[PATCH v8 6/7] KVM: arm64: PMU: Introduce FIXED_COUNTERS_ONLY
Akihiko Odaki
odaki at rsg.ci.i.u-tokyo.ac.jp
Mon Jul 6 03:03:29 PDT 2026
Introduce the KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY attribute to
create a "fixed-counters-only" PMU.
Much like KVM_ARM_VCPU_PMU_V3_IRQ and other read-write attributes, this
attribute provides a getter that facilitates kernel and userspace
debugging/testing.
Signed-off-by: Akihiko Odaki <odaki at rsg.ci.i.u-tokyo.ac.jp>
---
Documentation/virt/kvm/devices/vcpu.rst | 32 ++++++++++++++++++++++++++++----
arch/arm64/include/uapi/asm/kvm.h | 1 +
arch/arm64/kvm/pmu-emul.c | 26 +++++++++++++++++++++++++-
3 files changed, 54 insertions(+), 5 deletions(-)
diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
index 5e3805820010..58a6639c0196 100644
--- a/Documentation/virt/kvm/devices/vcpu.rst
+++ b/Documentation/virt/kvm/devices/vcpu.rst
@@ -71,7 +71,8 @@ irqchip.
-ENODEV PMUv3 not supported or GIC not initialized
-ENXIO PMUv3 not properly configured or in-kernel irqchip not
configured as required prior to calling this attribute
- -EBUSY PMUv3 already initialized or a VCPU has already run
+ -EBUSY PMUv3 already initialized, a VCPU has already run or
+ FIXED_COUNTERS_ONLY has already been set
-EINVAL Invalid filter range
======= ======================================================
@@ -113,14 +114,14 @@ using event 0x11 (CPU_CYCLES).
:Returns:
- ======= ====================================================
+ ======= ===========================================================
-EBUSY PMUv3 already initialized, a VCPU has already run or
- an event filter has already been set
+ an event filter or FIXED_COUNTERS_ONLY has already been set
-EFAULT Error accessing the PMU identifier
-ENXIO PMU not found
-ENODEV PMUv3 not supported or GIC not initialized
-ENOMEM Could not allocate memory
- ======= ====================================================
+ ======= ===========================================================
Request that the VCPU uses the specified hardware PMU when creating guest events
for the purpose of PMU emulation. The PMU identifier can be read from the "type"
@@ -162,6 +163,29 @@ explicitly selected, or the number of counters is out of range for the
selected PMU. Selecting a new PMU cancels the effect of setting this
attribute.
+1.6 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY
+------------------------------------------------------
+
+:Parameters: no additional parameter in kvm_device_attr.addr
+
+:Returns:
+
+ ======= ==================================================
+ -EBUSY PMUv3 already initialized, a VCPU has already run,
+ an event filter has already been set or
+ a hardware PMU has already been specified
+ -ENXIO Attempted to get before setting
+ -ENODEV Attempted to set while PMUv3 not supported
+ ======= ==================================================
+
+If set, KVM emulates PMUv3 without programmable event counters. Only fixed
+counters are exposed to the guest: the cycle counter today, and the instruction
+counter if support for FEAT_PMUv3_ICNTR is added.
+
+With programmable counters disabled, the VCPU can run on any physical CPU.
+This is particularly useful on heterogeneous systems where different hardware
+PMUs cover different physical CPUs. All VCPUs in a VM share this attribute.
+
2. GROUP: KVM_ARM_VCPU_TIMER_CTRL
=================================
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 1c13bfa2d38a..39a1a1e412e6 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -437,6 +437,7 @@ 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_FIXED_COUNTERS_ONLY 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-emul.c b/arch/arm64/kvm/pmu-emul.c
index 40cad183376c..ad9ff4d0d89c 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -1149,11 +1149,13 @@ static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id)
arm_pmu = entry->arm_pmu;
if (arm_pmu->pmu.type == pmu_id) {
if (kvm_vm_has_ran_once(kvm) ||
+ kvm_pmu_fixed_counters_only(kvm) ||
(kvm->arch.pmu_filter && kvm->arch.arm_pmu != arm_pmu)) {
ret = -EBUSY;
break;
}
+ set_bit(KVM_ARCH_FLAG_PMU_V3_EXPLICIT, &kvm->arch.flags);
kvm_arm_set_pmu(kvm, arm_pmu);
cpumask_copy(kvm->arch.supported_cpus, &arm_pmu->supported_cpus);
ret = 0;
@@ -1164,6 +1166,22 @@ static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id)
return ret;
}
+static int kvm_arm_pmu_v3_set_pmu_fixed_counters_only(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+
+ lockdep_assert_held(&kvm->arch.config_lock);
+
+ if (kvm_vm_has_ran_once(kvm) || kvm->arch.pmu_filter ||
+ test_bit(KVM_ARCH_FLAG_PMU_V3_EXPLICIT, &kvm->arch.flags))
+ return -EBUSY;
+
+ set_bit(KVM_ARCH_FLAG_PMU_V3_FIXED_COUNTERS_ONLY, &kvm->arch.flags);
+ kvm_arm_set_nr_counters(kvm, 0);
+
+ return 0;
+}
+
static int kvm_arm_pmu_v3_set_nr_counters(struct kvm_vcpu *vcpu, unsigned int n)
{
struct kvm *kvm = vcpu->kvm;
@@ -1238,7 +1256,7 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
filter.action != KVM_PMU_EVENT_DENY))
return -EINVAL;
- if (kvm_vm_has_ran_once(kvm))
+ if (kvm_vm_has_ran_once(kvm) || kvm_pmu_fixed_counters_only(kvm))
return -EBUSY;
if (!kvm->arch.pmu_filter) {
@@ -1283,6 +1301,8 @@ 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_FIXED_COUNTERS_ONLY:
+ return kvm_arm_pmu_v3_set_pmu_fixed_counters_only(vcpu);
case KVM_ARM_VCPU_PMU_V3_INIT:
return kvm_arm_pmu_v3_init(vcpu);
}
@@ -1309,6 +1329,9 @@ int kvm_arm_pmu_v3_get_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
irq = vcpu->arch.pmu.irq_num;
return put_user(irq, uaddr);
}
+ case KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY:
+ if (kvm_pmu_fixed_counters_only(vcpu->kvm))
+ return 0;
}
return -ENXIO;
@@ -1322,6 +1345,7 @@ 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_FIXED_COUNTERS_ONLY:
if (kvm_vcpu_has_pmu(vcpu))
return 0;
}
--
2.55.0
More information about the linux-arm-kernel
mailing list