Re: [PATCH 1/2] KVM: arm64: Add PMU event filtering infrastructure

[Robin Murphy <robin.murphy@xxxxxxx>]

Hi Marc,

On 2020-02-14 6:36 pm, Marc Zyngier wrote:
[...]
> @@ -585,6 +585,14 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
>   	    pmc->idx != ARMV8_PMU_CYCLE_IDX)
>   		return;
>   
> +	/*
> +	 * If we have a filter in place and that the event isn't allowed, do
> +	 * not install a perf event either.
> +	 */
> +	if (vcpu->kvm->arch.pmu_filter &&
> +	    !test_bit(eventsel, vcpu->kvm->arch.pmu_filter))
> +		return;

If I'm reading the derivation of eventsel right, this will end up 
treating cycle counter events (aliased to SW_INCR) differently from 
CPU_CYCLES, which doesn't seem desirable.

Also, if the user did try to blacklist SW_INCR for ridiculous reasons, 
we'd need to special-case kvm_pmu_software_increment() to make it (not) 
work as expected, right?

Robin.

> +
>   	memset(&attr, 0, sizeof(struct perf_event_attr));
>   	attr.type = PERF_TYPE_RAW;
>   	attr.size = sizeof(attr);