Re: [PATCH 1/3] KVM: x86: Omit PMU MSRs from KVM_GET_MSR_INDEX_LIST if !enable_pmu

[Yang, Weijiang]

On 12/27/2022 8:59 AM, Yang, Weijiang wrote:
> On 12/26/2022 7:17 PM, Like Xu wrote:
> > From: Like Xu <likexu@xxxxxxxxxxx>
> >
> > When the PMU is disabled, don't bother sharing the PMU MSRs with
> > userspace through KVM_GET_MSR_INDEX_LIST.  Instead, filter them out
> > so userspace doesn't have to keep track of them.
> >
> > Note that 'enable_pmu' is read-only, so userspace has no control over
> > whether the PMU MSRs are included in the list or not.


[...]


> > +		case MSR_ARCH_PERFMON_FIXED_CTR0 ... MSR_ARCH_PERFMON_FIXED_CTR_MAX:
> > +			if (!enable_pmu || msrs_to_save_all[i] - MSR_ARCH_PERFMON_FIXED_CTR0 >=
> > +			    min(KVM_PMC_MAX_FIXED, kvm_pmu_cap.num_counters_fixed))
> > +				continue;
> > +			break;
> > +		case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5:
> > +		case MSR_K7_EVNTSEL0 ... MSR_K7_PERFCTR3:
> > +		case MSR_CORE_PERF_FIXED_CTR_CTRL:
> > +		case MSR_CORE_PERF_GLOBAL_STATUS:
> > +		case MSR_CORE_PERF_GLOBAL_CTRL:
> > +		case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
> > +		case MSR_IA32_DS_AREA:
> > +		case MSR_IA32_PEBS_ENABLE:
> > +		case MSR_PEBS_DATA_CFG:
> > +			if (!enable_pmu)
> > +				continue;
> > +			break;
>
> I prefer use a helper to wrap the hunk of PMU msr checks and move the
> helper to
>
> the "default" branch of switch, it makes the code looks nicer:
>
> default:
>
> if(!enable_pmu && !kvm_pmu_valid_msrlist(msr))


Typo, should be:

if (!enable_pmu || !kvm_pmu_valid_msrlist(msr))


>           continue;
>
>
> >    		case MSR_IA32_XFD:
> >    		case MSR_IA32_XFD_ERR:
> >    			if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
> > @@ -13468,3 +13485,4 @@ static void __exit kvm_x86_exit(void)
> >    	 */
> >    }
> >    module_exit(kvm_x86_exit);
> > +
>
> Extra newline.