arm64: KVM: Add a new feature bit for PMUv3

To support guest PMUv3, use one bit of the VCPU INIT feature array.
Initialize the PMU when initialzing the vcpu with that bit and PMU
overflow interrupt set.

Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Acked-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

virt/kvm/arm/pmu.c

@@ -405,3 +405,13 @@ void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
 
 	pmc->perf_event = event;
 }
+
+bool kvm_arm_support_pmu_v3(void)
+{
+	/*
+	 * Check if HW_PERF_EVENTS are supported by checking the number of
+	 * hardware performance counters. This could ensure the presence of
+	 * a physical PMU and CONFIG_PERF_EVENT is selected.
+	 */
+	return (perf_num_counters() > 0);
+}