[PATCH v3] arm64: errata: Work around AmpereOne's erratum AC04_CPU_23

[Oliver Upton]

Hey D Scott,

On Thu, May 08, 2025 at 02:00:09PM -0700, D Scott Phillips wrote:
> On AmpereOne AC04, updates to HCR_EL2 can rarely corrupt simultaneous
> translations for data addresses initiated by load/store instructions.
> Only instruction initiated translations are vulnerable, not translations
> from prefetches for example. A DSB before the store to HCR_EL2 is
> sufficient to prevent older instructions from hitting the window for
> corruption, and an ISB after is sufficient to prevent younger
> instructions from hitting the window for corruption.
> 
> Signed-off-by: D Scott Phillips <scott at os.amperecomputing.com>

Overall looks good, still needs an entry in Documentation/arch/arm64/silicon-errata.rst
which Marc noted in v2.

With that addressed:

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

Thanks,
Oliver