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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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Xen on ARM
Stefano Stabellini
What is Xen?● a type-1 hypervisor● small footprint (less than 90K LOC)
Xen: Open SourceGPLv2 with DCO (like Linux)Diverse contributor community
Xen: Open Sourcesource:Mike Dayhttp://code.ncultra.org
Xen: the gears of the cloud● large user base
more than 10 million individuals users
● power the largest clouds inproduction
● not just for servers
Xen Architecture
Hardware
Xen
Dom0 DomU
HW drivers
PV backends PV Frontends
DomU
PV Frontends
DomU
PV Frontends
Xen Architecture:driver domains
Hardware
Xen
Dom0 DomU
NetFront
Disk Driver Domain
Toolstack Disk Driver
BlockBack
Network Driver Domain
Network Driver
NetBack BlockFront
● 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.
Xen Architecture:driver domains
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
Xen on ARM architecture
Xen on ARM architecture
Code sizesometimes smaller is better
● X86_64-bit: ~120,000LOC (~4,000 ASM)● ARM code ~= 1/10 x86_64 code
Common ARMv7 ARMv8 Total
xen/arch/arm 5,122 1,969 821 7,912
C 5,023 406 344 5,773
ASM 99 1,563 477 2,139
xen/include/asm-arm 2,315 563 666 3,544
TOTAL 7,437 2,532 1,487 11,456
Achievements of one year
11/11 08/12 11/12 03/13 07/13
First Xen on ARM talk atXen Summit 2012
Xen support for ARM upstream in Linux 3.7
Xen running on real ARM hardware
09/12
Xen 64-bit on ARM64
01/13
Citrix announces that will be joining Linaro
Xen support for ARM64 upstream in Linux 3.11
06/13
Xen 4.3 released with ARM and ARM64 support
Part-time Xen ARM hacking starts
You are here
Xen-devel ARM traffic from August 2012: ● 4685 emails: 360 emails per month!● 39% of which are not from Citrix
A growing community
Hardware supportUpstream:● Versatile Express Cortex A15● Arndale board● ARMv8 FVP
In progress:● Cubieboard2● Calxeda “Midway”● Applied Micro “Mustang”● Broadcom Brahma-B15● OMAP5
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)
Upstream featuresXen 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
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
PV ProtocolsRequest Producer
Request Consumer
Response Producer
Response Consumer
Backend Frontend
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, …
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
Coming in Xen 4.4● 64-bit guest support● live-migration● SWIOTLB
A look into the future● IOMMU support in Xen● device assignment● UEFI booting● ACPI support
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
● http://www.xenproject.org
● Xen on ARM @wiki.xenproject.org goo.gl/FKNXe
● http://lists.xen.org/mailman/listinfo/xen-devel
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