[RFC] perf: Clear MSRs on kexec

[Peter Zijlstra]

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.