还是请你好好看看Intel自己是怎么说明VT-D技术实现的吧:
ntel VT-d enables protection by restricting direct memory access (DMA) of the devices to pre-assigned domains or physical memory regions. This is achieved by a hardware capability known as DMA-remapping. The VT-d DMA-remapping hardware logic in the chipset sits between the DMA capable peripheral I/O devices and the computer’s physical memory.