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3331,11 +3331,28 @@ 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, *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(*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;
 		}
 
 		/*
@@ -4824,8 +4841,11 @@ 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);
 	}
 
@@ -4837,6 +4857,7 @@ 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 v16 2/5] 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 been written-to (PAGE_IS_WRITTEN),
  file mapped (PAGE_IS_FILE), present (PAGE_IS_PRESENT) or swapped
  (PAGE_IS_SWAPPED).
- Find pages which have been written-to and/or write protect the pages
  (atomic PM_SCAN_OP_GET + PM_SCAN_OP_WP)

This IOCTL can be extended to get information about more PTE bits.

Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
---
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

Changes in v6:
- Rename variables and update comments
- Make IOCTL independent of soft_dirty config
- Change masks and bitmap type to _u64
- Improve code quality

Changes in v5:
- Remove tlb flushing even for clear operation

Changes in v4:
- Update the interface and implementation

Changes in v3:
- Tighten the user-kernel interface by using explicit types and add more
  error checking

Changes in v2:
- Convert the interface from syscall to ioctl
- Remove pidfd support as it doesn't make sense in ioctl
---
 fs/proc/task_mmu.c      | 503 ++++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/fs.h |  53 +++++
 2 files changed, 556 insertions(+)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 38b19a757281..cc31c37e6789 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -19,6 +19,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/uaccess.h>
 #include <linux/pkeys.h>
+#include <linux/minmax.h>
 
 #include <asm/elf.h>
 #include <asm/tlb.h>
@@ -1767,11 +1768,513 @@ static int pagemap_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
+#define PM_SCAN_FOUND_MAX_PAGES	(1)
+#define PM_SCAN_BITS_ALL	(PAGE_IS_WRITTEN | PAGE_IS_FILE |	\
+				 PAGE_IS_PRESENT | PAGE_IS_SWAPPED)
+#define PM_SCAN_OPS		(PM_SCAN_OP_GET | PM_SCAN_OP_WP)
+#define IS_PM_SCAN_GET(flags)	(flags & PM_SCAN_OP_GET)
+#define IS_PM_SCAN_WP(flags)	(flags & PM_SCAN_OP_WP)
+#define PM_SCAN_BITMAP(wt, file, present, swap)	\
+	((wt) | ((file) << 1) | ((present) << 2) | ((swap) << 3))
+
+struct pagemap_scan_private {
+	struct page_region *vec, cur;
+	unsigned long vec_len, vec_index, max_pages, found_pages, flags;
+	unsigned long required_mask, anyof_mask, excluded_mask, return_mask;
+};
+
+static inline bool is_pte_uffd_wp(pte_t pte)
+{
+	return (pte_present(pte) && pte_uffd_wp(pte)) ||
+	       pte_swp_uffd_wp_any(pte);
+}
+
+static inline void make_uffd_wp_pte(struct vm_area_struct *vma,
+				    unsigned long addr, pte_t *pte)
+{
+	pte_t ptent = *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);
+	}
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline bool is_pmd_uffd_wp(pmd_t pmd)
+{
+	return (pmd_present(pmd) && pmd_uffd_wp(pmd)) ||
+	       (is_swap_pmd(pmd) && pmd_swp_uffd_wp(pmd));
+}
+
+static inline 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
+
+#ifdef CONFIG_HUGETLB_PAGE
+static inline bool is_huge_pte_uffd_wp(pte_t pte)
+{
+	return ((pte_present(pte) && huge_pte_uffd_wp(pte)) ||
+	       pte_swp_uffd_wp_any(pte));
+}
+
+static inline void make_uffd_wp_huge_pte(struct vm_area_struct *vma,
+					 unsigned long addr, pte_t *ptep,
+					 pte_t ptent)
+{
+	pte_t old_pte;
+
+	if (!huge_pte_none(ptent)) {
+		old_pte = huge_ptep_modify_prot_start(vma, addr, ptep);
+		ptent = huge_pte_mkuffd_wp(old_pte);
+		ptep_modify_prot_commit(vma, addr, ptep, old_pte, ptent);
+	} else {
+		set_huge_pte_at(vma->vm_mm, addr, ptep,
+				make_pte_marker(PTE_MARKER_UFFD_WP));
+	}
+}
+#endif
+
+static inline bool pagemap_scan_check_page_written(struct pagemap_scan_private *p)
+{
+	return (p->required_mask | p->anyof_mask | p->excluded_mask) &
+	       PAGE_IS_WRITTEN;
+}
+
+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;
+
+	if (pagemap_scan_check_page_written(p) && (!userfaultfd_wp(vma) ||
+	    !userfaultfd_wp_async(vma)))
+		return -EPERM;
+
+	if (vma->vm_flags & VM_PFNMAP)
+		return 1;
+
+	return 0;
+}
+
+static int pagemap_scan_output(bool wt, bool file, bool pres, bool swap,
+			       struct pagemap_scan_private *p,
+			       unsigned long addr, unsigned int n_pages)
+{
+	unsigned long bitmap = PM_SCAN_BITMAP(wt, file, pres, swap);
+	struct page_region *cur = &p->cur;
+
+	if (!n_pages)
+		return -EINVAL;
+
+	if ((p->required_mask & bitmap) != p->required_mask)
+		return 0;
+	if (p->anyof_mask && !(p->anyof_mask & bitmap))
+		return 0;
+	if (p->excluded_mask & bitmap)
+		return 0;
+
+	bitmap &= p->return_mask;
+	if (!bitmap)
+		return 0;
+
+	if (cur->bitmap == bitmap &&
+	    cur->start + cur->len * PAGE_SIZE == addr) {
+		cur->len += n_pages;
+		p->found_pages += n_pages;
+	} else {
+		/*
+		 * All data is copied to cur first. When more data is found, we
+		 * push cur to vec and copy new data to cur. The vec_index
+		 * represents the current index of vec array. We add 1 to the
+		 * vec_index while performing checks to account for data in cur.
+		 */
+		if (cur->len && (p->vec_index + 1) >= p->vec_len)
+			return -ENOSPC;
+
+		if (cur->len) {
+			memcpy(&p->vec[p->vec_index], cur, sizeof(*p->vec));
+			p->vec_index++;
+		}
+
+		cur->start = addr;
+		cur->len = n_pages;
+		cur->bitmap = bitmap;
+		p->found_pages += n_pages;
+	}
+
+	if (p->max_pages && (p->found_pages == p->max_pages))
+		return PM_SCAN_FOUND_MAX_PAGES;
+
+	return 0;
+}
+
+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;
+	unsigned long addr = end;
+	pte_t *pte, *orig_pte;
+	spinlock_t *ptl;
+	bool is_written;
+	int ret = 0;
+
+	arch_enter_lazy_mmu_mode();
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	ptl = pmd_trans_huge_lock(pmd, vma);
+	if (ptl) {
+		unsigned long n_pages = (end - start)/PAGE_SIZE;
+
+		if (p->max_pages && n_pages > p->max_pages - p->found_pages)
+			n_pages = p->max_pages - p->found_pages;
+
+		is_written = !is_pmd_uffd_wp(*pmd);
+
+		/*
+		 * Break huge page into small pages if the WP operation need to
+		 * be performed is on a portion of the huge page.
+		 */
+		if (is_written && IS_PM_SCAN_WP(p->flags) &&
+		    n_pages < HPAGE_SIZE/PAGE_SIZE) {
+			spin_unlock(ptl);
+
+			split_huge_pmd(vma, pmd, start);
+			goto process_smaller_pages;
+		}
+
+		if (IS_PM_SCAN_GET(p->flags))
+			ret = pagemap_scan_output(is_written, vma->vm_file,
+						  pmd_present(*pmd),
+						  is_swap_pmd(*pmd),
+						  p, start, n_pages);
+
+		if (ret >= 0 && is_written && IS_PM_SCAN_WP(p->flags))
+			make_uffd_wp_pmd(vma, addr, pmd);
+
+		if (IS_PM_SCAN_WP(p->flags))
+			flush_tlb_range(vma, start, end);
+
+		spin_unlock(ptl);
+
+		arch_leave_lazy_mmu_mode();
+		return ret;
+	}
+
+process_smaller_pages:
+	if (pmd_trans_unstable(pmd)) {
+		arch_leave_lazy_mmu_mode();
+		return 0;
+	}
+#endif
+
+	orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
+	for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) {
+		is_written = !is_pte_uffd_wp(*pte);
+
+		if (IS_PM_SCAN_GET(p->flags))
+			ret = pagemap_scan_output(is_written, vma->vm_file,
+						  pte_present(*pte),
+						  is_swap_pte(*pte),
+						  p, addr, 1);
+
+		if (ret >= 0 && is_written && IS_PM_SCAN_WP(p->flags))
+			make_uffd_wp_pte(vma, addr, pte);
+	}
+
+	if (IS_PM_SCAN_WP(p->flags))
+		flush_tlb_range(vma, start, addr);
+
+	pte_unmap_unlock(orig_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)
+{
+	unsigned long n_pages = (end - start)/PAGE_SIZE;
+	struct pagemap_scan_private *p = walk->private;
+	struct vm_area_struct *vma = walk->vma;
+	struct hstate *h = hstate_vma(vma);
+	spinlock_t *ptl;
+	bool is_written;
+	int ret = 0;
+	pte_t pte;
+
+	arch_enter_lazy_mmu_mode();
+
+	if (p->max_pages && n_pages > p->max_pages - p->found_pages)
+		n_pages = p->max_pages - p->found_pages;
+
+	if (IS_PM_SCAN_WP(p->flags)) {
+		i_mmap_lock_write(vma->vm_file->f_mapping);
+		ptl = huge_pte_lock(h, vma->vm_mm, ptep);
+	}
+
+	pte = huge_ptep_get(ptep);
+	is_written = !is_huge_pte_uffd_wp(pte);
+
+	/*
+	 * Partial hugetlb page clear isn't supported
+	 */
+	if (is_written && IS_PM_SCAN_WP(p->flags) &&
+	    n_pages < HPAGE_SIZE/PAGE_SIZE) {
+		ret = -EPERM;
+		goto unlock_and_return;
+	}
+
+	if (IS_PM_SCAN_GET(p->flags)) {
+		ret = pagemap_scan_output(is_written, vma->vm_file,
+					  pte_present(pte), is_swap_pte(pte),
+					  p, start, n_pages);
+		if (ret < 0)
+			goto unlock_and_return;
+	}
+
+	if (is_written && IS_PM_SCAN_WP(p->flags)) {
+		make_uffd_wp_huge_pte(vma, start, ptep, pte);
+		flush_hugetlb_tlb_range(vma, start, end);
+	}
+
+unlock_and_return:
+	if (IS_PM_SCAN_WP(p->flags)) {
+		spin_unlock(ptl);
+		i_mmap_unlock_write(vma->vm_file->f_mapping);
+	}
+
+	arch_leave_lazy_mmu_mode();
+
+	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)
+{
+	unsigned long n_pages = (end - addr)/PAGE_SIZE;
+	struct pagemap_scan_private *p = walk->private;
+	struct vm_area_struct *vma = walk->vma;
+	int ret = 0;
+
+	if (!vma || !IS_PM_SCAN_GET(p->flags))
+		return 0;
+
+	if (p->max_pages && n_pages > p->max_pages - p->found_pages)
+		n_pages = p->max_pages - p->found_pages;
+
+	ret = pagemap_scan_output(false, vma->vm_file, false, false, p, addr,
+				  n_pages);
+
+	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_args_valid(struct pm_scan_arg *arg, unsigned long start,
+				   struct page_region __user *vec)
+{
+	/* Detect illegal size, flags, len and masks */
+	if (arg->size != sizeof(struct pm_scan_arg))
+		return -EINVAL;
+	if (arg->flags & ~PM_SCAN_OPS)
+		return -EINVAL;
+	if (!arg->len)
+		return -EINVAL;
+	if ((arg->required_mask | arg->anyof_mask | arg->excluded_mask |
+	     arg->return_mask) & ~PM_SCAN_BITS_ALL)
+		return -EINVAL;
+	if (!arg->required_mask && !arg->anyof_mask &&
+	    !arg->excluded_mask)
+		return -EINVAL;
+	if (!arg->return_mask)
+		return -EINVAL;
+
+	/* Validate memory range */
+	if (!IS_ALIGNED(start, PAGE_SIZE))
+		return -EINVAL;
+	if (!access_ok((void __user *)start, arg->len))
+		return -EFAULT;
+
+	if (IS_PM_SCAN_GET(arg->flags)) {
+		if (!arg->vec)
+			return -EINVAL;
+		if (arg->vec_len == 0)
+			return -EINVAL;
+	}
+
+	if (IS_PM_SCAN_WP(arg->flags)) {
+		if (!IS_PM_SCAN_GET(arg->flags) && arg->max_pages)
+			return -EINVAL;
+
+		if ((arg->required_mask | arg->anyof_mask | arg->excluded_mask) &
+		    ~PAGE_IS_WRITTEN)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+static long do_pagemap_scan(struct mm_struct *mm,
+			    struct pm_scan_arg __user *uarg)
+{
+	unsigned long start, end, walk_start, walk_end;
+	unsigned long empty_slots, vec_index = 0;
+	struct mmu_notifier_range range;
+	struct page_region __user *vec;
+	struct pagemap_scan_private p;
+	struct pm_scan_arg arg;
+	int ret = 0;
+
+	if (copy_from_user(&arg, uarg, sizeof(arg)))
+		return -EFAULT;
+
+	start = untagged_addr((unsigned long)arg.start);
+	vec = (struct page_region *)untagged_addr((unsigned long)arg.vec);
+
+	ret = pagemap_scan_args_valid(&arg, start, vec);
+	if (ret)
+		return ret;
+
+	end = start + arg.len;
+	p.max_pages = arg.max_pages;
+	p.found_pages = 0;
+	p.flags = arg.flags;
+	p.required_mask = arg.required_mask;
+	p.anyof_mask = arg.anyof_mask;
+	p.excluded_mask = arg.excluded_mask;
+	p.return_mask = arg.return_mask;
+	p.cur.start = p.cur.len = p.cur.bitmap = 0;
+	p.vec = NULL;
+	p.vec_len = PAGEMAP_WALK_SIZE >> PAGE_SHIFT;
+
+	/*
+	 * Allocate smaller buffer to get output from inside the page walk
+	 * functions and walk page range in PAGEMAP_WALK_SIZE size chunks. As
+	 * we want to return output to user in compact form where no two
+	 * consecutive regions should be continuous and have the same flags.
+	 * So store the latest element in p.cur between different walks and
+	 * store the p.cur at the end of the walk to the user buffer.
+	 */
+	if (IS_PM_SCAN_GET(p.flags)) {
+		p.vec = kmalloc_array(p.vec_len, sizeof(*p.vec), GFP_KERNEL);
+		if (!p.vec)
+			return -ENOMEM;
+	}
+
+	if (IS_PM_SCAN_WP(p.flags)) {
+		mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0,
+					mm, start, end);
+		mmu_notifier_invalidate_range_start(&range);
+	}
+
+	walk_start = walk_end = start;
+	while (walk_end < end && !ret) {
+		if (IS_PM_SCAN_GET(p.flags)) {
+			p.vec_index = 0;
+
+			empty_slots = arg.vec_len - vec_index;
+			p.vec_len = min(p.vec_len, empty_slots);
+		}
+
+		walk_end = (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK;
+		if (walk_end > end)
+			walk_end = end;
+
+		ret = mmap_read_lock_killable(mm);
+		if (ret)
+			goto free_data;
+		ret = walk_page_range(mm, walk_start, walk_end,
+				      &pagemap_scan_ops, &p);
+		mmap_read_unlock(mm);
+
+		if (ret && ret != -ENOSPC && ret != PM_SCAN_FOUND_MAX_PAGES)
+			goto free_data;
+
+		walk_start = walk_end;
+		if (IS_PM_SCAN_GET(p.flags) && p.vec_index) {
+			if (copy_to_user(&vec[vec_index], p.vec,
+					 p.vec_index * sizeof(*p.vec))) {
+				/*
+				 * Return error even though the OP succeeded
+				 */
+				ret = -EFAULT;
+				goto free_data;
+			}
+			vec_index += p.vec_index;
+		}
+	}
+
+	if (IS_PM_SCAN_WP(p.flags))
+		mmu_notifier_invalidate_range_end(&range);
+
+	if (IS_PM_SCAN_GET(p.flags) && p.cur.len) {
+		if (copy_to_user(&vec[vec_index], &p.cur, sizeof(*p.vec))) {
+			ret = -EFAULT;
+			goto free_data;
+		}
+		vec_index++;
+	}
+
+	ret = vec_index;
+
+free_data:
+	kfree(p.vec);
+	return ret;
+}
+
+static long do_pagemap_cmd(struct file *file, unsigned int cmd,
+			   unsigned long arg)
+{
+	struct pm_scan_arg __user *uarg = (struct pm_scan_arg __user *)arg;
+	struct mm_struct *mm = file->private_data;
+
+	switch (cmd) {
+	case PAGEMAP_SCAN:
+		return do_pagemap_scan(mm, uarg);
+
+	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/uapi/linux/fs.h b/include/uapi/linux/fs.h
index b7b56871029c..47879c38ce2f 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -305,4 +305,57 @@ 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 the bitmap of the page_region and masks in pm_scan_args */
+#define PAGE_IS_WRITTEN		(1 << 0)
+#define PAGE_IS_FILE		(1 << 1)
+#define PAGE_IS_PRESENT		(1 << 2)
+#define PAGE_IS_SWAPPED		(1 << 3)
+
+/*
+ * struct page_region - Page region with bitmap flags
+ * @start:	Start of the region
+ * @len:	Length of the region in pages
+ * bitmap:	Bits sets for the region
+ */
+struct page_region {
+	__u64 start;
+	__u64 len;
+	__u64 bitmap;
+};
+
+/*
+ * struct pm_scan_arg - Pagemap ioctl argument
+ * @size:		Size of the structure
+ * @flags:		Flags for the IOCTL
+ * @start:		Starting address of the region
+ * @len:		Length of the region (All the pages in this length are included)
+ * @vec:		Address of page_region struct array for output
+ * @vec_len:		Length of the page_region struct array
+ * @max_pages:		Optional max return pages
+ * @required_mask:	Required mask - All of these bits have to be set in the PTE
+ * @anyof_mask:		Any mask - Any of these bits are set in the PTE
+ * @excluded_mask:	Exclude mask - None of these bits are set in the PTE
+ * @return_mask:	Bits that are to be reported in page_region
+ */
+struct pm_scan_arg {
+	__u64 size;
+	__u64 flags;
+	__u64 start;
+	__u64 len;
+	__u64 vec;
+	__u64 vec_len;
+	__u64 max_pages;
+	__u64 required_mask;
+	__u64 anyof_mask;
+	__u64 excluded_mask;
+	__u64 return_mask;
+};
+
+/* Supported flags */
+#define PM_SCAN_OP_GET	(1 << 0)
+#define PM_SCAN_OP_WP	(1 << 1)
+
 #endif /* _UAPI_LINUX_FS_H */
-- 
2.39.2

