
171Virtualization
TheguestOSresides at ring 1 and has the least privilege than the hyper-
visor. Hence, the OS cannot communicate to the physical infrastruc-
ture directly. It requires the help of hypervisors to communicate with
the underlying infrastructure. The user applications reside at ring 3, as
shown in Figure 7.10. This approach uses binary translationand direct
executiontechniques. Binary translation is used to translate nonvirtual-
ized guest OS instructions with new sequences of instructions that have
the same intended effect on the virtual infrastructure. On the other hand,
direct execution is used for user application requests ...