Re: [PATCH v1 2/7] bpf: Add bpf_perf_event_aux_pause kfunc

[Leo Yan <leo.yan@arm.com>]

Hi Yonghong,

On Tue, Jul 15, 2025 at 10:12:02AM -0700, Yonghong Song wrote:

[...]

> > I'm not certain whether using __bpf_kfunc is appropriate here, or if I
> > should stick to BPF_CALL to ensure support for accessing bpf_map
> > pointers?
> 
> Using helpers (BPF_CALL) is not an option as the whole bpf ecosystem
> moves to kfunc mechanism. You can certainly use kfunc with 'struct bpf_map *'
> as the argument. For example the following kfunc:
>   __bpf_kfunc s64 bpf_map_sum_elem_count(const struct bpf_map *map)
> in kernel/bpf/map_iter.c

Thanks a lot for suggestion. I followed the idea to refactor the patch
with kfunc, see the new version:
https://lore.kernel.org/linux-perf-users/20250718-perf_aux_pause_resume_bpf_rebase-v2-0-992557b8fb16@arm.com/T/#m27a72255c93fa672e164cb87a322b979fe8f9408

Just clarify one thing, I defined the kfunc in new patch:

  int bpf_perf_event_aux_pause(void *p__map, u64 flags, u32 pause)

Unlike your suggestion, I defined the first parameter as "void
*p__map" (I refers to bpf_arena_alloc_pages()) rather than
"struct bpf_map *map". This is because the BPF program will pass a
variable from the map section, rather than passing a map pointer.

TBH, I do not watch closely the BPF mailing list, so I may not be
fully following the conventions. If anything is incorrect, please
correct it as needed.

Thank you,

Leo