linux-kernel - Re: [PATCH v5 11/20] x86: perf: Intel PT and LBR/BTS are mutually exclusive

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Message-ID: <20141022141547.GO12706@worktop.programming.kicks-ass.net>
Date:	Wed, 22 Oct 2014 16:15:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
	adrian.hunter@...el.com, acme@...radead.org
Subject: Re: [PATCH v5 11/20] x86: perf: Intel PT and LBR/BTS are mutually
 exclusive

On Mon, Oct 13, 2014 at 04:45:39PM +0300, Alexander Shishkin wrote:
> Intel PT cannot be used at the same time as LBR or BTS and will cause a
> general protection fault if they are used together. In order to avoid
> fixing up GPs in the fast path, instead we use flags to indicate that
> that one of these is in use so that the other avoids MSR access altogether.
> 

Yeah, don't like this. Like I've said many times before we should simply
disallow creating PT events when there are LBR events and vice versa.

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