KVM: arm64: Enable nested for GICv5 host with FEAT_GCIE_LEGACY

Extend the NV check to pass for a GICv5 host that has
FEAT_GCIE_LEGACY. The has_gcie_v3_compat flag is only set on GICv5
hosts (that explicitly support FEAT_GCIE_LEGACY), and hence the
explicit check for a VGIC_V5 is omitted.

As of this change, vGICv3-based VMs can run with nested on a
compatible GICv5 host.

Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Sticklyman1936

arch/arm64/kvm/arm.c

@@ -2315,8 +2315,9 @@ static int __init init_subsystems(void)
 	}
 
 	if (kvm_mode == KVM_MODE_NV &&
-	   !(vgic_present && kvm_vgic_global_state.type == VGIC_V3)) {
-		kvm_err("NV support requires GICv3, giving up\n");
+		!(vgic_present && (kvm_vgic_global_state.type == VGIC_V3 ||
+				   kvm_vgic_global_state.has_gcie_v3_compat))) {
+		kvm_err("NV support requires GICv3 or GICv5 with legacy support, giving up\n");
 		err = -EINVAL;
 		goto out;
 	}