From: Song Liu <songliubraving@fb.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: bpf <bpf@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Peter Ziljstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Kajol Jain <kjain@linux.ibm.com>,
Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot
Date: Thu, 2 Sep 2021 22:04:05 +0000 [thread overview]
Message-ID: <6C6E8C20-1EC7-46DD-84BB-6885F0C3F86A@fb.com> (raw)
In-Reply-To: <61313a8fda896_2c56f208bb@john-XPS-13-9370.notmuch>
> On Sep 2, 2021, at 1:56 PM, John Fastabend <john.fastabend@gmail.com> wrote:
>
> Song Liu wrote:
>> Introduce bpf_get_branch_snapshot(), which allows tracing pogram to get
>> branch trace from hardware (e.g. Intel LBR). To use the feature, the
>> user need to create perf_event with proper branch_record filtering
>> on each cpu, and then calls bpf_get_branch_snapshot in the bpf function.
>> On Intel CPUs, VLBR event (raw event 0x1b00) can be use for this.
>>
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>
> [...]
>
>>
>> +BPF_CALL_3(bpf_get_branch_snapshot, void *, buf, u32, size, u64, flags)
>> +{
>> +#ifndef CONFIG_X86
>> + return -ENOENT;
>> +#else
>> + static const u32 br_entry_size = sizeof(struct perf_branch_entry);
>> + u32 entry_cnt = size / br_entry_size;
>> +
>> + if (unlikely(flags))
>> + return -EINVAL;
>> +
>> + if (!buf || (size % br_entry_size != 0))
>> + return -EINVAL;
>
> LGTM, but why fail if buffer is slightly larger than expected? I guess its a slightly
> buggy program that would do this, but not actually harmful right?
This check was added because bpf_read_branch_records() has a similar check.
I guess it is OK either way.
>
> Acked-by: John Fastabend <john.fastabend@gmail.com>
Thanks for the review!
next prev parent reply other threads:[~2021-09-02 22:04 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-02 16:57 [PATCH v5 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Song Liu
2021-09-02 16:57 ` [PATCH v5 bpf-next 1/3] perf: enable branch record for software events Song Liu
2021-09-02 20:49 ` John Fastabend
2021-09-03 8:02 ` Peter Zijlstra
2021-09-03 16:50 ` Song Liu
2021-09-07 18:59 ` Song Liu
2021-09-07 20:50 ` Andrii Nakryiko
2021-09-03 8:27 ` Peter Zijlstra
2021-09-03 16:45 ` Song Liu
2021-09-04 10:18 ` Peter Zijlstra
2021-09-02 16:57 ` [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot Song Liu
2021-09-02 20:56 ` John Fastabend
2021-09-02 22:04 ` Song Liu [this message]
2021-09-02 22:53 ` Andrii Nakryiko
2021-09-02 23:03 ` Song Liu
2021-09-02 23:05 ` Andrii Nakryiko
2021-09-03 1:03 ` Alexei Starovoitov
2021-09-03 8:28 ` Peter Zijlstra
2021-09-03 16:58 ` Song Liu
2021-09-03 8:47 ` Peter Zijlstra
2021-09-03 17:06 ` Song Liu
2021-09-03 17:10 ` Andrii Nakryiko
2021-09-04 10:24 ` Peter Zijlstra
2021-09-04 10:55 ` Peter Zijlstra
2021-09-02 16:57 ` [PATCH v5 bpf-next 3/3] selftests/bpf: add test for bpf_get_branch_snapshot Song Liu
2021-09-02 21:05 ` John Fastabend
2021-09-02 22:54 ` [PATCH v5 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Andrii Nakryiko
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