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

From: Catalin Marinas <[email-masked]>
Date: Wed, 14 Jun 2023 17:58:50 +0100

On Fri, Jun 09, 2023 at 10:01:02PM +0000, Oliver Upton wrote:
> 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: [email-masked]
> Cc: D Scott Phillips <[email-masked]>
> Cc: Darren Hart <[email-masked]>
> Signed-off-by: Oliver Upton <[email-masked]>

For the non-KVM bits in here:

Acked-by: Catalin Marinas <[email-masked]>

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