linux-kernel - Re: [PATCH 2/2] perf, x86: Don't allow unusual PEBS raw flags

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Date:	Tue, 7 May 2013 13:04:15 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/2] perf, x86: Don't allow unusual PEBS raw flags


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, May 07, 2013 at 08:48:05AM +0200, Ingo Molnar wrote:
> > Also, this code only runs when the event is set up, so a bit of sanity 
> > checking can only help, right?
> 
> Nah, its all very circumspect. In fact; while what Andi states is 'true':
> 
> > documentation in the Intel SDM 18.6.1.1 states:
> >
> > """
> > PEBS events are only valid when the following fields of IA32_PERFEVTSELx are all
> > zero: AnyThread, Edge, Invert, CMask.
> > """
> 
> It is also true that Intel themselves gave us events that contradict this; look
> at the intel_pebs_aliases*() functions.
>
> This patch would make it impossible to manually create those events.

I missed that bit of obfuscation ...

> Further, there's something entirely different behind this.

Ok, I agree with you, this needs to be fully explained.

Thanks,

	Ingo
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