[PATCH 2/2] KVM: arm64: Contextualise the handling of PMCR_EL0.P writes

[Oliver Upton]

On Mon, Feb 17, 2025 at 11:24:12AM +0000, Marc Zyngier wrote:
> Contrary to what the comment says in kvm_pmu_handle_pmcr(),
> writing PMCR_EL0.P==1 has the following effects:
> 
> <quote>
> The event counters affected by this field are:
>   * All event counters in the first range.
>   * If any of the following are true, all event counters in the second
>     range:
>     - EL2 is disabled or not implemented in the current Security state.
>     - The PE is executing at EL2 or EL3.
> </quote>
> 
> where the "first range" represent the counters in the [0..HPMN-1]
> range, and the "second range" the counters in the [HPMN..MAX] range.
> 
> It so appears that writing P from EL2 should nuke all counters,
> and not just the "guest" view. Just do that, and nuke the misleading
> comment.
> 
> Reported-by: Joey Gouly <joey.gouly at arm.com>
> Signed-off-by: Marc Zyngier <maz at kernel.org>

Reviewed-by: Oliver Upton <oliver.upton at linux.dev>

Thanks,
Oliver