Linux Xen Virtual Server: Xen is an open source virtual machine monitor (VMM) developed at the University of Cambridge to support operating systems (OSs) that have been modified to run on top of the monitor. Intel has extended the Xen VMM to use Intel Virtualization Technology (VT) to support unmodified guest OSs also. This was done for IA-32 Intel Architecture processors as well as Itanium architecture processors.

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ABSTRACT

Xen* is an open source virtual machine monitor (VMM) developed at the University of Cambridge to support operating systems (OSs) that have been modified to run on top of the monitor. Intel has extended the Xen VMM to use Intel® Virtualization Technology? (VT) to support unmodified guest OSs also. This was done for IA-32 Intel® Architecture processors as well as Itanium® architecture processors.

In this paper we describe the changes that have been made to Xen to enable this support. We also highlight the optimizations that have been made to date to deliver good virtualized performance.

INTRODUCTION

Xen is an open source virtual machine monitor (VMM) that allows the hardware resources of a machine to be virtualized and dynamically shared between OSs running on top of it [1]. Each virtual machine (VM) is called a Domain, in Xen terminology. Xen provides isolated execution for each domain, preventing failures or malicious activities in one domain from impacting another domain. The Xen hypervisor and Domain0 (Dom0) are a required part of any Xen-based server. Multiple user domains, called DomainU in Xen terminology, can be created to run guest OSs.

Unlike the full virtualization solutions offered by the IBM VM/370*, or VMware’s ESX* and Microsoft’s Virtual PC product*, Xen began life as a VMM for guest OSs that have been modified to run on the Xen hypervisor. User applications within these OSs run as is, i.e., unmodified. This technique is called “paravirtualization,” and it delivers near native performance for the guest OS, only if the guest OSs source code can be modified.

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