From: Peter Zijlstra <peterz@infradead.org>
To: Song Liu <songliubraving@fb.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
open list <linux-kernel@vger.kernel.org>,
bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <Kernel-team@fb.com>,
"john.fastabend@gmail.com" <john.fastabend@gmail.com>,
"kpsingh@chromium.org" <kpsingh@chromium.org>,
"brouer@redhat.com" <brouer@redhat.com>
Subject: Re: [PATCH v3 bpf-next 1/2] bpf: separate bpf_get_[stack|stackid] for perf events BPF
Date: Wed, 22 Jul 2020 17:40:10 +0200 [thread overview]
Message-ID: <20200722154010.GO10769@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <42DEE452-F411-4098-917B-11B23AC99F5F@fb.com>
On Tue, Jul 21, 2020 at 10:40:19PM +0000, Song Liu wrote:
> We only need to block precise_ip >= 2. precise_ip == 1 is OK.
Uuuh, how? Anything PEBS would have the same problem. Sure, precise_ip
== 1 will not correct the IP, but the stack will not match regardless.
You need IP,SP(,BP) to be a consistent set _AND_ have it match the
current stack, PEBS simply cannot do that, because the regs get recorded
(much) earlier than the PMI and the stack can have changed in the
meantime.
next prev parent reply other threads:[~2020-07-22 15:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 22:59 [PATCH v3 bpf-next 0/2] bpf: fix stackmap on perf_events with PEBS Song Liu
2020-07-16 22:59 ` [PATCH v3 bpf-next 1/2] bpf: separate bpf_get_[stack|stackid] for perf events BPF Song Liu
2020-07-21 19:10 ` Alexei Starovoitov
2020-07-21 22:40 ` Song Liu
2020-07-21 22:43 ` Alexei Starovoitov
2020-07-21 22:51 ` Song Liu
2020-07-22 15:40 ` Peter Zijlstra [this message]
2020-07-22 16:49 ` Song Liu
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