HVM（Hardware-Assisted Virtualization）

A set of extra instructions is added that can be used by a process in VMX root
mode. These instructions do things like allocating a memory page on which to
store a full copy of the CPU state, start, and stop a VM. Finally, a set of bitmaps is
defined indicating whether a particular interrupt, instruction, or exception should
be passed to the virtual machine’s OS running in ring 0 or by the hypervisor
running in VMX root mode.

VT

Intel VT提供了一种新的运行模式（VMX root mode），可以理解为Ring -1。

同时提供几条新的指令，用来配置VMM的工作模式：

• 分配一个内存页，用来存放CPU state的一个完整拷贝
• 启动或者关闭一个VM
• 设置一个位图，其中的每一位用来表示哪些interrupt/instruction/exception应该由Ring 0层的操作系统来执行，哪些指令由Ring -1层的VMM来执行。