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

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Message-ID: <20130507084803.GD9688@dyad.programming.kicks-ass.net>
Date:	Tue, 7 May 2013 10:48:03 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.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

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.

Further, there's something entirely different behind this.
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