Xen High-Performance x86 Virtualization Released

Xen Team writes "The University of Cambridge Computer Laboratory Systems Research Group is pleased to announce the open source release of Xen, a virtual machine monitor for x86. Xen lets you run multiple operating system images at the same time on the same PC hardware, with unprecedented levels of performance and resource isolation. Even under the most demanding workloads the performance overhead is just a few percent --- considerably less than alternatives such as VMware Workstation and User Mode Linux. This makes Xen ideal for use in providing secure virtual hosting, or even just for running multiple OSes on a desktop machine."

The Xen team continues: "Xen requires guest operating systems to be ported to run over it. Crucially, only the kernel needs to be ported, and all user-level application binaries and libraries can run unmodified. We have a fully functional port of Linux 2.4.22 running over Xen, and regularly use it for running demanding applications like Apache, PostgreSQL and Mozilla. Any Linux distribution should run unmodified over the ported kernel. With assistance from Microsoft Research, we have a port of Windows XP to Xen nearly complete, and are planning a FreeBSD 4.8 port in the near future.

"Visit the project homepage to find out more, and download the project source code or the XenDemoCD, a bootable 'live iso' image that enables you to play with Xen/Linux 2.4 without needing to install it on your hard drive. The CD also contains full source code, build tools, and benchmarks. Our SOSP paper gives an overview of the design of Xen, and evaluates the performance against other virtualization techniques.

"Work on Xen is supported by UK EPSRC grant GR/S01894, Intel Research Cambridge, and Microsoft Research Cambridge via an Embedded XP IFP award."

Re:I bet it's not Open Source...

[Zigg]

RTFA. It's GPL.

(waiting for the 20 second delay to expire... @#%$! Slashdot)

Interesting ..

[Anonymous Coward]

I'm really surprised they got assistance for windows XP. You'd think that Microsoft would want to stay well clear of anything linked to the GPL.

I guess such assumptions are incorrect, and quite probably a result of reading Slashdot too much!

Not really like VMWare

[javatips]

We have a fully functional port of Linux 2.4 running over Xen

With assistance from Microsoft Research, we have a port of Windows XP to Xen nearly complete, and are planning a FreeBSD 4.8 port in the near future (volunteers welcome!).

If one need to port an OS to make it work within Xen, then I will NOT compare it to VMWare. VMare can run your stock OS on a VM whithout the need to tweak it.

The performance advantage it has over VMWare is probably related to that. By having a few restriction on the OS, they can probably offer better performances.

so its just an extra layer of abstraction?

[ikoleverhate]

So really, this is just an abstraction layer that means even the OS is unaware it's sharing hardware, so in theory theres no way for a malicious user to take advantage of other users. Pretty cool in a boring and limited sort of way. Kudos to the team who did it, I'm sure it's a real technological challenge. Not what the /. headline promised though ;)

Re:Interesting ..

[sjwt]

I dont know about it being becase you read too much /. , but i think the reson they would be willing to help is that this would look realy good in any future AnitTrust case..

"your honnor, we have helped the open source comunity devolpe a program that meens anyone can run any OS along side MS with out any problems, we dont see how you can accuse us of being Anti competive when we allow others to compeat on the same machene"

could you even imagen a futer MS install CD where it automaticly installs a VM *inx?

Re:MOL for x86?

[tgd]

This would not allow you to run Windows under Linux... it would allow you to run Windows and Linux under Xen, which is not nearly the same thing.

Contrary to the submitter's comments, this product is nothing like VMWare.

Re:Pfff

[kzinti]

In being so quick to chastise the guy for not reading the article, you missed the point. If anything at all needs to be ported, it means that an OS like XP can't be installed on Xen out of the box. It means that a port of the XP kernel has to be completed, and that MS has to authorize the ported kernel to be distributed. For lots of folks, this is not good enough... even assuming that MS ever would allow the ported kernel to be distributed (and then we have to worry about activation issues too). So, while Xen is great for allowing linux users to run multiple distros at max performance at the same time, it doesn't much help someone who wants to run XP, and might never help them. Those folks still have to resort to VMWare or Bochs.

Pfff...

xp licence/activation .

[leuk_he]

If they ever release the XP binary you will have to bet that it will be some hight priced version of xp that runs it. Or else you will run into all kind of license problems.

If it will be a concurrent of The virtual machine solution they bought from connectix [microsoft.com] This will not be released.

And if it will work with a standard XP home/pro you will have all kind of activation [vmware.com] loopholes like in vmware.

Re:Pfff

[beezly]

The license used to enable them to do this modification isn't the Shared Source License, it's the Microsoft Academic Source License. It's completely different.

Re:How many licenses per machine?

[steve_l]

I think it is something they havent had to deal with yet.

I am running Win2K+visual studio in one vmware vm right now; I can bring up Win2K3 to run office 2003 when I need to go on exchange. But with the block MSDN license *and* a volume 'no activation' key for XP, office, etc. I get to skip activation.

But imagine if I did have to activate stuff everytime I rebuilt a new VM? Within a month I'd have the activation police complaining I'd activated onto 5+ systems, and that therefore I was violating some license.

Yet at the same time, a VM image, once activated, can be shared and of VMware makes all the hardware look the same, the system doesnt have to think you need reactivation.

So legitimate users of activated apps under a VM will suffer -we have to go through reactivation grief- yet there is now a new way to bypass activation -ship an image of the OS+apps already activated; you just run it in a window.

I dont know how long it will take the 'activation' police to deal with it.

Great Idea! Why all the whining?

[HopeOS]

The x86 architecture is not designed to be virtualized, at least not for code expecting to run in ring 0. The work that VMWare must do to emulate ring 0 without the guest OS coming unglued is simply daunting, including traps for every detail from setting and clearing interrupts to modifying page tables. A lot of that work requires predicting code execution paths and dynamically modifying the code at runtime. It's a real nightmare.

Plex86 promised to provide an open-source solution to this problem, but the last time I checked (which admittedly was awhile ago), they were planning on using bochs to emulate ring 0. This is not exactly satisfactory, but I don't blame them. It's a hard problem, one for which VMWare is entitled and deserving of reward for having solved.

So how do you get real virtual host performance out of your x86 machine? You design around the flaw. Operating systems that are written to run in ring 1 and call the Xen hypervisor instead of performing ring 0 functions will run at nearly full speed. Those that do not or will not make these compromises will see at best, an emulated ring 0. It's really that simple.

Personally, I don't see much value in being able to run any arbitrary operating system in a single environment if it's impossible to get real, sustained performance out of it. Cross-platform testing: sure. Kernel debugging: certainly. But host virtualization? What I want is the capability of running multiple hosts simultaneously, and if the operating system needs delibrate tweaking to make this possible, then obviously that's the direction to go.

To answer the gripes of people who want just that transparent hosting of unmodified OSes, it would be interesting to see a follow-on project for dynamically modifying the guest OS to thunk-out all the privileged calls to use the Xen extensions directly rather than trapping exceptions as they do now. This would probably not work well for page tables modifications, so a hybrid system might be employed. In this fashion, the best of both worlds may be achieved.


-Hope

Why Is This So Hard?

[Chasuk]

Is it really that fucking difficult to write an accurate summary?

A person reads the summary, and reasonably thinks:
"Great! An Open Source equivalent of VMware Workstation! Now I'll be able to run multiple OS's on my Desktop machine without the expense!"

Then he reads:

"Xen requires guest operating systems to be ported to run over it..."

This changes the picture dramatically, and should have appeared MUCH earlier in the summary.

Come on, I know this is only Slashdot, but stupidity and dishonesty like this get really annoying.