linux-kernel - Re: [PATCH PATCH v2 v2 2/6] bpf: Add bpf_perf_event_aux

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Message-ID: <ac8266f19ecde10a49911192014dddf35b3b496d.camel@gmail.com>
Date: Mon, 21 Jul 2025 15:38:59 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Leo Yan <leo.yan@....com>, Peter Zijlstra <peterz@...radead.org>, Ingo
 Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim	 <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Ian
 Rogers	 <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, KP
 Singh	 <kpsingh@...nel.org>, Matt Bobrowski <mattbobrowski@...gle.com>,
 Song Liu	 <song@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel
 Borkmann	 <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau	 <martin.lau@...ux.dev>, Yonghong Song
 <yonghong.song@...ux.dev>, John Fastabend	 <john.fastabend@...il.com>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo	 <haoluo@...gle.com>, Steven
 Rostedt <rostedt@...dmis.org>, Masami Hiramatsu	 <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,  James Clark
 <james.clark@...aro.org>, Suzuki K Poulose <suzuki.poulose@....com>, Mike
 Leach	 <mike.leach@...aro.org>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	bpf@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH PATCH v2 v2 2/6] bpf: Add bpf_perf_event_aux_pause kfunc

On Fri, 2025-07-18 at 16:25 +0100, Leo Yan wrote:

[...]

> +__bpf_kfunc int bpf_perf_event_aux_pause(void *p__map, u64 flags, u32 pause)
> +{
> +	struct bpf_map *map = p__map;
> +	struct bpf_array *array = container_of(map, struct bpf_array, map);

Verifier makes sure that p__map is a not null pointer to an object of
type bpf_map, but it does not guarantee that the object is an instance
of bpf_array.
You need to check map->type, same way bpf_arena_alloc_pages() does.

> +	unsigned int cpu = smp_processor_id();
> +	u64 index = flags & BPF_F_INDEX_MASK;
> +	struct bpf_event_entry *ee;
> +	int ret = 0;
> +
> +	/* Disabling IRQ avoids race condition with perf event flows. */
> +	guard(irqsave)();
> +
> +	if (unlikely(flags & ~(BPF_F_INDEX_MASK))) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	if (index == BPF_F_CURRENT_CPU)
> +		index = cpu;
> +
> +	if (unlikely(index >= array->map.max_entries)) {
> +		ret = -E2BIG;
> +		goto out;
> +	}
> +
> +	ee = READ_ONCE(array->ptrs[index]);
> +	if (!ee) {
> +		ret = -ENOENT;
> +		goto out;
> +	}
> +
> +	if (!has_aux(ee->event))
> +		ret = -EINVAL;
> +
> +	perf_event_aux_pause(ee->event, pause);
> +out:
> +	return ret;
> +}

[...]