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SubjectRe: perf with precise attribute kills all KVM based VMs
On 7/9/12 8:39 AM, Avi Kivity wrote:
> 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.

I found this testing changes to perf-kvm, but found the problem extends
to just perf-record. With perf-record exclude_guest defaults to 1. See
tools/perf/util/util.c, event_attr_init().

>> 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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