On Wednesday 17 March 2010 10:34:33 Zhang, Yanmin wrote: > On Tue, 2010-03-16 at 11:32 +0200, Avi Kivity wrote: > > On 03/16/2010 09:48 AM, Zhang, Yanmin wrote: > > > Right, but there is a scope between kvm_guest_enter and really running > > > in guest os, where a perf event might overflow. Anyway, the scope is > > > very narrow, I will change it to use flag PF_VCPU. > > > > There is also a window between setting the flag and calling 'int $2' > > 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. > > I'm not sure if vmexit does break NMI context or not. Hardware NMI context > isn't reentrant till a IRET. YangSheng would like to double check it. After more check, I think VMX won't remained NMI block state for host. That's 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... -- regards Yang, Sheng -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