[PATCH v16 3/5] 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>
---
 tools/include/uapi/linux/fs.h | 53 +++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/tools/include/uapi/linux/fs.h b/tools/include/uapi/linux/fs.h
index b7b56871029c..47879c38ce2f 100644
--- a/tools/include/uapi/linux/fs.h
+++ b/tools/include/uapi/linux/fs.h
@@ -305,4 +305,57 @@ 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 the bitmap of the page_region and masks in pm_scan_args */
+#define PAGE_IS_WRITTEN		(1 << 0)
+#define PAGE_IS_FILE		(1 << 1)
+#define PAGE_IS_PRESENT		(1 << 2)
+#define PAGE_IS_SWAPPED		(1 << 3)
+
+/*
+ * struct page_region - Page region with bitmap flags
+ * @start:	Start of the region
+ * @len:	Length of the region in pages
+ * bitmap:	Bits sets for the region
+ */
+struct page_region {
+	__u64 start;
+	__u64 len;
+	__u64 bitmap;
+};
+
+/*
+ * struct pm_scan_arg - Pagemap ioctl argument
+ * @size:		Size of the structure
+ * @flags:		Flags for the IOCTL
+ * @start:		Starting address of the region
+ * @len:		Length of the region (All the pages in this length are included)
+ * @vec:		Address of page_region struct array for output
+ * @vec_len:		Length of the page_region struct array
+ * @max_pages:		Optional max return pages
+ * @required_mask:	Required mask - All of these bits have to be set in the PTE
+ * @anyof_mask:		Any mask - Any of these bits are set in the PTE
+ * @excluded_mask:	Exclude mask - None of these bits are set in the PTE
+ * @return_mask:	Bits that are to be reported in page_region
+ */
+struct pm_scan_arg {
+	__u64 size;
+	__u64 flags;
+	__u64 start;
+	__u64 len;
+	__u64 vec;
+	__u64 vec_len;
+	__u64 max_pages;
+	__u64 required_mask;
+	__u64 anyof_mask;
+	__u64 excluded_mask;
+	__u64 return_mask;
+};
+
+/* Supported flags */
+#define PM_SCAN_OP_GET	(1 << 0)
+#define PM_SCAN_OP_WP	(1 << 1)
+
 #endif /* _UAPI_LINUX_FS_H */
-- 
2.39.2

