Re: [PATCH v21 09/15] KVM: arm64: Allow GCS to be enabled for guests

[Lorenzo Stoakes (ARM)]

On Wed, Sep 30, 2026 at 10:48:19PM +0100, Mark Brown wrote:
> Now that required functionality for GCS is in place expose
> ID_AA64PFR1_EL1.GCS, allowing guests to be given the feature.
>
> Reviewed-by: Leonardo Bras <leo.bras@xxxxxxx>
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>

This looks straightforward and sensible so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---
>  arch/arm64/kvm/nested.c   | 3 +--
>  arch/arm64/kvm/sys_regs.c | 5 +++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index 3c4fc566eafc..f62d9ab7f31c 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -1702,11 +1702,10 @@ u64 limit_nv_id_reg(struct kvm *kvm, u32 reg, u64 val)
>  		break;
>
>  	case SYS_ID_AA64PFR1_EL1:
> -		/* Only support BTI, SSBS, CSV2_frac */
> +		/* Only support GCS, BTI, SSBS, CSV2_frac */
>  		val &= ~(ID_AA64PFR1_EL1_PFAR		|
>  			 ID_AA64PFR1_EL1_MTEX		|
>  			 ID_AA64PFR1_EL1_THE		|
> -			 ID_AA64PFR1_EL1_GCS		|
>  			 ID_AA64PFR1_EL1_MTE_frac	|
>  			 ID_AA64PFR1_EL1_NMI		|
>  			 ID_AA64PFR1_EL1_SME		|
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index faecf4657ec5..5de4ba1bef6b 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -2193,10 +2193,12 @@ static u64 sanitise_id_aa64pfr1_el1(const struct kvm_vcpu *vcpu, u64 val)
>  	      SYS_FIELD_GET(ID_AA64PFR0_EL1, RAS, pfr0) == ID_AA64PFR0_EL1_RAS_IMP))
>  		val &= ~ID_AA64PFR1_EL1_RAS_frac;
>
> +	if (!system_supports_gcs())
> +		val &= ~ID_AA64PFR1_EL1_GCS;
> +
>  	val &= ~ID_AA64PFR1_EL1_SME;
>  	val &= ~ID_AA64PFR1_EL1_RNDR_trap;
>  	val &= ~ID_AA64PFR1_EL1_NMI;
> -	val &= ~ID_AA64PFR1_EL1_GCS;
>  	val &= ~ID_AA64PFR1_EL1_THE;
>  	val &= ~ID_AA64PFR1_EL1_MTEX;
>  	val &= ~ID_AA64PFR1_EL1_PFAR;
> @@ -3444,7 +3446,6 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  				     ~(ID_AA64PFR1_EL1_PFAR |
>  				       ID_AA64PFR1_EL1_MTEX |
>  				       ID_AA64PFR1_EL1_THE |
> -				       ID_AA64PFR1_EL1_GCS |
>  				       ID_AA64PFR1_EL1_MTE_frac |
>  				       ID_AA64PFR1_EL1_NMI |
>  				       ID_AA64PFR1_EL1_RNDR_trap |
>
> --
> 2.47.3
>
>

--
Cheers, Lorenzo