64位模式 Limit取消，因此IDTR GDTR Limit值填入实际的值（Nx16)比较靠谱,不需要像32位模式下还要减一（Nx8-1)
<intel 手册第三卷 第五章 保护>
5.3.1 Limit Checking in 64-bit Mode
In 64-bit mode, the processor does not perform runtime limit checking on code or data segments. However, theprocessor does check descriptor-table limits.