KVM: PPC: Book3S HV: Allow HV module to load without hypervisor mode

With this, the KVM-HV module can be loaded in a guest running under
KVM-HV, and if the hypervisor supports nested virtualization, this
guest can now act as a nested hypervisor and run nested guests.

This also adds some checks to inform userspace that HPT guests are not
supported by nested hypervisors (by returning false for the
KVM_CAP_PPC_MMU_HASH_V3 capability), and to prevent userspace from
configuring a guest to use HPT mode.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kvm/book3s_hv.c

@@ -4811,11 +4811,15 @@ static int kvmppc_core_emulate_mfspr_hv(struct kvm_vcpu *vcpu, int sprn,
 
 static int kvmppc_core_check_processor_compat_hv(void)
 {
-	if (!cpu_has_feature(CPU_FTR_HVMODE) ||
-	    !cpu_has_feature(CPU_FTR_ARCH_206))
-		return -EIO;
+	if (cpu_has_feature(CPU_FTR_HVMODE) &&
+	    cpu_has_feature(CPU_FTR_ARCH_206))
+		return 0;
 
-	return 0;
+	/* POWER9 in radix mode is capable of being a nested hypervisor. */
+	if (cpu_has_feature(CPU_FTR_ARCH_300) && radix_enabled())
+		return 0;
+
+	return -EIO;
 }
 
 #ifdef CONFIG_KVM_XICS
@@ -5133,6 +5137,10 @@ static int kvmhv_configure_mmu(struct kvm *kvm, struct kvm_ppc_mmuv3_cfg *cfg)
 	if (radix && !radix_enabled())
 		return -EINVAL;
 
+	/* If we're a nested hypervisor, we currently only support radix */
+	if (kvmhv_on_pseries() && !radix)
+		return -EINVAL;
+
 	mutex_lock(&kvm->lock);
 	if (radix != kvm_is_radix(kvm)) {
 		if (kvm->arch.mmu_ready) {

arch/powerpc/kvm/powerpc.c

@@ -594,7 +594,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		r = !!(hv_enabled && radix_enabled());
 		break;
 	case KVM_CAP_PPC_MMU_HASH_V3:
-		r = !!(hv_enabled && cpu_has_feature(CPU_FTR_ARCH_300));
+		r = !!(hv_enabled && cpu_has_feature(CPU_FTR_ARCH_300) &&
+		       cpu_has_feature(CPU_FTR_HVMODE));
 		break;
 #endif
 	case KVM_CAP_SYNC_MMU: