[v4,0/7] Extend HID-BPF kfuncs (was: allow HID-BPF to do device IOs)

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

https://lore.kernel.org/all/20240315-hid-bpf-sleepable-v4-0-5658f2540564@kernel.org/

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: Jiri Kosina <jikos@kernel.org>
To: Benjamin Tissoires <benjamin.tissoires@redhat.com>
To: Jonathan Corbet <corbet@lwn.net>
To: Shuah Khan <shuah@kernel.org>
Cc: Benjamin Tissoires <bentiss@kernel.org>
Cc:  <linux-input@vger.kernel.org>
Cc:  <linux-kernel@vger.kernel.org>
Cc:  <bpf@vger.kernel.org>
Cc:  <linux-doc@vger.kernel.org>
Cc:  <linux-kselftest@vger.kernel.org>

---
Changes in v4:
- dropped the BPF changes, they can go independently in bpf-core
- dropped the HID-BPF integration tests with the sleppable timers,
  I'll re-add them once both series (this and sleepable timers) are
  merged
- Link to v3: https://lore.kernel.org/r/20240221-hid-bpf-sleepable-v3-0-1fb378ca6301@kernel.org

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/20240214-hid-bpf-sleepable-v2-0-5756b054724d@kernel.org

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/20240209-hid-bpf-sleepable-v1-0-4cc895b5adbd@kernel.org

---
Benjamin Tissoires (7):
      HID: bpf/dispatch: regroup kfuncs definitions
      HID: bpf: export hid_hw_output_report as a BPF kfunc
      selftests/hid: add KASAN to the VM tests
      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.

 Documentation/hid/hid-bpf.rst                      |   2 +-
 drivers/hid/bpf/hid_bpf_dispatch.c                 | 226 ++++++++++++++-------
 drivers/hid/hid-core.c                             |   2 +
 include/linux/hid_bpf.h                            |   3 +
 tools/testing/selftests/hid/config.common          |   1 +
 tools/testing/selftests/hid/hid_bpf.c              | 112 +++++++++-
 tools/testing/selftests/hid/progs/hid.c            |  46 +++++
 .../testing/selftests/hid/progs/hid_bpf_helpers.h  |   6 +
 8 files changed, 324 insertions(+), 74 deletions(-)
---
base-commit: 3e78a6c0d3e02e4cf881dc84c5127e9990f939d6
change-id: 20240314-b4-hid-bpf-new-funcs-ecf05d0ef870

Best regards,