Re: perf with precise attribute kills all KVM based VMs

[Avi Kivity <avi@redhat.com>]

On 07/09/2012 05:24 PM, Peter Zijlstra wrote:
> On Mon, 2012-07-09 at 17:19 +0300, Gleb Natapov wrote:
>> Yes, this is knows problem that I can't find time to fix. The crash is
>> cause by CPU using host PEBS virtual address while guest is running
>> which causes guest memory corruption. We should disable evens that use
>> PEBS at the guest entry. 
> 
> Whoops.. so the hardware is reading the DS address as programmed by the
> host (host linear address) and using it as a guest linear address?
> 
> Quality stuff..
> 
> Disabling PEBS events for guests isn't pretty though.. 

We already have atomic MSR switching at guest entry/exit time.  So it's
not pretty in terms of not getting full profiling, but the code won't be
too hard.  Basically we just have to exclude_guest any pebs event.

> but I guess the
> only alternative is mapping the DS into the guest and reprogramming
> MSR_IA32_DS_AREA which is all a little involved I suppose?

Way too involved, especially as it's virtual addresses and we don't
control the guest cr3.  Note that the hardware won't fail gracefully.

-- 
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