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 4988c32df4bf..42065138603b 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -3521,9 +3521,13 @@ 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 deb5c51bc00c..4ec3291f0ba7 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 019e5e3d892e..3bd7f201252a 100644 --- a/arch/arm64/include/uapi/asm/kvm.h +++ b/arch/arm64/include/uapi/asm/kvm.h @@ -438,6 +438,7 @@ 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 a19a913a8925..c68331cdfaf9 100644 --- a/arch/arm64/kvm/pmu-emul.c +++ b/arch/arm64/kvm/pmu-emul.c @@ -1003,8 +1003,8 @@ 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)) { @@ -1139,8 +1139,8 @@ 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()); @@ -1165,11 +1165,13 @@ 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); @@ -1191,6 +1193,22 @@ 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; +} + static int kvm_arm_pmu_v3_set_nr_counters(struct kvm_vcpu *vcpu, unsigned int n) { struct kvm *kvm = vcpu->kvm; @@ -1268,7 +1286,7 @@ 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.arm_pmu) @@ -1316,6 +1334,8 @@ 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); } @@ -1342,6 +1362,9 @@ 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; @@ -1355,6 +1378,7 @@ 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; } diff --git a/tools/arch/arm64/include/uapi/asm/kvm.h b/tools/arch/arm64/include/uapi/asm/kvm.h index 1c13bfa2d38a..39a1a1e412e6 100644 --- a/tools/arch/arm64/include/uapi/asm/kvm.h +++ b/tools/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 -- 2.55.0
