Messages in this thread | | | Date | Mon, 09 Jul 2012 08:47:47 -0600 | From | David Ahern <> | Subject | Re: perf with precise attribute kills all KVM based VMs |
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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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