linux-kernel - Re: [PATCH v3 bpf-next 1/2] bpf: separate bpf_get

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Date:   Tue, 21 Jul 2020 15:43:27 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "kpsingh@...omium.org" <kpsingh@...omium.org>,
        "brouer@...hat.com" <brouer@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>
Subject: Re: [PATCH v3 bpf-next 1/2] bpf: separate bpf_get_[stack|stackid] for
 perf events BPF

On Tue, Jul 21, 2020 at 3:40 PM Song Liu <songliubraving@...com> wrote:
>
> We only need to block precise_ip >= 2. precise_ip == 1 is OK.

Are you sure?
intel_pmu_hw_config() has:
if (event->attr.precise_ip) {
    if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
            event->attr.sample_type |= __PERF_SAMPLE_CALLCHAIN_EARLY;
}