[bpf-next,v4,0/6] sleepable bpf_timer (was: allow HID-BPF to do device IOs)

Message

Benjamin Tissoires March 15, 2024, 2:29 p.m. UTC

New version of the sleepable bpf_timer code, without the HID changes, as
they can now go through the HID tree independantly.

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.

bpf_timers are currently running in a soft IRQ context, this patch
series implements a sleppable context for them.

Cheers,
Benjamin

To: Alexei Starovoitov <[e-mail]>
To: Daniel Borkmann <[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: John Fastabend <[e-mail]>
To: KP Singh <[e-mail]>
To: Stanislav Fomichev <[e-mail]>
To: Hao Luo <[e-mail]>
To: Jiri Olsa <[e-mail]>
To: Mykola Lysenko <[e-mail]>
To: Shuah Khan <[e-mail]>
Cc: Benjamin Tissoires <[e-mail]>
Cc:  <[e-mail]>
Cc:  <[e-mail]>
Cc:  <[e-mail]>

---
Changes in v4:
- dropped the HID changes, they can go independently from bpf-core
- addressed Alexei's and Eduard's remarks
- added selftests
- Link to v3: https://lore.kernel.org/r/[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 (6):
      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
      tools: sync include/uapi/linux/bpf.h
      selftests/bpf: add sleepable timer tests

 include/linux/bpf_verifier.h                       |   1 +
 include/uapi/linux/bpf.h                           |   4 +
 kernel/bpf/helpers.c                               | 132 ++++++++++++++++++++-
 kernel/bpf/verifier.c                              |  92 +++++++++++++-
 tools/include/uapi/linux/bpf.h                     |   4 +
 tools/testing/selftests/bpf/bpf_experimental.h     |   4 +
 .../selftests/bpf/bpf_testmod/bpf_testmod.c        |   5 +
 .../selftests/bpf/bpf_testmod/bpf_testmod_kfunc.h  |   1 +
 tools/testing/selftests/bpf/prog_tests/timer.c     |   1 +
 tools/testing/selftests/bpf/progs/timer.c          |  40 ++++++-
 tools/testing/selftests/bpf/progs/timer_failure.c  | 114 +++++++++++++++++-
 11 files changed, 387 insertions(+), 11 deletions(-)
---
base-commit: 9187210eee7d87eea37b45ea93454a88681894a4
change-id: 20240205-hid-bpf-sleepable-c01260fd91c4

Best regards,