linux-kernel - Re: [RFC] perf: Clear MSRs on kexec

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Message-ID: <20150804055229.GD14481@krava.redhat.com>
Date:	Tue, 4 Aug 2015 07:52:29 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	Ingo Molnar <mingo@...nel.org>, dong.su@...csson.com,
	Vivek Goyal <vgoyal@...hat.com>,
	Haren Myneni <hbabu@...ibm.com>,
	Don Zickus <dzickus@...hat.com>
Subject: Re: [RFC] perf: Clear MSRs on kexec

On Mon, Aug 03, 2015 at 11:54:17PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 03, 2015 at 11:32:28PM +0200, Jiri Olsa wrote:
> > hi,
> > I'm getting following message on the kdump kernel start
> > 
> >   Broken BIOS detected, complain to your hardware vendor.\
> >   [Firmware Bug]: the BIOS has corrupted hw-PMU resources (MSR 38d is b0)
> > 
> > it seems to be caused by NMI watchdog being configured
> > and fixed counter values stays in MSRs, which triggers
> > warning in check_hw_exists and disables perf support
> > in kdump kernel.. which probably does not hurt ;-)
> > 
> > zeroing MSRs during kdump shutdown seems to work (attached)
> > but I'm not sure thats correct place for kdump perf callback
> 
> Right, but why bother? All that kernel needs to do is write a memory
> dump to someplace and reboot, right? The less you do, the less can go
> wrong.

well, I was hunting that 'Broken BIOS..' message which is wrong

I wouldn't think anyone wants to use perf under kdump kernel,
but you never know ;-)

jirka
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