[PATCH v20 09/14] KVM: arm64: Allow GCS to be enabled for guests

[Mark Brown]

On Wed, Sep 09, 2026 at 05:34:37PM +0100, Leonardo Bras wrote:
> On Tue, Sep 01, 2026 at 10:47:07PM +0100, Mark Brown wrote:

> > @@ -2193,10 +2193,12 @@ static u64 sanitise_id_aa64pfr1_el1(const struct kvm_vcpu *vcpu, u64 val)

> >  	val &= ~ID_AA64PFR1_EL1_THE;
> >  	val &= ~ID_AA64PFR1_EL1_MTEX;
> >  	val &= ~ID_AA64PFR1_EL1_PFAR;

> And here it says to only mask the feature bit if it's not available.

> IIUC this sanitize function is called when resetting a vcpu, is that right?

Yes.

> > @@ -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 |

> This one looks like to be a mask that's used to compare with 
> arm64_ftr_regs[] on arm64_check_features(). That seems to be called on 
> set_id_aa64pfr1_el1() which is used when we get an ioclt to set a system 
> register.

> So, basically, does it use this mask to check if the set value is valid?

Yes, this excludes values that are never supported.

> Reviewed-by: Leonardo Bras <leo.bras at arm.com>

Thanks!
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