KVM: nVMX: allow setting the VMFUNC controls MSR

Allow userspace to set a custom value for the VMFUNC controls MSR, as long
as the capabilities it advertises do not exceed those of the host.

Fixes: 27c42a1b ("KVM: nVMX: Enable VMFUNC for the L1 hypervisor", 2017-08-03)
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -1234,6 +1234,11 @@ int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
 	case MSR_IA32_VMX_VMCS_ENUM:
 		vmx->nested.msrs.vmcs_enum = data;
 		return 0;
+	case MSR_IA32_VMX_VMFUNC:
+		if (data & ~vmx->nested.msrs.vmfunc_controls)
+			return -EINVAL;
+		vmx->nested.msrs.vmfunc_controls = data;
+		return 0;
 	default:
 		/*
 		 * The rest of the VMX capability MSRs do not support restore.