Xen on Raspberry Pi 4

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The Xen Mission is labored as a lot as portion that the Xen Hypervisor now runs on Raspberry Pi. Right here’s an exhilarating step for every and every hobbyists and industries. Read extra to gain out about how Xen now runs on RPi and the map to birth. 

Written by Stefano Stabellini and Roman Shaposhnik, at the birth posted on Linux.com

Raspberry Pi (RPi) has been a key enabling tool for the Arm neighborhood for years, given the low tag and neatly-liked adoption. Consistent with the RPi Foundation, over 35 million were offered, with 44% of these offered into change. We have got the least bit times been alive to to safe the Xen hypervisor working on it, however technical variations between RPi and somewhat about a Arm platforms made it impractical for the longest time. Namely, a non-long-established interrupt controller with out virtualization give a enhance to.

Then the Raspberry Pi 4 came along, along with a long-established GIC-400 interrupt controller that Xen supports out of the box. Finally, we could well escape Xen on an RPi tool. Soon Roman Shaposhnik of Mission EVE and some somewhat about a neighborhood participants started asking about it on the xen-devel mailing list. “It needs to be easy,” we answered. “It goes to even figure out of the box,” we wrote in our acknowledge. We had been fully oblivious that we had been about to embark on an adventure deep in the belly of the Xen memory allocator and Linux take care of translation layers.

The first hurdle was once the provision of low memory addresses. RPi4 has devices that can handiest safe admission to the first 1GB of RAM. The quantity of memory below 1GB in Dom0 was once no longer passable. Julien Grall solved this area with a straightforward one-line repair to expand the memory allocation below 1GB for Dom0 on RPi4. The patch is now prove in Xen 4.14.

“This decrease-than-1GB limitation is distinctive, however now that it is miles mounted, it is miles correct going to work.” We had been outrageous all over again. The Xen subsystem in Linux uses virt_to_phys to rework virtual addresses to bodily addresses, which works for most virtual addresses however no longer all. It turns out that the RPi4 Linux kernel would on occasion trot virtual addresses that can’t be translated to bodily addresses the exhaust of virt_to_phys, and doing so would lead to necessary errors. The repair was once to make exhaust of a clear take care of translation objective when acceptable. The patch is now prove in Linux’s grasp branch.

We felt assured that we in the raze reached the tip of the line. “Memory allocations – check. Memory translations — check. We are correct to head!” No, no longer yet. It turns out that the most necessary area was once yet to be found. The Linux kernel has the least bit times had the belief of bodily addresses and DMA addresses, the build DMA addresses are old to program devices and have to be somewhat about a from bodily addresses. In apply, no longer surely one of many x86, ARM, and ARM64 platforms the build Xen could well escape had DMA addresses somewhat about a from bodily addresses. The Xen subsystem in Linux is exploiting the DMA/bodily take care of duality for its have take care of translations. It uses it to rework bodily addresses, as considered by the guest, to bodily addresses, as considered by Xen.

To our surprise and astonishment, the Raspberry Pi 4 was once the very first platform to have bodily addresses somewhat about a from DMA addresses, causing the Xen subsystem in Linux to destroy. It wasn’t easy to slim down the subject. Once we understood the subject, a dozen patches later, we had beefy give a enhance to for handling DMA/bodily take care of conversions in Linux. The Linux patches are in grasp and have to be on hand in Linux 5.9.

Fixing the take care of translation area was once the tip of our fun hacking adventure. With the Xen and Linux patches utilized, Xen and Dom0 work flawlessly. Once Linux 5.9 is out, we can have Xen engaged on RPi4 out of the box.

We can reduction you escape Xen on RPi4, the accurate Xen hacker map, and as portion of a downstream distribution for a a lot more uncomplicated conclude-user skills.

Hacking Xen on Raspberry Pi 4

Even as you realizing to hack on Xen on ARM and would purchase to make exhaust of the RPi4 to achieve it, right here’s what or no longer it is essential to achieve to safe Xen up and working the exhaust of UBoot and TFTP. I purchase to make exhaust of TFTP because it makes it extraordinarily hasty to change any binary in the center of trend.  Have confidence this tutorial on how to self-discipline up and configure a TFTP server. You furthermore want a UART connection to safe early output from Xen and Linux; please relate over with this text.

