KVM: x86/pmu: Handle emulated instruction for mediated vPMU

Mediated vPMU needs to accumulate the emulated instructions into counter
and load the counter into HW at vm-entry.

Moreover, if the accumulation leads to counter overflow, KVM needs to
update GLOBAL_STATUS and inject PMI into guest as well.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Tested-by: Xudong Hao <xudong.hao@intel.com>
Tested-by: Manali Shukla <manali.shukla@amd.com>
Link: https://patch.msgid.link/20251206001720.468579-30-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: Dapeng Mi

arch/x86/kvm/pmu.c

@@ -1031,10 +1031,45 @@ void kvm_pmu_destroy(struct kvm_vcpu *vcpu)
 	kvm_pmu_reset(vcpu);
 }
 
+static bool pmc_is_pmi_enabled(struct kvm_pmc *pmc)
+{
+	u8 fixed_ctr_ctrl;
+
+	if (pmc_is_gp(pmc))
+		return pmc->eventsel & ARCH_PERFMON_EVENTSEL_INT;
+
+	fixed_ctr_ctrl = fixed_ctrl_field(pmc_to_pmu(pmc)->fixed_ctr_ctrl,
+					  pmc->idx - KVM_FIXED_PMC_BASE_IDX);
+	return fixed_ctr_ctrl & INTEL_FIXED_0_ENABLE_PMI;
+}
+
 static void kvm_pmu_incr_counter(struct kvm_pmc *pmc)
 {
-	pmc->emulated_counter++;
-	kvm_pmu_request_counter_reprogram(pmc);
+	struct kvm_vcpu *vcpu = pmc->vcpu;
+
+	/*
+	 * For perf-based PMUs, accumulate software-emulated events separately
+	 * from pmc->counter, as pmc->counter is offset by the count of the
+	 * associated perf event. Request reprogramming, which will consult
+	 * both emulated and hardware-generated events to detect overflow.
+	 */
+	if (!kvm_vcpu_has_mediated_pmu(vcpu)) {
+		pmc->emulated_counter++;
+		kvm_pmu_request_counter_reprogram(pmc);
+		return;
+	}
+
+	/*
+	 * For mediated PMUs, pmc->counter is updated when the vCPU's PMU is
+	 * put, and will be loaded into hardware when the PMU is loaded. Simply
+	 * increment the counter and signal overflow if it wraps to zero.
+	 */
+	pmc->counter = (pmc->counter + 1) & pmc_bitmask(pmc);
+	if (!pmc->counter) {
+		pmc_to_pmu(pmc)->global_status |= BIT_ULL(pmc->idx);
+		if (pmc_is_pmi_enabled(pmc))
+			kvm_make_request(KVM_REQ_PMI, vcpu);
+	}
 }
 
 static inline bool cpl_is_matched(struct kvm_pmc *pmc)