Tag Archives: RC2

Xen Project 4.6 RC2 Test Day is September 1, 2015

Join 4.6 Release Candidate Testing on September 1, 2015

39833137_mAlthough the Xen Project performs automated testing through the project’s Test Lab, we also depend on manual testing of release candidates by our users. Our Test Days help insure that upcoming releases are ready for production. It is particularly important that our users test out the upcoming release in their own environment. In addition, functional testing of features (in particular those which can’t be automated), stress-testing, edge case testing and performance testing are important for a new release.

Xen 4.6 Release Candidate Testing

A few weeks ago, Xen 4.6 went into code freeze and Xen 4.6 RC2 is now ready for testing. With this in mind the Test Day for Xen 4.6 RC2 has been set for next Tuesday, September 1, 2015.

Subsequent Test Days are expected to be scheduled roughly ever other week until Xen 4.6 is ready for release.

Test Day Information

General Information about Test Days can be found here:

Join us on Tuesday in #xentest on Freenode IRC!
Test a Release Candidate! Help others, get help! And have fun!
If you can’t make Tuesday, remember that Test and Issue Reports are welcome any time.

Will you give Xen a ride … or will Xen give you a ride?

And by “a ride”, we actually mean a ride. Like this:



Like, will Xen run in your car?  Well, it appears it will!

It all started with ARM Support

In fact, Xen Project developers started woking on supporting the ARM architecture (with hardware virtualization capabilities) a couple of years ago. The goal was simple: as soon as ARM server are available, it must be possible to run Xen Project software on them. That goal has been achieved, but that is another story!

It is well known that processors employing the ARM architecture are powering already the vast majority of the so called Embedded Systems, ranging from phones, tablets and smart TVs up to cars or even airplanes. But does that mean that at some point we will start to see virtualization capable chips in cars? And if yes, when? The answers to these questions are “Yes” and “really really really soon”! In fact, the Xen Project Hypervisor is uniquely placed to support this new range of use-cases. Its isolation and security features, flexible virtualization mode and architecture, not to mention driver disaggregation and the fact that it now supports ARM (and does it with only ~90K lines of code), make it a perfect fit for the embedded world.

Some Recent ‘History’

Mobile and embedded virtualization on ARM has a long history within the Xen Project, with research projects such as Samsung’s ARM PV port and the Embedded Xen effort. However these projects were mainly research focused. With ARM support becoming a part of the Xen Project Hypervisor last year and various market factors coming together, Xen Project based products are now on the horizon. Last autumn was pivotal in generating momentum for this concept. A number of companies showed real demos and prototypes at our 2013 Developer Summit, such as

  • The Xen Project Hypervisor running on a Nexus 10 (slides and video)
  • The Xen Project Hypervisor powering an in-vehicle infotainment (IVI) system, and other systems on the TI Jacinto 6 automotive platform designed for cars (slides and video).

Since then, momentum has built within the community – as can be seen on xen-devel mailing list discussions – to port embedded OSes to the Xen Hypervisor  (some examples: FreeRTOS, Erika and QNX). Contributions and patches for making The Xen Project Hypervisor work better in such environments started to arrive too, from individuals, research institutions and small and big companies. Among the companies, GlobalLogic Inc., a full-lifecycle product development services company, has made the largest contribution so far, but we must also mention DornerWorks, GaloisUniversity of Washington and Evidence (in collaboration with the University of Modena).

A summary of the past and ongoing activities of this kind is below:

What about now?

On Monday (we told you: “really really really soon” :-D), The Xen Collaborative Project and The Linux Foundation announced a new Embedded and Automotive initiative. Artem Mygaiev, AVP Development at GlobalLogic, will serve as the Embedded and Automotive Project Lead.

The Embedded and Automotive team within The Xen Project intends to build a platform around the Xen Hypervisor that enables using it for all the non-data center use cases (automotive, internet TV, mobile, etc.) by providing a community focal-point within the Xen Project community as well as within the wider open source community.

The team plans to:

  • develop and upstream necessary changes to The Xen Project Hypervisor and Linux
  • implement new drivers (such as GPU, HID, …), protocols, capabilities and functionality that are needed for a complete automotive/embedded/mobile virtualization stack
  • upstream all necessary changes to support such functionality in operating systems that are needed for these use-cases (e.g. Android, Linux, etc.)

For the occasion, Alex Agizim, CTO of Embedded Systems at GlobalLogic, which also is a member of The Linux Foundation Automotive Grade Linux Steering Committee, said:

With ARM support, Xen Project technology is a perfect fit for embedded systems and automotive use. For example, our Nautilus platform, based on The Xen Project virtualization, enables ourin-vehicle infotainment (IVI) and auto manufacturing partners to quickly and cost-effectively develop hybrid Android/Linux-based systems. Using Nautilus, developers are able to run multiple sandboxed OSes on a single System-on-Chip (SOC). This provides superior functionality and security for both infotainment and operational functions within a car.

The latest demo of GlobalLogic‘s Nautilus Platform has been shown at the latest edition of the Automotive Linux Summit, in Tokyo. Check out the video and slides. We also heard about further use cases for Xen Project Software at this week’s Developer Summit. The rate of innovation in our community in this area is staggering: fasten your seat belts! We will tell you about these more in an upcoming event report. All this activity is also creating many benefits for the cloud and traditional server use use-cases. Certification will lead to quality improvements across shared components. Realtime scheduling can be used for graphics and gaming use-cases in the cloud and for Network Function Virtualization. And so on, and so on, …

Learn More

GlobalLogic, in partnership with The Linux Foundation, will present a free webinar at 9 a.m. PDT, Wednesday, August 27, 2014, titled “Virtualization in the Automotive Industry.” Register today to learn how Xen Project technology adds reliability and security when adopting virtualization for automotive software development.

