KVM: VMX: Preserve segment limit and access rights in real mode

While this is undocumented, real processors do not reload the segment
limit and access rights when loading a segment register in real mode.
Real programs rely on it so we need to comply with this behaviour.
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/vmx.c

@@ -3113,6 +3113,9 @@ static void vmx_get_segment(struct kvm_vcpu *vcpu,
 		if (seg == VCPU_SREG_TR
 		    || var->selector == vmx_read_guest_seg_selector(vmx, seg))
 			return;
+		var->base = vmx_read_guest_seg_base(vmx, seg);
+		var->selector = vmx_read_guest_seg_selector(vmx, seg);
+		return;
 	}
 	var->base = vmx_read_guest_seg_base(vmx, seg);
 	var->limit = vmx_read_guest_seg_limit(vmx, seg);