[PATCH v16 4/5] 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 v16:
- Update the documentation

Changes in v11:
- Add more documentation
---
 Documentation/admin-guide/mm/pagemap.rst | 58 ++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index c8f380271cad..3b977526d4b3 100644
--- a/Documentation/admin-guide/mm/pagemap.rst
+++ b/Documentation/admin-guide/mm/pagemap.rst
@@ -227,3 +227,61 @@ 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 been written-to (``PAGE_IS_WRITTEN``),
+  file mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``) or swapped
+  (``PAGE_IS_SWAPPED``).
+- Find pages which have been written-to and/or write protect the pages atomically
+  (atomic ``PM_SCAN_OP_GET + PM_SCAN_OP_WP``)
+
+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_OP_GET``
+    and ``PM_SCAN_OP_WP`` are the only added flags at this time.
+ 3. The range is specified through ``start`` and ``len``.
+ 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 ``required_mask``, ``anyof_mask``,
+    ``excluded_ mask`` 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`` un-set, ``required_mask``
+        is set to ``PAGE_IS_FILE``, ``exclude_mask`` 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, ``anyof_masks`` is set to  ``PAGE_IS_FILE | PAGE_IS_SWAPPED``.
+    3. To find written pages and engage write protect, ``PAGE_IS_WRITTEN`` is
+       specified in ``required_mask`` and ``return_mask``. In addition to
+       specifying the output buffer in ``vec`` and length in ``vec_len``, the
+       ``PM_SCAN_OP_WP`` 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 household 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 the 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 v16 5/5] 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 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..92
ok 1 sanity_tests_sd memory size must be valid
ok 2 sanity_tests_sd output buffer must be specified
ok 3 sanity_tests_sd output buffer size must be valid
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 cannot be specified with PM_SCAN_OP_WP
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
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 46 50
ok 19 Page testing: all new pages must not be written (dirty)
ok 20 Page testing: all pages must be written (dirty)
ok 21 Page testing: all pages dirty other than first and the last one
ok 22 Page testing: PM_SCAN_OP_WP
ok 23 Page testing: only middle page dirty
ok 24 Page testing: only two middle pages dirty
ok 25 Large Page testing: all new pages must not be written (dirty)
ok 26 Large Page testing: all pages must be written (dirty)
ok 27 Large Page testing: all pages dirty other than first and the last one
ok 28 Large Page testing: PM_SCAN_OP_WP
ok 29 Large Page testing: only middle page dirty
ok 30 Large Page testing: only two middle pages dirty
ok 31 Huge page testing: all new pages must not be written (dirty)
ok 32 Huge page testing: all pages must be written (dirty)
ok 33 Huge page testing: all pages dirty other than first and the last one
ok 34 Huge page testing: PM_SCAN_OP_WP
ok 35 Huge page testing: only middle page dirty
ok 36 Huge page testing: only two middle pages dirty
ok 37 Hugetlb shmem testing: all new pages must not be written (dirty)
ok 38 Hugetlb shmem testing: all pages must be written (dirty)
ok 39 Hugetlb shmem testing: all pages dirty other than first and the last one
ok 40 Hugetlb shmem testing: PM_SCAN_OP_WP
ok 41 Hugetlb shmem testing: only middle page dirty
ok 42 Hugetlb shmem testing: only two middle pages dirty
ok 43 Hugetlb mem testing: all new pages must not be written (dirty)
ok 44 Hugetlb mem testing: all pages must be written (dirty)
ok 45 Hugetlb mem testing: all pages dirty other than first and the last one
ok 46 Hugetlb mem testing: PM_SCAN_OP_WP
ok 47 Hugetlb mem testing: only middle page dirty
ok 48 Hugetlb mem testing: only two middle pages dirty
ok 49 File memory testing: all new pages must not be written (dirty)
ok 50 File memory testing: all pages must be written (dirty)
ok 51 File memory testing: all pages dirty other than first and the last one
ok 52 File memory testing: PM_SCAN_OP_WP
ok 53 File memory testing: only middle page dirty
ok 54 File memory testing: only two middle pages dirty
ok 55 File anonymous memory testing: all new pages must not be written (dirty)
ok 56 File anonymous memory testing: all pages must be written (dirty)
ok 57 File anonymous memory testing: all pages dirty other than first and the last one
ok 58 File anonymous memory testing: PM_SCAN_OP_WP
ok 59 File anonymous memory testing: only middle page dirty
ok 60 File anonymous memory testing: only two middle pages dirty
ok 61 hpage_unit_tests all new huge page must not be written (dirty)
ok 62 hpage_unit_tests all the huge page must not be written
ok 63 hpage_unit_tests all the huge page must be written and clear
ok 64 hpage_unit_tests only middle page written
ok 65 hpage_unit_tests clear first half of huge page
ok 66 hpage_unit_tests clear first half of huge page with limited buffer
ok 67 hpage_unit_tests clear second half huge page
ok 68 hpage_unit_tests get half huge page
ok 69 hpage_unit_tests get half huge page
ok 70 Test test_simple
ok 71 mprotect_tests Both pages written
ok 72 mprotect_tests Both pages are not written (dirty)
ok 73 mprotect_tests Both pages written after remap and mprotect
ok 74 mprotect_tests Clear and make the pages written
ok 75 transact_test count 192
ok 76 transact_test count 0
ok 77 transact_test Extra pages 0 (0.0%), extra thread faults 0.
ok 78 sanity_tests clear op can only be specified with PAGE_IS_WRITTEN
ok 79 sanity_tests required_mask specified
ok 80 sanity_tests anyof_mask specified
ok 81 sanity_tests excluded_mask specified
ok 82 sanity_tests required_mask and anyof_mask specified
ok 83 sanity_tests Get sd and present pages with anyof_mask
ok 84 sanity_tests Get all the pages with required_mask
ok 85 sanity_tests Get sd and present pages with required_mask and anyof_mask
ok 86 sanity_tests Don't get sd pages
ok 87 sanity_tests Don't get present pages
ok 88 sanity_tests Find written present pages with return mask
ok 89 sanity_tests Memory mapped file
ok 90 sanity_tests Read/write to private memory mapped file
ok 91 unmapped_region_tests Get status of pages
ok 92 userfaultfd_tests all new pages must not be written (dirty)
 # Totals: pass:92 fail:0 xfail:0 xpass:0 skip:0 error:0
---
 tools/testing/selftests/mm/.gitignore      |    1 +
 tools/testing/selftests/mm/Makefile        |    3 +-
 tools/testing/selftests/mm/config          |    1 +
 tools/testing/selftests/mm/pagemap_ioctl.c | 1459 ++++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh  |    4 +
 5 files changed, 1467 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/mm/pagemap_ioctl.c
 mode change 100644 => 100755 tools/testing/selftests/mm/run_vmtests.sh

diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
index 8917455f4f51..f1a06f842d55 100644
--- a/tools/testing/selftests/mm/.gitignore
+++ b/tools/testing/selftests/mm/.gitignore
@@ -17,6 +17,7 @@ mremap_dontunmap
 mremap_test
 on-fault-limit
 transhuge-stress
+pagemap_ioctl
 protection_keys
 protection_keys_32
 protection_keys_64
diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index dda8598bf5ef..f28c10c3dc8b 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -30,7 +30,7 @@ MACHINE ?= $(shell echo $(uname_M) | sed -e 's/aarch64.*/arm64/' -e 's/ppc64.*/p
 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
@@ -55,6 +55,7 @@ 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 be087c4bc396..4309916f629e 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 000000000000..1c2d0034c0dc
--- /dev/null
+++ b/tools/testing/selftests/mm/pagemap_ioctl.c
@@ -0,0 +1,1459 @@
+// 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_WRITTEN | PAGE_IS_FILE |	\
+					 PAGE_IS_PRESENT | PAGE_IS_SWAPPED)
+#define PAGEMAP_NON_WRITTEN_BITS	(PAGE_IS_FILE |	PAGE_IS_PRESENT |	\
+					 PAGE_IS_SWAPPED)
+
+#define TEST_ITERATIONS 100
+#define PAGEMAP "/proc/self/pagemap"
+int pagemap_fd;
+int uffd;
+int page_size;
+int hpage_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.len = 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.required_mask = required_mask;
+	arg.anyof_mask = anyof_mask;
+	arg.excluded_mask = excluded_mask;
+	arg.return_mask = return_mask;
+
+	return ioctl(pagemap_fd, PAGEMAP_SCAN, &arg);
+}
+
+int init_uffd(void)
+{
+	struct uffdio_api uffdio_api;
+
+	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
+	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_OP_WP,
+				  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_OP_GET | PM_SCAN_OP_WP,
+				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 += vec[i].len;
+
+	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];
+
+	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, PM_SCAN_OP_GET,
+				       0, PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL) < 0,
+			 "%s memory size must be valid\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, NULL, vec_size, PM_SCAN_OP_GET,
+				       0, PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL) < 0,
+			 "%s output buffer must be specified\n", __func__);
+
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, 0, PM_SCAN_OP_GET,
+				       0, PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL) < 0,
+			 "%s output buffer size must be valid\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_OP_GET | PM_SCAN_OP_WP | 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, PM_SCAN_OP_GET,
+				       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, PM_SCAN_OP_GET,
+				       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, PM_SCAN_OP_GET,
+				       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_OP_GET | PM_SCAN_OP_WP,
+				       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_OP_GET | PM_SCAN_OP_WP,
+				       0, 0, 0, PAGEMAP_BITS_ALL, PAGE_IS_WRITTEN) < 0,
+			 "%s PAGEMAP_BITS_ALL cannot be specified with PM_SCAN_OP_WP\n", __func__);
+
+	/* 2. Clear area with larger vec size */
+	ret = pagemap_ioctl(mem, mem_size, vec, vec_size, PM_SCAN_OP_GET | PM_SCAN_OP_WP, 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, PM_SCAN_OP_GET, 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_OP_GET | PM_SCAN_OP_WP,
+			    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, PM_SCAN_OP_GET, 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_OP_GET | PM_SCAN_OP_WP,
+			     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\n",
+			 __func__);
+
+	/* 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_OP_GET | PM_SCAN_OP_WP,
+			    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_OP_GET | PM_SCAN_OP_WP,
+			     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_OP_GET | PM_SCAN_OP_WP,
+			    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, PM_SCAN_OP_GET, 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 && vec[0].len == 2 &&
+			 vec[0].start == (uintptr_t)(mem + page_size) &&
+			 ret2 == 2 && vec2[0].len == 1 && vec2[0].start == (uintptr_t)mem &&
+			 vec2[1].len == 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, PM_SCAN_OP_GET, 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].len == 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_OP_GET | PM_SCAN_OP_WP, 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_OP_GET | PM_SCAN_OP_WP,
+			    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_OP_GET | PM_SCAN_OP_WP,
+			    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_OP_GET | PM_SCAN_OP_WP,
+			    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;//mem_size/(page_size * 10);
+
+	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;
+
+		for (i = 0; i < mem_size; i += page_size) {
+			if (rand() % 2) {
+				mem[i]++;
+				total_writes++;
+			}
+		}
+
+		while (total_reads < total_writes) {
+			ret = pagemap_ioctl(mem, mem_size, vec, vec_size,
+					    PM_SCAN_OP_GET | PM_SCAN_OP_WP,
+					    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));
+
+			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 %d %d\n", ret, vec_size);
+
+	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_OP_WP\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_OP_GET | PM_SCAN_OP_WP, 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, PM_SCAN_OP_GET, 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].len == 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_OP_GET | PM_SCAN_OP_WP, 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_OP_GET | PM_SCAN_OP_WP, 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].len >= vec_size - 2 && vec[0].len <= vec_size,
+			 "%s all pages dirty other than first and the last one\n", prefix);
+
+	written = pagemap_ioctl(mem, mem_size, vec, 1, PM_SCAN_OP_GET, 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_OP_WP\n", prefix);
+
+	/* 4. only middle page dirty */
+	written = pagemap_ioctl(mem, mem_size, vec, 1, PM_SCAN_OP_GET | PM_SCAN_OP_WP, 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, PM_SCAN_OP_GET, 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].len >= 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_OP_GET | PM_SCAN_OP_WP, 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, PM_SCAN_OP_GET,
+				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])
+			 && vec[0].len == 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_OP_GET | PM_SCAN_OP_WP, 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, PM_SCAN_OP_GET, 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_OP_GET | PM_SCAN_OP_WP,
+				    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 &&
+				 vec[0].len == vec_size && vec[0].bitmap == 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, PM_SCAN_OP_GET, 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].len > 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, PM_SCAN_OP_GET, 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].len == 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_OP_GET | PM_SCAN_OP_WP,
+				    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, PM_SCAN_OP_GET, 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].len == 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_OP_GET | PM_SCAN_OP_WP, 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, PM_SCAN_OP_GET, 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].len == 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_OP_GET | PM_SCAN_OP_WP,
+				    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 && vec[0].len == hpage_size/(2*page_size),
+				 "%s get half huge page\n", __func__);
+
+		ret2 = pagemap_ioctl(map, map_size, vec, vec_size, PM_SCAN_OP_GET, 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 && vec[0].len == (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, PM_SCAN_OP_GET, 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, PM_SCAN_OP_GET, 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, PM_SCAN_OP_GET, 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;
+
+	/* 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_OP_GET | PM_SCAN_OP_WP, 0, PAGEMAP_BITS_ALL, 0, 0,
+				       PAGEMAP_BITS_ALL) < 0,
+			 "%s clear op can only be specified with PAGE_IS_WRITTEN\n", __func__);
+	ksft_test_result(pagemap_ioctl(mem, mem_size, vec, vec_size, PM_SCAN_OP_GET, 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, PM_SCAN_OP_GET, 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, PM_SCAN_OP_GET, 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, PM_SCAN_OP_GET, 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, PM_SCAN_OP_GET, 0,
+			    0, PAGEMAP_BITS_ALL, 0, PAGEMAP_BITS_ALL);
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)mem && vec[0].len == vec_size &&
+			 vec[0].bitmap == (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, PM_SCAN_OP_GET, 0,
+			    PAGEMAP_BITS_ALL, 0, 0, PAGEMAP_BITS_ALL);
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)mem && vec[0].len == vec_size &&
+			 vec[0].bitmap == (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, PM_SCAN_OP_GET, 0,
+			    PAGE_IS_WRITTEN, PAGE_IS_PRESENT, 0, PAGEMAP_BITS_ALL);
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)mem && vec[0].len == vec_size &&
+			 vec[0].bitmap == (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, PM_SCAN_OP_GET, 0,
+			    0, 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, PM_SCAN_OP_GET, 0,
+			    0, 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_OP_GET, 0,
+			    0, PAGEMAP_BITS_ALL, 0, PAGE_IS_WRITTEN);
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)mem && vec[0].len == vec_size &&
+			 vec[0].bitmap == 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));
+
+	ret = pagemap_ioctl(fmem, sbuf.st_size, vec, vec_size, PM_SCAN_OP_GET, 0,
+			    0, PAGEMAP_NON_WRITTEN_BITS, 0, PAGEMAP_NON_WRITTEN_BITS);
+
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)fmem &&
+			 vec[0].len == ceilf((float)sbuf.st_size/page_size) &&
+			 vec[0].bitmap == 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, 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");
+
+	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] = i;
+
+	ret = pagemap_ioctl(fmem, buf_size, vec, vec_size, PM_SCAN_OP_GET, 0,
+			    PAGE_IS_WRITTEN | PAGE_IS_FILE, PAGE_IS_PRESENT | PAGE_IS_SWAPPED, 0,
+			    PAGEMAP_BITS_ALL);
+
+	ksft_test_result(ret >= 0 && vec[0].start == (uintptr_t)fmem &&
+			 vec[0].len == (buf_size/page_size) &&
+			 (vec[0].bitmap | PAGE_IS_WRITTEN) && (vec[0].bitmap | PAGE_IS_FILE),
+			 "%s Read/write to private memory mapped file\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, PM_SCAN_OP_GET, 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.len == 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, PM_SCAN_OP_GET, 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, PM_SCAN_OP_GET, 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.len == 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, PM_SCAN_OP_GET, 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.len == 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.len = count * page_size;
+	arg.vec = (uintptr_t)rgns;
+	arg.vec_len = sizeof(rgns) / sizeof(*rgns);
+	arg.flags = PM_SCAN_OP_GET;
+	if (reset)
+		arg.flags |= PM_SCAN_OP_WP;
+	arg.required_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].bitmap != PAGE_IS_WRITTEN)
+			ksft_exit_fail_msg("wrong bitmap\n");
+
+		for (j = 0; j < rgns[i].len; ++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(92);
+
+	page_size = getpagesize();
+	hpage_size = read_pmd_pagesize();
+
+	pagemap_fd = open(PAGEMAP, O_RDWR);
+	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
old mode 100644
new mode 100755
index eb25f238f5b8..fa77c8af2b0c
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -53,6 +53,8 @@ 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"
@@ -282,6 +284,8 @@ 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 v16 0/5] Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

Hello Peter, David, Michal, Mike, Danylo and Andrei,

I hope you are well. You (and some other) guys have been helping and
reviewing up to this point. Thank you so much! Please review them again and
mention if anything comes to your mind. Please send review tags or tested
by tags in the hope that we merge these soon for next release. Current
patches fulfill all of our requirement regarding ABI and performance. I
guess, we should merge now (if somethings comes up, we can always fix them
along the way).

Any thoughts/comments are welcome. I'm sending this email as we have not
had much reviews in the past 3-4 revisions.

Thanks,
Usama

On 5/25/23 1:55 PM, Muhammad Usama Anjum wrote:
> *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() syscall [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.
> 
> 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 been written-to (PAGE_IS_WRITTEN),
>   file mapped (PAGE_IS_FILE), present (PAGE_IS_PRESENT) or swapped
>   (PAGE_IS_SWAPPED).
> - Write-protect the pages (PAGEMAP_WP_ENGAGE) to start finding which
>   pages have been written-to.
> - Find pages which have been written-to and write protect the pages
>   (atomic PAGE_IS_WRITTEN + PAGEMAP_WP_ENGAGE)
> 
> 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-dirtyi 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 (4):
>   fs/proc/task_mmu: Implement IOCTL to get and optionally clear info
>     about PTEs
>   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     |   58 +
>  Documentation/admin-guide/mm/userfaultfd.rst |   35 +
>  fs/proc/task_mmu.c                           |  503 ++++++
>  fs/userfaultfd.c                             |   26 +-
>  include/linux/userfaultfd_k.h                |   21 +-
>  include/uapi/linux/fs.h                      |   53 +
>  include/uapi/linux/userfaultfd.h             |    9 +-
>  mm/hugetlb.c                                 |   32 +-
>  mm/memory.c                                  |   27 +-
>  tools/include/uapi/linux/fs.h                |   53 +
>  tools/testing/selftests/mm/.gitignore        |    1 +
>  tools/testing/selftests/mm/Makefile          |    3 +-
>  tools/testing/selftests/mm/config            |    1 +
>  tools/testing/selftests/mm/pagemap_ioctl.c   | 1459 ++++++++++++++++++
>  tools/testing/selftests/mm/run_vmtests.sh    |    4 +
>  15 files changed, 2262 insertions(+), 23 deletions(-)
>  create mode 100644 tools/testing/selftests/mm/pagemap_ioctl.c
>  mode change 100644 => 100755 tools/testing/selftests/mm/run_vmtests.sh
> 

-- 
BR,
Muhammad Usama Anjum

Re: [PATCH v16 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Peter Xu]

Muhammad,

Sorry, I probably can only review the non-interface part, and leave the
interface/buffer handling, etc. review for others and real potential users
of it..

On Thu, May 25, 2023 at 01:55:14PM +0500, Muhammad Usama Anjum wrote:
> +static inline void make_uffd_wp_huge_pte(struct vm_area_struct *vma,
> +					 unsigned long addr, pte_t *ptep,
> +					 pte_t ptent)
> +{
> +	pte_t old_pte;
> +
> +	if (!huge_pte_none(ptent)) {
> +		old_pte = huge_ptep_modify_prot_start(vma, addr, ptep);
> +		ptent = huge_pte_mkuffd_wp(old_pte);
> +		ptep_modify_prot_commit(vma, addr, ptep, old_pte, ptent);

huge_ptep_modify_prot_start()?

