[RFC,bpf-next,v2,00/10] allow HID-BPF to do device IOs

[Still a RFC: there are a lot of FIXMEs in the code, and
calling the sleepable timer cb actually crashes.]
[Also using bpf-next as the base tree as there will be conflicting
changes otherwise]

This is crashing, and I have a few questions in the code (look for all
of the FIXMEs), so sending this now before I become insane :)

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 <ast@kernel.org>
To: Daniel Borkmann <daniel@iogearbox.net>
To: John Fastabend <john.fastabend@gmail.com>
To: Andrii Nakryiko <andrii@kernel.org>
To: Martin KaFai Lau <martin.lau@linux.dev>
To: Eduard Zingerman <eddyz87@gmail.com>
To: Song Liu <song@kernel.org>
To: Yonghong Song <yonghong.song@linux.dev>
To: KP Singh <kpsingh@kernel.org>
To: Stanislav Fomichev <sdf@google.com>
To: Hao Luo <haoluo@google.com>
To: Jiri Olsa <jolsa@kernel.org>
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:  <bpf@vger.kernel.org>
Cc:  <linux-kernel@vger.kernel.org>
Cc:  <linux-input@vger.kernel.org>
Cc:  <linux-doc@vger.kernel.org>
Cc:  <linux-kselftest@vger.kernel.org>
Signed-off-by: Benjamin Tissoires <bentiss@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 (10):
      bpf/verifier: introduce in_sleepable() helper
      bpf/helpers: introduce sleepable timers
      bpf/verifier: allow more maps in sleepable bpf programs
      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

 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                           |  12 ++
 kernel/bpf/helpers.c                               | 105 +++++++++-
 kernel/bpf/verifier.c                              |  91 +++++++-
 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 +
 11 files changed, 756 insertions(+), 94 deletions(-)
---
base-commit: 4f7a05917237b006ceae760507b3d15305769ade
change-id: 20240205-hid-bpf-sleepable-c01260fd91c4

Best regards,