[PATCH 1/3] arm64: errata: Mitigate Ampere1 erratum AC03_CPU_38 at stage-2

[D Scott Phillips]

Oliver Upton <oliver.upton at linux.dev> writes:

> AmpereOne has an erratum in its implementation of FEAT_HAFDBS that
> required disabling the feature on the design. This was done by reporting
> the feature as not implemented in the ID register, although the
> corresponding control bits were not actually RES0. This does not align
> well with the requirements of the architecture, which mandates these
> bits be RES0 if HAFDBS isn't implemented.
>
> The kernel's use of stage-1 is unaffected, as the HA and HD bits are
> only set if HAFDBS is detected in the ID register. KVM, on the other
> hand, relies on the RES0 behavior at stage-2 to use the same value for
> VTCR_EL2 on any cpu in the system. Mitigate the non-RES0 behavior by
> leaving VTCR_EL2.HA clear on affected systems.
>
> Cc: stable at vger.kernel.org
> Cc: D Scott Phillips <scott at os.amperecomputing.com>
> Cc: Darren Hart <darren at os.amperecomputing.com>
> Signed-off-by: Oliver Upton <oliver.upton at linux.dev>

Acked-by: D Scott Phillips <scott at os.amperecomputing.com>