linux-kernel - Re: [BUG] perf: bogus correlation of kernel symbols

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Date:	Thu, 12 May 2011 23:38:37 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] perf: bogus correlation of kernel symbols

On Thu, May 12, 2011 at 11:35 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Stephane Eranian <eranian@...gle.com> wrote:
>
>> The other contradiction, I see, is that you have perf_event paranoia level
>> and this new kptr masquerading feature which conflict with each
>> other.
>>
>> You can be allowed to monitor at the kernel level (paranoid=1, default)
>> but you cannot correlate symbols:
>>
>> $ perf record -e cycles:k foo
>>
>> I suspect if you have this kptr thing turned on, then you need to disallow
>> monitoring at the kernel level too.
>
> The better (and consistent) solution would be to turn the kptr_restrict thing
> off - see the patch i sent.
>
I saw that. But I think that when someone turns it back on, then you need
to increase the perf_events paranoia level to disallow kernel monitoring to
regular users such that you maintain consistency across the board.
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