Messages in this thread | | | Date | Wed, 17 Mar 2010 11:14:52 -1000 | From | Zachary Amsden <> | Subject | Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side |
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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.
Zach
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