Re: [PATCH v8 04/13] KVM: arm64: PMU: Set PMCR_EL0.N for vCPU based on the associated PMU

[Sebastian Ott]

On Fri, 20 Oct 2023, Raghavendra Rao Ananta wrote:
> The number of PMU event counters is indicated in PMCR_EL0.N.
> For a vCPU with PMUv3 configured, the value is set to the same
> value as the current PE on every vCPU reset.  Unless the vCPU is
> pinned to PEs that has the PMU associated to the guest from the
> initial vCPU reset, the value might be different from the PMU's
> PMCR_EL0.N on heterogeneous PMU systems.
>
> Fix this by setting the vCPU's PMCR_EL0.N to the PMU's PMCR_EL0.N
> value. Track the PMCR_EL0.N per guest, as only one PMU can be set
> for the guest (PMCR_EL0.N must be the same for all vCPUs of the
> guest), and it is convenient for updating the value.
>
> To achieve this, the patch introduces a helper,
> kvm_arm_pmu_get_max_counters(), that reads the maximum number of
> counters from the arm_pmu associated to the VM. Make the function
> global as upcoming patches will be interested to know the value
> while setting the PMCR.N of the guest from userspace.
>
> KVM does not yet support userspace modifying PMCR_EL0.N.
> The following patch will add support for that.
>
> Signed-off-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
> Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>

Reviewed-by: Sebastian Ott <sebott@xxxxxxxxxx>