[PATCH v2 5/5] KVM: arm/arm64: support chained PMU counters

[Andrew Murray <andrew.murray@arm.com>]

Emulate chained PMU counters by creating a single 64 bit event counter
for a pair of chained KVM counters.

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
---
 include/kvm/arm_pmu.h |   1 +
 virt/kvm/arm/pmu.c    | 321 +++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 269 insertions(+), 53 deletions(-)

diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index b73f31b..8e691ee 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -29,6 +29,7 @@ struct kvm_pmc {
 	u8 idx;	/* index into the pmu->pmc array */
 	struct perf_event *perf_event;
 	u64 bitmask;
+	u64 overflow_count;
 };
 
 struct kvm_pmu {
diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index a64aeb2..9318130 100644
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c
@@ -24,9 +24,25 @@
 #include <kvm/arm_pmu.h>
 #include <kvm/arm_vgic.h>
 
+#define ARMV8_PMUV3_PERFCTR_CHAIN 0x1E
+static void kvm_pmu_stop_release_perf_event_pair(struct kvm_vcpu *vcpu,
+					    u64 pair_low);
+static void kvm_pmu_stop_release_perf_event(struct kvm_vcpu *vcpu,
+					      u64 select_idx);
+static void kvm_pmu_sync_counter_enable_pair(struct kvm_vcpu *vcpu, u64 pair_low);
 static void kvm_pmu_sync_counter_enable(struct kvm_vcpu *vcpu, u64 select_idx);
 static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx);
-static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc);
+
+/**
+ * kvm_pmu_counter_is_high_word - is select_idx high counter of 64bit event
+ * @pmc: The PMU counter pointer
+ * @select_idx: The counter index
+ */
+static inline bool kvm_pmu_counter_is_high_word(struct kvm_pmc *pmc)
+{
+	return ((pmc->perf_event->attr.config1 & 0x1)
+		&& (pmc->idx % 2));
+}
 
 /**
  * kvm_pmu_get_counter_value - get PMU counter value
@@ -35,22 +51,70 @@ static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc);
  */
 u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
 {
-	u64 counter, reg, enabled, running;
+	u64 counter_idx, reg, enabled, running, incr;
 	struct kvm_pmu *pmu = &vcpu->arch.pmu;
 	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
 
 	reg = (select_idx == ARMV8_PMU_CYCLE_IDX)
 	      ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + select_idx;
-	counter = __vcpu_sys_reg(vcpu, reg);
+	counter_idx = __vcpu_sys_reg(vcpu, reg);
 
 	/* The real counter value is equal to the value of counter register plus
 	 * the value perf event counts.
 	 */
-	if (pmc->perf_event)
-		counter += perf_event_read_value(pmc->perf_event, &enabled,
+	if (pmc->perf_event) {
+		incr = perf_event_read_value(pmc->perf_event, &enabled,
 						 &running);
 
-	return counter & pmc->bitmask;
+		if (kvm_pmu_counter_is_high_word(pmc)) {
+			u64 counter_low, counter;
+
+			reg = (select_idx == ARMV8_PMU_CYCLE_IDX)
+			      ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + select_idx - 1;
+			counter_low = __vcpu_sys_reg(vcpu, reg);
+			counter = lower_32_bits(counter_low) | (counter_idx << 32);
+			counter_idx = upper_32_bits(counter + incr);
+		} else {
+			counter_idx += incr;
+		}
+	}
+
+	return counter_idx & pmc->bitmask;
+}
+
+/**
+ * kvm_pmu_counter_is_enabled - is a counter active
+ * @vcpu: The vcpu pointer
+ * @select_idx: The counter index
+ */
+static bool kvm_pmu_counter_is_enabled(struct kvm_vcpu *vcpu, u64 select_idx)
+{
+	u64 mask = kvm_pmu_valid_counter_mask(vcpu);
+
+	return (__vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMU_PMCR_E) &&
+	       (__vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask & BIT(select_idx));
+}
+
+/**
+ * kvnm_pmu_event_is_chained - is a pair of counters chained and enabled
+ * @vcpu: The vcpu pointer
+ * @select_idx: The low counter index
+ */
+static bool kvm_pmu_event_is_chained(struct kvm_vcpu *vcpu, u64 pair_low)
+{
+	u64 eventsel, reg;
+
+	reg = (pair_low + 1 == ARMV8_PMU_CYCLE_IDX)
+	      ? PMCCFILTR_EL0 : PMEVTYPER0_EL0 + pair_low + 1;
+	eventsel = __vcpu_sys_reg(vcpu, reg) & ARMV8_PMU_EVTYPE_EVENT;
+	if (eventsel != ARMV8_PMUV3_PERFCTR_CHAIN)
+		return false;
+
+	if (kvm_pmu_counter_is_enabled(vcpu, pair_low) !=
+	    kvm_pmu_counter_is_enabled(vcpu, pair_low + 1))
+		return false;
+
+	return true;
 }
 
