Subject: Re: [PATCH v4 2/9] perf/core: open access for CAP_SYS_PERFMON privileged process

From: [email-masked]
Date: Fri, 10 Jan 2020 21:35:12 -0300

<[email-masked]>,Jann Horn <[email-masked]>,Thomas Gleixner <[email-masked]>,Tvrtko Ursulin <[email-masked]>,Lionel Landwerlin <[email-masked]>,linux-kernel <[email-masked]>,"[email-masked]" <[email-masked]>,"[email-masked]" <[email-masked]>,"[email-masked]" <[email-masked]>,"[email-masked]" <[email-masked]>,"[email-masked]" <[email-masked]>,"[email-masked]" <[email-masked]>,"[email-masked]" <[email-masked]>,"[email-masked]" <[email-masked]>,"[email-masked]" <[email-masked]>
From: Arnaldo Carvalho de Melo <[email-masked]>
Message-ID: <[email-masked]>

On January 10, 2020 9:23:27 PM GMT-03:00, Song Liu <[email-masked]> wrote:
>
>
>> On Jan 10, 2020, at 3:47 PM, Masami Hiramatsu <[email-masked]>
>wrote:
>> 
>> On Fri, 10 Jan 2020 13:45:31 -0300
>> Arnaldo Carvalho de Melo <[email-masked]> wrote:
>> 
>>> Em Sat, Jan 11, 2020 at 12:52:13AM +0900, Masami Hiramatsu escreveu:
>>>> On Fri, 10 Jan 2020 15:02:34 +0100 Peter Zijlstra
><[email-masked]> wrote:
>>>>> Again, this only allows attaching to previously created kprobes,
>it does
>>>>> not allow creating kprobes, right?
>>> 
>>>>> That is; I don't think CAP_SYS_PERFMON should be allowed to create
>>>>> kprobes.
>>> 
>>>>> As might be clear; I don't actually know what the user-ABI is for
>>>>> creating kprobes.
>>> 
>>>> There are 2 ABIs nowadays, ftrace and ebpf. perf-probe uses ftrace
>interface to
>>>> define new kprobe events, and those events are treated as
>completely same as
>>>> tracepoint events. On the other hand, ebpf tries to define new
>probe event
>>>> via perf_event interface. Above one is that interface. IOW, it
>creates new kprobe.
>>> 
>>> Masami, any plans to make 'perf probe' use the perf_event_open()
>>> interface for creating kprobes/uprobes?
>> 
>> Would you mean perf probe to switch to perf_event_open()?
>> No, perf probe is for setting up the ftrace probe events. I think we
>can add an
>> option to use perf_event_open(). But current kprobe creation from
>perf_event_open()
>> is separated from ftrace by design.
>
>I guess we can extend event parser to understand kprobe directly.
>Instead of
>
>	perf probe kernel_func
>	perf stat/record -e probe:kernel_func ...
>
>We can just do 
>
>	perf stat/record -e kprobe:kernel_func ...

You took the words from my mouth, exactly, that is a perfect use case, an alternative to the 'perf probe' one of making a disabled event that then gets activated via record/stat/trace, in many cases it's better, removes the explicit probe setup case.

Regards, 

- Arnaldo

>Thanks,
>Song