Re: [PATCH 3/3] KVM: x86/pmu: Support PERF_METRICS MSR in mediated vPMU

[Mi, Dapeng]

On 2/27/2026 7:06 AM, Zide Chen wrote:
> From: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
>
> Bit 15 in IA32_PERF_CAPABILITIES indicates that the CPU provides
> built-in support for Topdown Microarchitecture Analysis (TMA) L1
> metrics via the IA32_PERF_METRICS MSR.
>
> Expose this capability only when mediated vPMU is enabled, as emulating
> IA32_PERF_METRICS in the legacy vPMU model is impractical.
>
> Pass IA32_PERF_METRICS through to the guest only when mediated vPMU is
> enabled and bit 15 is set in guest IA32_PERF_CAPABILITIES is.  Allow
> kvm_pmu_{get,set}_msr() to handle this MSR for host accesses.
>
> Save and restore this MSR on host/guest PMU context switches so that
> host PMU activity does not clobber the guest value, and guest state
> is not leaked into the host.
>
> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
> ---
>  arch/x86/include/asm/kvm_host.h   |  1 +
>  arch/x86/include/asm/msr-index.h  |  1 +
>  arch/x86/include/asm/perf_event.h |  1 +
>  arch/x86/kvm/vmx/pmu_intel.c      | 31 +++++++++++++++++++++++++++++++
>  arch/x86/kvm/vmx/pmu_intel.h      |  5 +++++
>  arch/x86/kvm/vmx/vmx.c            |  6 ++++++
>  arch/x86/kvm/x86.c                |  6 +++++-
>  7 files changed, 50 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4666b2c7988f..bf817c613451 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -575,6 +575,7 @@ struct kvm_pmu {
>  	u64 global_status_rsvd;
>  	u64 reserved_bits;
>  	u64 raw_event_mask;
> +	u64 perf_metrics;
>  	struct kvm_pmc gp_counters[KVM_MAX_NR_GP_COUNTERS];
>  	struct kvm_pmc fixed_counters[KVM_MAX_NR_FIXED_COUNTERS];
>  
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index da5275d8eda6..337667a7ad1b 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -331,6 +331,7 @@
>  #define PERF_CAP_PEBS_FORMAT		0xf00
>  #define PERF_CAP_FW_WRITES		BIT_ULL(13)
>  #define PERF_CAP_PEBS_BASELINE		BIT_ULL(14)
> +#define PERF_CAP_PERF_METRICS		BIT_ULL(15)
>  #define PERF_CAP_PEBS_TIMING_INFO	BIT_ULL(17)
>  #define PERF_CAP_PEBS_MASK		(PERF_CAP_PEBS_TRAP | PERF_CAP_ARCH_REG | \
>  					 PERF_CAP_PEBS_FORMAT | PERF_CAP_PEBS_BASELINE | \
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index ff5acb8b199b..dfead3a34b74 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -445,6 +445,7 @@ static inline bool is_topdown_idx(int idx)
>  #define GLOBAL_STATUS_ARCH_PEBS_THRESHOLD_BIT	54
>  #define GLOBAL_STATUS_ARCH_PEBS_THRESHOLD	BIT_ULL(GLOBAL_STATUS_ARCH_PEBS_THRESHOLD_BIT)
>  #define GLOBAL_STATUS_PERF_METRICS_OVF_BIT	48
> +#define GLOBAL_STATUS_PERF_METRICS_OVF		BIT_ULL(GLOBAL_STATUS_PERF_METRICS_OVF_BIT)
>  
>  #define GLOBAL_CTRL_EN_PERF_METRICS		BIT_ULL(48)
>  /*
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 9da47cf2af63..61bb2086f94a 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -180,6 +180,8 @@ static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
>  	switch (msr) {
>  	case MSR_CORE_PERF_FIXED_CTR_CTRL:
>  		return kvm_pmu_has_perf_global_ctrl(pmu);
> +	case MSR_PERF_METRICS:
> +		return vcpu_has_perf_metrics(vcpu);
>  	case MSR_IA32_PEBS_ENABLE:
>  		ret = vcpu_get_perf_capabilities(vcpu) & PERF_CAP_PEBS_FORMAT;
>  		break;
> @@ -335,6 +337,10 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_CORE_PERF_FIXED_CTR_CTRL:
>  		msr_info->data = pmu->fixed_ctr_ctrl;
>  		break;
> +	case MSR_PERF_METRICS:
> +		WARN_ON(!msr_info->host_initiated);

WARN_ON_ONCE() should be good enough.


> +		msr_info->data = pmu->perf_metrics;
> +		break;
>  	case MSR_IA32_PEBS_ENABLE:
>  		msr_info->data = pmu->pebs_enable;
>  		break;
> @@ -384,6 +390,10 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		if (pmu->fixed_ctr_ctrl != data)
>  			reprogram_fixed_counters(pmu, data);
>  		break;
> +	case MSR_PERF_METRICS:
> +		WARN_ON(!msr_info->host_initiated);

ditto.


> +		pmu->perf_metrics = data;
> +		break;
>  	case MSR_IA32_PEBS_ENABLE:
>  		if (data & pmu->pebs_enable_rsvd)
>  			return 1;
> @@ -579,6 +589,11 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
>  		pmu->global_status_rsvd &=
>  				~MSR_CORE_PERF_GLOBAL_OVF_CTRL_TRACE_TOPA_PMI;
>  
> +	if (perf_capabilities & PERF_CAP_PERF_METRICS) {
> +		pmu->global_ctrl_rsvd &= ~GLOBAL_CTRL_EN_PERF_METRICS;
> +		pmu->global_status_rsvd &= ~GLOBAL_STATUS_PERF_METRICS_OVF;
> +	}
> +
>  	if (perf_capabilities & PERF_CAP_PEBS_FORMAT) {
>  		if (perf_capabilities & PERF_CAP_PEBS_BASELINE) {
>  			pmu->pebs_enable_rsvd = counter_rsvd;
> @@ -622,6 +637,9 @@ static void intel_pmu_init(struct kvm_vcpu *vcpu)
>  
>  static void intel_pmu_reset(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> +
> +	pmu->perf_metrics = 0;
>  	intel_pmu_release_guest_lbr_event(vcpu);
>  }
>  
> @@ -793,6 +811,13 @@ static void intel_mediated_pmu_load(struct kvm_vcpu *vcpu)
>  	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>  	u64 global_status, toggle;
>  
> +	/*
> +	 * PERF_METRICS MSR must be restored closely after fixed counter 3
> +	 * (kvm_pmu_load_guest_pmcs()).
> +	 */
> +	if (vcpu_has_perf_metrics(vcpu))
> +		wrmsrq(MSR_PERF_METRICS, pmu->perf_metrics);
> +
>  	rdmsrq(MSR_CORE_PERF_GLOBAL_STATUS, global_status);
>  	toggle = pmu->global_status ^ global_status;
>  	if (global_status & toggle)
> @@ -821,6 +846,12 @@ static void intel_mediated_pmu_put(struct kvm_vcpu *vcpu)
>  	 */
>  	if (pmu->fixed_ctr_ctrl_hw)
>  		wrmsrq(MSR_CORE_PERF_FIXED_CTR_CTRL, 0);
> +
> +	if (vcpu_has_perf_metrics(vcpu)) {
> +		pmu->perf_metrics = rdpmc(INTEL_PMC_FIXED_RDPMC_METRICS);
> +		if (pmu->perf_metrics)
> +			wrmsrq(MSR_PERF_METRICS, 0);
> +	}
>  }
>  
>  struct kvm_pmu_ops intel_pmu_ops __initdata = {
> diff --git a/arch/x86/kvm/vmx/pmu_intel.h b/arch/x86/kvm/vmx/pmu_intel.h
> index 5d9357640aa1..2ec547223b09 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.h
> +++ b/arch/x86/kvm/vmx/pmu_intel.h
> @@ -40,4 +40,9 @@ struct lbr_desc {
>  
>  extern struct x86_pmu_lbr vmx_lbr_caps;
>  
> +static inline bool vcpu_has_perf_metrics(struct kvm_vcpu *vcpu)
> +{
> +	return !!(vcpu_get_perf_capabilities(vcpu) & PERF_CAP_PERF_METRICS);
> +}
> +
>  #endif /* __KVM_X86_VMX_PMU_INTEL_H */
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 967b58a8ab9d..4ade1394460a 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4338,6 +4338,9 @@ static void vmx_recalc_pmu_msr_intercepts(struct kvm_vcpu *vcpu)
>  				  MSR_TYPE_RW, intercept);
>  	vmx_set_intercept_for_msr(vcpu, MSR_CORE_PERF_GLOBAL_OVF_CTRL,
>  				  MSR_TYPE_RW, intercept);
> +
> +	vmx_set_intercept_for_msr(vcpu, MSR_PERF_METRICS, MSR_TYPE_RW,
> +				  !vcpu_has_perf_metrics(vcpu));
>  }
>  
>  static void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
> @@ -8183,6 +8186,9 @@ static __init u64 vmx_get_perf_capabilities(void)
>  		perf_cap &= ~PERF_CAP_PEBS_BASELINE;
>  	}
>  
> +	if (enable_mediated_pmu)
> +		perf_cap |= host_perf_cap & PERF_CAP_PERF_METRICS;
> +
>  	return perf_cap;
>  }
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 2ab7a4958620..4d0e38303aa5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -357,7 +357,7 @@ static const u32 msrs_to_save_pmu[] = {
>  	MSR_ARCH_PERFMON_FIXED_CTR0, MSR_ARCH_PERFMON_FIXED_CTR1,
>  	MSR_ARCH_PERFMON_FIXED_CTR2, MSR_ARCH_PERFMON_FIXED_CTR3,
>  	MSR_CORE_PERF_FIXED_CTR_CTRL, MSR_CORE_PERF_GLOBAL_STATUS,
> -	MSR_CORE_PERF_GLOBAL_CTRL,
> +	MSR_CORE_PERF_GLOBAL_CTRL, MSR_PERF_METRICS,
>  	MSR_IA32_PEBS_ENABLE, MSR_IA32_DS_AREA, MSR_PEBS_DATA_CFG,
>  
>  	/* This part of MSRs should match KVM_MAX_NR_INTEL_GP_COUNTERS. */
> @@ -7675,6 +7675,10 @@ static void kvm_probe_msr_to_save(u32 msr_index)
>  		     intel_pt_validate_hw_cap(PT_CAP_num_address_ranges) * 2))
>  			return;
>  		break;
> +	case MSR_PERF_METRICS:
> +		if (!(kvm_caps.supported_perf_cap & PERF_CAP_PERF_METRICS))
> +			return;
> +		break;
>  	case MSR_ARCH_PERFMON_PERFCTR0 ...
>  	     MSR_ARCH_PERFMON_PERFCTR0 + KVM_MAX_NR_GP_COUNTERS - 1:
>  		if (msr_index - MSR_ARCH_PERFMON_PERFCTR0 >=