 /**
@@ -61,29 +125,45 @@ u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
  */
 void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val)
 {
-	u64 reg;
-	struct kvm_pmu *pmu = &vcpu->arch.pmu;
-	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
+	u64 reg, pair_low;
 
 	reg = (select_idx == ARMV8_PMU_CYCLE_IDX)
 	      ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + select_idx;
 	__vcpu_sys_reg(vcpu, reg) += (s64)val - kvm_pmu_get_counter_value(vcpu, select_idx);
 
-	kvm_pmu_stop_counter(vcpu, pmc);
-	kvm_pmu_sync_counter_enable(vcpu, select_idx);
+	pair_low = (select_idx % 2) ? select_idx - 1 : select_idx;
+
+	/* Recreate the perf event to reflect the updated sample_period */
+	if (kvm_pmu_event_is_chained(vcpu, pair_low)) {
+		kvm_pmu_stop_release_perf_event_pair(vcpu, pair_low);
+		kvm_pmu_sync_counter_enable_pair(vcpu, pair_low);
+	} else {
+		kvm_pmu_stop_release_perf_event(vcpu, select_idx);
+		kvm_pmu_sync_counter_enable(vcpu, select_idx);
+	}
 }
 
 /**
  * kvm_pmu_release_perf_event - remove the perf event
  * @pmc: The PMU counter pointer
  */
-static void kvm_pmu_release_perf_event(struct kvm_pmc *pmc)
+static void kvm_pmu_release_perf_event(struct kvm_vcpu *vcpu,
+				       struct kvm_pmc *pmc)
 {
-	if (pmc->perf_event) {
-		perf_event_disable(pmc->perf_event);
+	struct kvm_pmu *pmu = &vcpu->arch.pmu;
+	struct kvm_pmc *pmc_alt;
+	u64 pair_alt;
+
+	pair_alt = (pmc->idx % 2) ? pmc->idx - 1 : pmc->idx + 1;
+	pmc_alt = &pmu->pmc[pair_alt];
+
+	if (pmc->perf_event)
 		perf_event_release_kernel(pmc->perf_event);
-		pmc->perf_event = NULL;
-	}
+
+	if (pmc->perf_event == pmc_alt->perf_event)
+		pmc_alt->perf_event = NULL;
+
+	pmc->perf_event = NULL;
 }
 
 /**
@@ -91,22 +171,65 @@ static void kvm_pmu_release_perf_event(struct kvm_pmc *pmc)
  * @vcpu: The vcpu pointer
  * @pmc: The PMU counter pointer
  *
- * If this counter has been configured to monitor some event, release it here.
+ * If this counter has been configured to monitor some event, stop it here.
  */
 static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc)
 {
 	u64 counter, reg;
 
 	if (pmc->perf_event) {
+		perf_event_disable(pmc->perf_event);
 		counter = kvm_pmu_get_counter_value(vcpu, pmc->idx);
 		reg = (pmc->idx == ARMV8_PMU_CYCLE_IDX)
 		       ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + pmc->idx;
 		__vcpu_sys_reg(vcpu, reg) = counter;
-		kvm_pmu_release_perf_event(pmc);
 	}
 }
 