The other thing is what if it's a pte marker already?  What if a hugetlb
migration entry?  Please check hugetlb_change_protection().

> +	} else {
> +		set_huge_pte_at(vma->vm_mm, addr, ptep,
> +				make_pte_marker(PTE_MARKER_UFFD_WP));
> +	}
> +}
> +#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;
> +	unsigned long addr = end;
> +	pte_t *pte, *orig_pte;
> +	spinlock_t *ptl;
> +	bool is_written;
> +	int ret = 0;
> +
> +	arch_enter_lazy_mmu_mode();
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	ptl = pmd_trans_huge_lock(pmd, vma);
> +	if (ptl) {
> +		unsigned long n_pages = (end - start)/PAGE_SIZE;
> +
> +		if (p->max_pages && n_pages > p->max_pages - p->found_pages)
> +			n_pages = p->max_pages - p->found_pages;
> +
> +		is_written = !is_pmd_uffd_wp(*pmd);
> +
> +		/*
> +		 * Break huge page into small pages if the WP operation need to
> +		 * be performed is on a portion of the huge page.
> +		 */
> +		if (is_written && IS_PM_SCAN_WP(p->flags) &&
> +		    n_pages < HPAGE_SIZE/PAGE_SIZE) {
> +			spin_unlock(ptl);
> +
> +			split_huge_pmd(vma, pmd, start);
> +			goto process_smaller_pages;
> +		}
> +
> +		if (IS_PM_SCAN_GET(p->flags))
> +			ret = pagemap_scan_output(is_written, vma->vm_file,
> +						  pmd_present(*pmd),
> +						  is_swap_pmd(*pmd),
> +						  p, start, n_pages);
> +
> +		if (ret >= 0 && is_written && IS_PM_SCAN_WP(p->flags))
> +			make_uffd_wp_pmd(vma, addr, pmd);
> +
> +		if (IS_PM_SCAN_WP(p->flags))
> +			flush_tlb_range(vma, start, end);
> +
> +		spin_unlock(ptl);
> +
> +		arch_leave_lazy_mmu_mode();
> +		return ret;
> +	}
> +
> +process_smaller_pages:
> +	if (pmd_trans_unstable(pmd)) {
> +		arch_leave_lazy_mmu_mode();
> +		return 0;

I'm not sure whether this is right..  Shouldn't you return with -EAGAIN and
let the user retry?  Returning 0 means you'll move on with the next pmd
afaict and ignoring this one.

> +	}
> +#endif
> +
> +	orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);

Just a heads-up that this may start to fail at some point if Hugh's work
will land earlier:

https://lore.kernel.org/linux-mm/68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com/

> +	for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) {
> +		is_written = !is_pte_uffd_wp(*pte);
> +
> +		if (IS_PM_SCAN_GET(p->flags))
> +			ret = pagemap_scan_output(is_written, vma->vm_file,
> +						  pte_present(*pte),
> +						  is_swap_pte(*pte),
> +						  p, addr, 1);
> +
> +		if (ret >= 0 && is_written && IS_PM_SCAN_WP(p->flags))
> +			make_uffd_wp_pte(vma, addr, pte);
> +	}
> +
> +	if (IS_PM_SCAN_WP(p->flags))
> +		flush_tlb_range(vma, start, addr);
> +
> +	pte_unmap_unlock(orig_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)
> +{
> +	unsigned long n_pages = (end - start)/PAGE_SIZE;
> +	struct pagemap_scan_private *p = walk->private;
> +	struct vm_area_struct *vma = walk->vma;
> +	struct hstate *h = hstate_vma(vma);
> +	spinlock_t *ptl;
> +	bool is_written;
> +	int ret = 0;
> +	pte_t pte;
> +
> +	arch_enter_lazy_mmu_mode();

This _seems_ to be not needed for hugetlb entries.

> +
> +	if (p->max_pages && n_pages > p->max_pages - p->found_pages)
> +		n_pages = p->max_pages - p->found_pages;
> +
> +	if (IS_PM_SCAN_WP(p->flags)) {
> +		i_mmap_lock_write(vma->vm_file->f_mapping);
> +		ptl = huge_pte_lock(h, vma->vm_mm, ptep);
> +	}
> +
> +	pte = huge_ptep_get(ptep);
> +	is_written = !is_huge_pte_uffd_wp(pte);
> +
> +	/*
> +	 * Partial hugetlb page clear isn't supported
> +	 */
> +	if (is_written && IS_PM_SCAN_WP(p->flags) &&
> +	    n_pages < HPAGE_SIZE/PAGE_SIZE) {
> +		ret = -EPERM;
> +		goto unlock_and_return;
> +	}
> +
> +	if (IS_PM_SCAN_GET(p->flags)) {
> +		ret = pagemap_scan_output(is_written, vma->vm_file,
> +					  pte_present(pte), is_swap_pte(pte),
> +					  p, start, n_pages);
> +		if (ret < 0)
> +			goto unlock_and_return;
> +	}
> +
> +	if (is_written && IS_PM_SCAN_WP(p->flags)) {
> +		make_uffd_wp_huge_pte(vma, start, ptep, pte);
> +		flush_hugetlb_tlb_range(vma, start, end);
> +	}
> +
> +unlock_and_return:
> +	if (IS_PM_SCAN_WP(p->flags)) {
> +		spin_unlock(ptl);
> +		i_mmap_unlock_write(vma->vm_file->f_mapping);
> +	}
> +
> +	arch_leave_lazy_mmu_mode();

Same here.

> +
> +	return ret;
> +}

[...]

-- 
Peter Xu

Re: [PATCH v16 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

On 6/1/23 2:46 AM, Peter Xu wrote:
> Muhammad,
> 
> Sorry, I probably can only review the non-interface part, and leave the
> interface/buffer handling, etc. review for others and real potential users
> of it..
Thank you so much for the review. I think mostly we should be okay with
interface as everybody has been making suggestions over the past revisions.

> 
> On Thu, May 25, 2023 at 01:55:14PM +0500, Muhammad Usama Anjum wrote:
>> +static inline void make_uffd_wp_huge_pte(struct vm_area_struct *vma,
>> +					 unsigned long addr, pte_t *ptep,
>> +					 pte_t ptent)
>> +{
>> +	pte_t old_pte;
>> +
>> +	if (!huge_pte_none(ptent)) {
>> +		old_pte = huge_ptep_modify_prot_start(vma, addr, ptep);
>> +		ptent = huge_pte_mkuffd_wp(old_pte);
>> +		ptep_modify_prot_commit(vma, addr, ptep, old_pte, ptent);
> 
> huge_ptep_modify_prot_start()?
Sorry, I didn't realized that huge_ptep_modify_prot_start() is different
from its pte version.

> 
> The other thing is what if it's a pte marker already?  What if a hugetlb
> migration entry?  Please check hugetlb_change_protection().
I've updated it in more better way. Please let me know what do you think
about the following:

static inline 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))
		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));
}

As we always set UNPOPULATED, so markers are always set on none ptes
initially. Is it possible that a none pte becomes present, then swapped and
finally none again? So I'll do the following addition for make_uffd_wp_pte():

--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1800,6 +1800,9 @@ static inline void make_uffd_wp_pte(struct
vm_area_struct *vma,
 	} 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));
 	}
 }




> 
>> +	} else {
>> +		set_huge_pte_at(vma->vm_mm, addr, ptep,
>> +				make_pte_marker(PTE_MARKER_UFFD_WP));
>> +	}
>> +}
>> +#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;
>> +	unsigned long addr = end;
>> +	pte_t *pte, *orig_pte;
>> +	spinlock_t *ptl;
>> +	bool is_written;
>> +	int ret = 0;
>> +
>> +	arch_enter_lazy_mmu_mode();
>> +
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> +	ptl = pmd_trans_huge_lock(pmd, vma);
>> +	if (ptl) {
>> +		unsigned long n_pages = (end - start)/PAGE_SIZE;
>> +
>> +		if (p->max_pages && n_pages > p->max_pages - p->found_pages)
>> +			n_pages = p->max_pages - p->found_pages;
>> +
>> +		is_written = !is_pmd_uffd_wp(*pmd);
>> +
>> +		/*
>> +		 * Break huge page into small pages if the WP operation need to
>> +		 * be performed is on a portion of the huge page.
>> +		 */
>> +		if (is_written && IS_PM_SCAN_WP(p->flags) &&
>> +		    n_pages < HPAGE_SIZE/PAGE_SIZE) {
>> +			spin_unlock(ptl);
>> +
>> +			split_huge_pmd(vma, pmd, start);
>> +			goto process_smaller_pages;
>> +		}
>> +
>> +		if (IS_PM_SCAN_GET(p->flags))
>> +			ret = pagemap_scan_output(is_written, vma->vm_file,
>> +						  pmd_present(*pmd),
>> +						  is_swap_pmd(*pmd),
>> +						  p, start, n_pages);
>> +
>> +		if (ret >= 0 && is_written && IS_PM_SCAN_WP(p->flags))
>> +			make_uffd_wp_pmd(vma, addr, pmd);
>> +
>> +		if (IS_PM_SCAN_WP(p->flags))
>> +			flush_tlb_range(vma, start, end);
>> +
>> +		spin_unlock(ptl);
>> +
>> +		arch_leave_lazy_mmu_mode();
>> +		return ret;
>> +	}
>> +
>> +process_smaller_pages:
>> +	if (pmd_trans_unstable(pmd)) {
>> +		arch_leave_lazy_mmu_mode();
>> +		return 0;
> 
> I'm not sure whether this is right..  Shouldn't you return with -EAGAIN and
> let the user retry?  Returning 0 means you'll move on with the next pmd
> afaict and ignoring this one.
This has come up before. We are just replicating pagemap_pmd_range() here
as we are doing almost the same thing through IOCTL. It doesn't return any
error in this case and just skips it. So we are doing the same.

> 
>> +	}
>> +#endif
>> +
>> +	orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
> 
> Just a heads-up that this may start to fail at some point if Hugh's work
> will land earlier:
> 
> https://lore.kernel.org/linux-mm/68a97fbe-5c1e-7ac6-72c-7b9c6290b370@google.com/
Thank you so much for the heads up.

