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Date:	Fri, 21 Mar 2014 14:55:24 -0700
From:	"H. Peter Anvin" <>
To:	Andi Kleen <>
CC:	Peter Wu <>,
	Peter Zijlstra <>,
	Ingo Molnar <>,
Subject: Re: GPF in intel_pmu_lbr_reset() with qemu -cpu host

On 03/21/2014 02:48 PM, Andi Kleen wrote:
> "H. Peter Anvin" <> writes:
>> That's why at least to some extent The Right Thing is not to try to
>> pretend to be a CPU you don't even know how to emulate.
>> But again, that has its own issues, too, mostly with userspace
>> optimization, and making the Linux code more resilient wouldn't hurt.
>> In that sense #GP(0) is *much* better than 0: it unambiguously gives an
>> error to work with.
> That means we could just throw rdmsr() away and it would be completely
> replaced with rdmsr_safe(). But then that will likely cause all kinds
> of problems with how to handle these errors and where and how to handle
> these exceptions.
> I much prefer just to fix KVM. I cannot think of any case
> where 0 would cause a major issue.
> After all it's virtualization not "rewrite complete kernel for it"

Actually, Ingo, Borislav and I have been discussing making rdmsr_safe()
more of the default, especially for things like this where the error
handling is obvious (doesn't work?  Disable the PMU.)


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