Hi Alex,
On Mon, Dec 6, 2021 at 9:02 AM Alexandru Elisei
<alexandru.elisei@xxxxxxx> wrote:
>
> When KVM creates an event and there are more than one PMUs present on the
> system, perf_init_event() will go through the list of available PMUs and
> will choose the first one that can create the event. The order of the PMUs
> in the PMU list depends on the probe order, which can change under various
> circumstances, for example if the order of the PMU nodes change in the DTB
> or if asynchronous driver probing is enabled on the kernel command line
> (with the driver_async_probe=armv8-pmu option).
>
> Another consequence of this approach is that, on heteregeneous systems,
> all virtual machines that KVM creates will use the same PMU. This might
> cause unexpected behaviour for userspace: when a VCPU is executing on
> the physical CPU that uses this PMU, PMU events in the guest work
> correctly; but when the same VCPU executes on another CPU, PMU events in
> the guest will suddenly stop counting.
>
> Fortunately, perf core allows user to specify on which PMU to create an
> event by using the perf_event_attr->type field, which is used by
> perf_init_event() as an index in the radix tree of available PMUs.
>
> Add the KVM_ARM_VCPU_PMU_V3_CTRL(KVM_ARM_VCPU_PMU_V3_SET_PMU) VCPU
> attribute to allow userspace to specify the arm_pmu that KVM will use when
> creating events for that VCPU. KVM will make no attempt to run the VCPU on
> the physical CPUs that share this PMU, leaving it up to userspace to
> manage the VCPU threads' affinity accordingly.
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> ---
> Documentation/virt/kvm/devices/vcpu.rst | 25 +++++++++++++++++
> arch/arm64/include/uapi/asm/kvm.h | 1 +
> arch/arm64/kvm/pmu-emul.c | 37 +++++++++++++++++++++++--
> include/kvm/arm_pmu.h | 1 +
> tools/arch/arm64/include/uapi/asm/kvm.h | 1 +
> 5 files changed, 63 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
> index 60a29972d3f1..c82be5cbc268 100644
> --- a/Documentation/virt/kvm/devices/vcpu.rst
> +++ b/Documentation/virt/kvm/devices/vcpu.rst
> @@ -104,6 +104,31 @@ hardware event. Filtering event 0x1E (CHAIN) has no effect either, as it
> isn't strictly speaking an event. Filtering the cycle counter is possible
> using event 0x11 (CPU_CYCLES).
>
> +1.4 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_SET_PMU
> +------------------------------------------
> +
> +:Parameters: in kvm_device_attr.addr the address to an int representing the PMU
> + identifier.
> +
> +:Returns:
> +
> + ======= ===============================================
> + -EBUSY PMUv3 already initialized
> + -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"
> +file for the desired PMU instance under /sys/devices (or, equivalent,
> +/sys/bus/even_source). This attribute is particularly useful on heterogeneous
> +systems where there are at least two CPU PMUs on the system.
> +
> +Note that KVM will not make any attempts to run the VCPU on the physical CPUs
> +associated with the PMU specified by this attribute. This is entirely left to
> +userspace.
>
> 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 b3edde68bc3e..1d0a0a2a9711 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -362,6 +362,7 @@ struct kvm_arm_copy_mte_tags {
> #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_SET_PMU 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 eaaad4c06561..618138c5f792 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -603,6 +603,7 @@ static bool kvm_pmu_counter_is_enabled(struct kvm_vcpu *vcpu, u64 select_idx)
> static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
> {
> struct kvm_pmu *pmu = &vcpu->arch.pmu;
> + struct arm_pmu *arm_pmu = pmu->arm_pmu;
> struct kvm_pmc *pmc;
> struct perf_event *event;
> struct perf_event_attr attr;
> @@ -638,8 +639,7 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
> return;
>
> memset(&attr, 0, sizeof(struct perf_event_attr));
> - attr.type = PERF_TYPE_RAW;
> - attr.size = sizeof(attr);
> + attr.type = arm_pmu ? arm_pmu->pmu.type : PERF_TYPE_RAW;
> attr.pinned = 1;
> attr.disabled = !kvm_pmu_counter_is_enabled(vcpu, pmc->idx);
> attr.exclude_user = data & ARMV8_PMU_EXCLUDE_EL0 ? 1 : 0;
> @@ -941,6 +941,29 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int irq)
> return true;
> }
>
> +static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id)
> +{
> + struct kvm_pmu *kvm_pmu = &vcpu->arch.pmu;
> + struct arm_pmu_entry *entry;
> + struct arm_pmu *arm_pmu;
> + int ret = -ENXIO;
> +
> + mutex_lock(&arm_pmus_lock);
> +
> + list_for_each_entry(entry, &arm_pmus, entry) {
> + arm_pmu = entry->arm_pmu;
> + if (arm_pmu->pmu.type == pmu_id) {
> + kvm_pmu->arm_pmu = arm_pmu;
Shouldn't kvm->arch.pmuver be updated based on the pmu that
is used for the guest ?
Thanks,
Reiji
> + ret = 0;
> + goto out_unlock;
> + }
> + }
> +
> +out_unlock:
> + mutex_unlock(&arm_pmus_lock);
> + return ret;
> +}
> +
> int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
> {
> if (!kvm_vcpu_has_pmu(vcpu))
> @@ -1027,6 +1050,15 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
>
> return 0;
> }
> + case KVM_ARM_VCPU_PMU_V3_SET_PMU: {
> + int __user *uaddr = (int __user *)(long)attr->addr;
> + int pmu_id;
> +
> + if (get_user(pmu_id, uaddr))
> + return -EFAULT;
> +
> + return kvm_arm_pmu_v3_set_pmu(vcpu, pmu_id);
> + }
> case KVM_ARM_VCPU_PMU_V3_INIT:
> return kvm_arm_pmu_v3_init(vcpu);
> }
> @@ -1064,6 +1096,7 @@ 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_SET_PMU:
> if (kvm_vcpu_has_pmu(vcpu))
> return 0;
> }
> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> index e249c5f172aa..ab3046a8f9bb 100644
> --- a/include/kvm/arm_pmu.h
> +++ b/include/kvm/arm_pmu.h
> @@ -34,6 +34,7 @@ struct kvm_pmu {
> bool created;
> bool irq_level;
> struct irq_work overflow_work;
> + struct arm_pmu *arm_pmu;
> };
>
> struct arm_pmu_entry {
> diff --git a/tools/arch/arm64/include/uapi/asm/kvm.h b/tools/arch/arm64/include/uapi/asm/kvm.h
> index b3edde68bc3e..1d0a0a2a9711 100644
> --- a/tools/arch/arm64/include/uapi/asm/kvm.h
> +++ b/tools/arch/arm64/include/uapi/asm/kvm.h
> @@ -362,6 +362,7 @@ struct kvm_arm_copy_mte_tags {
> #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_SET_PMU 3
> #define KVM_ARM_VCPU_TIMER_CTRL 1
> #define KVM_ARM_VCPU_TIMER_IRQ_VTIMER 0
> #define KVM_ARM_VCPU_TIMER_IRQ_PTIMER 1
> --
> 2.34.1
>
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