Messages in this thread | | | Date | Fri, 14 Mar 2014 16:07:10 -0700 | From | Venkatesh Srinivas <> | Subject | Re: [PATCH] perf/x86/intel: Use rdmsrl_safe when initializing RAPL PMU. |
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On Fri, Mar 14, 2014 at 10:57:58AM -0600, David Ahern wrote: >On 3/14/14, 10:17 AM, Andi Kleen wrote: >>>The Intel ISR section for RDMSR seems to say: "Specifying a reserved >>>or unimplemented >>>MSR address in ECX will also cause a general protection exception". >>> >>> From a guest's perspective, MSR_RAPL_POWER_UNIT is unimplemented; kvm matches >>>this behavior. >> >>MSRs are model specific and defined per model number. If you report a model >>number you're expected to implement the MSRs defined for that model number. >> >>AFAIK Xen just reports 0 for unknown MSRs (and I'm surprised KVM doesn't too) >> >>I would suggest to fix KVM. > >I believe ignore_msrs parameter to kvm handles that. > >David
Hi,
cc-ing the virtualization mailing list for more detail on the kvm default for ignore_msrs (it defaults off).
1) Just returning 0 for unsupported MSRs is not workable -- 0 may be a meaningful value for an MSR. RDMSR/WRMSR already have a mechanism for out-of-band errors, #GP.
2) #GP has been KVM's default behavior for quite some time. Even if we believe changing KVM's default is appropriate, Linux w/ the RAPL PMU code enabled will fail to boot on existing KVM versions. W/ this change, Linux will boot on prior KVM versions.
Thanks, -- vs;
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