KVM: arm64: Keep a per-VM pointer to the default PMU

As we are about to allow selection of the PMU exposed to a guest, start by
keeping track of the default one instead of only the PMU version.
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Link: https://lore.kernel.org/r/20220127161759.53553-4-alexandru.elisei@arm.com

arch/arm64/include/asm/kvm_host.h

@@ -129,7 +129,7 @@ struct kvm_arch {
 	 * up to 2^10 events (ARMv8.0) or 2^16 events (ARMv8.1+).
 	 */
 	unsigned long *pmu_filter;
-	unsigned int pmuver;
+	struct arm_pmu *arm_pmu;
 
 	u8 pfr0_csv2;
 	u8 pfr0_csv3;

arch/arm64/kvm/pmu-emul.c

@@ -24,7 +24,11 @@ static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc);
 
 static u32 kvm_pmu_event_mask(struct kvm *kvm)
 {
-	switch (kvm->arch.pmuver) {
+	unsigned int pmuver;
+
+	pmuver = kvm->arch.arm_pmu->pmuver;
+
+	switch (pmuver) {
 	case ID_AA64DFR0_PMUVER_8_0:
 		return GENMASK(9, 0);
 	case ID_AA64DFR0_PMUVER_8_1:
@@ -33,7 +37,7 @@ static u32 kvm_pmu_event_mask(struct kvm *kvm)
 	case ID_AA64DFR0_PMUVER_8_7:
 		return GENMASK(15, 0);
 	default:		/* Shouldn't be here, just for sanity */
-		WARN_ONCE(1, "Unknown PMU version %d\n", kvm->arch.pmuver);
+		WARN_ONCE(1, "Unknown PMU version %d\n", pmuver);
 		return 0;
 	}
 }
@@ -600,6 +604,7 @@ static bool kvm_pmu_counter_is_enabled(struct kvm_vcpu *vcpu, u64 select_idx)
  */
 static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
 {
+	struct arm_pmu *arm_pmu = vcpu->kvm->arch.arm_pmu;
 	struct kvm_pmu *pmu = &vcpu->arch.pmu;
 	struct kvm_pmc *pmc;
 	struct perf_event *event;
@@ -636,7 +641,7 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
 		return;
 
 	memset(&attr, 0, sizeof(struct perf_event_attr));
-	attr.type = PERF_TYPE_RAW;
+	attr.type = arm_pmu->pmu.type;
 	attr.size = sizeof(attr);
 	attr.pinned = 1;
 	attr.disabled = !kvm_pmu_counter_is_enabled(vcpu, pmc->idx);
@@ -750,12 +755,11 @@ void kvm_host_pmu_init(struct arm_pmu *pmu)
 		static_branch_enable(&kvm_arm_pmu_available);
 }
 
-static int kvm_pmu_probe_pmuver(void)
+static struct arm_pmu *kvm_pmu_probe_armpmu(void)
 {
 	struct perf_event_attr attr = { };
 	struct perf_event *event;
-	struct arm_pmu *pmu;
-	int pmuver = ID_AA64DFR0_PMUVER_IMP_DEF;
+	struct arm_pmu *pmu = NULL;
 
 	/*
 	 * Create a dummy event that only counts user cycles. As we'll never
@@ -780,19 +784,20 @@ static int kvm_pmu_probe_pmuver(void)
 	if (IS_ERR(event)) {
 		pr_err_once("kvm: pmu event creation failed %ld\n",
 			    PTR_ERR(event));
-		return ID_AA64DFR0_PMUVER_IMP_DEF;
+		return NULL;
 	}
 
 	if (event->pmu) {
 		pmu = to_arm_pmu(event->pmu);
-		if (pmu->pmuver)
-			pmuver = pmu->pmuver;
+		if (pmu->pmuver == 0 ||
+		    pmu->pmuver == ID_AA64DFR0_PMUVER_IMP_DEF)
+			pmu = NULL;
 	}
 
 	perf_event_disable(event);
 	perf_event_release_kernel(event);
 
-	return pmuver;
+	return pmu;
 }
 
 u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
@@ -810,7 +815,7 @@ u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
 		 * Don't advertise STALL_SLOT, as PMMIR_EL0 is handled
 		 * as RAZ
 		 */
-		if (vcpu->kvm->arch.pmuver >= ID_AA64DFR0_PMUVER_8_4)
+		if (vcpu->kvm->arch.arm_pmu->pmuver >= ID_AA64DFR0_PMUVER_8_4)
 			val &= ~BIT_ULL(ARMV8_PMUV3_PERFCTR_STALL_SLOT - 32);
 		base = 32;
 	}
@@ -932,11 +937,16 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	if (vcpu->arch.pmu.created)
 		return -EBUSY;
 
-	if (!vcpu->kvm->arch.pmuver)
-		vcpu->kvm->arch.pmuver = kvm_pmu_probe_pmuver();
-
-	if (vcpu->kvm->arch.pmuver == ID_AA64DFR0_PMUVER_IMP_DEF)
-		return -ENODEV;
+	mutex_lock(&kvm->lock);
+	if (!kvm->arch.arm_pmu) {
+		/* No PMU set, get the default one */
+		kvm->arch.arm_pmu = kvm_pmu_probe_armpmu();
+		if (!kvm->arch.arm_pmu) {
+			mutex_unlock(&kvm->lock);
+			return -ENODEV;
+		}
+	}
+	mutex_unlock(&kvm->lock);
 
 	switch (attr->attr) {
 	case KVM_ARM_VCPU_PMU_V3_IRQ: {