On Mon, Jun 02, 2025 at 07:27:01PM +0000, Colton Lewis wrote:
> + case KVM_ARM_PARTITION_PMU: {
This should be a vCPU attribute similar to the other PMUv3 controls we
already have. Ideally a single attribute where userspace tells us it
wants paritioning and specifies the PMU ID to use. None of this can be
changed after INIT'ing the PMU.
> + struct arm_pmu *pmu;
> + u8 host_counters;
> +
> + if (unlikely(!kvm_vcpu_initialized(vcpu)))
> + return -ENOEXEC;
> +
> + if (!kvm_pmu_partition_supported())
> + return -EPERM;
> +
> + if (copy_from_user(&host_counters, argp, sizeof(host_counters)))
> + return -EFAULT;
> +
> + pmu = vcpu->kvm->arch.arm_pmu;
> + return kvm_pmu_partition(pmu, host_counters);
Yeah, we really can't be changing the counters available to the ARM PMU
driver at this point. What happens to host events already scheduled on
the CPU?
Either the partition of host / KVM-owned counters needs to be computed
up front (prior to scheduling events) or KVM needs a way to direct perf
to reschedule events on the PMU based on the new operating constraints.
Thanks,
Oliver
