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Date: Wed, 17 Mar 2010 18:50:58 -1000 From: Zachary Amsden <zamsden@...hat.com> To: Sheng Yang <sheng@...ux.intel.com> CC: Avi Kivity <avi@...hat.com>, "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>, Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, Marcelo Tosatti <mtosatti@...hat.com>, oerg Roedel <joro@...tes.org>, Jes Sorensen <Jes.Sorensen@...hat.com>, Gleb Natapov <gleb@...hat.com>, "Huang, Zhiteng" <zhiteng.huang@...el.com>, Joerg Roedel <joerg.roedel@....com> Subject: Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side 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. Zach -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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