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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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