[PATCH v7 17/20] KVM: arm64: Add vCPU device attr to partition the PMU

Colton Lewis
2026-05-04T21:19:12Z

Add a new PMU device attr to enable the partitioned PMU for a given
VM. This capability can be set when the PMU is initially configured
before the vCPU starts running and is allowed where PMUv3 and VHE are
supported and the host driver was configured with
arm_pmuv3.reserved_host_counters.

The enabled capability is tracked by the new flag
KVM_ARCH_FLAG_PARTITION_PMU_ENABLED.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
arch/arm64/include/asm/kvm_host.h | 2 ++
arch/arm64/include/uapi/asm/kvm.h | 2 ++
arch/arm64/kvm/pmu-direct.c | 35 ++++++++++++++++++++++++++++---
arch/arm64/kvm/pmu.c | 14 +++++++++++++
include/kvm/arm_pmu.h | 9 ++++++++
5 files changed, 59 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 891433fe304ac..22b3985b978de 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -353,6 +353,8 @@ struct kvm_arch {
#define KVM_ARCH_FLAG_WRITABLE_IMP_ID_REGS 10
/* Unhandled SEAs are taken to userspace */
#define KVM_ARCH_FLAG_EXIT_SEA 11
+ /* Partitioned PMU Enabled */
+#define KVM_ARCH_FLAG_PARTITION_PMU_ENABLED 12
unsigned long flags;

/* VM-wide vCPU feature set */
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index a792a599b9d68..3e0b7619f781d 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -436,6 +436,8 @@ enum {
#define KVM_ARM_VCPU_PMU_V3_FILTER 2
#define KVM_ARM_VCPU_PMU_V3_SET_PMU 3
#define KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS 4
+#define KVM_ARM_VCPU_PMU_V3_ENABLE_PARTITION 5
+
#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-direct.c b/arch/arm64/kvm/pmu-direct.c
index 9693d9eb69daa..47fd143cf4ac7 100644
--- a/arch/arm64/kvm/pmu-direct.c
+++ b/arch/arm64/kvm/pmu-direct.c
@@ -44,8 +44,8 @@ bool kvm_pmu_is_partitioned(struct arm_pmu *pmu)
}

/**
- * kvm_vcpu_pmu_is_partitioned() - Determine if given VCPU has a partitioned PMU
- * @vcpu: Pointer to kvm_vcpu struct
+ * kvm_pmu_is_partitioned() - Determine if given VCPU has a partitioned PMU
+ * @kvm: Pointer to kvm_vcpu struct
*
* Determine if given VCPU has a partitioned PMU by extracting that
* field and passing it to :c:func:`kvm_pmu_is_partitioned`
@@ -55,7 +55,36 @@ bool kvm_pmu_is_partitioned(struct arm_pmu *pmu)
bool kvm_vcpu_pmu_is_partitioned(struct kvm_vcpu *vcpu)
{
return kvm_pmu_is_partitioned(vcpu->kvm->arch.arm_pmu) &&
- false;
+ test_bit(KVM_ARCH_FLAG_PARTITION_PMU_ENABLED, &vcpu->kvm->arch.flags);
+}
+
+/**
+ * has_kvm_pmu_partition_support() - If we can enable/disable partition
+ *
+ * Return: true if allowed, false otherwise.
+ */
+bool has_kvm_pmu_partition_support(void)
+{
+ return has_host_pmu_partition_support() &&
+ kvm_supports_guest_pmuv3() &&
+ armv8pmu_is_partitioned;
+}
+
+/**
+ * kvm_pmu_partition_enable() - Enable/disable partition flag
+ * @kvm: Pointer to vcpu
+ * @enable: Whether to enable or disable
+ *
+ * If we want to enable the partition, the guest is free to grab
+ * hardware by accessing PMU registers. Otherwise, the host maintains
+ * control.
+ */
+void kvm_pmu_partition_enable(struct kvm *kvm, bool enable)
+{
+ if (enable)
+ set_bit(KVM_ARCH_FLAG_PARTITION_PMU_ENABLED, &kvm->arch.flags);
+ else
+ clear_bit(KVM_ARCH_FLAG_PARTITION_PMU_ENABLED, &kvm->arch.flags);
}

/**
diff --git a/arch/arm64/kvm/pmu.c b/arch/arm64/kvm/pmu.c
index f1c66ce678840..add5e7da830b2 100644
--- a/arch/arm64/kvm/pmu.c
+++ b/arch/arm64/kvm/pmu.c
@@ -759,6 +759,19 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)

return kvm_arm_pmu_v3_set_nr_counters(vcpu, n);
}
+ case KVM_ARM_VCPU_PMU_V3_ENABLE_PARTITION: {
+ unsigned int __user *uaddr = (unsigned int __user *)(long)attr->addr;
+ bool enable;
+
+ if (get_user(enable, uaddr))
+ return -EFAULT;
+
+ if (!has_kvm_pmu_partition_support())
+ return -EPERM;
+
+ kvm_pmu_partition_enable(kvm, enable);
+ return 0;
+ }
case KVM_ARM_VCPU_PMU_V3_INIT:
return kvm_arm_pmu_v3_init(vcpu);
}
@@ -798,6 +811,7 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
case KVM_ARM_VCPU_PMU_V3_FILTER:
case KVM_ARM_VCPU_PMU_V3_SET_PMU:
case KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS:
+ case KVM_ARM_VCPU_PMU_V3_ENABLE_PARTITION:
if (kvm_vcpu_has_pmu(vcpu))
return 0;
}
diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index 4af8abf2dde0f..131c4b8eec194 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -107,6 +107,8 @@ void kvm_pmu_load(struct kvm_vcpu *vcpu);
void kvm_pmu_put(struct kvm_vcpu *vcpu);

void kvm_pmu_set_guest_owned(struct kvm_vcpu *vcpu);
+bool has_kvm_pmu_partition_support(void);
+void kvm_pmu_partition_enable(struct kvm *kvm, bool enable);

#if !defined(__KVM_NVHE_HYPERVISOR__)
bool kvm_vcpu_pmu_is_partitioned(struct kvm_vcpu *vcpu);
@@ -295,6 +297,13 @@ static inline u64 kvm_pmu_guest_counter_mask(void *kvm)

static inline void kvm_pmu_handle_guest_irq(struct arm_pmu *pmu, u64 pmovsr) {}

+static inline bool has_kvm_pmu_partition_support(void)
+{
+ return false;
+}
+
+static inline void kvm_pmu_partition_enable(struct kvm *kvm, bool enable) {}
+
#endif

#endif
--
2.54.0.545.g6539524ca2-goog