Vendors and individual developers interested in collaborating on embedded, automotive and mobile use cases are encouraged to join the new Xen Project subproject at http://xenproject.org/developers/teams/embedded-and-automotive.html.

SWIOTLB by Morpheus

The following monologue explains how Linux drivers are able to program a device when running in a Xen virtual machine on ARM.

The problem that needs to be solved is that Xen on ARM guests run with second stage translation in hardware enabled. That means that what the Linux kernel sees as a physical address doesn’t actually correspond to a machine address. An additional translation layer is set by the hypervisor to do the conversion in hardware.

Many devices use DMA to read or write buffers in main memory and they need to be programmed with the addresses of the buffers. In the absence of an IOMMU, DMA requests don’t go through the same physical to machine translation set by the hypervisor for virtual machines, devices need to be programmed with machine addresses rather than physical addresses. Hence the problem we are trying to solve.

Definitions of some of the technical terms used in this article are available at the bottom of the page.

Given the complexity of the topic, we decided to ask for help to somebody with hands-on experience with teaching the recognition of the differences between “virtual” and “real”.


At last.
Please. Come. Sit.
Xen Project Matrix

Do you realize that everything running on Xen is a virtual machine — that Dom0, the OS from which you control the rest of the system, is just the first virtual machine created by the hypervisor? Usually Xen assigns all the devices on the platform to Dom0, which runs the drivers for them.

I imagine, right now, you must be feeling a bit like Alice, tumbling down the rabbit hole?
Let me tell you why you are here.

You are here because you want to know how to program a device in Linux on Xen on ARM.

Continue reading

Indirect descriptors for Xen PV disks

Some time ago Konrad Rzeszutek Wilk (the Xen Linux maintainer) came up with a list of possible improvements to the Xen PV block protocol, which is used by Xen guests to reduce the overhead of emulated disks.

This document is quite long, and the list of possible improvements is also not small, so we decided to go implementing them step by step. One of the first items that seemed like a good candidate for performance improvement was what is called “indirect descriptors”. This idea is borrowed from the VirtIO protocol, and to put it clear consists on fitting more data in a request. I am going to expand how is this done later in the blog post, but first I would like to speak a little bit about the Xen PV disk protocol in order to understand it better.

Xen PV disk protocol

The Xen PV disk protocol is very simple, it only requires a shared memory page between the guest and the driver domain in order to queue requests and read responses. This shared memory page has a size of 4KB, and is mapped by both the guest and the driver domain. The structure used by the fronted and the backend to exchange data is also very simple, and is usually known as a ring, which is a circular queue and some counters pointing to the last produced requests and responses.

Continue reading

Linux Stub-Domain

The “Normal” Case

To explain what is a Stub-Domain (often called stubdom), let’s start with the basics. When you start a new guest with Xen, you would need a Device Model which does some emulation if the guest does not have PV drivers. This is the case for an HVM domain.
This device model (which is QEMU), needs to run somewhere. By default it runs in the Dom0, as root.

Here is a picture:

Now, every time the guest do an IO, like reading a file on the disk, there is an event sends through Xen to the device model. It does the emulation and send the result to the guest.

Continue reading

Xen ARM in Linux!

Last weekend Linus Torvalds pulled the Xen on ARM patches in his Linux tree, so as of Saturday the 7th of October, we have Xen ARM in upstream Linux!

This makes Xen the first hypervisor supported by Linux on the ARM platform!

Working on ARM has been a very pleasant experience for me: the documentation of the hardware is well written and complete, the virtualization extensions are useful and fit our architecture very well, the ARM emulator comes with a nice debugger that helped me figure out some of the most difficult problems I had.

But beyond the hardware and the development tools, I was really impressed by how welcoming the Linux ARM Community has been to me: from the invite to the ARM session at the Kernel Summit, to the guidance through the upstreaming process and in general the feedback I received to my work. Nowadays, the Linux Community is usually perceived as not being friendly to newcomers, but it hasn’t certainly been the case for me! In particular I would like to thanks Arnd Bergmann, Marc Zyngier, and the Linaro folks. It has been great working with you. I would also like to thank Konrad Rzeszutek Wilk because he went out of his way to help me upstream my ARM work: I couldn’t have done it without him.

As the Xen on ARM patches were pulled by Linus, I was also appointed as Xen ARM maintainer in the Linux kernel. This is a new responsibility for me and I am not going to take it lightly. I am looking forward to work closely with Arnd, Russell, Konrad and the other Linux maintainers to make Linux the best operating system to run virtual machines and inside virtual machines on Xen on ARM!

What’s next

While Xen on ARM in Linux is certainly a major milestone, there are still a lot of things to do. Right now I am busy trying to run Xen on a Cortex A15 Versatile Express development platform while Ian Campbell already started the ARMv8 Xen port!
Stay tuned if you want to run Xen 64-bit on ARM.

See Also

If you are interested in the Xen on ARM project, you might want to read the slides of the presentation I gave at XenSummit 2012: