[PATCH] KVM: arm64: Allow to limit number of PMU counters

[Alexander Graf]

We currently pass through the number of PMU counters that we have available
in hardware to guests. So if my host supports 10 concurrently active PMU
counters, my guest will be able to spawn 10 counters as well.

This is undesireable if we also want to use the PMU on the host for
monitoring. In that case, we want to split the PMU between guest and
host.

To help that case, let's add a PMU attr that allows us to limit the number
of PMU counters that we expose. With this patch in place, user space can
keep some counters free for host use.

Signed-off-by: Alexander Graf <graf at amazon.com>

---

Because this patch touches the same code paths as the vPMU filtering one
and the vPMU filtering generalized a few conditions in the attr path,
I've based it on top. Please let me know if you want it independent instead.
---
 arch/arm64/include/uapi/asm/kvm.h |  7 ++++---
 arch/arm64/kvm/pmu-emul.c         | 22 ++++++++++++++++++++++
 arch/arm64/kvm/sys_regs.c         |  5 +++++
 include/kvm/arm_pmu.h             |  1 +
 4 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 7b1511d6ce44..db025c0b5a40 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -342,9 +342,10 @@ struct kvm_vcpu_events {
 
 /* Device Control API on vcpu fd */
 #define KVM_ARM_VCPU_PMU_V3_CTRL	0
-#define   KVM_ARM_VCPU_PMU_V3_IRQ	0
-#define   KVM_ARM_VCPU_PMU_V3_INIT	1
-#define   KVM_ARM_VCPU_PMU_V3_FILTER	2
+#define   KVM_ARM_VCPU_PMU_V3_IRQ		0
+#define   KVM_ARM_VCPU_PMU_V3_INIT		1
+#define   KVM_ARM_VCPU_PMU_V3_FILTER		2
+#define   KVM_ARM_VCPU_PMU_V3_NUM_EVENTS	3
 #define KVM_ARM_VCPU_TIMER_CTRL		1
 #define   KVM_ARM_VCPU_TIMER_IRQ_VTIMER		0
 #define   KVM_ARM_VCPU_TIMER_IRQ_PTIMER		1
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 9f0fd0224d5b..40848e17d0cb 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -238,6 +238,8 @@ void kvm_pmu_vcpu_init(struct kvm_vcpu *vcpu)
 
 	for (i = 0; i < ARMV8_PMU_MAX_COUNTERS; i++)
 		pmu->pmc[i].idx = i;
+
+	pmu->num_events = perf_num_counters() - 1;
 }
 
 /**
@@ -875,6 +877,25 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 
 		return 0;
 	}
+	case KVM_ARM_VCPU_PMU_V3_NUM_EVENTS: {
+		u64 mask = ARMV8_PMU_PMCR_N_MASK << ARMV8_PMU_PMCR_N_SHIFT;
+		int __user *uaddr = (int __user *)(long)attr->addr;
+		unsigned int num_events;
+
+		if (get_user(num_events, uaddr))
+			return -EFAULT;
+
+		if (num_events >= perf_num_counters())
+			return -EINVAL;
+
+		vcpu->arch.pmu.num_events = num_events;
+
+		num_events <<= ARMV8_PMU_PMCR_N_SHIFT;
+		__vcpu_sys_reg(vcpu, SYS_PMCR_EL0) &= ~mask;
+		__vcpu_sys_reg(vcpu, SYS_PMCR_EL0) |= num_events;
+
+		return 0;
+	}
 	case KVM_ARM_VCPU_PMU_V3_INIT:
 		return kvm_arm_pmu_v3_init(vcpu);
 	}
@@ -912,6 +933,7 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	case KVM_ARM_VCPU_PMU_V3_IRQ:
 	case KVM_ARM_VCPU_PMU_V3_INIT:
 	case KVM_ARM_VCPU_PMU_V3_FILTER:
+	case KVM_ARM_VCPU_PMU_V3_NUM_EVENTS:
 		if (kvm_arm_support_pmu_v3() &&
 		    test_bit(KVM_ARM_VCPU_PMU_V3, vcpu->arch.features))
 			return 0;
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 077293b5115f..fca0bba6d97b 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -672,6 +672,11 @@ static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 	       | (ARMV8_PMU_PMCR_MASK & 0xdecafbad)) & (~ARMV8_PMU_PMCR_E);
 	if (!system_supports_32bit_el0())
 		val |= ARMV8_PMU_PMCR_LC;
+
+	/* Override number of event selectors */
+	val &= ~(ARMV8_PMU_PMCR_N_MASK << ARMV8_PMU_PMCR_N_SHIFT);
+	val |= (u32)vcpu->arch.pmu.num_events << ARMV8_PMU_PMCR_N_SHIFT;
+
 	__vcpu_sys_reg(vcpu, r->reg) = val;
 }
 
diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index 6db030439e29..5557024edce5 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -27,6 +27,7 @@ struct kvm_pmu {
 	bool ready;
 	bool created;
 	bool irq_level;
+	u8 num_events;
 };
 
 #define kvm_arm_pmu_v3_ready(v)		((v)->arch.pmu.ready)
-- 
2.16.4




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