[PATCH 07/20] KVM: arm64: Allow RES1 bits to be inferred from configuration

[Joey Gouly]

On Mon, Jan 26, 2026 at 12:16:41PM +0000, Marc Zyngier wrote:
> So far, when a bit field is tied to an unsupported feature, we set
> it as RES0. This is almost forrect, but there are a few exceptions

forrect is almost correct too!

> where the bits become RES1.
> 
> Add a AS_RES1 qualifier that instruct the RESx computing code to
> simply do that.
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>

Reviewed-by: Joey Gouly <joey.gouly at arm.com>

Thanks,
Joey

> ---
>  arch/arm64/kvm/config.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/config.c b/arch/arm64/kvm/config.c
> index 8d152605999ba..6a4674fabf865 100644
> --- a/arch/arm64/kvm/config.c
> +++ b/arch/arm64/kvm/config.c
> @@ -24,6 +24,7 @@ struct reg_bits_to_feat_map {
>  #define	CALL_FUNC	BIT(1)	/* Needs to evaluate tons of crap */
>  #define	FIXED_VALUE	BIT(2)	/* RAZ/WI or RAO/WI in KVM */
>  #define	MASKS_POINTER	BIT(3)	/* Pointer to fgt_masks struct instead of bits */
> +#define	AS_RES1		BIT(4)	/* RES1 when not supported */
>  
>  	unsigned long	flags;
>  
> @@ -1316,8 +1317,12 @@ struct resx __compute_fixed_bits(struct kvm *kvm,
>  		else
>  			match = idreg_feat_match(kvm, &map[i]);
>  
> -		if (!match || (map[i].flags & FIXED_VALUE))
> -			resx.res0 |= reg_feat_map_bits(&map[i]);
> +		if (!match || (map[i].flags & FIXED_VALUE)) {
> +			if (map[i].flags & AS_RES1)
> + 				resx.res1 |= reg_feat_map_bits(&map[i]);
> +			else
> +				resx.res0 |= reg_feat_map_bits(&map[i]);
> +		}
>  	}
>  
>  	return resx;
> -- 
> 2.47.3
>