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Message-ID: <CALMp9eSXTpkKpmqJiS=0NuQOjCFKDeOqjN3wWfyPCBhx-H=Vsw@mail.gmail.com>
Date: Tue, 6 Sep 2022 21:11:51 -0700
From: Jim Mattson <jmattson@...gle.com>
To: Like Xu <like.xu.linux@...il.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Sandipan Das <sandipan.das@....com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] KVM: x86/cpuid: Add AMD CPUID ExtPerfMonAndDbg leaf 0x80000022
On Tue, Sep 6, 2022 at 8:59 PM Like Xu <like.xu.linux@...il.com> wrote:
>
> On 7/9/2022 4:08 am, Jim Mattson wrote:
> > On Tue, Sep 6, 2022 at 5:53 AM Like Xu <like.xu.linux@...il.com> wrote:
> >>
> >> On 6/9/2022 1:36 am, Jim Mattson wrote:
> >>> On Mon, Sep 5, 2022 at 5:45 AM Like Xu <like.xu.linux@...il.com> wrote:
> >>>>
> >>>> From: Sandipan Das <sandipan.das@....com>
> >>>>
> >>>> CPUID leaf 0x80000022 i.e. ExtPerfMonAndDbg advertises some
> >>>> new performance monitoring features for AMD processors.
> >>>>
> >>>> Bit 0 of EAX indicates support for Performance Monitoring
> >>>> Version 2 (PerfMonV2) features. If found to be set during
> >>>> PMU initialization, the EBX bits of the same CPUID function
> >>>> can be used to determine the number of available PMCs for
> >>>> different PMU types.
> >>>>
> >>>> Expose the relevant bits via KVM_GET_SUPPORTED_CPUID so
> >>>> that guests can make use of the PerfMonV2 features.
> >>>>
> >>>> Co-developed-by: Like Xu <likexu@...cent.com>
> >>>> Signed-off-by: Like Xu <likexu@...cent.com>
> >>>> Signed-off-by: Sandipan Das <sandipan.das@....com>
> >>>> ---
> >>>> arch/x86/include/asm/perf_event.h | 8 ++++++++
> >>>> arch/x86/kvm/cpuid.c | 21 ++++++++++++++++++++-
> >>>> 2 files changed, 28 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> >>>> index f6fc8dd51ef4..c848f504e467 100644
> >>>> --- a/arch/x86/include/asm/perf_event.h
> >>>> +++ b/arch/x86/include/asm/perf_event.h
> >>>> @@ -214,6 +214,14 @@ union cpuid_0x80000022_ebx {
> >>>> unsigned int full;
> >>>> };
> >>>>
> >>>> +union cpuid_0x80000022_eax {
> >>>> + struct {
> >>>> + /* Performance Monitoring Version 2 Supported */
> >>>> + unsigned int perfmon_v2:1;
> >>>> + } split;
> >>>> + unsigned int full;
> >>>> +};
> >>>> +
> >>>> struct x86_pmu_capability {
> >>>> int version;
> >>>> int num_counters_gp;
> >>>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> >>>> index 75dcf7a72605..08a29ab096d2 100644
> >>>> --- a/arch/x86/kvm/cpuid.c
> >>>> +++ b/arch/x86/kvm/cpuid.c
> >>>> @@ -1094,7 +1094,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> >>>> entry->edx = 0;
> >>>> break;
> >>>> case 0x80000000:
> >>>> - entry->eax = min(entry->eax, 0x80000021);
> >>>> + entry->eax = min(entry->eax, 0x80000022);
> >>>> /*
> >>>> * Serializing LFENCE is reported in a multitude of ways, and
> >>>> * NullSegClearsBase is not reported in CPUID on Zen2; help
> >>>> @@ -1203,6 +1203,25 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> >>>> if (!static_cpu_has_bug(X86_BUG_NULL_SEG))
> >>>> entry->eax |= BIT(6);
> >>>> break;
> >>>> + /* AMD Extended Performance Monitoring and Debug */
> >>>> + case 0x80000022: {
> >>>> + union cpuid_0x80000022_eax eax;
> >>>> + union cpuid_0x80000022_ebx ebx;
> >>>> +
> >>>> + entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
> >>>> + if (!enable_pmu)
> >>>> + break;
> >>>> +
> >>>> + if (kvm_pmu_cap.version > 1) {
> >>>> + /* AMD PerfMon is only supported up to V2 in the KVM. */
> >>>> + eax.split.perfmon_v2 = 1;
> >>>> + ebx.split.num_core_pmc = min(kvm_pmu_cap.num_counters_gp,
> >>>> + KVM_AMD_PMC_MAX_GENERIC);
> >>>
> >>> Note that the number of core PMCs has to be at least 6 if
> >>> guest_cpuid_has(vcpu, X86_FEATURE_PERFCTR_CORE). I suppose this leaf
> >>> could claim fewer, but the first 6 PMCs must work, per the v1 PMU
> >>> spec. That is, software that knows about PERFCTR_CORE, but not about
> >>> PMU v2, can rightfully expect 6 PMCs.
