Re: [PATCH] KVM: arm64: Change default caching mode for {PEND, PROP}BASER.outer

[Marc Zyngier <maz@kernel.org>]

On Wed, 01 Jul 2020 15:02:06 +0100,
Alexander Graf <graf@amazon.com> wrote:
> 
> PENDBASER and PROPBASER define the outer caching mode for LPI tables.
> The memory backing them may not be outer sharable, so we mark them as nC
> by default. This however, breaks Windows on ARM which only accepts
> SameAsInner or RaWaWb as values for outer cachability.
> 
> We do today already allow the outer mode to be set to SameAsInner
> explicitly, so the easy fix is to default to that instead of nC for
> situations when an OS asks for a not fulfillable cachability request.
> 
> This fixes booting Windows in KVM with vgicv3 and ITS enabled for me.
> 
> Signed-off-by: Alexander Graf <graf@amazon.com>
> ---
>  arch/arm64/kvm/vgic/vgic-mmio-v3.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> index d2339a2b9fb9..5c786b915cd3 100644
> --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> @@ -389,7 +389,7 @@ u64 vgic_sanitise_outer_cacheability(u64 field)
>  	case GIC_BASER_CACHE_nC:
>  		return field;
>  	default:
> -		return GIC_BASER_CACHE_nC;
> +		return GIC_BASER_CACHE_SameAsInner;
>  	}
>  }
>  

I am going to provisionally queue this for 5.9, with the explicit
reserve that it will be reverted if it causes a regression for other
guests (as this is an observable change in behaviour).

Thanks,

	M.

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