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Ian Pratt - XenSource / University of Cambridge

Xen 3.0 and the Art of Virtualization

The Xen Virtual Machine Monitor will soon be undergoing its third major release. With support from Intel, HP, IBM and AMD, Xen is maturing into a stable, secure, and full-featured virtualization solution for Linux and other operating systems.

This new release of Xen supports a number of key new features, such as:

• SMP guest operating systems as well as SMP hosts;
• x86_64 suport, with further ports to ppc and ia-64 in progress;
• support for Intel`s forthcoming VT-x virtualization extensions, enabling Xen/Linux to host "legacy" OSes such as Windows XP

This paper reviews and explains some of Xen's key design features, with particular reference to Linux 2.6. The evolution of memory virtualisation techniques supported by Xen are compared and benchmarked. We discuss how Xen/Linux achieves high-performance IO virtualization by using zero-copy `device-channels` to move data between virtual machines. We then discuss our approach for supporting SMP guest OSes, and how modifications to Linux's spinlock code allow us to optimise scheduling of virtual CPUs.