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Message-ID: <41834a9f-e8d9-11a2-d391-1ce80758128c@gmail.com>
Date:   Wed, 7 Sep 2022 11:50:06 +0800
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Subject: Re: [PATCH 3/4] KVM: x86/svm/pmu: Add AMD PerfMonV2 support
Content-Language: en-US
To:     Jim Mattson <jmattson@google.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sandipan Das <sandipan.das@amd.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20220905123946.95223-1-likexu@tencent.com>
 <20220905123946.95223-4-likexu@tencent.com>
 <CALMp9eSBK3xVKoqrk4j2yNqk+Jh0z-Nk-rwCTaTE0Dca5DQoPA@mail.gmail.com>
 <c9b3d50e-ec3d-3fa3-2706-5672100ffe09@gmail.com>
 <CALMp9eSQ1QkmECM4at9XDPUew0h2nxG5=YUSN=aWnQpZkXy2dw@mail.gmail.com>
From:   Like Xu <like.xu.linux@gmail.com>
In-Reply-To: <CALMp9eSQ1QkmECM4at9XDPUew0h2nxG5=YUSN=aWnQpZkXy2dw@mail.gmail.com>
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On 7/9/2022 4:19 am, Jim Mattson wrote:
> On Tue, Sep 6, 2022 at 5:45 AM Like Xu <like.xu.linux@gmail.com> wrote:
>>
>> On 6/9/2022 2:00 am, Jim Mattson wrote:
>>> On Mon, Sep 5, 2022 at 5:44 AM Like Xu <like.xu.linux@gmail.com> wrote:
>>>>
>>>> From: Like Xu <likexu@tencent.com>
>>>>
>>>> If AMD Performance Monitoring Version 2 (PerfMonV2) is detected
>>>> by the guest, it can use a new scheme to manage the Core PMCs using
>>>> the new global control and status registers.
>>>>
>>>> In addition to benefiting from the PerfMonV2 functionality in the same
>>>> way as the host (higher precision), the guest also can reduce the number
>>>> of vm-exits by lowering the total number of MSRs accesses.
>>>>
>>>> In terms of implementation details, amd_is_valid_msr() is resurrected
>>>> since three newly added MSRs could not be mapped to one vPMC.
>>>> The possibility of emulating PerfMonV2 on the mainframe has also
>>>> been eliminated for reasons of precision.
>>>>
>>>> Co-developed-by: Sandipan Das <sandipan.das@amd.com>
>>>> Signed-off-by: Sandipan Das <sandipan.das@amd.com>
>>>> Signed-off-by: Like Xu <likexu@tencent.com>
>>>> ---
>>>>    arch/x86/kvm/pmu.c     |  6 +++++
>>>>    arch/x86/kvm/svm/pmu.c | 50 +++++++++++++++++++++++++++++++++---------
>>>>    arch/x86/kvm/x86.c     | 11 ++++++++++
>>>>    3 files changed, 57 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
>>>> index 7002e1b74108..56b4f898a246 100644
>>>> --- a/arch/x86/kvm/pmu.c
>>>> +++ b/arch/x86/kvm/pmu.c
>>>> @@ -455,12 +455,15 @@ int kvm_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>>>
>>>>           switch (msr) {
>>>>           case MSR_CORE_PERF_GLOBAL_STATUS:
>>>> +       case MSR_AMD64_PERF_CNTR_GLOBAL_STATUS:
>>>>                   msr_info->data = pmu->global_status;
>>>>                   return 0;
>>>>           case MSR_CORE_PERF_GLOBAL_CTRL:
>>>> +       case MSR_AMD64_PERF_CNTR_GLOBAL_CTL:
>>>>                   msr_info->data = pmu->global_ctrl;
>>>>                   return 0;
>>>>           case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
>>>> +       case MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR:
>>>>                   msr_info->data = 0;
>>>>                   return 0;
>>>>           default:
>>>> @@ -479,12 +482,14 @@ int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>>>
>>>>           switch (msr) {
>>>>           case MSR_CORE_PERF_GLOBAL_STATUS:
