On Thursday 18 March 2010 13:22:28 Sheng Yang wrote: > On Thursday 18 March 2010 12:50:58 Zachary Amsden wrote: > > On 03/17/2010 03:19 PM, Sheng Yang wrote: > > > 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. > > > > That's the only defined case, and it is defined because the vector field > > is ignore for DM_NMI. Vol 3A (exact section numbers may vary depending > > on your version). > > > > 8.5.1 / 8.6.1 > > > > '100 (NMI) Delivers an NMI interrupt to the target processor or > > processors. The vector information is ignored' > > > > 8.5.2 Valid Interrupt Vectors > > > > 'Local and I/O APICs support 240 of these vectors (in the range of 16 to > > 255) as valid interrupts.' > > > > 8.8.4 Interrupt Acceptance for Fixed Interrupts > > > > '...; vectors 0 through 15 are reserved by the APIC (see also: Section > > 8.5.2, "Valid Interrupt Vectors")' > > > > So I misremembered, apparently you can deliver interrupts 0x10-0x1f, but > > vectors 0x00-0x0f are not valid to send via APIC or I/O APIC. > > As you pointed out, NMI is not "Fixed interrupt". If we want to send NMI, > it would need a specific delivery mode rather than vector number. > > And if you look at code, if we specific NMI_VECTOR, the delivery mode would > be set to NMI. > > So what's wrong here? OK, I think I understand your points now. You meant that these vectors can't be filled in vector field directly, right? But NMI is a exception due to DM_NMI. Is that your point? I think we agree on this. -- 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
