Hardware-based Virtualization

DevX has an introductory article on Intel’s new hardware-based virtualization. Virtualization enable data centers to consolidate their hardware by running say, four servers on a server with 4-CPU.

Most operating systems need to operate the CPU at Ring 0. How does software-based virtualization like VMWare and VirtualPC get around this problem? A special driver is installed by VMWare or Virtual in the kernel that runs at ring 0, and does an expensive context-switch when the guest VM is run. Less than ideal, but it works.

Check out the article on software virtualization at ExtremeTech.

Hardware based virtualization solve the problem in a different way. Intel’s solution involves adding “VMX-root” and “VMX-non root” levels. It is not clear from the article whether this is orthogonal to the Ring-based privileged. Their idea is basically having the guest OS running under VMX-non root privileged, that way, when the guest OS attempts to access hardware, it is mediated by a process running as VMX-root.