From: Like Xu <like.xu.linux@gmail.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Sandipan Das <sandipan.das@amd.com>
Subject: Re: [PATCH v4 12/12] KVM: x86/cpuid: Add AMD CPUID ExtPerfMonAndDbg leaf 0x80000022
Date: Fri, 7 Apr 2023 15:19:53 +0800 [thread overview]
Message-ID: <23262f06-44d1-1b3d-6d2d-c0c418e564f6@gmail.com> (raw)
In-Reply-To: <ZC92/WkJf9/AnABP@google.com>
On 7/4/2023 9:50 am, Sean Christopherson wrote:
> On Tue, Feb 14, 2023, Like Xu wrote:
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index f4a4691b4f4e..2472fa8746c2 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -4916,6 +4916,12 @@ static __init void svm_set_cpu_caps(void)
>> } else {
>> /* AMD PMU PERFCTR_CORE CPUID */
>> kvm_cpu_cap_check_and_set(X86_FEATURE_PERFCTR_CORE);
>> + /*
>> + * KVM only supports AMD PerfMon V2, even if it supports V3+.
>
> Ha! A perfect example of why I strongly prefer that changelogs and comments avoid
> pronouns. The above "it" reads as:
>
> * KVM only supports AMD PerfMon V2, even if KVM supports V3+.
>
> which is clearly nonsensical.
I get your point. Thanks.
>
>
>> + * For PerfMon V3+, it's unsafe to expect V2 bit is set or cleared.
>
> If it's unsafe to assume anything v3+ implying v2 support, then it's definitely
> not safe to assume that KVM can blindly set v2 without future changes. I don't
> see any reason not to do
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index bd324962bb7e..1192f605ad47 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -756,6 +756,10 @@ void kvm_set_cpu_caps(void)
> F(NULL_SEL_CLR_BASE) | F(AUTOIBRS) | 0 /* PrefetchCtlMsr */
> );
>
> + kvm_cpu_cap_mask(CPUID_8000_0022_EAX,
> + F(PERFMON_V2)
> + );
> +
> /*
> * Synthesize "LFENCE is serializing" into the AMD-defined entry in
> * KVM's supported CPUID if the feature is reported as supported by the
>
>
> and then this code can be:
>
> if (kvm_pmu_cap.version != 2)
> kvm_cpu_cap_clear(X86_FEATURE_PERFMON_V2);
>
> Ah, but presumably the
>
> if (kvm_pmu_cap.num_counters_gp < AMD64_NUM_COUNTERS_CORE)
>
> path also needs to clear PERFMON_V2. I think I'd still vote to grab host CPUID
> and clear here (instead of setting).
Looks good to me.
>
> What is the relationship between PERFCTR_CORE and PERFMON_V2? E.g. if v2 depends
> on having PERFCTR_CORE, then we can do:
Yes, the PERFCTR_CORE bit will always be set if the v2 bit is set.
>
> if (enable_pmu) {
> if (kvm_pmu_cap.num_counters_gp < AMD64_NUM_COUNTERS_CORE)
> kvm_pmu_cap.num_counters_gp = AMD64_NUM_COUNTERS;
> else
> kvm_cpu_cap_check_and_set(X86_FEATURE_PERFCTR_CORE);
>
> if (kvm_pmu_cap.version != 2 ||
> !kvm_cpu_cap_has(X86_FEATURE_PERFCTR_CORE))
> kvm_cpu_cap_clear(X86_FEATURE_PERFMON_V2);
next prev parent reply other threads:[~2023-04-07 7:20 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-14 5:07 [PATCH v4 00/12] KVM: x86: Add AMD Guest PerfMonV2 PMU support Like Xu
2023-02-14 5:07 ` [PATCH v4 01/12] KVM: x86/pmu: Rename pmc_is_enabled() to pmc_is_globally_enabled() Like Xu
2023-02-14 5:07 ` [PATCH v4 02/12] KVM: VMX: Refactor intel_pmu_set_msr() to align with other set_msr() helpers Like Xu
2023-02-16 21:13 ` Sean Christopherson
2023-02-21 8:44 ` Like Xu
2023-03-23 7:43 ` Like Xu
2023-03-23 14:28 ` Sean Christopherson
2023-02-14 5:07 ` [PATCH v4 03/12] KVM: x86/pmu: Rewrite reprogram_counters() to improve performance Like Xu
2023-02-14 5:07 ` [PATCH v4 04/12] KVM: x86/pmu: Expose reprogram_counters() in pmu.h Like Xu
2023-02-14 5:07 ` [PATCH v4 05/12] KVM: x86/pmu: Error when user sets the GLOBAL_STATUS reserved bits Like Xu
2023-04-06 23:45 ` Sean Christopherson
2023-04-07 5:08 ` Like Xu
2023-04-07 15:43 ` Sean Christopherson
2023-02-14 5:07 ` [PATCH v4 06/12] KVM: x86/pmu: Make part of the Intel v2 PMU MSRs handling x86 generic Like Xu
2023-04-06 23:57 ` Sean Christopherson
2023-04-07 1:39 ` Sean Christopherson
2023-02-14 5:07 ` [PATCH v4 07/12] KVM: x86/cpuid: Use fast return for cpuid "0xa" leaf when !enable_pmu Like Xu
2023-04-06 23:59 ` Sean Christopherson
2023-02-14 5:07 ` [PATCH v4 08/12] KVM: x86/pmu: Disable vPMU if the minimum num of counters isn't met Like Xu
2023-04-07 0:06 ` Sean Christopherson
2023-04-07 0:23 ` Sean Christopherson
2023-02-14 5:07 ` [PATCH v4 09/12] KVM: x86/pmu: Forget PERFCTR_CORE if the min " Like Xu
2023-04-07 0:32 ` Sean Christopherson
2023-02-14 5:07 ` [PATCH v4 10/12] KVM: x86/cpuid: Add X86_FEATURE_PERFMON_V2 as a scattered flag Like Xu
2023-04-07 0:41 ` Sean Christopherson
2023-02-14 5:07 ` [PATCH v4 11/12] KVM: x86/svm/pmu: Add AMD PerfMonV2 support Like Xu
2023-04-07 1:35 ` Sean Christopherson
2023-04-07 7:08 ` Like Xu
2023-04-07 14:44 ` Sean Christopherson
2023-04-10 11:34 ` Like Xu
2023-02-14 5:07 ` [PATCH v4 12/12] KVM: x86/cpuid: Add AMD CPUID ExtPerfMonAndDbg leaf 0x80000022 Like Xu
2023-04-07 1:50 ` Sean Christopherson
2023-04-07 7:19 ` Like Xu [this message]
2023-04-07 2:02 ` [PATCH v4 00/12] KVM: x86: Add AMD Guest PerfMonV2 PMU support Sean Christopherson
2023-04-07 7:28 ` Like Xu
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