Re: [PATCH v2 3/4] KVM: arm64: Add KVM_ARM_VCPU_PMU_V3_SET_PMU attribute

[Reiji Watanabe <reijiw@google.com>]

Hi Alex,

On Mon, Dec 6, 2021 at 9:02 AM Alexandru Elisei
<alexandru.elisei@arm.com> 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@arm.com>
> ---
>  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
>
> _______________________________________________
> kvmarm mailing list
> kvmarm@lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm