RISC-V: KVM: Treat SBI HFENCE calls as NOPs

We should treat SBI HFENCE calls as NOPs until nested virtualization
is supported by KVM RISC-V. This will help us test booting a hypervisor
under KVM RISC-V.
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

arch/riscv/kvm/vcpu_sbi_replace.c

@@ -117,7 +117,11 @@ static int kvm_sbi_ext_rfence_handler(struct kvm_vcpu *vcpu, struct kvm_run *run
 	case SBI_EXT_RFENCE_REMOTE_HFENCE_GVMA_VMID:
 	case SBI_EXT_RFENCE_REMOTE_HFENCE_VVMA:
 	case SBI_EXT_RFENCE_REMOTE_HFENCE_VVMA_ASID:
-	/* TODO: implement for nested hypervisor case */
+		/*
+		 * Until nested virtualization is implemented, the
+		 * SBI HFENCE calls should be treated as NOPs
+		 */
+		break;
 	default:
 		ret = -EOPNOTSUPP;
 	}