 /**
+ * kvm_pmu_stop_release_perf_event_pair - stop and release a pair of counters
+ * @vcpu: The vcpu pointer
+ * @pmc_low: The PMU counter pointer for lower word
+ * @pmc_high: The PMU counter pointer for higher word
+ *
+ * As chained counters share the underlying perf event, we stop them
+ * both first before discarding the underlying perf event
+ */
+static void kvm_pmu_stop_release_perf_event_pair(struct kvm_vcpu *vcpu,
+					    u64 idx_low)
+{
+	struct kvm_pmu *pmu = &vcpu->arch.pmu;
+	struct kvm_pmc *pmc_low = &pmu->pmc[idx_low];
+	struct kvm_pmc *pmc_high = &pmu->pmc[idx_low + 1];
+
+	/* Stopping a counter involves adding the perf event value to the
+	 * vcpu sys register value prior to releasing the perf event. As
+	 * kvm_pmu_get_counter_value may depend on the low counter value we
+	 * must always stop the high counter first
+	 */
+	kvm_pmu_stop_counter(vcpu, pmc_high);
+	kvm_pmu_stop_counter(vcpu, pmc_low);
+
+	kvm_pmu_release_perf_event(vcpu, pmc_high);
+	kvm_pmu_release_perf_event(vcpu, pmc_low);
+}
+
+/**
+ * kvm_pmu_stop_release_perf_event - stop and release a counter
+ * @vcpu: The vcpu pointer
+ * @select_idx: The counter index
+ */
+static void kvm_pmu_stop_release_perf_event(struct kvm_vcpu *vcpu,
+					      u64 select_idx)
+{
+	struct kvm_pmu *pmu = &vcpu->arch.pmu;
+	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
+
+	kvm_pmu_stop_counter(vcpu, pmc);
+	kvm_pmu_release_perf_event(vcpu, pmc);
+}
+
+/**
  * kvm_pmu_vcpu_reset - reset pmu state for cpu
  * @vcpu: The vcpu pointer
  *
@@ -117,7 +240,7 @@ void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu)
 	struct kvm_pmu *pmu = &vcpu->arch.pmu;
 
 	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++) {
-		kvm_pmu_stop_counter(vcpu, &pmu->pmc[i]);
+		kvm_pmu_stop_release_perf_event(vcpu, i);
 		pmu->pmc[i].idx = i;
 		pmu->pmc[i].bitmask = 0xffffffffUL;
 	}
@@ -134,7 +257,7 @@ void kvm_pmu_vcpu_destroy(struct kvm_vcpu *vcpu)
 	struct kvm_pmu *pmu = &vcpu->arch.pmu;
 
 	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++)
-		kvm_pmu_release_perf_event(&pmu->pmc[i]);
+		kvm_pmu_release_perf_event(vcpu, &pmu->pmc[i]);
 }
 
 u64 kvm_pmu_valid_counter_mask(struct kvm_vcpu *vcpu)
@@ -167,53 +290,115 @@ static void kvm_pmu_enable_counter(struct kvm_vcpu *vcpu, u64 select_idx)
 }
 
 /**
+ * kvm_pmu_sync_counter_enable - reenable a counter if it should be enabled
+ * @vcpu: The vcpu pointer
+ * @select_idx: The counter index
+ */
+static void kvm_pmu_sync_counter_enable(struct kvm_vcpu *vcpu,
+					    u64 select_idx)
+{
+	kvm_pmu_enable_counter_mask(vcpu, BIT(select_idx));
+}
+
+/**
+ * kvm_pmu_sync_counter_enable_pair - reenable a pair if they should be enabled
+ * @vcpu: The vcpu pointer
+ * @pair_low: The low counter index
+ */
+static void kvm_pmu_sync_counter_enable_pair(struct kvm_vcpu *vcpu, u64 pair_low)
+{
+	kvm_pmu_enable_counter_mask(vcpu, BIT(pair_low) | BIT(pair_low + 1));
+}
+
+/**
+ * kvm_pmu_enable_counter_pair - enable counters pair at a time
+ * @vcpu: The vcpu pointer
+ * @val: counters to enable
+ * @pair_low: The low counter index
+ */
+static void kvm_pmu_enable_counter_pair(struct kvm_vcpu *vcpu, u64 val,
+					u64 pair_low)
+{
+	struct kvm_pmu *pmu = &vcpu->arch.pmu;
+	struct kvm_pmc *pmc_low = &pmu->pmc[pair_low];
+	struct kvm_pmc *pmc_high = &pmu->pmc[pair_low + 1];
+
+	if (kvm_pmu_event_is_chained(vcpu, pair_low)) {
+		if (pmc_low->perf_event != pmc_high->perf_event)
+			kvm_pmu_stop_release_perf_event_pair(vcpu, pair_low);
+	}
+
+	if (val & BIT(pair_low))
+		kvm_pmu_enable_counter(vcpu, pair_low);
+
+	if (val & BIT(pair_low+1))
+		kvm_pmu_enable_counter(vcpu, pair_low + 1);
+}
+
+/**
  * kvm_pmu_enable_counter_mask - enable selected PMU counters
  * @vcpu: The vcpu pointer
- * @val: the value guest writes to PMCNTENSET register
+ * @val: the value guest writes to PMCNTENSET register or a subset
  *
  * Call perf_event_enable to start counting the perf event
  */
 void kvm_pmu_enable_counter_mask(struct kvm_vcpu *vcpu, u64 val)
 {
 	int i;
+	u64 mask = kvm_pmu_valid_counter_mask(vcpu);
+	u64 set = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask;
 
