Messages in this thread | | | Subject | Re: [PATCH v2 3/4] Add support for AMD Core Perf Extension in guest | From | "Natarajan, Janakarajan" <> | Date | Wed, 6 Dec 2017 14:19:11 -0600 |
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On 12/5/2017 11:56 AM, Radim Krcmar wrote: > 2017-12-01 13:30-0600, Natarajan, Janakarajan: >> On 11/17/2017 5:44 AM, Borislav Petkov wrote: >>> On Thu, Nov 16, 2017 at 12:00:11PM -0600, Natarajan, Janakarajan wrote: >>>> Ah my apologies. So when the pmu is initialized the cpuid entries >>>> aren't available then. >>> So let's see: >>> >>> ... kvm_arch_vcpu_create() -> >>> svm_create_vcpu() -> >>> kvm_vcpu_init() -> >>> kvm_arch_vcpu_init() -> >>> >>> <--- HERE >>> >>> kvm_pmu_init() >>> >>> But at HERE in kvm_arch_vcpu_init() right before kvm_pmu_init() we do already query >>> cpuid: >>> >>> vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu); >>> >>> so it's not like we don't know about cpuid leafs at that point. Which >>> would mean that the code can be made to set the CPU family earlier, >>> before kvm_pmu_init() runs so that you have the proper CPU family and >>> thus have this thing properly designed. >>> >>> Maybe Paolo and Radim have a better suggestion here... >> Paolo, Radim any suggestions about this. I feel that the number of counters >> initialized can be 6 > This is the best solution with the current framework.
Okay.
> >> and the subsequent code (kvm_pmu_refresh()) takes care of the number of >> counters to be used (4 or 6) >> based on the vcpu family. > Can't we look only at X86_FEATURE_PERFCTR_CORE and completely ignore the > AMD family? > Using the family would bring problems with compatiblity.
Yeah. We can just use the X86_FEATURE_PERFCTR_CORE flag as a check. I'll send a v3 with the changes.
Thanks.
> > Thanks.
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