KVM: x86/pmu: Implement Intel mediated PMU requirements and constraints

Implement Intel PMU requirements and constraints for mediated PMU support.
Require host PMU version 4+ so that PERF_GLOBAL_STATUS_SET can be used to
precisely load the guest's status value into hardware, and require full-
width writes so that KVM can precisely load guest counter values.

Disable PEBS and LBRs if mediated PMU support is enabled, as they won't be
supported in the initial implementation.

Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Co-developed-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
[sean: split to separate patch, add full-width writes dependency]
Tested-by: Xudong Hao <xudong.hao@intel.com>
Tested-by: Manali Shukla <manali.shukla@amd.com>
Link: https://patch.msgid.link/20251206001720.468579-18-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: Dapeng Mi

arch/x86/kvm/vmx/capabilities.h

@@ -395,7 +395,8 @@ static inline bool vmx_pt_mode_is_host_guest(void)
 
 static inline bool vmx_pebs_supported(void)
 {
-	return boot_cpu_has(X86_FEATURE_PEBS) && kvm_pmu_cap.pebs_ept;
+	return boot_cpu_has(X86_FEATURE_PEBS) && kvm_pmu_cap.pebs_ept &&
+	       !enable_mediated_pmu;
 }
 
 static inline bool cpu_has_notify_vmexit(void)

arch/x86/kvm/vmx/pmu_intel.c

@@ -767,6 +767,20 @@ void intel_pmu_cross_mapped_check(struct kvm_pmu *pmu)
 	}
 }
 
+static bool intel_pmu_is_mediated_pmu_supported(struct x86_pmu_capability *host_pmu)
+{
+	u64 host_perf_cap = 0;
+
+	if (boot_cpu_has(X86_FEATURE_PDCM))
+		rdmsrq(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
+
+	/*
+	 * Require v4+ for MSR_CORE_PERF_GLOBAL_STATUS_SET, and full-width
+	 * writes so that KVM can precisely load guest counter values.
+	 */
+	return host_pmu->version >= 4 && host_perf_cap & PERF_CAP_FW_WRITES;
+}
+
 struct kvm_pmu_ops intel_pmu_ops __initdata = {
 	.rdpmc_ecx_to_pmc = intel_rdpmc_ecx_to_pmc,
 	.msr_idx_to_pmc = intel_msr_idx_to_pmc,
@@ -778,6 +792,9 @@ struct kvm_pmu_ops intel_pmu_ops __initdata = {
 	.reset = intel_pmu_reset,
 	.deliver_pmi = intel_pmu_deliver_pmi,
 	.cleanup = intel_pmu_cleanup,
+
+	.is_mediated_pmu_supported = intel_pmu_is_mediated_pmu_supported,
+
 	.EVENTSEL_EVENT = ARCH_PERFMON_EVENTSEL_EVENT,
 	.MAX_NR_GP_COUNTERS = KVM_MAX_NR_INTEL_GP_COUNTERS,
 	.MIN_NR_GP_COUNTERS = 1,

arch/x86/kvm/vmx/vmx.c

@@ -7958,7 +7958,8 @@ static __init u64 vmx_get_perf_capabilities(void)
 	if (boot_cpu_has(X86_FEATURE_PDCM))
 		rdmsrq(MSR_IA32_PERF_CAPABILITIES, host_perf_cap);
 
-	if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR)) {
+	if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR) &&
+	    !enable_mediated_pmu) {
 		x86_perf_get_lbr(&vmx_lbr_caps);
 
 		/*