> 
>> +	for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) {
>> +		is_written = !is_pte_uffd_wp(*pte);
>> +
>> +		if (IS_PM_SCAN_GET(p->flags))
>> +			ret = pagemap_scan_output(is_written, vma->vm_file,
>> +						  pte_present(*pte),
>> +						  is_swap_pte(*pte),
>> +						  p, addr, 1);
>> +
>> +		if (ret >= 0 && is_written && IS_PM_SCAN_WP(p->flags))
>> +			make_uffd_wp_pte(vma, addr, pte);
>> +	}
>> +
>> +	if (IS_PM_SCAN_WP(p->flags))
>> +		flush_tlb_range(vma, start, addr);
>> +
>> +	pte_unmap_unlock(orig_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)
>> +{
>> +	unsigned long n_pages = (end - start)/PAGE_SIZE;
>> +	struct pagemap_scan_private *p = walk->private;
>> +	struct vm_area_struct *vma = walk->vma;
>> +	struct hstate *h = hstate_vma(vma);
>> +	spinlock_t *ptl;
>> +	bool is_written;
>> +	int ret = 0;
>> +	pte_t pte;
>> +
>> +	arch_enter_lazy_mmu_mode();
> 
> This _seems_ to be not needed for hugetlb entries.
I'll remove it.

> 
>> +
>> +	if (p->max_pages && n_pages > p->max_pages - p->found_pages)
>> +		n_pages = p->max_pages - p->found_pages;
>> +
>> +	if (IS_PM_SCAN_WP(p->flags)) {
>> +		i_mmap_lock_write(vma->vm_file->f_mapping);
>> +		ptl = huge_pte_lock(h, vma->vm_mm, ptep);
>> +	}
>> +
>> +	pte = huge_ptep_get(ptep);
>> +	is_written = !is_huge_pte_uffd_wp(pte);
>> +
>> +	/*
>> +	 * Partial hugetlb page clear isn't supported
>> +	 */
>> +	if (is_written && IS_PM_SCAN_WP(p->flags) &&
>> +	    n_pages < HPAGE_SIZE/PAGE_SIZE) {
>> +		ret = -EPERM;
>> +		goto unlock_and_return;
>> +	}
>> +
>> +	if (IS_PM_SCAN_GET(p->flags)) {
>> +		ret = pagemap_scan_output(is_written, vma->vm_file,
>> +					  pte_present(pte), is_swap_pte(pte),
>> +					  p, start, n_pages);
>> +		if (ret < 0)
>> +			goto unlock_and_return;
>> +	}
>> +
>> +	if (is_written && IS_PM_SCAN_WP(p->flags)) {
>> +		make_uffd_wp_huge_pte(vma, start, ptep, pte);
>> +		flush_hugetlb_tlb_range(vma, start, end);
>> +	}
>> +
>> +unlock_and_return:
>> +	if (IS_PM_SCAN_WP(p->flags)) {
>> +		spin_unlock(ptl);
>> +		i_mmap_unlock_write(vma->vm_file->f_mapping);
>> +	}
>> +
>> +	arch_leave_lazy_mmu_mode();
> 
> Same here.
> 
>> +
>> +	return ret;
>> +}
> 
> [...]
> 

-- 
BR,
Muhammad Usama Anjum

Re: [PATCH v16 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Peter Xu]

On Thu, Jun 01, 2023 at 01:16:14PM +0500, Muhammad Usama Anjum wrote:
> On 6/1/23 2:46 AM, Peter Xu wrote:
> > Muhammad,
> > 
> > Sorry, I probably can only review the non-interface part, and leave the
> > interface/buffer handling, etc. review for others and real potential users
> > of it..
> Thank you so much for the review. I think mostly we should be okay with
> interface as everybody has been making suggestions over the past revisions.
> 
> > 
> > On Thu, May 25, 2023 at 01:55:14PM +0500, Muhammad Usama Anjum wrote:
> >> +static inline void make_uffd_wp_huge_pte(struct vm_area_struct *vma,
> >> +					 unsigned long addr, pte_t *ptep,
> >> +					 pte_t ptent)
> >> +{
> >> +	pte_t old_pte;
> >> +
> >> +	if (!huge_pte_none(ptent)) {
> >> +		old_pte = huge_ptep_modify_prot_start(vma, addr, ptep);
> >> +		ptent = huge_pte_mkuffd_wp(old_pte);
> >> +		ptep_modify_prot_commit(vma, addr, ptep, old_pte, ptent);
> > 
> > huge_ptep_modify_prot_start()?
> Sorry, I didn't realized that huge_ptep_modify_prot_start() is different
> from its pte version.

Here I meant huge_ptep_modify_prot_commit()..

> 
> > 
> > The other thing is what if it's a pte marker already?  What if a hugetlb
> > migration entry?  Please check hugetlb_change_protection().
> I've updated it in more better way. Please let me know what do you think
> about the following:
> 
> static inline 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))
> 		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));
> }

the is_pte_marker() check can be extended to double check
pte_marker_uffd_wp() bit, but shouldn't matter a lot since besides the
uffd-wp bit currently we only support swapin error which should sigbus when
accessed, so no point in tracking anyway.

> 
> As we always set UNPOPULATED, so markers are always set on none ptes
> initially. Is it possible that a none pte becomes present, then swapped and
> finally none again? So I'll do the following addition for make_uffd_wp_pte():
> 
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1800,6 +1800,9 @@ static inline void make_uffd_wp_pte(struct
> vm_area_struct *vma,
>  	} 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));
>  	}
>  }

Makes sense, you can leverage userfaultfd_wp_use_markers() here, and you
should probably keep the protocol (only set the marker when WP_UNPOPULATED
for anon).

> 
> 
> 
> 
> > 
> >> +	} else {
> >> +		set_huge_pte_at(vma->vm_mm, addr, ptep,
> >> +				make_pte_marker(PTE_MARKER_UFFD_WP));
> >> +	}
> >> +}
> >> +#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;
> >> +	unsigned long addr = end;
> >> +	pte_t *pte, *orig_pte;
> >> +	spinlock_t *ptl;
> >> +	bool is_written;
> >> +	int ret = 0;
> >> +
> >> +	arch_enter_lazy_mmu_mode();
> >> +
> >> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >> +	ptl = pmd_trans_huge_lock(pmd, vma);
> >> +	if (ptl) {
> >> +		unsigned long n_pages = (end - start)/PAGE_SIZE;
> >> +
> >> +		if (p->max_pages && n_pages > p->max_pages - p->found_pages)
> >> +			n_pages = p->max_pages - p->found_pages;
> >> +
> >> +		is_written = !is_pmd_uffd_wp(*pmd);
> >> +
> >> +		/*
> >> +		 * Break huge page into small pages if the WP operation need to
> >> +		 * be performed is on a portion of the huge page.
> >> +		 */
> >> +		if (is_written && IS_PM_SCAN_WP(p->flags) &&
> >> +		    n_pages < HPAGE_SIZE/PAGE_SIZE) {
> >> +			spin_unlock(ptl);
> >> +
> >> +			split_huge_pmd(vma, pmd, start);
> >> +			goto process_smaller_pages;
> >> +		}
> >> +
> >> +		if (IS_PM_SCAN_GET(p->flags))
> >> +			ret = pagemap_scan_output(is_written, vma->vm_file,
> >> +						  pmd_present(*pmd),
> >> +						  is_swap_pmd(*pmd),
> >> +						  p, start, n_pages);
> >> +
> >> +		if (ret >= 0 && is_written && IS_PM_SCAN_WP(p->flags))
> >> +			make_uffd_wp_pmd(vma, addr, pmd);
> >> +
> >> +		if (IS_PM_SCAN_WP(p->flags))
> >> +			flush_tlb_range(vma, start, end);
> >> +
> >> +		spin_unlock(ptl);
> >> +
> >> +		arch_leave_lazy_mmu_mode();
> >> +		return ret;
> >> +	}
> >> +
> >> +process_smaller_pages:
> >> +	if (pmd_trans_unstable(pmd)) {
> >> +		arch_leave_lazy_mmu_mode();
> >> +		return 0;
> > 
> > I'm not sure whether this is right..  Shouldn't you return with -EAGAIN and
> > let the user retry?  Returning 0 means you'll move on with the next pmd
> > afaict and ignoring this one.
> This has come up before. We are just replicating pagemap_pmd_range() here
> as we are doing almost the same thing through IOCTL. It doesn't return any
> error in this case and just skips it. So we are doing the same.

Hmm, is it a bug for pagemap?  pagemapread.buffer should be linear to the
address range to be scanned to me.  If it skips some unstable pmd without
filling in anything it seems everything later will be shifted with
PMD_SIZE..  I had a feeling that it should set walk->action==ACTION_AGAIN
before return.

-- 
Peter Xu

Re: [PATCH v16 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

On 6/2/23 1:11 AM, Peter Xu wrote:
> On Thu, Jun 01, 2023 at 01:16:14PM +0500, Muhammad Usama Anjum wrote:
>> On 6/1/23 2:46 AM, Peter Xu wrote:
>>> Muhammad,
>>>
>>> Sorry, I probably can only review the non-interface part, and leave the
>>> interface/buffer handling, etc. review for others and real potential users
>>> of it..
>> Thank you so much for the review. I think mostly we should be okay with
>> interface as everybody has been making suggestions over the past revisions.
>>
>>>
>>> On Thu, May 25, 2023 at 01:55:14PM +0500, Muhammad Usama Anjum wrote:
>>>> +static inline void make_uffd_wp_huge_pte(struct vm_area_struct *vma,
>>>> +					 unsigned long addr, pte_t *ptep,
>>>> +					 pte_t ptent)
>>>> +{
>>>> +	pte_t old_pte;
>>>> +
>>>> +	if (!huge_pte_none(ptent)) {
>>>> +		old_pte = huge_ptep_modify_prot_start(vma, addr, ptep);
>>>> +		ptent = huge_pte_mkuffd_wp(old_pte);
>>>> +		ptep_modify_prot_commit(vma, addr, ptep, old_pte, ptent);
>>>
>>> huge_ptep_modify_prot_start()?
>> Sorry, I didn't realized that huge_ptep_modify_prot_start() is different
>> from its pte version.
> 
> Here I meant huge_ptep_modify_prot_commit()..
I'll update.

