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Date: Wed, 7 Sep 2022 11:50:06 +0800
From: Like Xu <like.xu.linux@...il.com>
To: Jim Mattson <jmattson@...gle.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 3/4] KVM: x86/svm/pmu: Add AMD PerfMonV2 support
On 7/9/2022 4:19 am, Jim Mattson wrote:
> On Tue, Sep 6, 2022 at 5:45 AM Like Xu <like.xu.linux@...il.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@...il.com> wrote:
>>>>
>>>> From: Like Xu <likexu@...cent.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@....com>
>>>> Signed-off-by: Sandipan Das <sandipan.das@....com>
>>>> Signed-off-by: Like Xu <likexu@...cent.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;
>> }
>>
>> ?
>>
>>
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