KVM: arm64: pmu: Don't mark a counter as chained if the odd one is disabled

At the moment we update the chain bitmap on type setting. This
does not take into account the enable state of the odd register.

Let's make sure a counter is never considered as chained if
the high counter is disabled.

We recompute the chain state on enable/disable and type changes.

Also let create_perf_event() use the chain bitmap and not use
kvm_pmu_idx_has_chain_evtype().
Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200124142535.29386-3-eric.auger@redhat.com

virt/kvm/arm/pmu.c

@@ -15,6 +15,8 @@
 #include <kvm/arm_vgic.h>
 
 static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx);
+static void kvm_pmu_update_pmc_chained(struct kvm_vcpu *vcpu, u64 select_idx);
+static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc);
 
 #define PERF_ATTR_CFG1_KVM_PMU_CHAINED 0x1
 
@@ -75,6 +77,13 @@ static struct kvm_pmc *kvm_pmu_get_canonical_pmc(struct kvm_pmc *pmc)
 
 	return pmc;
 }
+static struct kvm_pmc *kvm_pmu_get_alternate_pmc(struct kvm_pmc *pmc)
+{
+	if (kvm_pmu_idx_is_high_counter(pmc->idx))
+		return pmc - 1;
+	else
+		return pmc + 1;
+}
 
 /**
  * kvm_pmu_idx_has_chain_evtype - determine if the event type is chain
@@ -294,15 +303,9 @@ void kvm_pmu_enable_counter_mask(struct kvm_vcpu *vcpu, u64 val)
 
 		pmc = &pmu->pmc[i];
 
-		/*
-		 * For high counters of chained events we must recreate the
-		 * perf event with the long (64bit) attribute set.
-		 */
-		if (kvm_pmu_pmc_is_chained(pmc) &&
-		    kvm_pmu_idx_is_high_counter(i)) {
+		/* A change in the enable state may affect the chain state */
+		kvm_pmu_update_pmc_chained(vcpu, i);
 		kvm_pmu_create_perf_event(vcpu, i);
-			continue;
-		}
 
 		/* At this point, pmc must be the canonical */
 		if (pmc->perf_event) {
@@ -335,15 +338,9 @@ void kvm_pmu_disable_counter_mask(struct kvm_vcpu *vcpu, u64 val)
 
 		pmc = &pmu->pmc[i];
 
-		/*
-		 * For high counters of chained events we must recreate the
-		 * perf event with the long (64bit) attribute unset.
-		 */
-		if (kvm_pmu_pmc_is_chained(pmc) &&
-		    kvm_pmu_idx_is_high_counter(i)) {
+		/* A change in the enable state may affect the chain state */
+		kvm_pmu_update_pmc_chained(vcpu, i);
 		kvm_pmu_create_perf_event(vcpu, i);
-			continue;
-		}
 
 		/* At this point, pmc must be the canonical */
 		if (pmc->perf_event)
@@ -585,14 +582,13 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
 
 	counter = kvm_pmu_get_pair_counter_value(vcpu, pmc);
 
-	if (kvm_pmu_idx_has_chain_evtype(vcpu, pmc->idx)) {
+	if (kvm_pmu_pmc_is_chained(pmc)) {
 		/**
 		 * The initial sample period (overflow count) of an event. For
 		 * chained counters we only support overflow interrupts on the
 		 * high counter.
 		 */
 		attr.sample_period = (-counter) & GENMASK(63, 0);
-		if (kvm_pmu_counter_is_enabled(vcpu, pmc->idx + 1))
 		attr.config1 |= PERF_ATTR_CFG1_KVM_PMU_CHAINED;
 
 		event = perf_event_create_kernel_counter(&attr, -1, current,
@@ -624,25 +620,33 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
  * @select_idx: The number of selected counter
  *
  * Update the chained bitmap based on the event type written in the
- * typer register.
+ * typer register and the enable state of the odd register.
  */
 static void kvm_pmu_update_pmc_chained(struct kvm_vcpu *vcpu, u64 select_idx)
 {
 	struct kvm_pmu *pmu = &vcpu->arch.pmu;
-	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
+	struct kvm_pmc *pmc = &pmu->pmc[select_idx], *canonical_pmc;
+	bool new_state, old_state;
+
+	old_state = kvm_pmu_pmc_is_chained(pmc);
+	new_state = kvm_pmu_idx_has_chain_evtype(vcpu, pmc->idx) &&
+		    kvm_pmu_counter_is_enabled(vcpu, pmc->idx | 0x1);
+
+	if (old_state == new_state)
+		return;
 
-	if (kvm_pmu_idx_has_chain_evtype(vcpu, pmc->idx)) {
+	canonical_pmc = kvm_pmu_get_canonical_pmc(pmc);
+	kvm_pmu_stop_counter(vcpu, canonical_pmc);
+	if (new_state) {
 		/*
 		 * During promotion from !chained to chained we must ensure
 		 * the adjacent counter is stopped and its event destroyed
 		 */
-		if (!kvm_pmu_pmc_is_chained(pmc))
-			kvm_pmu_stop_counter(vcpu, pmc);
-
+		kvm_pmu_stop_counter(vcpu, kvm_pmu_get_alternate_pmc(pmc));
 		set_bit(pmc->idx >> 1, vcpu->arch.pmu.chained);
-	} else {
-		clear_bit(pmc->idx >> 1, vcpu->arch.pmu.chained);
+		return;
 	}
+	clear_bit(pmc->idx >> 1, vcpu->arch.pmu.chained);
 }
 
 /**