> 
>>
>>>
>>> The other thing is what if it's a pte marker already?  What if a hugetlb
>>> migration entry?  Please check hugetlb_change_protection().
>> I've updated it in more better way. Please let me know what do you think
>> about the following:
>>
>> static inline 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))
>> 		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));
>> }
> 
> the is_pte_marker() check can be extended to double check
> pte_marker_uffd_wp() bit, but shouldn't matter a lot since besides the
> uffd-wp bit currently we only support swapin error which should sigbus when
> accessed, so no point in tracking anyway.
Yeah, we are good with what we have as even if more bits are supported in
pte markers, this function is only reached when UNPOPULATED + ASYNC WP are
enabled. So no other bit would be set on the marker.

> 
>>
>> As we always set UNPOPULATED, so markers are always set on none ptes
>> initially. Is it possible that a none pte becomes present, then swapped and
>> finally none again? So I'll do the following addition for make_uffd_wp_pte():
>>
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
>> @@ -1800,6 +1800,9 @@ static inline void make_uffd_wp_pte(struct
>> vm_area_struct *vma,
>>  	} 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));
>>  	}
>>  }
> 
> Makes sense, you can leverage userfaultfd_wp_use_markers() here, and you
> should probably keep the protocol (only set the marker when WP_UNPOPULATED
> for anon).
This function is only reachable when UNPOPULATED + Async WP are set. So we
don't need to use userfaultfd_wp_use_markers().

> 
>>
>>
>>
>>
>>>
>>>> +	} else {
>>>> +		set_huge_pte_at(vma->vm_mm, addr, ptep,
>>>> +				make_pte_marker(PTE_MARKER_UFFD_WP));
>>>> +	}
>>>> +}
>>>> +#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;
>>>> +	unsigned long addr = end;
>>>> +	pte_t *pte, *orig_pte;
>>>> +	spinlock_t *ptl;
>>>> +	bool is_written;
>>>> +	int ret = 0;
>>>> +
>>>> +	arch_enter_lazy_mmu_mode();
>>>> +
>>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>>> +	ptl = pmd_trans_huge_lock(pmd, vma);
>>>> +	if (ptl) {
>>>> +		unsigned long n_pages = (end - start)/PAGE_SIZE;
>>>> +
>>>> +		if (p->max_pages && n_pages > p->max_pages - p->found_pages)
>>>> +			n_pages = p->max_pages - p->found_pages;
>>>> +
>>>> +		is_written = !is_pmd_uffd_wp(*pmd);
>>>> +
>>>> +		/*
>>>> +		 * Break huge page into small pages if the WP operation need to
>>>> +		 * be performed is on a portion of the huge page.
>>>> +		 */
>>>> +		if (is_written && IS_PM_SCAN_WP(p->flags) &&
>>>> +		    n_pages < HPAGE_SIZE/PAGE_SIZE) {
>>>> +			spin_unlock(ptl);
>>>> +
>>>> +			split_huge_pmd(vma, pmd, start);
>>>> +			goto process_smaller_pages;
>>>> +		}
>>>> +
>>>> +		if (IS_PM_SCAN_GET(p->flags))
>>>> +			ret = pagemap_scan_output(is_written, vma->vm_file,
>>>> +						  pmd_present(*pmd),
>>>> +						  is_swap_pmd(*pmd),
>>>> +						  p, start, n_pages);
>>>> +
>>>> +		if (ret >= 0 && is_written && IS_PM_SCAN_WP(p->flags))
>>>> +			make_uffd_wp_pmd(vma, addr, pmd);
>>>> +
>>>> +		if (IS_PM_SCAN_WP(p->flags))
>>>> +			flush_tlb_range(vma, start, end);
>>>> +
>>>> +		spin_unlock(ptl);
>>>> +
>>>> +		arch_leave_lazy_mmu_mode();
>>>> +		return ret;
>>>> +	}
>>>> +
>>>> +process_smaller_pages:
>>>> +	if (pmd_trans_unstable(pmd)) {
>>>> +		arch_leave_lazy_mmu_mode();
>>>> +		return 0;
>>>
>>> I'm not sure whether this is right..  Shouldn't you return with -EAGAIN and
>>> let the user retry?  Returning 0 means you'll move on with the next pmd
>>> afaict and ignoring this one.
>> This has come up before. We are just replicating pagemap_pmd_range() here
>> as we are doing almost the same thing through IOCTL. It doesn't return any
>> error in this case and just skips it. So we are doing the same.
> 
> Hmm, is it a bug for pagemap?  pagemapread.buffer should be linear to the
> address range to be scanned to me.  If it skips some unstable pmd without
> filling in anything it seems everything later will be shifted with
> PMD_SIZE..  I had a feeling that it should set walk->action==ACTION_AGAIN
> before return.
I don't think this is a bug if this is how it was implemented in the first
place. In this task_mmu.c file, we can find several examples of the same
pattern that error isn't returned if pmd_trans_unstable() succeeds.

> 

-- 
BR,
Muhammad Usama Anjum

Re: [PATCH v16 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Peter Xu]

On Fri, Jun 02, 2023 at 04:18:38PM +0500, Muhammad Usama Anjum wrote:
> On 6/2/23 1:11 AM, Peter Xu wrote:
> > On Thu, Jun 01, 2023 at 01:16:14PM +0500, Muhammad Usama Anjum wrote:
> >> On 6/1/23 2:46 AM, Peter Xu wrote:
> >>> Muhammad,
> >>>
> >>> Sorry, I probably can only review the non-interface part, and leave the
> >>> interface/buffer handling, etc. review for others and real potential users
> >>> of it..
> >> Thank you so much for the review. I think mostly we should be okay with
> >> interface as everybody has been making suggestions over the past revisions.
> >>
> >>>
> >>> On Thu, May 25, 2023 at 01:55:14PM +0500, Muhammad Usama Anjum wrote:
> >>>> +static inline void make_uffd_wp_huge_pte(struct vm_area_struct *vma,
> >>>> +					 unsigned long addr, pte_t *ptep,
> >>>> +					 pte_t ptent)
> >>>> +{
> >>>> +	pte_t old_pte;
> >>>> +
> >>>> +	if (!huge_pte_none(ptent)) {
> >>>> +		old_pte = huge_ptep_modify_prot_start(vma, addr, ptep);
> >>>> +		ptent = huge_pte_mkuffd_wp(old_pte);
> >>>> +		ptep_modify_prot_commit(vma, addr, ptep, old_pte, ptent);
> >>>
> >>> huge_ptep_modify_prot_start()?
> >> Sorry, I didn't realized that huge_ptep_modify_prot_start() is different
> >> from its pte version.
> > 
> > Here I meant huge_ptep_modify_prot_commit()..
> I'll update.
> 
> > 
> >>
> >>>
> >>> The other thing is what if it's a pte marker already?  What if a hugetlb
> >>> migration entry?  Please check hugetlb_change_protection().
> >> I've updated it in more better way. Please let me know what do you think
> >> about the following:
> >>
> >> static inline 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))
> >> 		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));
> >> }
> > 
> > the is_pte_marker() check can be extended to double check
> > pte_marker_uffd_wp() bit, but shouldn't matter a lot since besides the
> > uffd-wp bit currently we only support swapin error which should sigbus when
> > accessed, so no point in tracking anyway.
> Yeah, we are good with what we have as even if more bits are supported in
> pte markers, this function is only reached when UNPOPULATED + ASYNC WP are
> enabled. So no other bit would be set on the marker.

I think we don't know?  swapin error bit can be set there afaiu, if someone
swapoff -a and found a swap device broken for some swapped out ptes.

But again I think that's fine for now.

> 
> > 
> >>
> >> As we always set UNPOPULATED, so markers are always set on none ptes
> >> initially. Is it possible that a none pte becomes present, then swapped and
> >> finally none again? So I'll do the following addition for make_uffd_wp_pte():
> >>
> >> --- a/fs/proc/task_mmu.c
> >> +++ b/fs/proc/task_mmu.c
> >> @@ -1800,6 +1800,9 @@ static inline void make_uffd_wp_pte(struct
> >> vm_area_struct *vma,
> >>  	} 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));
> >>  	}
> >>  }
> > 
> > Makes sense, you can leverage userfaultfd_wp_use_markers() here, and you
> > should probably keep the protocol (only set the marker when WP_UNPOPULATED
> > for anon).
> This function is only reachable when UNPOPULATED + Async WP are set. So we
> don't need to use userfaultfd_wp_use_markers().

I don't remember where you explicitly checked that to make sure it'll
always be the case, but if you do it'll still be nice if you can add a
comment right above here explaining.

Or, maybe you can still use userfaultfd_wp_use_markers() here, then you can
just WARN_ON_ONCE() on it, which looks even better?

[...]

> > Hmm, is it a bug for pagemap?  pagemapread.buffer should be linear to the
> > address range to be scanned to me.  If it skips some unstable pmd without
> > filling in anything it seems everything later will be shifted with
> > PMD_SIZE..  I had a feeling that it should set walk->action==ACTION_AGAIN
> > before return.
> I don't think this is a bug if this is how it was implemented in the first
> place. In this task_mmu.c file, we can find several examples of the same
> pattern that error isn't returned if pmd_trans_unstable() succeeds.

I don't see why multiple same usages mean it's correct.. maybe they're all
buggy?

I can post a patch for this to collect opinions to see if I missed
something. I'd suggest you figure out what's the right thing to do for the
new interface and make it right from the start, no matter how it was
implemented elsewhere.

Thanks,

-- 
Peter Xu

Re: [PATCH v16 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

Thank you for reviewing and helping out.

On 6/2/23 9:47 PM, Peter Xu wrote:
[...]
>>>> static inline 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))
>>>> 		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));
>>>> }
>>>
>>> the is_pte_marker() check can be extended to double check
>>> pte_marker_uffd_wp() bit, but shouldn't matter a lot since besides the
>>> uffd-wp bit currently we only support swapin error which should sigbus when
>>> accessed, so no point in tracking anyway.
>> Yeah, we are good with what we have as even if more bits are supported in
>> pte markers, this function is only reached when UNPOPULATED + ASYNC WP are
>> enabled. So no other bit would be set on the marker.
> 
> I think we don't know?  swapin error bit can be set there afaiu, if someone
> swapoff -a and found a swap device broken for some swapped out ptes.
Oops, so I remove returning on pte marker detection. Instead the last else
is already setting marker wp-ed.

