linux-kernel - Re: [PATCH 1/3] KVM: x86: Omit PMU MSRs from KVM_GET_MSR_INDEX_LIST if !enable

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Date:   Tue, 27 Dec 2022 10:18:12 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Like Xu <like.xu.linux@...il.com>
CC:     "Christopherson,, Sean" <seanjc@...gle.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Aaron Lewis <aaronlewis@...gle.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>
Subject: Re: [PATCH 1/3] KVM: x86: Omit PMU MSRs from KVM_GET_MSR_INDEX_LIST
 if !enable_pmu


On 12/27/2022 8:59 AM, Yang, Weijiang wrote:
> On 12/26/2022 7:17 PM, Like Xu wrote:
>> From: Like Xu <likexu@...cent.com>
>>
>> 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.
>
>
>