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

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Message-ID: <20150803215417.GG25159@twins.programming.kicks-ass.net>
Date:	Mon, 3 Aug 2015 23:54:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
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 11:32:28PM +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.
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