[PATCH v2 0/6] KVM: arm64: EL2 PMU handling fixes

[Oliver Upton]

On Wed, Apr 09, 2025 at 05:01:00PM +0100, Marc Zyngier wrote:
> Joey reports that some of his PMU tests do not behave quite as
> expected:
> 
> - MDCR_EL2.HPMN is set to 0 out of reset
> 
> - PMCR_EL0.P should reset all the counters when written from EL2
> 
> Oliver points out that setting PMCR_EL0.N from userspace by writing to
> the register is silly with NV, and that we need a new PMU attribute
> instead.
> 
> On top of that, I figured out that we had a number of little gotchas:
> 
> - It is possible for a guest to write an HPMN value that is out of
>   bound, and it seems valuable to limit it
> 
> - PMCR_EL0.N should be the maximum number of counters when read from
>   EL2, and MDCR_EL2.HPMN when read from EL0/EL1
> 
> - Prevent userspace from updating PMCR_EL0.N when EL2 is available
> 
> I haven't added any Cc stable, as NV is not functional upstream yet.

Similarly, I don't see a compelling reason for this to go in as a fix
for 6.15, especially since you're adding new UAPI. Do you mind grabbing
it for the next merge window?

With the comments addressed:

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

Thanks,
Oliver