Virtual Machine Monitor Execution Modes: in VMware vSphere 4.0
Prior to the introduction of hardware support for virtualization, the VMM could only use software techniques for virtualizing x86 processors and providing virtual hardware. This software approach, binary translation (BT), was used for instruction set virtualization and shadow page tables for memory management unit virtualization. Today, both Intel and AMD provide hardware support for CPU virtualization with Intel VT-x and AMD AMD-V, respectively. More recently they added support for memory management unit (MMU) virtualization with Intel EPT and AMD RVI. In the rest of this paper, the following are referred as follows: hardware support for CPU virtualization as hardware virtualization (HV), hardware support for MMU virtualization as hwMMU, and software memory management unit virtualization as swMMU.