>>>> +       case MSR_AMD64_PERF_CNTR_GLOBAL_STATUS:
>>>>                   if (msr_info->host_initiated) {
>>>>                           pmu->global_status = data;
>>>>                           return 0;
>>>>                   }
>>>>                   break; /* RO MSR */
>>>>           case MSR_CORE_PERF_GLOBAL_CTRL:
>>>> +       case MSR_AMD64_PERF_CNTR_GLOBAL_CTL:
>>>>                   if (pmu->global_ctrl == data)
>>>>                           return 0;
>>>>                   if (kvm_valid_perf_global_ctrl(pmu, data)) {
>>>> @@ -495,6 +500,7 @@ int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>>>                   }
>>>>                   break;
>>>>           case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
>>>> +       case MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR:
>>>>                   if (!(data & pmu->global_ovf_ctrl_mask)) {
>>>>                           if (!msr_info->host_initiated)
>>>>                                   pmu->global_status &= ~data;
>>>> diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
>>>> index 3a20972e9f1a..4c7d408e3caa 100644
>>>> --- a/arch/x86/kvm/svm/pmu.c
>>>> +++ b/arch/x86/kvm/svm/pmu.c
>>>> @@ -92,12 +92,6 @@ static struct kvm_pmc *amd_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
>>>>           return amd_pmc_idx_to_pmc(vcpu_to_pmu(vcpu), idx & ~(3u << 30));
>>>>    }
>>>>
>>>> -static bool amd_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
>>>> -{
>>>> -       /* All MSRs refer to exactly one PMC, so msr_idx_to_pmc is enough.  */
>>>> -       return false;
>>>> -}
>>>> -
>>>>    static struct kvm_pmc *amd_msr_idx_to_pmc(struct kvm_vcpu *vcpu, u32 msr)
>>>>    {
>>>>           struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>>>> @@ -109,6 +103,29 @@ static struct kvm_pmc *amd_msr_idx_to_pmc(struct kvm_vcpu *vcpu, u32 msr)
>>>>           return pmc;
>>>>    }
>>>>
>>>> +static bool amd_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
>>>> +{
>>>> +       struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>>>> +
>>>> +       switch (msr) {
>>>> +       case MSR_K7_EVNTSEL0 ... MSR_K7_PERFCTR3:
>>>> +               return pmu->version > 0;
>>>> +       case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5:
>>>> +               return guest_cpuid_has(vcpu, X86_FEATURE_PERFCTR_CORE);
>>>> +       case MSR_AMD64_PERF_CNTR_GLOBAL_STATUS:
>>>> +       case MSR_AMD64_PERF_CNTR_GLOBAL_CTL:
>>>> +       case MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR:
>>>> +               return pmu->version > 1;
>>>> +       default:
>>>> +               if (msr > MSR_F15H_PERF_CTR5 &&
>>>> +                   msr < MSR_F15H_PERF_CTL0 + 2 * KVM_AMD_PMC_MAX_GENERIC)
>>>> +                       return pmu->version > 1;
>>>
>>> Should this be bounded by guest CPUID.80000022H:EBX[NumCorePmc]
>>> (unless host-initiated)?
>>
>> Indeed, how about:
>>
>>          default:
>>                  if (msr > MSR_F15H_PERF_CTR5 &&
>>                      msr < MSR_F15H_PERF_CTL0 + 2 * pmu->nr_arch_gp_counters)
>>                          return pmu->version > 1;
>>
>> and for host-initiated:
>>
>> #define MSR_F15H_PERF_MSR_MAX  \
>>          (MSR_F15H_PERF_CTR0 + 2 * (KVM_AMD_PMC_MAX_GENERIC - 1))
> 
> I think there may be an off-by-one error here.