> >>
> >> I thought the NumCorePmc number would only make sense if
> >> CPUID.80000022.eax.perfmon_v2
> >> bit was present, but considering that the user space is perfectly fine with just
> >> configuring the
> >> NumCorePmc number without setting perfmon_v2 bit at all, so how about:
> >
> > CPUID.80000022H might only make sense if X86_FEATURE_PERFCTR_CORE is
> > present. It's hard to know in the absence of documentation.
>
> Whenever this happens, we may always leave the definition of behavior to the
> hypervisor.
I disagree. If CPUID.0H reports "AuthenticAMD," then AMD is the sole
authority on behavior.
> >
> >> /* AMD Extended Performance Monitoring and Debug */
> >> case 0x80000022: {
> >> union cpuid_0x80000022_eax eax;
> >> union cpuid_0x80000022_ebx ebx;
> >> bool perfctr_core;
> >>
> >> entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
> >> if (!enable_pmu)
> >> break;
> >>
> >> perfctr_core = kvm_cpu_cap_has(X86_FEATURE_PERFCTR_CORE);
> >> if (!perfctr_core)
> >> ebx.split.num_core_pmc = AMD64_NUM_COUNTERS;
> >> if (kvm_pmu_cap.version > 1) {
> >> /* AMD PerfMon is only supported up to V2 in the KVM. */
> >> eax.split.perfmon_v2 = 1;
> >> ebx.split.num_core_pmc = min(kvm_pmu_cap.num_counters_gp,
> >> KVM_AMD_PMC_MAX_GENERIC);
> >> }
> >> if (perfctr_core) {
> >> ebx.split.num_core_pmc = max(ebx.split.num_core_pmc,
> >> AMD64_NUM_COUNTERS_CORE);
> >> }
> >
> > This still isn't quite right. All AMD CPUs must support a minimum of 4 PMCs.
>
> K7 at least. I could not confirm that all antique AMD CPUs have 4 counters w/o
> perfctr_core.
The APM says, "All implementations support the base set of four
performance counter / event-select pairs." That is unequivocal.
> >
> >>
> >> entry->eax = eax.full;
> >> entry->ebx = ebx.full;
> >> break;
> >> }
> >>
> >> ?
> >>
> >> Once 0x80000022 appears, ebx.split.num_core_pmc will report only
> >> the real "Number of Core Performance Counters" regardless of perfmon_v2.
> >>
> >>>
> >>>
> >>>> + }
> >>>> + entry->eax = eax.full;
> >>>> + entry->ebx = ebx.full;
> >>>> + break;
> >>>> + }
> >>>> /*Add support for Centaur's CPUID instruction*/
> >>>> case 0xC0000000:
> >>>> /*Just support up to 0xC0000004 now*/
> >>>> --
> >>>> 2.37.3
> >>>>
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