Hypervisors are becoming more and more widespread in embedded environments, from automotive to medical and avionics. Their use case is different from traditional server and desktop virtualization, and so are their requirements. This talk will explain why hypervisors are used in embedded, and the unique challenges posed by these environments to virtualization technologies. Xen, a popular open source hypervisor, was born to virtualize x86 Linux systems for the data center. It is now the leading open source hypervisor for ARM embedded platforms. The presentation will show how the ARM port of Xen differs from its x86 counterpart. It will go through the fundamental design decisions that made Xen a good choice for ARM embedded virtualization. The talk will explain the implementation of key features such as device assignment and interrupt virtualization.

1. Stefano Stabellini @stabellinist
Xen on ARM,
and the Art of Embedded Virtualization
Security, Isolation, Partitioning

2. Why Xen?
Why an hypervisor?

4. Galois
SMACCMPPilot
Demo
Xen Summit 2014

5. Why Xen?
• Efficiency and Consolidation
• Isolation and Partitioning
• Componentization
• Resilience
• Scaling
• Portability

6. Xen: a type-1 hypervisor
Hardware
Xen
Dom0 DomU
HW drivers
PV backends
PV
Frontends
DomU
PV
Frontends
DomU
PV
Frontends

7. Xen: the gears of the cloud
• Large user base (> 10M individual users)
• Powers the largest clouds in production
• Not just servers

8. Xen: Open Source

9. Xen: Open Source
partial

10. Embedded != Cloud
Different requirements:
• short boot times
• small footprint
• small codebase (certifications)
• non-PCI device assignment
• driver domains
• low, deterministic irq latency
• real time schedulers
• co-processor virtualization

11. Xen on ARM
• A lean and simple architecture
– No cruft
– No emulation, No QEMU
– Small attack surface
– One type of guest
• Exploit the hardware as much as possible
• A very good match for the hardware
• Clean architecture = a very small code base
– Xen, ARM and ARM64 =~ 30K LOC

12. Xen on ARM: a perfect match for the HW

13. Xen on ARM: unique features
• Device Passthrough (even Non-Discoverable Devices)
– iomem and irqs VM config parameters
• No guest firmware by default - fast VM boot
• Certifications efforts ongoing
• Low, Deterministic IRQ latency (WARM_MAX < 2000ns)

14. Low IRQ latency: no maintenance interrupts
DomU
Xen
irq 109
virq 109
DomU
Xen
EOI
DomU
Xen
Maintenance
interrupt
GICH_LR
Write
GICH_LR
Clear

15. Low IRQ latency: physical follow virtual
vcpu0 vcpu1
pcpu0 pcpu1
irq 109
virq 109

16. Low IRQ latency: physical follow virtual
vcpu0 vcpu1
pcpu0 pcpu1
irq 109
virq 109

17. Low IRQ latency: physical follow virtual
vcpu0 vcpu1
pcpu0 pcpu1
irq 109
virq 109

18. Xen Schedulers
CPU CPU CPU CPU
CPU CPU CPU CPU

19. Xen Schedulers
CPU CPU CPU CPU
CPU CPU CPU CPU
Real Time Scheduler
ARINC 653
Regular VM Scheduler
Credit
Dedicated
to 1 VCPU
Dedicated
to 1 VCPU

20. Memory Introspection

21. PV Protocols
Existing: net, block, console, keyboard, mouse, framebuffer,
XenGT
New: 9pfs, PVCalls, Multi Touch, Sound, Display

22. Driver Domains
Hardware
Xen
Dom0 DomU
NetFront
Disk Driver
Domain
Toolstack Disk Driver
BlockBack
Network
Driver
Domain
Network
Driver
NetBack BlockFront

23. Automotive
Hardware
Xen
Dom0
Linux Control Domain
UI Domain
Automotive Grade Android
HW Drivers
GPU
Driver
PV Block & Net
frontends
PV Block & Net
Backends
Audio
Driver

24. GlobalLogic

25. EPAMEPAM

26. EPAM: DEMO
https://www.youtube.com/watch?v=jMmz1odBZb8

27. Xilinx Zynq MPSoC
Xen
Dom0
Linux
Baremetal
App
Toolstack FPGA Driver
Baremetal
App
FPGA Driver
Baremetal
App
FPGA Driver
Baremetal
App
FPGA Driver
FPGA
Dedicated CPU Dedicated CPU Dedicated CPU Dedicated CPU

28. Xen: best security process in the industry
• A very transparent process
• Responsible disclosure
• Few security issues for Xen on ARM
• Xen stable trees maintained for security for 3 years

29. Release process
• 6 month release
– December
– June
• Xen 4.8 released on the 5th of December 2016
• Xen 4.9 planned for the 2nd of June 2017

30. Xen on ARM: what’s next
● Guest creation directly from Xen at boot via Device Tree
● Dynamic Memory Map
● Setup VM-to-VM communication channels from VM
config

31. More resources
• Port Xen to a new SOC: https://goo.gl/384aD8
• Add Xen support Xen to your OS: https://goo.gl/3qgqcM
• Xen on ARM whitepaper: https://goo.gl/TcuqXd
• Xen on ARM wiki: https://goo.gl/9qsfMf
• Device Passthrough presentation: https://goo.gl/KM0f8c
• OE meta-virtualization Xen recipe:
https://goo.gl/m7GuXR
• OpenXT (Xen + OpenEmbedded): http://openxt.org
• Biweekly ARM Community Call: https://goo.gl/8ULYRn

32. Please engage!
• Xen devel ML: xen-devel@lists.xenproject.org
• Xen user ML: xen-users@lists.xenproject.org
• IRC on freenode: #xenarm or #xen-devel

33. Fin