[RFC,bpf-next,v3,00/16] sleepable bpf_timer (was: allow HID-BPF to do device IOs)

Message

Benjamin Tissoires Feb. 21, 2024, 4:25 p.m. UTC

[Partly a RFC/formal submission: there are still FIXMEs in the code]
[Also using bpf-next as the base tree for HID changes as there will
be conflicting changes otherwise, so I'm personaly fine for the HID
commits to go through bpf-next]

IMO, patches 1-3 and 9-14 are ready to go, rest is still pending review.

For reference, the use cases I have in mind:

---

Basically, I need to be able to defer a HID-BPF program for the
following reasons (from the aforementioned patch):
1. defer an event:
   Sometimes we receive an out of proximity event, but the device can not
   be trusted enough, and we need to ensure that we won't receive another
   one in the following n milliseconds. So we need to wait those n
   milliseconds, and eventually re-inject that event in the stack.

2. inject new events in reaction to one given event:
   We might want to transform one given event into several. This is the
   case for macro keys where a single key press is supposed to send
   a sequence of key presses. But this could also be used to patch a
   faulty behavior, if a device forgets to send a release event.

3. communicate with the device in reaction to one event:
   We might want to communicate back to the device after a given event.
   For example a device might send us an event saying that it came back
   from sleeping state and needs to be re-initialized.

Currently we can achieve that by keeping a userspace program around,
raise a bpf event, and let that userspace program inject the events and
commands.
However, we are just keeping that program alive as a daemon for just
scheduling commands. There is no logic in it, so it doesn't really justify
an actual userspace wakeup. So a kernel workqueue seems simpler to handle.

The other part I'm not sure is whether we can say that BPF maps of type
queue/stack can be used in sleepable context.
I don't see any warning when running the test programs, but that's probably
not a guarantee I'm doing the things properly :)

Cheers,
Benjamin

To: Alexei Starovoitov <[e-mail]>
To: Daniel Borkmann <[e-mail]>
To: John Fastabend <[e-mail]>
To: Andrii Nakryiko <[e-mail]>
To: Martin KaFai Lau <[e-mail]>
To: Eduard Zingerman <[e-mail]>
To: Song Liu <[e-mail]>
To: Yonghong Song <[e-mail]>
To: KP Singh <[e-mail]>
To: Stanislav Fomichev <[e-mail]>
To: Hao Luo <[e-mail]>
To: Jiri Olsa <[e-mail]>
To: Jiri Kosina <[e-mail]>
To: Benjamin Tissoires <[e-mail]>
To: Jonathan Corbet <[e-mail]>
To: Shuah Khan <[e-mail]>
Cc:  <[e-mail]>
Cc:  <[e-mail]>
Cc:  <[e-mail]>
Cc:  <[e-mail]>
Cc:  <[e-mail]>
Signed-off-by: Benjamin Tissoires <[e-mail]>

---
Changes in v3:
- fixed the crash from v2
- changed the API to have only BPF_F_TIMER_SLEEPABLE for
  bpf_timer_start()
- split the new kfuncs/verifier patch into several sub-patches, for
  easier reviews
- Link to v2: https://lore.kernel.org/r/[e-mail]

Changes in v2:
- make use of bpf_timer (and dropped the custom HID handling)
- implemented bpf_timer_set_sleepable_cb as a kfunc
- still not implemented global subprogs
- no sleepable bpf_timer selftests yet
- Link to v1: https://lore.kernel.org/r/[e-mail]

---
Benjamin Tissoires (16):
      bpf/verifier: allow more maps in sleepable bpf programs
      bpf/verifier: introduce in_sleepable() helper
      bpf/verifier: add is_async_callback_calling_insn() helper
      bpf/helpers: introduce sleepable bpf_timers
      bpf/verifier: add bpf_timer as a kfunc capable type
      bpf/helpers: introduce bpf_timer_set_sleepable_cb() kfunc
      bpf/helpers: mark the callback of bpf_timer_set_sleepable_cb() as sleepable
      bpf/verifier: do_misc_fixups for is_bpf_timer_set_sleepable_cb_kfunc
      HID: bpf/dispatch: regroup kfuncs definitions
      HID: bpf: export hid_hw_output_report as a BPF kfunc
      selftests/hid: Add test for hid_bpf_hw_output_report
      HID: bpf: allow to inject HID event from BPF
      selftests/hid: add tests for hid_bpf_input_report
      HID: bpf: allow to use bpf_timer_set_sleepable_cb() in tracing callbacks.
      selftests/hid: add test for bpf_timer
      selftests/hid: add KASAN to the VM tests

 Documentation/hid/hid-bpf.rst                      |   2 +-
 drivers/hid/bpf/hid_bpf_dispatch.c                 | 232 ++++++++++++++-------
 drivers/hid/hid-core.c                             |   2 +
 include/linux/bpf_verifier.h                       |   2 +
 include/linux/hid_bpf.h                            |   3 +
 include/uapi/linux/bpf.h                           |   4 +
 kernel/bpf/helpers.c                               | 140 +++++++++++--
 kernel/bpf/verifier.c                              | 114 ++++++++--
 tools/testing/selftests/hid/config.common          |   1 +
 tools/testing/selftests/hid/hid_bpf.c              | 195 ++++++++++++++++-
 tools/testing/selftests/hid/progs/hid.c            | 198 ++++++++++++++++++
 .../testing/selftests/hid/progs/hid_bpf_helpers.h  |   8 +
 12 files changed, 795 insertions(+), 106 deletions(-)
---
base-commit: 5c331823b3fc52ffd27524bf5b7e0d137114f470
change-id: 20240205-hid-bpf-sleepable-c01260fd91c4

Best regards,

Comments

Eduard Zingerman Feb. 23, 2024, 4:19 p.m. UTC | #1

On Wed, 2024-02-21 at 17:25 +0100, Benjamin Tissoires wrote:
> [Partly a RFC/formal submission: there are still FIXMEs in the code]
> [Also using bpf-next as the base tree for HID changes as there will
> be conflicting changes otherwise, so I'm personaly fine for the HID
> commits to go through bpf-next]

[...]

Could you please also add verifier selftests, e.g. extend
tools/testing/selftests/bpf/progs/timer.c       (bpf side)
tools/testing/selftests/bpf/prog_tests/timer.c  (userspace side triggering
                                                 bpf side)
Negative tests could be added in
tools/testing/selftests/bpf/progs/timer_failure.c

Please let me know if you need any help setting up local BPF test
environment, I have a short writeup on how to set it up in chroot.

Benjamin Tissoires Feb. 23, 2024, 7:42 p.m. UTC | #2

Hi,

On Feb 23 2024, Eduard Zingerman wrote:
> On Wed, 2024-02-21 at 17:25 +0100, Benjamin Tissoires wrote:
> > [Partly a RFC/formal submission: there are still FIXMEs in the code]
> > [Also using bpf-next as the base tree for HID changes as there will
> > be conflicting changes otherwise, so I'm personaly fine for the HID
> > commits to go through bpf-next]
> 
> [...]
> 
> Could you please also add verifier selftests, e.g. extend
> tools/testing/selftests/bpf/progs/timer.c       (bpf side)
> tools/testing/selftests/bpf/prog_tests/timer.c  (userspace side triggering
>                                                  bpf side)
> Negative tests could be added in
> tools/testing/selftests/bpf/progs/timer_failure.c
> 
> Please let me know if you need any help setting up local BPF test
> environment, I have a short writeup on how to set it up in chroot.

Thanks a lot for your review (and Alexei's). I was actually off today
and will be off next Monday too, but I'll work on those tests next week.

Cheers,
Benjamin