[PATCH 0/4] KVM/ARM: Misc PMU fixes

[PATCH 0/4] KVM/ARM: Misc PMU fixes

[Eric Auger]

While writing new PMUv3 event counter kvm-unit-tests I found
some bugs related to the chained counter implementation:

- the enable state of the high counter is not taken into account,
- chain counters are not implemented along with SW_INCR type,
- SW_INCR does not take into account the global enable state

The last patch rather is an optimization that avoids manipulating
non supported counters.

Best Regards

Eric

This series can be found at:
https://github.com/eauger/linux/tree/v5.5-rc7-pmu-fixes-v1

Test:
Tested with kvm-unit-tests [1]: all tests now pass,
at the exception of one sub-test in pmu-chain-promotion
but this is a bug in test.

Other testing at higher level (perf) appreciated.

references:
[1] KVM: arm64: PMUv3 Event Counter Tests
(https://lore.kernel.org/kvmarm/c1831b6c-dc75-1bd3-6657-0375682c30af@redhat.com/T/)

History:

RFC -> v1:
- remove  [RFC 3/3] KVM: arm64: pmu: Enforce PMEVTYPER evtCount size
- add KVM: arm64: pmu: Only handle supported event counters
- Take into account the enable state of the CHAIN high counter
- revisit kvm_pmu_software_increment() implementation as suggested
  by Marc


Eric Auger (4):
  KVM: arm64: pmu: Don't increment SW_INCR if PMCR.E is unset
  KVM: arm64: pmu: Don't mark a counter as chained if the odd one is
    disabled
  KVM: arm64: pmu: Fix chained SW_INCR counters
  KVM: arm64: pmu: Only handle supported event counters

 virt/kvm/arm/pmu.c | 114 +++++++++++++++++++++++++++------------------
 1 file changed, 69 insertions(+), 45 deletions(-)

-- 
2.20.1

[PATCH 1/4] KVM: arm64: pmu: Don't increment SW_INCR if PMCR.E is unset

[Eric Auger]

The specification says PMSWINC increments PMEVCNTR<n>_EL1 by 1
if PMEVCNTR<n>_EL0 is enabled and configured to count SW_INCR.

For PMEVCNTR<n>_EL0 to be enabled, we need both PMCNTENSET to
be set for the corresponding event counter but we also need
the PMCR.E bit to be set.

Fixes: 7a0adc7064b8 ("arm64: KVM: Add access handler for PMSWINC register")
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
---
 virt/kvm/arm/pmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index 8731dfeced8b..c3f8b059881e 100644
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c
@@ -486,6 +486,9 @@ void kvm_pmu_software_increment(struct kvm_vcpu *vcpu, u64 val)
 	if (val == 0)
 		return;
 
+	if (!(__vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMU_PMCR_E))
+		return;
+
 	enable = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
 	for (i = 0; i < ARMV8_PMU_CYCLE_IDX; i++) {
 		if (!(val & BIT(i)))
-- 
2.20.1

[PATCH 2/4] KVM: arm64: pmu: Don't mark a counter as chained if the odd one is disabled

[Eric Auger]

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_pu_idx_has_chain_evtype().

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Suggested-by: Marc Zyngier <maz@kernel.org>
---
 virt/kvm/arm/pmu.c | 62 ++++++++++++++++++++++++----------------------
 1 file changed, 33 insertions(+), 29 deletions(-)

diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index c3f8b059881e..9f605e0b8dd7 100644
--- a/virt/kvm/arm/pmu.c
+++ b/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)) {
-			kvm_pmu_create_perf_event(vcpu, i);
-			continue;
-		}
+		/* 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);
 
 		/* 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)) {
-			kvm_pmu_create_perf_event(vcpu, i);
-			continue;
-		}
+		/* 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);
 
 		/* At this point, pmc must be the canonical */
 		if (pmc->perf_event)
@@ -585,15 +582,14 @@ 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;
+		attr.config1 |= PERF_ATTR_CFG1_KVM_PMU_CHAINED;
 
 		event = perf_event_create_kernel_counter(&attr, -1, current,
 							 kvm_pmu_perf_overflow,
@@ -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;
 
-	if (kvm_pmu_idx_has_chain_evtype(vcpu, pmc->idx)) {
+	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;
+
+	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);
 }
 
 /**
-- 
2.20.1

[PATCH 3/4] KVM: arm64: pmu: Fix chained SW_INCR counters

[Eric Auger]

At the moment a SW_INCR counter always overflows on 32-bit
boundary, independently on whether the n+1th counter is
programmed as CHAIN.

Check whether the SW_INCR counter is a 64b counter and if so,
implement the 64b logic.

Fixes: 80f393a23be6 ("KVM: arm/arm64: Support chained PMU counters")
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

---

v1 -> v2:
- Reorganize the kvm_pmu_software_increment() flow as suggested by
  Marc. At the exception I did not use kvm_pmu_get_counter_value()
  as it returns only the right half of the 64b counter.
---
 virt/kvm/arm/pmu.c | 43 ++++++++++++++++++++++++++++++-------------
 1 file changed, 30 insertions(+), 13 deletions(-)

diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index 9f605e0b8dd7..560db6282137 100644
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c
@@ -477,28 +477,45 @@ static void kvm_pmu_perf_overflow(struct perf_event *perf_event,
  */
 void kvm_pmu_software_increment(struct kvm_vcpu *vcpu, u64 val)
 {
+	struct kvm_pmu *pmu = &vcpu->arch.pmu;
 	int i;
-	u64 type, enable, reg;
-
-	if (val == 0)
-		return;
 
 	if (!(__vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMU_PMCR_E))
 		return;
 
-	enable = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
+	/* Weed out disabled counters */
+	val &= __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
+
 	for (i = 0; i < ARMV8_PMU_CYCLE_IDX; i++) {
+		u64 type, reg;
+
 		if (!(val & BIT(i)))
 			continue;
-		type = __vcpu_sys_reg(vcpu, PMEVTYPER0_EL0 + i)
-		       & ARMV8_PMU_EVTYPE_EVENT;
-		if ((type == ARMV8_PMUV3_PERFCTR_SW_INCR)
-		    && (enable & BIT(i))) {
-			reg = __vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i) + 1;
+
+		/* PMSWINC only applies to ... SW_INC! */
+		type = __vcpu_sys_reg(vcpu, PMEVTYPER0_EL0 + i);
+		type &= ARMV8_PMU_EVTYPE_EVENT;
+		if (type != ARMV8_PMUV3_PERFCTR_SW_INCR)
+			continue;
+
+		/* increment this even SW_INC counter */
+		reg = __vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i) + 1;
+		reg = lower_32_bits(reg);
+		__vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i) = reg;
+
+		if (reg) /* no overflow on the low part */
+			continue;
+
+		if (kvm_pmu_pmc_is_chained(&pmu->pmc[i])) {
+			/* increment the high counter */
+			reg = __vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i + 1) + 1;
 			reg = lower_32_bits(reg);
-			__vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i) = reg;
-			if (!reg)
-				__vcpu_sys_reg(vcpu, PMOVSSET_EL0) |= BIT(i);
+			__vcpu_sys_reg(vcpu, PMEVCNTR0_EL0 + i + 1) = reg;
+			if (!reg) /* mark overflow on the high counter */
+				__vcpu_sys_reg(vcpu, PMOVSSET_EL0) |= BIT(i + 1);
+		} else {
+			/* mark overflow on low counter */
+			__vcpu_sys_reg(vcpu, PMOVSSET_EL0) |= BIT(i);
 		}
 	}
 }
-- 
2.20.1

[PATCH 4/4] KVM: arm64: pmu: Only handle supported event counters

[Eric Auger]

Let the code never use unsupported event counters. Change
kvm_pmu_handle_pmcr() to only reset supported counters and
kvm_pmu_vcpu_reset() to only sto supported counters.

Other actions are filtered on the supported counters in
kvm/sysregs.c

Signed-off-by: Eric Auger <eric.auger@redhat.com>
---
 virt/kvm/arm/pmu.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index 560db6282137..f0d0312c0a55 100644
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c
@@ -247,10 +247,11 @@ void kvm_pmu_vcpu_init(struct kvm_vcpu *vcpu)
  */
 void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu)
 {
-	int i;
+	unsigned long mask = kvm_pmu_valid_counter_mask(vcpu);
 	struct kvm_pmu *pmu = &vcpu->arch.pmu;
+	int i;
 
-	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++)
+	for_each_set_bit(i, &mask, 32)
 		kvm_pmu_stop_counter(vcpu, &pmu->pmc[i]);
 
 	bitmap_zero(vcpu->arch.pmu.chained, ARMV8_PMU_MAX_COUNTER_PAIRS);
@@ -527,10 +528,9 @@ void kvm_pmu_software_increment(struct kvm_vcpu *vcpu, u64 val)
  */
 void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
 {
-	u64 mask;
+	unsigned long mask = kvm_pmu_valid_counter_mask(vcpu);
 	int i;
 
-	mask = kvm_pmu_valid_counter_mask(vcpu);
 	if (val & ARMV8_PMU_PMCR_E) {
 		kvm_pmu_enable_counter_mask(vcpu,
 		       __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask);
@@ -542,7 +542,7 @@ void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
 		kvm_pmu_set_counter_value(vcpu, ARMV8_PMU_CYCLE_IDX, 0);
 
 	if (val & ARMV8_PMU_PMCR_P) {
-		for (i = 0; i < ARMV8_PMU_CYCLE_IDX; i++)
+		for_each_set_bit(i, &mask, 32)
 			kvm_pmu_set_counter_value(vcpu, i, 0);
 	}
 }
-- 
2.20.1