 	if (!(__vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMU_PMCR_E) || !val)
 		return;
 
-	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++) {
-		if (!(val & BIT(i)))
-			continue;
-
-		kvm_pmu_enable_counter(vcpu, i);
-	}
+	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i += 2)
+		kvm_pmu_enable_counter_pair(vcpu, val & set, i);
 }
 
 /**
- * kvm_pmu_sync_counter_enable - reenable a counter if it should be enabled
+ * kvm_pmu_disable_counter - disable selected PMU counter
  * @vcpu: The vcpu pointer
  * @select_idx: The counter index
  */
-static void kvm_pmu_sync_counter_enable(struct kvm_vcpu *vcpu,
-					    u64 select_idx)
+static void kvm_pmu_disable_counter(struct kvm_vcpu *vcpu, u64 select_idx)
 {
-	u64 set = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
+	struct kvm_pmu *pmu = &vcpu->arch.pmu;
+	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
 
-	if (set & BIT(select_idx))
-		kvm_pmu_enable_counter_mask(vcpu, BIT(select_idx));
+	if (pmc->perf_event) {
+		perf_event_disable(pmc->perf_event);
+		if (pmc->perf_event->state != PERF_EVENT_STATE_ACTIVE)
+			kvm_debug("fail to enable perf event\n");
+	}
 }
 
 /**
- * kvm_pmu_disable_counter - disable selected PMU counter
- * @vcpu: The vcpu pointer
- * @pmc: The counter to disable
+ * kvm_pmu_disable_counter_pair - disable counters pair at a time
+ * @val: counters to disable
+ * @pair_low: The low counter index
  */
-static void kvm_pmu_disable_counter(struct kvm_vcpu *vcpu, u64 select_idx)
+static void kvm_pmu_disable_counter_pair(struct kvm_vcpu *vcpu, u64 val,
+					 u64 pair_low)
 {
 	struct kvm_pmu *pmu = &vcpu->arch.pmu;
-	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
+	struct kvm_pmc *pmc_low = &pmu->pmc[pair_low];
+	struct kvm_pmc *pmc_high = &pmu->pmc[pair_low + 1];
+
+	if (!kvm_pmu_event_is_chained(vcpu, pair_low)) {
+		if (pmc_low->perf_event == pmc_high->perf_event) {
+			if (pmc_low->perf_event) {
+				kvm_pmu_stop_release_perf_event_pair(vcpu,
+								pair_low);
+				kvm_pmu_sync_counter_enable_pair(vcpu, pair_low);
+			}
+		}
+	}
 
-	if (pmc->perf_event)
-		perf_event_disable(pmc->perf_event);
+	if (val & BIT(pair_low))
+		kvm_pmu_disable_counter(vcpu, pair_low);
+
+	if (val & BIT(pair_low + 1))
+		kvm_pmu_disable_counter(vcpu, pair_low + 1);
 }
 
 /**
@@ -230,12 +415,8 @@ void kvm_pmu_disable_counter_mask(struct kvm_vcpu *vcpu, u64 val)
 	if (!val)
 		return;
 
-	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++) {
-		if (!(val & BIT(i)))
-			continue;
-
-		kvm_pmu_disable_counter(vcpu, i);
-	}
+	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i += 2)
+		kvm_pmu_disable_counter_pair(vcpu, val, i);
 }
 
 static u64 kvm_pmu_overflow_status(struct kvm_vcpu *vcpu)
@@ -346,6 +527,17 @@ static void kvm_pmu_perf_overflow(struct perf_event *perf_event,
 
 	__vcpu_sys_reg(vcpu, PMOVSSET_EL0) |= BIT(idx);
 
+	if (kvm_pmu_event_is_chained(vcpu, idx)) {
+		struct kvm_pmu *pmu = &vcpu->arch.pmu;
+		struct kvm_pmc *pmc_high = &pmu->pmc[idx + 1];
+
+		if (!(--pmc_high->overflow_count)) {
+			__vcpu_sys_reg(vcpu, PMOVSSET_EL0) |= BIT(idx + 1);
+			pmc_high->overflow_count = U32_MAX + 1UL;
+		}
+
+	}
+
 	if (kvm_pmu_overflow_status(vcpu)) {
 		kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
 		kvm_vcpu_kick(vcpu);
@@ -440,6 +632,10 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
 	    select_idx != ARMV8_PMU_CYCLE_IDX)
 		return;
 
+	/* Handled by even event */
+	if (eventsel == ARMV8_PMUV3_PERFCTR_CHAIN)
+		return;
+
 	memset(&attr, 0, sizeof(struct perf_event_attr));
 	attr.type = PERF_TYPE_RAW;
 	attr.size = sizeof(attr);
@@ -452,6 +648,9 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
 	attr.config = (select_idx == ARMV8_PMU_CYCLE_IDX) ?
 		ARMV8_PMUV3_PERFCTR_CPU_CYCLES : eventsel;
 
+	if (kvm_pmu_event_is_chained(vcpu, select_idx))
+		attr.config1 |= 0x1;
+
 	counter = kvm_pmu_get_counter_value(vcpu, select_idx);
 	/* The initial sample period (overflow count) of an event. */
 	attr.sample_period = (-counter) & pmc->bitmask;
@@ -464,6 +663,14 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
 		return;
 	}
 
+	if (kvm_pmu_event_is_chained(vcpu, select_idx)) {
+		struct kvm_pmc *pmc_next = &pmu->pmc[select_idx + 1];
+
+		pmc_next->perf_event = event;
+		counter = kvm_pmu_get_counter_value(vcpu, select_idx + 1);
+		pmc_next->overflow_count = (-counter) & pmc->bitmask;
+	}
+
 	pmc->perf_event = event;
 }
 
@@ -480,17 +687,25 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
 void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
 				    u64 select_idx)
 {
-	struct kvm_pmu *pmu = &vcpu->arch.pmu;
-	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
-	u64 reg, event_type = data & ARMV8_PMU_EVTYPE_MASK;
-
-	kvm_pmu_stop_counter(vcpu, pmc);
+	u64 eventsel, event_type, pair_low, reg;
 
 	reg = (select_idx == ARMV8_PMU_CYCLE_IDX)
 	      ? PMCCFILTR_EL0 : PMEVTYPER0_EL0 + select_idx;
 
-	__vcpu_sys_reg(vcpu, reg) = event_type;
-	kvm_pmu_sync_counter_enable(vcpu, select_idx);
+	eventsel = data & ARMV8_PMU_EVTYPE_EVENT;
+	event_type = data & ARMV8_PMU_EVTYPE_MASK;
+	pair_low = (select_idx % 2) ? select_idx - 1 : select_idx;
+
+	if (kvm_pmu_event_is_chained(vcpu, pair_low) ||
+	    eventsel == ARMV8_PMUV3_PERFCTR_CHAIN) {
+		kvm_pmu_stop_release_perf_event_pair(vcpu, pair_low);
+		__vcpu_sys_reg(vcpu, reg) = event_type;
+		kvm_pmu_sync_counter_enable_pair(vcpu, pair_low);
+	} else {
+		kvm_pmu_stop_release_perf_event(vcpu, pair_low);
+		__vcpu_sys_reg(vcpu, reg) = event_type;
+		kvm_pmu_sync_counter_enable(vcpu, pair_low);
+	}
 }
 
 bool kvm_arm_support_pmu_v3(void)
-- 
2.7.4


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