linux-kernel - Re: [RFC][PATCH] perf, intel: Don't touch MSR_IA32

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Message-ID: <1347471911.15764.72.camel@twins>
Date:	Wed, 12 Sep 2012 19:45:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC][PATCH] perf, intel: Don't touch MSR_IA32_DEBUGCTLMSR from
 NMI context

On Wed, 2012-09-12 at 19:37 +0200, Peter Zijlstra wrote:
> Ah, so I do think EIO will re-enable LBR,

OK, it does not, but the:

>  also the handler is wrapped in
> x86_pmu::{dis,en}able_all() which does end up calling
> intel_pmu_lbr_{dis,en}able_all().

Thing does the re-enable for us,

>  However that leaves the MSR in the
> exact same state on exit as it was on enter, so that's not a problem for
> the: read-modify-write change. 

in a safe way.
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