[PATCH 0/4] KVM: arm64: PMU: Fix PMUVer handling on heterogeneous PMU systems

[Marc Zyngier]

On Sat, 27 May 2023 05:02:32 +0100,
Reiji Watanabe <reijiw at google.com> wrote:
> 
> This series fixes issues with PMUVer handling for a guest with
> PMU configured on heterogeneous PMU systems.
> Specifically, it addresses the following two issues.
> 
> [A] The default value of ID_AA64DFR0_EL1.PMUVer of the vCPU is set
>     to its sanitized value.  This could be inappropriate on
>     heterogeneous PMU systems, as arm64_ftr_bits for PMUVer is defined
>     as FTR_EXACT with safe_val == 0 (when ID_AA64DFR0_EL1.PMUVer of all
>     PEs on the host is not uniform, the sanitized value will be 0).

Why is this a problem? The CPUs don't implement the same version of
the architecture, we don't get a PMU. Why should we try to do anything
better? I really don't think we should go out or out way and make the
code more complicated for something that doesn't really exist.

Or am I missing the problem altogether?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.