[PATCH 11/18] KVM: ARM64: Add reset and access handlers for PMCNTENSET_EL0... | linux-arm-kernel

[PATCH 11/18] KVM: ARM64: Add reset and access handlers for PMCNTENSET_EL0 and PMCNTENCLR_EL0 register

From: Christoffer Dall <hidden>
Date: 2015-07-17 14:52:33
Also in: kvm, kvmarm

On Mon, Jul 06, 2015 at 10:17:41AM +0800, shannon.zhao at linaro.org wrote:

quoted hunk ↗ jump to hunk

From: Shannon Zhao <redacted>

Since the reset value of PMCNTENSET_EL0 and PMCNTENCLR_EL0 is UNKNOWN,
use reset_unknown for its reset handler. Add access handler which
emulates writing and reading PMCNTENSET_EL0 or PMCNTENCLR_EL0 register.
When writing to PMCNTENSET_EL0, call perf_event_enable to enable the
perf event. When writing to PMCNTENCLR_EL0, call perf_event_disable to
disable the perf event.

Signed-off-by: Shannon Zhao <redacted>
---
 arch/arm64/kvm/sys_regs.c | 56 +++++++++++++++++++++++++++++++++++++++++++++--
 include/kvm/arm_pmu.h     |  4 ++++
 virt/kvm/arm/pmu.c        | 41 ++++++++++++++++++++++++++++++++++
 3 files changed, 99 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 29883df..c14ec8d 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c

@@ -392,6 +392,58 @@ static bool access_pmccntr(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+/* PMCNTENSET_EL0 accessor. */
+static bool access_pmcntenset(struct kvm_vcpu *vcpu,
+			      const struct sys_reg_params *p,
+			      const struct sys_reg_desc *r)
+{
+	unsigned long val;
+
+	if (p->is_write) {
+		val = *vcpu_reg(vcpu, p->Rt);
+		if (!p->is_aarch32)
+			vcpu_sys_reg(vcpu, r->reg) |= val;
+		else
+			vcpu_cp15(vcpu, r->reg) |= val & 0xffffffffUL;
+
+		kvm_pmu_enable_counter(vcpu, val);
+	} else {
+		if (!p->is_aarch32)
+			val = vcpu_sys_reg(vcpu, r->reg);
+		else
+			val = vcpu_cp15(vcpu, r->reg);
+		*vcpu_reg(vcpu, p->Rt) = val;
+	}
+
+	return true;
+}
+
+/* PMCNTENCLR_EL0 accessor. */
+static bool access_pmcntenclr(struct kvm_vcpu *vcpu,
+			      const struct sys_reg_params *p,
+			      const struct sys_reg_desc *r)
+{
+	unsigned long val;
+
+	if (p->is_write) {
+		val = *vcpu_reg(vcpu, p->Rt);
+		if (!p->is_aarch32)
+			vcpu_sys_reg(vcpu, r->reg) |= val;

huh, this is the clear register, don't you need to &= ~val ?

also, there's a lot of code duplication between these two functions, it
must be worthwhile having a single static function that they both call
if a bool differentiating between set/clear.

quoted hunk ↗ jump to hunk

+		else
+			vcpu_cp15(vcpu, r->reg) |= val & 0xffffffffUL;
+
+		kvm_pmu_disable_counter(vcpu, val);
+	} else {
+		if (!p->is_aarch32)
+			val = vcpu_sys_reg(vcpu, r->reg);
+		else
+			val = vcpu_cp15(vcpu, r->reg);
+		*vcpu_reg(vcpu, p->Rt) = val;
+	}
+
+	return true;
+}
+
 /* Silly macro to expand the DBG{BCR,BVR,WVR,WCR}n_EL1 registers in one go */
 #define DBG_BCR_BVR_WCR_WVR_EL1(n)					\
 	/* DBGBVRn_EL1 */						\

@@ -586,10 +638,10 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	  access_pmcr, reset_pmcr_el0, PMCR_EL0, },
 	/* PMCNTENSET_EL0 */
 	{ Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1100), Op2(0b001),
-	  trap_raz_wi },
+	  access_pmcntenset, reset_unknown, PMCNTENSET_EL0 },
 	/* PMCNTENCLR_EL0 */
 	{ Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1100), Op2(0b010),
-	  trap_raz_wi },
+	  access_pmcntenclr, reset_unknown, PMCNTENCLR_EL0 },
 	/* PMOVSCLR_EL0 */
 	{ Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1100), Op2(0b011),
 	  trap_raz_wi },

diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index 40ab4a0..2cfd9be 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h

@@ -49,6 +49,8 @@ void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, unsigned long select_idx,
 			       unsigned long val);
 unsigned long kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu,
 					unsigned long select_idx);
+void kvm_pmu_disable_counter(struct kvm_vcpu *vcpu, unsigned long val);
+void kvm_pmu_enable_counter(struct kvm_vcpu *vcpu, unsigned long val);
 void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, unsigned long data,
 				    unsigned long select_idx);
 void kvm_pmu_init(struct kvm_vcpu *vcpu);

@@ -61,6 +63,8 @@ unsigned long kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu,
 {
 	return 0;
 }
+void kvm_pmu_disable_counter(struct kvm_vcpu *vcpu, unsigned long val) {}
+void kvm_pmu_enable_counter(struct kvm_vcpu *vcpu, unsigned long val) {}
 void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, unsigned long data,
 				    unsigned long select_idx) {}
 static inline void kvm_pmu_init(struct kvm_vcpu *vcpu) {}

diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index 361fa51..cf59998 100644
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c

@@ -134,6 +134,47 @@ unsigned long kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu,
 }
 
 /**
+ * kvm_pmu_enable_counter - enable selected PMU counter
+ * @vcpu: The vcpu pointer
+ * @val: the value guest writes to PMCNTENSET_EL0 register
+ *
+ * Call perf_event_enable to start counting the perf event
+ */
+void kvm_pmu_enable_counter(struct kvm_vcpu *vcpu, unsigned long val)
+{
+	int select_idx = find_first_bit(&val, 32);

Both of these functions should be able to handle more than one bit set
in val though, right?

Or perhaps you should make the parameter be select_idx and loop over the
bits in the caller, your choice.

+	struct kvm_pmu *pmu = &vcpu->arch.pmu;
+	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
+
+	if (pmc->perf_event) {
+		local64_set(&pmc->perf_event->count, 0);

why local64_set?  Is this local to this CPU somehow?

why do we clear the count?  Is it architecturally mandated?

+		perf_event_enable(pmc->perf_event);
+		if (pmc->perf_event->state != PERF_EVENT_STATE_ACTIVE)
+			printk("kvm: fail to enable event\n");

do you really want this print here?  What could cause this error,
anything the VM can provoke?

+	}

what's the difference between having pmc->perf_event == NULL and having
pmc->perf_event->state == PERF_EVENT_STATE_INACTIVE ?

+	pmc->enable = true;
+}
+
+/**
+ * kvm_pmu_disable_counter - disable selected PMU counter
+ * @vcpu: The vcpu pointer
+ * @val: the value guest writes to PMCNTENCLR_EL0 register
+ *
+ * Call perf_event_disable to stop counting the perf event
+ */
+void kvm_pmu_disable_counter(struct kvm_vcpu *vcpu, unsigned long val)
+{
+	int select_idx = find_first_bit(&val, 32);

ditto, see above.

+	struct kvm_pmu *pmu = &vcpu->arch.pmu;
+	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
+
+	if (pmc->perf_event)
+		perf_event_disable(pmc->perf_event);
+
+	pmc->enable = false;
+}
+
+/**
  * kvm_pmu_find_hw_event - find hardware event
  * @pmu: The pmu pointer
  * @event_select: The number of selected event type
-- 
2.1.0

Thanks,
-Christoffer

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