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    SubjectRe: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift
    On Thu, Nov 18, 2010 at 11:28:50PM +0300, Cyrill Gorcunov wrote:
    > On Thu, Nov 18, 2010 at 03:08:07PM -0500, Don Zickus wrote:
    > > On Thu, Nov 18, 2010 at 01:51:44PM -0600, Jason Wessel wrote:
    > > > > So the problem is when the nmi watchdog is enabled, the perf event is
    > > > > 'active' and thus tries to read the counter value. Because it is always
    > > > > zero, perf just assumes the counter overflowed and the NMI is his.
    > > > >
    > > > > Not sure how to fix it yet, other than include the logic that detects we
    > > > > are on a guest and disable perf??
    > > > >
    > > > >
    > > >
    > > > I highly doubt we want to disable perf. I would rather use the source
    > > > and fix the nmi emulation in KVM/Qemu after we hear back the results
    > >
    > > Well I think Peter does not have a positive opinion about emulating perf
    > > inside a guest. Nor are the KVM folks having much success in doing so.
    > >
    > > Just to clarify, perf counter emulation is _not_ implemented in kvm.
    > > Therefore disabling perf in the guest makes sense until someone gets
    > > around to actually writing the emulation code for perf in a guest. :-)
    > >
    > > Cheers,
    > > Don
    >
    > Don, Robert,
    >
    > I still have suspicious on ours 'pending' nmi handler. Look what I mean --
    > (keep in mind that p4 has a a way more counters than others).
    >

    To be precise -- it seems this scenario may force the back-to-back
    nmi handler to eat unknown nmi.

    Cyrill


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