Re: [PATCH 2/3] KVM: arm64: Set ID_{AA64PFR0,PFR1}_EL1.GIC when GICv3 is configured

[Oliver Upton <oliver.upton@linux.dev>]

On Mon, Oct 13, 2025 at 09:32:06AM +0100, Marc Zyngier wrote:
> Drive the idreg fields indicating the presence of GICv3 directly from
> the vgic code. This avoids having to do any sort of runtime clearing
> of the idreg.
> 
> Fixes: 5cb57a1aff755 ("KVM: arm64: Zero ID_AA64PFR0_EL1.GIC when no GICv3 is presented to the guest")
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/vgic/vgic-init.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
> index 4c3c0d82e4760..2c518b0a4d81b 100644
> --- a/arch/arm64/kvm/vgic/vgic-init.c
> +++ b/arch/arm64/kvm/vgic/vgic-init.c
> @@ -161,10 +161,16 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
>  
>  	kvm->arch.vgic.vgic_dist_base = VGIC_ADDR_UNDEF;
>  
> -	if (type == KVM_DEV_TYPE_ARM_VGIC_V2)
> +	*__vm_id_reg(&kvm->arch, SYS_ID_AA64PFR0_EL1) &= ~ID_AA64PFR0_EL1_GIC;
> +	*__vm_id_reg(&kvm->arch, SYS_ID_PFR1_EL1) &= ~ID_PFR1_EL1_GIC;

I'd prefer this to be done as a kvm_read_vm_id_reg() / kvm_set_vm_id_reg(),
if only to ensure this flow hits the config_lock lockdep assertion like
other writers of the ID registers.

Thanks,
Oliver