From: "Daniel Xu" <dxu@dxuuu.xyz>
To: "Daniel Borkmann" <daniel@iogearbox.net>,
"John Fastabend" <john.fastabend@gmail.com>,
<bpf@vger.kernel.org>, <ast@kernel.org>, <songliubraving@fb.com>,
<yhs@fb.com>, <andriin@fb.com>
Cc: <linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
<peterz@infradead.org>, <mingo@redhat.com>, <acme@kernel.org>
Subject: Re: [PATCH v2 bpf-next 1/3] bpf: Add bpf_perf_prog_read_branches() helper
Date: Thu, 23 Jan 2020 14:30:00 -0800 [thread overview]
Message-ID: <C03IYDPABSU1.1C6OL4DJ7ID1H@dlxu-fedora-R90QNFJV> (raw)
In-Reply-To: <297f40e7-667b-63ea-c7d7-6d03a636c4c7@iogearbox.net>
On Thu Jan 23, 2020 at 11:23 PM, Daniel Borkmann wrote:
[...]
>
> Yes, so we've been following this practice for all the BPF helpers no
> matter
> which program type. Though for tracing it may be up to debate whether it
> makes
> still sense given there's nothing to be leaked here since you can read
> this data
> anyway via probe read if you'd wanted to. So we might as well get rid of
> the
> clearing for all tracing helpers.
Right, that makes sense. Do you want me to leave it in for this patchset
and then remove all of them in a followup patchset?
>
> Different question related to your set. It looks like br_stack is only
> available
> on x86, is that correct? For other archs this will always bail out on
> !br_stack
> test. Perhaps we should document this fact so users are not surprised
> why their
> prog using this helper is not working on !x86. Wdyt?
I think perf_event_open() should fail on !x86 if a user tries to configure
it with branch stack collection. So there would not be the opportunity for
the bpf prog to be attached and run. I haven't tested this, though. I'll
look through the code / install a VM and test it.
[...]
Thanks,
Daniel
next prev parent reply other threads:[~2020-01-23 22:30 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 20:22 [PATCH v2 bpf-next 0/3] Add bpf_perf_prog_read_branches() helper Daniel Xu
2020-01-22 20:22 ` [PATCH v2 bpf-next 1/3] bpf: " Daniel Xu
2020-01-23 5:39 ` John Fastabend
2020-01-23 20:09 ` Daniel Xu
2020-01-23 22:23 ` Daniel Borkmann
2020-01-23 22:30 ` Daniel Xu [this message]
2020-01-23 22:41 ` Andrii Nakryiko
2020-01-23 23:09 ` Daniel Borkmann
2020-01-23 22:44 ` Daniel Borkmann
2020-01-23 23:07 ` Martin Lau
2020-01-23 23:27 ` Daniel Xu
2020-01-22 20:22 ` [PATCH v2 bpf-next 2/3] tools/bpf: Sync uapi header bpf.h Daniel Xu
2020-01-22 20:22 ` [PATCH v2 bpf-next 3/3] selftests/bpf: add bpf_perf_prog_read_branches() selftest Daniel Xu
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