On Thursday 18 March 2010 05:14:52 Zachary Amsden wrote: > On 03/16/2010 11:28 PM, Sheng Yang wrote: > > 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... > > You can't use the APIC to send vectors 0x00-0x1f, or at least, aren't > supposed to be able to. Um? Why? Especially kernel is already using it to deliver NMI. -- 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