*Changes in v17*
- Rebase on top of next-20230606
- Minor improvements in PAGEMAP_SCAN IOCTL patch
*Changes in v16*
- Fix a corner case
- Add exclusive PM_SCAN_OP_WP back
*Changes in v15*
- Build fix (Add missed build fix in RESEND)
*Changes in v14*
- Fix build error caused by #ifdef added at last minute in some configs
*Changes in v13*
- Rebase on top of next-20230414
- Give-up on using uffd_wp_range() and write new helpers, flush tlb only
once
*Changes in v12*
- Update and other memory types to UFFD_FEATURE_WP_ASYNC
- Rebaase on top of next-20230406
- Review updates
*Changes in v11*
- Rebase on top of next-20230307
- Base patches on UFFD_FEATURE_WP_UNPOPULATED
- Do a lot of cosmetic changes and review updates
- Remove ENGAGE_WP + !GET operation as it can be performed with
UFFDIO_WRITEPROTECT
*Changes in v10*
- Add specific condition to return error if hugetlb is used with wp
async
- Move changes in tools/include/uapi/linux/fs.h to separate patch
- Add documentation
*Changes in v9:*
- Correct fault resolution for userfaultfd wp async
- Fix build warnings and errors which were happening on some configs
- Simplify pagemap ioctl's code
*Changes in v8:*
- Update uffd async wp implementation
- Improve PAGEMAP_IOCTL implementation
*Changes in v7:*
- Add uffd wp async
- Update the IOCTL to use uffd under the hood instead of soft-dirty
flags
*Motivation*
The real motivation for adding PAGEMAP_SCAN IOCTL is to emulate Windows
GetWriteWatch() 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-…
[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.…
[8] https://lore.kernel.org/all/20221220162606.1595355-1-usama.anjum@collabora.…
[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…
[2] https://lore.kernel.org/all/20221220162606.1595355-1-usama.anjum@collabora.…
[3] https://lore.kernel.org/all/20221122115007.2787017-1-usama.anjum@collabora.…
[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 | 505 ++++++
fs/userfaultfd.c | 26 +-
include/linux/hugetlb.h | 1 +
include/linux/userfaultfd_k.h | 21 +-
include/uapi/linux/fs.h | 53 +
include/uapi/linux/userfaultfd.h | 9 +-
mm/hugetlb.c | 34 +-
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 +
16 files changed, 2266 insertions(+), 24 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
Hi,
This follows the discussion here:
https://lore.kernel.org/linux-kselftest/20230324123157.bbwvfq4gsxnlnfwb@hou…
This shows a couple of inconsistencies with regard to how device-managed
resources are cleaned up. Basically, devm resources will only be cleaned up
if the device is attached to a bus and bound to a driver. Failing any of
these cases, a call to device_unregister will not end up in the devm
resources being released.
We had to work around it in DRM to provide helpers to create a device for
kunit tests, but the current discussion around creating similar, generic,
helpers for kunit resumed interest in fixing this.
This can be tested using the command:
./tools/testing/kunit/kunit.py run --kunitconfig=drivers/base/test/
Let me know what you think,
Maxime
Signed-off-by: Maxime Ripard <maxime(a)cerno.tech>
---
Maxime Ripard (2):
drivers: base: Add basic devm tests for root devices
drivers: base: Add basic devm tests for platform devices
drivers/base/test/.kunitconfig | 2 +
drivers/base/test/Kconfig | 4 +
drivers/base/test/Makefile | 3 +
drivers/base/test/platform-device-test.c | 278 +++++++++++++++++++++++++++++++
drivers/base/test/root-device-test.c | 120 +++++++++++++
5 files changed, 407 insertions(+)
---
base-commit: a6faf7ea9fcb7267d06116d4188947f26e00e57e
change-id: 20230329-kunit-devm-inconsistencies-test-5e5a7d01e60d
Best regards,
--
Maxime Ripard <mripard(a)kernel.org>
Add documentation for the new Virtual PCM Test Driver. It covers all
possible usage cases: errors and delay injections, random and
pattern-based data generation, playback and ioctl redefinition
functionalities testing.
We have a lot of different virtual media drivers, which can be used for
testing of the userspace applications and media subsystem middle layer.
However, all of them are aimed at testing the video functionality and
simulating the video devices. For audio devices we have only snd-dummy
module, which is good in simulating the correct behavior of an ALSA device.
I decided to write a tool, which would help to test the userspace ALSA
programs (and the PCM middle layer as well) under unusual circumstances
to figure out how they would behave. So I came up with this Virtual PCM
Test Driver.
This new Virtual PCM Test Driver has several features which can be useful
during the userspace ALSA applications testing/fuzzing, or testing/fuzzing
of the PCM middle layer. Not all of them can be implemented using the
existing virtual drivers (like dummy or loopback). Here is what can this
driver do:
- Simulate both capture and playback processes
- Check the playback stream for containing the looped pattern
- Generate random or pattern-based capture data
- Inject delays into the playback and capturing processes
- Inject errors during the PCM callbacks
Also, this driver can check the playback stream for containing the
predefined pattern, which is used in the corresponding selftest to check
the PCM middle layer data transferring functionality. Additionally, this
driver redefines the default RESET ioctl, and the selftest covers this PCM
API functionality as well.
The driver supports both interleaved and non-interleaved access modes, and
have separate pattern buffers for each channel. The driver supports up to
4 channels and up to 8 substreams.
Signed-off-by: Ivan Orlov <ivan.orlov0322(a)gmail.com>
---
V1 -> V2:
- Rename the driver from from 'valsa' to 'pcmtest'.
