Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os statistics from host side

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On 04/20/2010 06:32 AM, Sheng Yang wrote:
On Monday 19 April 2010 16:25:17 Avi Kivity wrote:
On 04/17/2010 09:12 PM, Avi Kivity wrote:
I think you were right the first time around.
Re-reading again (esp. the part about treatment of indirect NMI
vmexits), I think this was wrong, and that the code is correct.  I am
now thoroughly confused.

My fault...

Not at all, it's really confusingly worded.

To my understanding now, "If an event causes a VM exit directly, it does not
update architectural state as it would have if it had it not caused the VM
exit:", means: in NMI case, NMI would involve the NMI handler, and change the
"architectural state" to NMI block. In VMX non-root mode, the behavior of
calling NMI handler changed(determine by some VMCS fields), but not the
affection to the "architectural state". So the NMI block state would remain
the same.

Agree. It's confusing because the internal "nmi pending" flag is not set, while the "nmi blocking" flag is set.

(on svm both are set, but the NMI is not taken until the vmexit completes and the host unmasks NMIs).

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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