linux-kernel - Re: [PATCH v1 2/7] bpf: Add bpf_perf_event_aux

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Message-ID: <20250718153801.GB3137075@e132581.arm.com>
Date: Fri, 18 Jul 2025 16:38:01 +0100
From: Leo Yan <leo.yan@....com>
To: Yonghong Song <yonghong.song@...ux.dev>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	James Clark <james.clark@...aro.org>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Matt Bobrowski <mattbobrowski@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	bpf@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>
Subject: Re: [PATCH v1 2/7] bpf: Add bpf_perf_event_aux_pause kfunc

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