[PATCH v7 07/20] KVM: arm64: Set up FGT for Partitioned PMU

[Colton Lewis]

Hi Oliver. Thanks for the review.

Oliver Upton <oupton at kernel.org> writes:

> On Mon, May 04, 2026 at 09:18:00PM +0000, Colton Lewis wrote:
>> +static void __compute_hdfgrtr(struct kvm_vcpu *vcpu)
>> +{
>> +	__compute_fgt(vcpu, HDFGRTR_EL2);
>> +
>> +	*vcpu_fgt(vcpu, HDFGRTR_EL2) |=
>> +		HDFGRTR_EL2_PMOVS
>> +		| HDFGRTR_EL2_PMCCFILTR_EL0
>> +		| HDFGRTR_EL2_PMEVTYPERn_EL0
>> +		| HDFGRTR_EL2_PMCEIDn_EL0
>> +		| HDFGRTR_EL2_PMMIR_EL1;
>> +}
>> +

> I've given this feedback at least twice already...

> Operators go on the preceding line in the case of line continuations.

I apologize for letting that slip through again.

>> +
>> +/**
>> + * kvm_pmu_is_partitioned() - Determine if given PMU is partitioned
>> + * @pmu: Pointer to arm_pmu struct
>> + *
>> + * Determine if given PMU is partitioned by looking at hpmn field. The
>> + * PMU is partitioned if this field is less than the number of
>> + * counters in the system.
>> + *
>> + * Return: True if the PMU is partitioned, false otherwise
>> + */
>> +bool kvm_pmu_is_partitioned(struct arm_pmu *pmu)
>> +{
>> +	if (!pmu)
>> +		return false;
>> +
>> +	return pmu->max_guest_counters >= 0 &&
>> +		pmu->max_guest_counters <= *host_data_ptr(nr_event_counters);
>> +}
>> +
>> +/**
>> + * kvm_vcpu_pmu_is_partitioned() - Determine if given VCPU has a  
>> partitioned PMU
>> + * @vcpu: Pointer to kvm_vcpu struct
>> + *
>> + * Determine if given VCPU has a partitioned PMU by extracting that
>> + * field and passing it to :c:func:`kvm_pmu_is_partitioned`
>> + *
>> + * Return: True if the VCPU PMU is partitioned, false otherwise
>> + */
>> +bool kvm_vcpu_pmu_is_partitioned(struct kvm_vcpu *vcpu)
>> +{
>> +	return kvm_pmu_is_partitioned(vcpu->kvm->arch.arm_pmu) &&
>> +		false;
>> +}

> Ok, I'm thoroughly confused about these predicates.

> Whether or not a vCPU is using a partitioned PMU is a per-VM property.
> This is separate from whether or not the backing arm_pmu has a range of
> available counters for the guest to use.

> It is entirely possible that a VM *isn't* using the partitioned PMU
> feature (i.e. backed with perf events) yet the supporting arm_pmu has a
> guest counter range.

Yes and I add that to this predicate in a later patch when I introduce
the flag. I can always reorder to introduce the flag before (or along
with) this predicate.

>> +#if !defined(__KVM_NVHE_HYPERVISOR__)
>> +bool kvm_vcpu_pmu_is_partitioned(struct kvm_vcpu *vcpu);
>> +bool kvm_vcpu_pmu_use_fgt(struct kvm_vcpu *vcpu);
>> +#else
>> +static inline bool kvm_vcpu_pmu_is_partitioned(struct kvm_vcpu *vcpu)
>> +{
>> +	return false;
>> +}
>> +
>> +static inline bool kvm_vcpu_pmu_use_fgt(struct kvm_vcpu *vcpu)
>> +{
>> +	return false;
>> +}
>> +#endif
>> +

> Don't use ifdeffery for this. Aim to have a single definition and rely
> on has_vhe() to do the rest of the work.

Will do.


> Thanks,
> Oliver