On Wednesday 17 March 2010 10:34:33 Zhang, Yanmin wrote:
On Tue, 2010-03-16 at 11:32 +0200, Avi Kivity wrote:After more check, I think VMX won't remained NMI block state for host. That's
On 03/16/2010 09:48 AM, Zhang, Yanmin wrote:I'm not sure if vmexit does break NMI context or not. Hardware NMI context
Right, but there is a scope between kvm_guest_enter and really runningThere is also a window between setting the flag and calling 'int $2'
in guest os, where a perf event might overflow. Anyway, the scope is
very narrow, I will change it to use flag PF_VCPU.
where an NMI might happen and be accounted incorrectly.
Perhaps separate the 'int $2' into a direct call into perf and another
call for the rest of NMI handling. I don't see how it would work on svm
though - AFAICT the NMI is held whereas vmx swallows it.
I guess NMIs
will be disabled until the next IRET so it isn't racy, just tricky.
isn't reentrant till a IRET. YangSheng would like to double check it.
means, if NMI happened and processor is in VMX non-root mode, it would only
result in VMExit, with a reason indicate that it's due to NMI happened, but no
more state change in the host.
So in that meaning, there _is_ a window between VMExit and KVM handle the NMI.
Moreover, I think we _can't_ stop the re-entrance of NMI handling code because
"int $2" don't have effect to block following NMI.
And if the NMI sequence is not important(I think so), then we need to generate
a real NMI in current vmexit-after code. Seems let APIC send a NMI IPI to
itself is a good idea.
I am debugging a patch based on apic->send_IPI_self(NMI_VECTOR) to replace
"int $2". Something unexpected is happening...