At this point, you can see that there is a lot of effort for putting all of this to work. In fact, this architecture is only possible because hardware and software companies worked together in the past. The main goal of both type of companies was to enable virtualization of operating systems without changing them.
Intel and AMD created, each one with its own implementation, a processor feature called virtualization assistance so that the Hypervisor could run on Ring 0, as explained before. But this is just the first requirement. There are other requirement as well, which are as follows: