Re: [PATCH 3/4] KVM: x86/svm/pmu: Add AMD PerfMonV2 support

From: Jim Mattson
Date: Mon Sep 05 2022 - 14:00:57 EST

On Mon, Sep 5, 2022 at 5:44 AM Like Xu <like.xu.linux@xxxxxxxxx> wrote:
>
> From: Like Xu <likexu@xxxxxxxxxxx>
>
> 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@xxxxxxx>
> Signed-off-by: Sandipan Das <sandipan.das@xxxxxxx>
> Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
> ---
> 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)?

> + 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.