An Introduction to Xen:

Everyone close your eyes and touch the tip of your first finger to your thumb and chant softly

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History of virtualization development

1965 IBM M44/44X paging system

1965 IBM System/360-67 virtual memory hardware

1967 IBM CP-40 (January) and CP-67 (April) time-sharing

1972 IBM VM/370 run VM under VM

1997 Connectix First version of Virtual PC

1998 VMWare U.S. Patent 6,397,242

1999 VMware Virtual Platform for the Intel IA-32 architecture

2000 IBM z/VM

2001 Connectix Virtual PC for Windows

2003 Microsoft acquired Connectix

2003 EMC acquired Vmware

2003 VERITAS acquired Ejascent

2005 HP Integrity Virtual Machines

2005 Intel VT

2006 AMD VT

2005 XEN

2006 VMWare Server

2006 Virtual PC 2006

2006 HP IVM Version 2.0

2006 Virtual Iron 3.1

2007 InnoTek VirtualBox

2007 KVM in Linux Kernel

2007 XEN in Linux Kernel

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Definitions

Guest Operating System The operating system that Xen hosts

Domain The virtual machine under which a guest operating

system executes Guest OS and a domain similar to idea of a

program and a process Hypervisor

A particular Xen version which handles low level functionality

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Xen 3.0

Available from Xen Source (http://www.xensource.com)

In association with University of Cambridge (http://www.cl.cam.ac.uk/Research/SRG/netos/xen/)

Support for 64-Bit and 32-way machines Supports IntelVT Linux support only, Windows expected later this

year Open Source Product – One of the most actively

maintained projects in the open source community $ - Free

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Types of virtualization

Two categories exist Full Virtualization

Disco and VMWare Paravirtualization

Xen

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VMM Approach

In traditional VMM (Virtual Machine Monitor) the virtual hardware is functionally equivalent to the physical hardware Possibly difficult to implement (x86 systems in

particular) Potentially useful to provide real and virtual

resource information The “guest” machine would not have access to

this information

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Xen Approach

Virtual machine is NOT 100% functionally equivalent to the hardware

Xen uses paravirtualization instead Paravirtualization is a process where the guest

operating system is modified to run in parallel with other modified systems Advantage: Improved performance Disadvantage: The hosted operating system must

be modified before it can be hosted by the Xen Hypervisor (can be difficult)

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Xen Design

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Xen Implementation

What Xen does differently-- CPU

Virtualization of the CPU CPU Scheduling Time & Timers

Memory Management Virtual Address Translation Physical Memory

Device I/O Network Disk

Control Transfer

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CPU

Most change is required here by the guest OS

Xen takes exception to the basic idea that an OS is the most privileged

Privileged instructions Instructions are paravirtualized by requiring to

be validated/executed within Xen

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CPU Virtualization

Virtualization easier with x86

Why? Has built in security

levels (Rings 0, 1, 2, 3)

Ring 0 – OS Software (most privileged)

Ring 3 – User software

Ring 1 & 2 – Not used Xen modifies the OS to

execute on Ring 1

Increasing Privilege Level

Ring 0

Ring 1

Ring 2

Ring 3

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Hypervisor Control

In Xen Domain0 is given

greater access to the hardware and the hypervisor. It has: A guest OS running

above the domain Hypervisor Manager

software to manage elements within other existing domains.

In VMWare Host OS acts

underneath the domain.

Host Operating System

VMWare Drivers

Other Drivers

Guest OS

VMWare

Guest OS

VM VM

VM Specific Drivers

VM Specific Drivers

Guest OS on Domain 0

Hypervisor

Domain 0

Hypervisor Manager

Guest OS on Domain X

Domain 1

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Currently Xen patches the kernel. Future processors will support virtualization

so that the kernel can run on it unpatched. For example,

Both Intel VT and AMD Pacifica processors will include such support.

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Xen

Xen already is bundled in some distributions,

Fedora Core 4, Debian and SuSE Professional 9.3

And it will be included in RHEL5. The Fedora Project has RPMs for installing Xen, and other Linux distros have prepared installation packages for Xen as well.

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DONE

Questions