Exercise the rpi-imager to format an SD card with the long-established default Raspberry Pi OS. Mount the first SD card partition and edit config.txt. Originate determined that to add the next:




Web a lawful UBoot binary for RPi4 (u-boot.bin) from any distro, for event OpenSUSE. Web the JeOS enlighten, then open it and repair u-boot.bin:

    xz -d 

   kpartx -a 

    mount /dev/mapper/loop0p1 /mnt
    cp /mnt/u-boot.bin /tmp

Space u-boot.bin in the first SD card partition along with config.txt. Next time the design boots, it is advisable to well safe a UBoot advised that capacity that you just can load Xen, the Linux kernel for Dom0, the Dom0 rootfs, and the tool tree from a TFTP server over the network. I automated the loading steps by placing a UBoot boot.scr script on the SD card:

    setenv serverip

    setenv ipaddr

    tftpb 0xC00000 boot2.scr

    source 0xC00000

The build:

serverip is the IP of your TFTP server

ipaddr is the IP of the RPi4

Exercise mkimage to generate boot.scr and location it next to config.txt and u-boot.bin:

   mkimage -T script -A arm64 -C none -a 0x2400000 -e 0x2400000 -d boot.source boot.scr

The build:

boot.source is the input

boot.scr is the output

UBoot will mechanically function the offered boot.scr, which items up the network and fetches a second script (boot2.scr) from the TFTP server. boot2.scr have to near with the total instructions to load Xen and the somewhat about a required binaries. You should well well presumably generate boot2.scr the exhaust of ImageBuilder.

Originate determined that to make exhaust of Xen 4.14 or later. The Linux kernel needs to be grasp (or 5.9 when it is miles out, 5.4-rc4 works.) The Linux ARM64 default config works gleaming as kernel config. Any 64-bit rootfs have to work for Dom0. Exercise the tool tree that incorporates upstream Linux for RPi4 (arch/arm64/boot/dts/broadcom/bcm2711-rpi-4-b.dtb). RPi4 has two UARTs; the default is bcm2835-aux-uart at take care of 0x7e215040. It is specified as “serial1” in the tool tree in desire to serial0. You should well well presumably checklist Xen to make exhaust of serial1 by specifying on the Xen teach line:

  console=dtuart dtuart=serial1 sync_console

The Xen teach line is equipped by the boot2.scr script generated by ImageBuilder as “xen,xen-bootargs“. After editing boot2.source it is advisable to well regenerate boot2.scr with mkimage:

 mkimage -A arm64 -T script -C none -a 0xC00000 -e 0xC00000 -d boot2.source boot2.scr

Xen on Raspberry Pi 4: an easy button

Getting your fingers soiled by constructing and booting Xen on Raspberry Pi 4 from scratch will doubtless be no longer handiest deeply gratifying however can furthermore give you numerous insight into how every thing suits together on ARM. Generally, alternatively, you correct have to safe a immediate style for what it would feel to have Xen on this board. Right here’s frequently no longer a area for Xen, since somewhat a lot every Linux distribution offers Xen applications and having a truly practical Xen working on your design is a mere “factual” or “zypper” invocation away. Nonetheless, provided that Raspberry Pi 4 give a enhance to is handiest about a months faded, the integration work hasn’t been accomplished yet. The ideal operating design with completely constructed-in and examined give a enhance to for Xen on Raspberry Pi 4 is LF Edge’s Mission EVE.

Mission EVE is a obtain-by-blueprint operating design that supports working Edge Containers on compute devices deployed in the sector. These devices will doubtless be IoT gateways, Industrial PCs, or total-objective ruggedized computers. All applications working on EVE are represented as Edge Containers and are area to container orchestration insurance policies driven by k3s. Edge containers themselves can encapsulate Virtual Machines, Containers, or Unikernels. 

Yow will hit upon extra about EVE on the mission’s net location at http://projecteve.dev and its GitHub repo https://github.com/lf-edge/eve/blob/grasp/doctors/README.md. The latest instructions for establishing a bootable media for Raspberry Pi 4 are furthermore on hand at: 


As a result of EVE publishes completely baked downloadable binaries, the exhaust of it to give Xen on Raspberry Pi 4 a are attempting is as easy as:

$ docker pull lfedge/eve:5.9.0-rpi-xen-arm64 # it is advisable to well safe a clear 5.x.y unencumber have to you love

$ docker escape lfedge/eve:5.9.0-rpi-xen-arm64 are residing > are residing.raw

Right here’s adopted by flashing the ensuing are residing.raw binary onto an SD card the exhaust of your accepted tool. 

Once these steps are accomplished, it is advisable to well insert the cardboard into your Raspberry Pi 4, join the keyboard and the show screen and bask in a minimalistic Linux distribution (per Alpine Linux and Linuxkit) that’s Mission EVE working as Dom0 below Xen.

As a long way as Linux distributions trot, EVE items a a puny unusual blueprint for an operating design, however at the identical time, it is miles closely impressed by tips from Qubes OS, ChromeOS, Core OS, and Desirable OS. Even as it is advisable to well purchase to purchase it beyond easy console tasks and explore how to escape user domains on it, we recommend heading over to EVE’s sister mission Eden: https://github.com/lf-edge/eden#raspberry-pi-4-give a enhance to and following a immediate tutorial over there.

If one thing else goes outrageous, it is advisable to well the least bit times gain an brisk neighborhood of EVE and Eden customers on LF Edge’s Slack channels starting with #eve over at http://lfedge.slack.com/ — we’d like to listen to your recommendations.

Within the duration in-between – gratified hacking!

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