- Implement support for interleaved and non-interleaved access modes
- Add support for 8 substreams and 4 channels
- Extend supported formats
- Extend and rewrite in C the selftest for the driver
V2 -> V3:
- Add separate pattern buffers for each channel
- Speed up the capture data generation when using interleaved access mode
- Extend the corresponding selftest to cover the multiple channels
capturing and playback functionalities when using interleaved access mode.
- Fix documentation issues
Documentation/sound/cards/index.rst | 1 +
Documentation/sound/cards/pcmtest.rst | 120 ++++++++++++++++++++++++++
2 files changed, 121 insertions(+)
create mode 100644 Documentation/sound/cards/pcmtest.rst
diff --git a/Documentation/sound/cards/index.rst b/Documentation/sound/cards/index.rst
index c016f8c3b88b..49c1f2f688f8 100644
--- a/Documentation/sound/cards/index.rst
+++ b/Documentation/sound/cards/index.rst
@@ -17,3 +17,4 @@ Card-Specific Information
hdspm
serial-u16550
img-spdif-in
+ pcmtest
diff --git a/Documentation/sound/cards/pcmtest.rst b/Documentation/sound/cards/pcmtest.rst
new file mode 100644
index 000000000000..e163522f3205
--- /dev/null
+++ b/Documentation/sound/cards/pcmtest.rst
@@ -0,0 +1,120 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+The Virtual PCM Test Driver
+===========================
+
+The Virtual PCM Test Driver emulates a generic PCM device, and can be used for
+testing/fuzzing of the userspace ALSA applications, as well as for testing/fuzzing of
+the PCM middle layer. Additionally, it can be used for simulating hard to reproduce
+problems with PCM devices.
+
+What can this driver do?
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+At this moment the driver can do the following things:
+ * Simulate both capture and playback processes
+ * Generate random or pattern-based capturing data
+ * Inject delays into the playback and capturing processes
+ * Inject errors during the PCM callbacks
+
+It supports up to 8 substreams and 4 channels. Also it supports both interleaved and
+non-interleaved access modes.
+
+Also, this driver can check the playback stream for containing the predefined pattern,
+which is used in the corresponding selftest (alsa/pcmtest-test.sh) to check the PCM middle
+layer data transferring functionality. Additionally, this driver redefines the default
+RESET ioctl, and the selftest covers this PCM API functionality as well.
+
+Configuration
+-------------
+
+The driver has several parameters besides the common ALSA module parameters:
+
+ * fill_mode (bool) - Buffer fill mode (see below)
+ * inject_delay (int)
+ * inject_hwpars_err (bool)
+ * inject_prepare_err (bool)
+ * inject_trigger_err (bool)
+
+
+Capture Data Generation
+-----------------------
+
+The driver has two modes of data generation: the first (0 in the fill_mode parameter)
+means random data generation, the second (1 in the fill_mode) - pattern-based
+data generation. Let's look at the second mode.
+
+First of all, you may want to specify the pattern for data generation. You can do it
+by writing the pattern to the debugfs file. There are pattern buffer debugfs entries
+for each channel, as well as entries which contain the pattern buffer length.
+
+ * /sys/kernel/debug/pcmtest/fill_pattern[0-3]
+ * /sys/kernel/debug/pcmtest/fill_pattern[0-3]_len
+
+To set the pattern for the channel 0 you can execute the following command:
+
+.. code-block:: bash
+
+ echo -n mycoolpattern > /sys/kernel/debug/pcmtest/fill_pattern0
+
+Then, after every capture action performed on the 'pcmtest' device the buffer for the
+channel 0 will contain 'mycoolpatternmycoolpatternmycoolpatternmy...'.
+
+The pattern itself can be up to 4096 bytes long.
+
+Delay injection
+---------------
+
+The driver has 'inject_delay' parameter, which has very self-descriptive name and
+can be used for time delay/speedup simulations. The parameter has integer type, and
+it means the delay added between module's internal timer ticks.
+
+If the 'inject_delay' value is positive, the buffer will be filled slower, if it is
+negative - faster. You can try it yourself by starting a recording in any
+audiorecording application (like Audacity) and selecting the 'pcmtest' device as a
+source.
+
+This parameter can be also used for generating a huge amount of sound data in a very
+short period of time (with the negative 'inject_delay' value).
+
+Errors injection
+----------------
+
+This module can be used for injecting errors into the PCM communication process. This
+action can help you to figure out how the userspace ALSA program behaves under unusual
+circumstances.
+
+For example, you can make all 'hw_params' PCM callback calls return EBUSY error by
+writing '1' to the 'inject_hwpars_err' module parameter:
+
+.. code-block:: bash
+
+ echo 1 > /sys/module/snd_pcmtest/parameters/inject_hwpars_err
+
+Errors can be injected into the following PCM callbacks:
+
+ * hw_params (EBUSY)
+ * prepare (EINVAL)
+ * trigger (EINVAL)
+
+Playback test
+-------------
+
+This driver can be also used for the playback functionality testing - every time you
+write the playback data to the 'pcmtest' PCM device and close it, the driver checks the
+buffer for containing the looped pattern (which is specified in the fill_pattern
+debugfs file for each channel). If the playback buffer content represents the looped
+pattern, 'pc_test' debugfs entry is set into '1'. Otherwise, the driver sets it to '0'.
+
+ioctl redefinition test
+-----------------------
+
+The driver redefines the 'reset' ioctl, which is default for all PCM devices. To test
+this functionality, we can trigger the reset ioctl and check the 'ioctl_test' debugfs
+entry:
+
+.. code-block:: bash
+
+ cat /sys/kernel/debug/pcmtest/ioctl_test
+
+If the ioctl is triggered successfully, this file will contain '1', and '0' otherwise.
--
2.34.1