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ALSF13: Xen on ARM - Virtualization for the Automotive Industry - Stefano Stabellini, Citrix


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During the last few months of 2011 the Xen Community started an effort to port Xen to ARMv7 with virtualization extensions, using the Cortex A15 processor as reference platform.

The new Xen port is exploiting this set of hardware capabilities to run guest VMs in the most efficient way possible while keeping the ARM specific changes to the hypervisor and the Linux kernel to a minimum. Developing the new port we took the chance to remove legacy concepts like PV or HVM guests and only support a single kind of guests that is comparable to "PVH" in the Xen X86 world.

Linux 3.7 was the first kernel release to run on Xen on ARM as Dom0 and DomU. Xen 4.3, out in July 2013, is the first hypervisor release to support ARMv7 with virtualization extensions and ARMv8.

This talk will explain why ARM virtualization is set to be increasingly relevant for the automotive industry in the coming years. We will go on to describe how Xen exploits the strengths of the hardware to meet the requirements of the industry. We will illustrate the early design choices and we will evaluate whether they were proven successful or a failure.

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ALSF13: Xen on ARM - Virtualization for the Automotive Industry - Stefano Stabellini, Citrix

  1. 1. Xen on ARM Stefano Stabellini
  2. 2. What is Xen? ● a type-1 hypervisor ● small footprint (less than 90K LOC)
  3. 3. Xen: Open Source GPLv2 with DCO (like Linux) Diverse contributor community
  4. 4. Xen: Open Source source: Mike Day
  5. 5. Xen: the gears of the cloud ● large user base more than 10 million individuals users ● power the largest clouds in production ● not just for servers
  6. 6. Xen Architecture Dom0 DomU DomU DomU PV backends PV Frontends PV Frontends PV Frontends HW drivers Xen Hardware
  7. 7. Xen Architecture: driver domains Toolstack Disk Driver Domain Network Driver Domain DomU BlockBack Dom0 NetBack BlockFront Disk Driver Network Driver NetFront Xen Hardware
  8. 8. Xen Architecture: driver domains ● disaggregation and componentization ● security and isolation ● resilience ● hardware vendors can run their drivers in separate VMs ○ could run in a RTOS environment ○ hidden from the user ■ media codecs, crypto keys, etc.
  9. 9. Xen on ARM: not just a port ● a lean and simple architecture ○ ○ ○ ○ ○ removed cruft accumulated during the years no emulation, no QEMU use PV drivers for IO as early as possible one type of guest exploit the hardware as much as possible ● a very good match for the hardware ● clean architecture = small code base
  10. 10. Xen on ARM architecture
  11. 11. Xen on ARM architecture
  12. 12. Code size sometimes smaller is better Common ARMv7 ARMv8 Total xen/arch/arm 5,122 1,969 821 7,912 C 5,023 406 344 5,773 99 1,563 477 2,139 2,315 563 666 3,544 2,532 1,487 11,456 ASM xen/include/asm-arm TOTAL 7,437 ● X86_64-bit: ~120,000LOC (~4,000 ASM) ● ARM code ~= 1/10 x86_64 code
  13. 13. Achievements of one year Xen support for ARM upstream in Linux 3.7 Xen support for ARM64 upstream in Linux 3.11 Xen 64-bit on ARM64 You are here 11/11 08/12 09/12 Part-time Xen ARM hacking starts 11/12 Xen running on real ARM hardware First Xen on ARM talk at Xen Summit 2012 01/13 03/13 Citrix announces that will be joining Linaro 06/13 07/13 Xen 4.3 released with ARM and ARM64 support
  14. 14. A growing community Xen-devel ARM traffic from August 2012: ● 4685 emails: 360 emails per month! ● 39% of which are not from Citrix
  15. 15. Hardware support Upstream: ● Versatile Express Cortex A15 ● Arndale board ● ARMv8 FVP In progress: ● ● ● ● ● Cubieboard2 Calxeda “Midway” Applied Micro “Mustang” Broadcom Brahma-B15 OMAP5
  16. 16. Porting Xen to a new board ● Xen only relies on GIC and GT ● platform specific code in Xen is reduced to: ○ secondary cpus bring up ○ UART drivers ○ any platform specific bootup quirks (ideally none)
  17. 17. Upstream features Xen v4.3: ● basic lifecycle operations ● memory ballooning ● scheduler configurations and vcpu pinning Linux v3.11: ● dom0 and domU support ● 32-bit and 64-bit support ● SMP support ● PV disk, network and console
  18. 18. Android on Xen on ARM ● Android is based on the Linux kernel ○ Jelly Bean uses Linux 3.4, when it updates to 3.7 will get Xen on ARM support out of the box ● Additional work needed to support client devices (compass, GPS, etc.) on multiple VMs ○ easy to export 1 device to 1 VM ○ otherwise each type of device needs a PV drivers pair
  19. 19. PV Protocols Backend Request Producer Frontend Request Consumer Response Consumer Response Producer
  20. 20. PV Protocols ● ● ● ● ● shared ring protocol software interrupts AKA event channels consensual memory sharing: grant table easy to write plenty of examples ○ network, block, console, PCI, keyboard, mouse, framebuffer, sound, SCSI, USB, …
  21. 21. Porting other OSes to Xen on ARM ● No invasive modifications needed ● only some new drivers: ○ grant table, xenbus and event channels ○ PV drivers for network, block, console, etc. ● BSD drivers already exist in NetBSD and FreeBSD, can they be reused? ● FreeBSD port to Xen on ARM in progress
  22. 22. Coming in Xen 4.4 ● 64-bit guest support ● live-migration ● SWIOTLB
  23. 23. A look into the future ● ● ● ● IOMMU support in Xen device assignment UEFI booting ACPI support
  24. 24. Xen for automotive: why? ● type-1 ● small footprint ○ small codebase ○ no QEMU, no emulation ● driver domains / service VMs ○ componentization ○ security ○ support for legacy drivers ● supports Linux out of the box ● easy to port other OSes to Xen on ARM
  25. 25. More Information ● ● Xen on ARM goo. gl/FKNXe ●
  26. 26. Questions?