> 
> But again I think that's fine for now.
> 
>>
>>>
>>>>
>>>> As we always set UNPOPULATED, so markers are always set on none ptes
>>>> initially. Is it possible that a none pte becomes present, then swapped and
>>>> finally none again? So I'll do the following addition for make_uffd_wp_pte():
>>>>
>>>> --- a/fs/proc/task_mmu.c
>>>> +++ b/fs/proc/task_mmu.c
>>>> @@ -1800,6 +1800,9 @@ static inline void make_uffd_wp_pte(struct
>>>> vm_area_struct *vma,
>>>>  	} 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));
>>>>  	}
>>>>  }
>>>
>>> Makes sense, you can leverage userfaultfd_wp_use_markers() here, and you
>>> should probably keep the protocol (only set the marker when WP_UNPOPULATED
>>> for anon).
>> This function is only reachable when UNPOPULATED + Async WP are set. So we
>> don't need to use userfaultfd_wp_use_markers().
> 
> I don't remember where you explicitly checked that to make sure it'll
> always be the case, but if you do it'll still be nice if you can add a
> comment right above here explaining.
I was only testing for WP and WP Async in pagemap_scan_test_walk() as WP
async can only be enabled if unpopulated is enabled which in turn enables
the markers. I'll add userfaultfd_wp_use_markers() to pagemap_scan_test_walk().

> 
> Or, maybe you can still use userfaultfd_wp_use_markers() here, then you can
> just WARN_ON_ONCE() on it, which looks even better?
> 
> [...]
> 
>>> Hmm, is it a bug for pagemap?  pagemapread.buffer should be linear to the
>>> address range to be scanned to me.  If it skips some unstable pmd without
>>> filling in anything it seems everything later will be shifted with
>>> PMD_SIZE..  I had a feeling that it should set walk->action==ACTION_AGAIN
>>> before return.
>> I don't think this is a bug if this is how it was implemented in the first
>> place. In this task_mmu.c file, we can find several examples of the same
>> pattern that error isn't returned if pmd_trans_unstable() succeeds.
> 
> I don't see why multiple same usages mean it's correct.. maybe they're all
> buggy?
> 
> I can post a patch for this to collect opinions to see if I missed
> something. I'd suggest you figure out what's the right thing to do for the
> new interface and make it right from the start, no matter how it was
> implemented elsewhere.
Alright. At first sight, it seems I should return -EAGAIN here. But there
maybe a case where there are 3 THPs. I've cleared WP over the first THP and
put data in the user buffer. If I return -EAGAIN, the data in the user
buffer would be not used by the user correctly as negative value has been
returned. So the best way here would be to skip this second VMA and don't
abort the operation. Thus we'll not be giving any information about the
second THP as it was in transition.

I'll think about it again before sending next version.

> 
> Thanks,
> 

-- 
BR,
Muhammad Usama Anjum

Re: [PATCH v16 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Peter Xu]

On Fri, Jun 02, 2023 at 10:42:45PM +0500, Muhammad Usama Anjum wrote:
> Thank you for reviewing and helping out.
> 
> On 6/2/23 9:47 PM, Peter Xu wrote:
> [...]
> >>>> static inline 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))
> >>>> 		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));
> >>>> }
> >>>
> >>> the is_pte_marker() check can be extended to double check
> >>> pte_marker_uffd_wp() bit, but shouldn't matter a lot since besides the
> >>> uffd-wp bit currently we only support swapin error which should sigbus when
> >>> accessed, so no point in tracking anyway.
> >> Yeah, we are good with what we have as even if more bits are supported in
> >> pte markers, this function is only reached when UNPOPULATED + ASYNC WP are
> >> enabled. So no other bit would be set on the marker.
> > 
> > I think we don't know?  swapin error bit can be set there afaiu, if someone
> > swapoff -a and found a swap device broken for some swapped out ptes.
> Oops, so I remove returning on pte marker detection. Instead the last else
> is already setting marker wp-ed.

What I meant is your current code is fine, please don't remove the check.

Removing is_pte_marker() means you could potentially overwrite one swap
error entry with a marker only having uffd-wp bit set.  It can corrupt the
guest because swapin error is not recoverable and higher priority than wp.

> 
> > 
> > But again I think that's fine for now.
> > 
> >>
> >>>
> >>>>
> >>>> As we always set UNPOPULATED, so markers are always set on none ptes
> >>>> initially. Is it possible that a none pte becomes present, then swapped and
> >>>> finally none again? So I'll do the following addition for make_uffd_wp_pte():
> >>>>
> >>>> --- a/fs/proc/task_mmu.c
> >>>> +++ b/fs/proc/task_mmu.c
> >>>> @@ -1800,6 +1800,9 @@ static inline void make_uffd_wp_pte(struct
> >>>> vm_area_struct *vma,
> >>>>  	} 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));
> >>>>  	}
> >>>>  }
> >>>
> >>> Makes sense, you can leverage userfaultfd_wp_use_markers() here, and you
> >>> should probably keep the protocol (only set the marker when WP_UNPOPULATED
> >>> for anon).
> >> This function is only reachable when UNPOPULATED + Async WP are set. So we
> >> don't need to use userfaultfd_wp_use_markers().
> > 
> > I don't remember where you explicitly checked that to make sure it'll
> > always be the case, but if you do it'll still be nice if you can add a
> > comment right above here explaining.
> I was only testing for WP and WP Async in pagemap_scan_test_walk() as WP
> async can only be enabled if unpopulated is enabled which in turn enables
> the markers. I'll add userfaultfd_wp_use_markers() to pagemap_scan_test_walk().

OK.

> 
> > 
> > Or, maybe you can still use userfaultfd_wp_use_markers() here, then you can
> > just WARN_ON_ONCE() on it, which looks even better?
> > 
> > [...]
> > 
> >>> Hmm, is it a bug for pagemap?  pagemapread.buffer should be linear to the
> >>> address range to be scanned to me.  If it skips some unstable pmd without
> >>> filling in anything it seems everything later will be shifted with
> >>> PMD_SIZE..  I had a feeling that it should set walk->action==ACTION_AGAIN
> >>> before return.
> >> I don't think this is a bug if this is how it was implemented in the first
> >> place. In this task_mmu.c file, we can find several examples of the same
> >> pattern that error isn't returned if pmd_trans_unstable() succeeds.
> > 
> > I don't see why multiple same usages mean it's correct.. maybe they're all
> > buggy?
> > 
> > I can post a patch for this to collect opinions to see if I missed
> > something. I'd suggest you figure out what's the right thing to do for the
> > new interface and make it right from the start, no matter how it was
> > implemented elsewhere.
> Alright. At first sight, it seems I should return -EAGAIN here. But there
> maybe a case where there are 3 THPs. I've cleared WP over the first THP and
> put data in the user buffer. If I return -EAGAIN, the data in the user
> buffer would be not used by the user correctly as negative value has been
> returned. So the best way here would be to skip this second VMA and don't
> abort the operation. Thus we'll not be giving any information about the
> second THP as it was in transition.
> 
> I'll think about it again before sending next version.

Here when reaching unstable==true I think it means a rare race happened,
that a thp was _just_ installed.  You can try to read the comment over
pmd_trans_unstable() and pmd_none_or_trans_huge_or_clear_bad() to
understand what it wants to avoid.

Basically afaiu that's the ultimate guard if one wants to walk the pte
pgtable (that fact can change again if Hugh's series will land, but that's
another story).

As said, a patch will be posted (will have you copied) soon just for that,
so people can also comment and may help you / us know which is the right
way, probably not in a few hours (need to go very soon..), but shouldn't be
too long.  I just need to double check more users out of task_mmu.c when
we're at it.

-- 
Peter Xu

Re: [PATCH v16 0/5] Implement IOCTL to get and optionally clear info about PTEs

[Muhammad Usama Anjum]

On 5/30/23 7:07 PM, Muhammad Usama Anjum wrote:
> Hello Peter, David, Michal, Mike, Danylo and Andrei,
> 
> I hope you are well. You (and some other) guys have been helping and
> reviewing up to this point. Thank you so much! Please review them again and
> mention if anything comes to your mind. Please send review tags or tested
> by tags in the hope that we merge these soon for next release. Current
> patches fulfill all of our requirement regarding ABI and performance. I
> guess, we should merge now (if somethings comes up, we can always fix them
> along the way).
Your ack/review/tested by would be much appreciated. You guys have
contributed while development. I believe we are very close. I really want
your comments to get this merged soon.

Latest revision (v17) for review:
https://lore.kernel.org/all/20230606060822.1065182-1-usama.anjum@collabora.com

> 
> Any thoughts/comments are welcome. I'm sending this email as we have not
> had much reviews in the past 3-4 revisions.
> 
> Thanks,
> Usama
> 
> On 5/25/23 1:55 PM, Muhammad Usama Anjum wrote:
>> *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() syscall [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.
>>
>> 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 been written-to (PAGE_IS_WRITTEN),
>>   file mapped (PAGE_IS_FILE), present (PAGE_IS_PRESENT) or swapped
>>   (PAGE_IS_SWAPPED).
>> - Write-protect the pages (PAGEMAP_WP_ENGAGE) to start finding which
>>   pages have been written-to.
>> - Find pages which have been written-to and write protect the pages
>>   (atomic PAGE_IS_WRITTEN + PAGEMAP_WP_ENGAGE)
>>
>> 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-dirtyi 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 (4):
>>   fs/proc/task_mmu: Implement IOCTL to get and optionally clear info
>>     about PTEs
>>   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     |   58 +
>>  Documentation/admin-guide/mm/userfaultfd.rst |   35 +
>>  fs/proc/task_mmu.c                           |  503 ++++++
>>  fs/userfaultfd.c                             |   26 +-
>>  include/linux/userfaultfd_k.h                |   21 +-
>>  include/uapi/linux/fs.h                      |   53 +
>>  include/uapi/linux/userfaultfd.h             |    9 +-
>>  mm/hugetlb.c                                 |   32 +-
>>  mm/memory.c                                  |   27 +-
>>  tools/include/uapi/linux/fs.h                |   53 +
>>  tools/testing/selftests/mm/.gitignore        |    1 +
>>  tools/testing/selftests/mm/Makefile          |    3 +-
>>  tools/testing/selftests/mm/config            |    1 +
>>  tools/testing/selftests/mm/pagemap_ioctl.c   | 1459 ++++++++++++++++++
>>  tools/testing/selftests/mm/run_vmtests.sh    |    4 +
>>  15 files changed, 2262 insertions(+), 23 deletions(-)
>>  create mode 100644 tools/testing/selftests/mm/pagemap_ioctl.c
>>  mode change 100644 => 100755 tools/testing/selftests/mm/run_vmtests.sh
>>
> 

-- 
BR,
Muhammad Usama Anjum