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.
Allow strict PMUv3 vCPUs to initialize the PMU after selecting
fixed-counters-only mode, without selecting a VM-wide hardware PMU.
Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Akihiko Odaki <[email protected]>
---
Documentation/virt/kvm/api.rst | 8 +++++--
Documentation/virt/kvm/devices/vcpu.rst | 42 ++++++++++++++++++++++++++-------
arch/arm64/include/uapi/asm/kvm.h | 1 +
arch/arm64/kvm/pmu-emul.c | 34 ++++++++++++++++++++++----
tools/arch/arm64/include/uapi/asm/kvm.h | 1 +
5 files changed, 71 insertions(+), 15 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 1a90598901c5..a6aef405ef87 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -3531,9 +3531,13 @@ Possible features:
* Userspace must explicitly select a PMU implementation before
initializing the PMU or configuring a PMU event filter
+ (KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY also satisfies the
+ initialization requirement; event filtering remains unavailable
+ in that mode)
- * If the PMU implements FEAT_PMUv3p4, PMMIR_EL1.SLOTS provides the
- hardware value of the underlying implementation
+ * If a hardware PMU is selected and implements FEAT_PMUv3p4,
+ PMMIR_EL1.SLOTS provides its hardware value. In
fixed-counters-only
+ mode, PMMIR_EL1 reads as zero
* Writes to PMCR_EL0.N via KVM_SET_ONE_REG are ignored
diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
index a3f20a4ee4b1..41f6d708ff43 100644
--- a/Documentation/virt/kvm/devices/vcpu.rst
+++ b/Documentation/virt/kvm/devices/vcpu.rst
@@ -53,9 +53,9 @@ Returns:
======= ======================================================
-EEXIST Interrupt number already used
-ENODEV PMUv3 not supported or GIC not initialized
- -ENXIO PMUv3 not supported, missing VCPU feature, missing
- hardware PMU, or interrupt number not set (non-GICv5
- guests, only)
+ -ENXIO PMUv3 not supported, missing VCPU feature,
+ neither hardware PMU nor FIXED_COUNTERS_ONLY selected,
+ or interrupt number not set (non-GICv5 guests only)
-EBUSY PMUv3 already initialized
======= ======================================================
@@ -64,7 +64,8 @@ virtual GIC implementation, this must be done after initializing the in-kernel
irqchip.
When the KVM_ARM_VCPU_PMU_V3_STRICT vCPU feature is enabled this must be done
-after selecting a hardware PMU.
+after selecting a hardware PMU or enabling
+KVM_ARM_VCPU_PMU_V3_FIXED_COUNTERS_ONLY.
1.3 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_FILTER
-----------------------------------------
@@ -78,7 +79,8 @@ after selecting a hardware PMU.
-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
======= ======================================================
@@ -123,14 +125,14 @@ after selecting a hardware PMU.
: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"
@@ -172,6 +174,30 @@ 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.
+
+With KVM_ARM_VCPU_PMU_V3_STRICT, enabling this attribute satisfies the
+PMU selection requirement for KVM_ARM_VCPU_PMU_V3_INIT.
+
+When this attribute is enabled, the vCPU can run on any physical CPU
+that has a PMU, regardless of the underlying implementation. This
+attribute is VM-scoped.
+
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 65ee09bd1463..7a6a0af14f5a 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -453,6 +453,7 @@ struct kvm_vgic_v5_ist {
#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 9c1e2f3e41db..ebb648eabdc6 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -1017,8 +1017,8 @@ int kvm_arm_pmu_v3_enable(struct kvm_vcpu *vcpu)
static int kvm_arm_pmu_v3_init(struct kvm_vcpu *vcpu)
{
- /* Only possible when using KVM_ARM_VCPU_PMU_V3_STRICT */
- if (!vcpu->kvm->arch.arm_pmu)
+ /* Strict PMUv3 requires a hardware PMU or fixed-counters-only mode. */
+ if (!vcpu->kvm->arch.arm_pmu && !kvm_pmu_fixed_counters_only(vcpu->kvm))
return -ENXIO;
if (irqchip_in_kernel(vcpu->kvm)) {
@@ -1153,8 +1153,8 @@ int kvm_arm_set_default_pmu(struct kvm *kvm)
* affines the VMM to a particular cluster of cores.
*
* In any case, userspace should just do the sane thing and use the UAPI
- * to select a PMU type directly. But, be wary of the baggage being
- * carried here.
+ * to select a PMU type directly, or request fixed-counters-only
+ * emulation. But, be wary of the baggage being carried here.
*/
struct arm_pmu *arm_pmu = kvm_pmu_probe_armpmu(raw_smp_processor_id());
@@ -1179,11 +1179,13 @@ 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);
@@ -1205,6 +1207,22 @@ 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->arch.nr_pmu_counters = 0;
+
+ return 0;
+}
+