If KVM_AMD_PMC_MAX_GENERIC is 6:

#define MSR_F15H_PERF_CTL		0xc0010200
#define MSR_F15H_PERF_CTL5		(MSR_F15H_PERF_CTL + 10)

#define MSR_F15H_PERF_CTR		0xc0010201
#define MSR_F15H_PERF_CTR0		MSR_F15H_PERF_CTR
#define MSR_F15H_PERF_CTR5		(MSR_F15H_PERF_CTR + 10)

> 
>>
>> kvm_{set|get}_msr_common()
>>          case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_MSR_MAX:

the original code is "case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5:",

in that case, MSR_F15H_PERF_MSR_MAX make sense, right ?

>>                   if (kvm_pmu_is_valid_msr(vcpu, msr))
>>                           return kvm_pmu_set_msr(vcpu, msr_info);
>> ?
>>
>>>
>>>> +               break;
>>>> +       }
>>>> +
>>>> +       return amd_msr_idx_to_pmc(vcpu, msr);
>>>> +}
>>>> +
>>>>    static int amd_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>>>    {
>>>>           struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>>>> @@ -162,20 +179,31 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>>>    static void amd_pmu_refresh(struct kvm_vcpu *vcpu)
>>>>    {
>>>>           struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>>>> +       struct kvm_cpuid_entry2 *entry;
>>>> +       union cpuid_0x80000022_ebx ebx;
>>>>
>>>> -       if (guest_cpuid_has(vcpu, X86_FEATURE_PERFCTR_CORE))
>>>> +       pmu->version = 1;
>>>> +       entry = kvm_find_cpuid_entry_index(vcpu, 0x80000022, 0);
>>>> +       if (kvm_pmu_cap.version > 1 && entry && (entry->eax & BIT(0))) {
>>>> +               pmu->version = 2;
>>>> +               ebx.full = entry->ebx;
>>>> +               pmu->nr_arch_gp_counters = min3((unsigned int)ebx.split.num_core_pmc,
>>>> +                                               (unsigned int)kvm_pmu_cap.num_counters_gp,
>>>> +                                               (unsigned int)KVM_AMD_PMC_MAX_GENERIC);
>>>> +               pmu->global_ctrl_mask = ~((1ull << pmu->nr_arch_gp_counters) - 1);
>>>> +               pmu->global_ovf_ctrl_mask = pmu->global_ctrl_mask;
>>>> +       } else if (guest_cpuid_has(vcpu, X86_FEATURE_PERFCTR_CORE)) {
>>>>                   pmu->nr_arch_gp_counters = AMD64_NUM_COUNTERS_CORE;
>>>
>>> The logic above doesn't seem quite right, since guest_cpuid_has(vcpu,
>>> X86_FEATURE_PERFCTR_CORE) promises 6 PMCs, regardless of what
>>> CPUID.80000022 says.
>>
>> I would have expected the appearance of CPUID.80000022 to override PERFCTR_CORE,
>> now I don't think it's a good idea as you do, so how about:
>>
>> amd_pmu_refresh():
>>
>>          bool perfctr_core = guest_cpuid_has(vcpu, X86_FEATURE_PERFCTR_CORE);
>>
>>          pmu->version = 1;
>>          if (kvm_pmu_cap.version > 1)
>>                  entry = kvm_find_cpuid_entry_index(vcpu, 0x80000022, 0);
>>
>>          if (!perfctr_core)
>>                  pmu->nr_arch_gp_counters = AMD64_NUM_COUNTERS;
>>          if (entry && (entry->eax & BIT(0))) {
>>                  pmu->version = 2;
>>                  ebx.full = entry->ebx;
>>                  pmu->nr_arch_gp_counters = min3((unsigned int)ebx.split.num_core_pmc,
>>                                                  (unsigned int)kvm_pmu_cap.num_counters_gp,
>>                                                  (unsigned int)KVM_AMD_PMC_MAX_GENERIC);
>>          }
>>          /* PERFCTR_CORE promises 6 PMCs, regardless of CPUID.80000022 */
>>          if (perfctr_core) {
>>                  pmu->nr_arch_gp_counters = max(pmu->nr_arch_gp_counters,
>>                                                 AMD64_NUM_COUNTERS_CORE);
>>          }
> 
> Even if X86_FEATURE_PERFCTR_CORE is clear, all AMD CPUs promise 4 PMCs.
> 
>>
>>          if (pmu->version > 1) {
>>                  pmu->global_ctrl_mask = ~((1ull << pmu->nr_arch_gp_counters) - 1);
>>                  pmu->global_ovf_ctrl_mask = pmu->global_ctrl_mask;
>>          }
>>
>> ?
>>
>>