Messages in this thread | | | From | Sheng Yang <> | Subject | Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side | Date | Wed, 17 Mar 2010 17:51:01 +0800 |
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On Wednesday 17 March 2010 17:41:58 Avi Kivity wrote: > On 03/17/2010 11:28 AM, Sheng Yang wrote: > >> 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. > > That's pretty bad, as NMI runs on a separate stack (via IST). So if > another NMI happens while our int $2 is running, the stack will be > corrupted.
Though hardware didn't provide this kind of block, software at least would warn about it... nmi_enter() still would be executed by "int $2", and result in BUG() if we are already in NMI context(OK, it is a little better than mysterious crash due to corrupted stack). > > > 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... > > I think you need DM_NMI for that to work correctly. > > An alternative is to call the NMI handler directly.
apic_send_IPI_self() already took care of APIC_DM_NMI.
And NMI handler would block the following NMI?
-- regards Yang, Sheng
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