KVM: VMX: don't configure RM TSS for unrestricted guest

An unrestricted guest can run with CR0.PG==0 and/or CR0.PE==0,
e.g. it can run in Real Mode without requiring host emulation.
The RM TSS is only used for emulating RM, i.e. it will never
be used when unrestricted guest is enabled and so doesn't need
to be configured.
Signed-off-by: NSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/vmx.c

@@ -6044,6 +6044,9 @@ static int vmx_set_tss_addr(struct kvm *kvm, unsigned int addr)
 {
 	int ret;
 
+	if (enable_unrestricted_guest)
+		return 0;
+
 	ret = x86_set_memory_region(kvm, TSS_PRIVATE_MEMSLOT, addr,
 				    PAGE_SIZE * 3);
 	if (ret)