xen arm

1. XEN – ARM port
CS523 Midterm Presentation
Michael LeMay
Dongyun Jin
Sundeep Reddy
Brian Schoudel I2CS

2. Phase #1
 Compile ARM/Linux
 Familiarized us with QEMU and ARM
architecture
 Necessary, since Xen hosts Linux guest OSs
 Outcomes/deliverables:
 Instructions for building Linux kernel and software
packages for ARM on QEMU
 Instructions for using NFS from within ARM/Linux
on QEMU

3. Xen Architecture

4. QEMU system emulator
 http://www.qemu.org
 Processor emulator including support for
ARM Integrator/CP
 ARM1026EJ-S processor
 Achieves good performance through
dynamic translation
 Open source emulator

5. QEMU stumbling blocks
 QEMU mailing lists are unresponsive
 Paul Brook was personally very helpful, however
 Only offers support for ARM1026EJ-S processor,
not newer ARMv6 series
 Doesn’t support VGA, causes Linux to crash if
VGA enabled in kernel config
 Enabled verbose kernel messages to detect error

6. ARM Linux Compilation
 Cross compiler needed for any XEN, Linux
compilations involving the ARM architecture
 Downloaded from CodeSourcery:
http://www.codesourcery.com/gnu_toolchains/arm/d
 Supports new ARM EABI
 Used kernel patches from arm.com, and
compiled Linux v.2.6.16-rc3-xen for ARM
 Xen support disabled

7. ARM Linux System Creation
 Arm.com provides filesystem construction
scripts
 Contains precompiled version of busybox, ftp,
etc.
 Produces cramfs system image, loaded as
ramdisk during QEMU/ARM bootup

8. ARM and NFS
 Client-Server model – server exports filesystem to
client
 QEMU emulates network card on Integrator
 Host system acts as server
 Emulated Linux system running on QEMU acts as client
 Provides the means to install software and transfer files after
booting up Linux on QEMU
 Should be possible to boot directly from NFS root fs, but
difficult on QEMU (received strange error)
 Works under ARM Linux!
 We created script to install proper /etc/fstab in cramfs system
image produced previously

9. Demonstration
 Connect to Michael’s home server
 Run QEMU with ARM/Linux
 Connect to NFS server
 Transfer file between AMD64/Linux server
and ARM/Linux client

10. Phase #2
 Port Xen hypervisor to ARM
 This is the bottom layer in the Xen
architecture
 First software to boot on system

11. Xen Architecture

12. Beginnings
 Based on Xen 3.0.1
 Based on Linux 2.6.12 kernel
 Supports IA32, IA32 PAE, AMD64, IA64
 Doesn’t include any support for ARM

13. Xen Source Layout
 xen-3.0.1
 buildconfigs: Makefiles
 docs: Documentation
 extras
 mini-os: Minimal OS used for testing
 linux-2.6-xen-sparse: Sources for stripped-
down dom0 and domU
 patches: Patches for full Linux sources
 tools: Large collection of tools to run on dom0
 xen: Hypervisor sources

14. Xen Source Layout (cont.)
 xen
 acm: sHype mandatory access control
 arch: Architecture-specific implementation
 ia64: Itanium sources
 x86: IA32, IA32 PAE, and AMD64 sources
 common: Architecture-independent sources
 drivers: Common drivers for ACPI and console
 include: Include files
 tools: Figlet, for making block letter ASCII art, and
other simple tools

15. Modifications
 Copied IA64-specific directories to form ARM-
specific directories
 IA64 is simpler and better-organized than x86
 Copied ARM-specific architectural
implementation files from Linux 2.6.16-rc3-xen
into xen/arch
 Copied ARM headers from Linux into include/
asm-arm
 Modified Makefile rules to use CodeSourcery
cross-compilers and pass proper flags

16. Challenges/Successes
 Large base of architecture-specific C code
 Wanted to have hypervisor booted by this
time, but simply too large a job
 Everything in xen directory compiles,
except most of arch subdirectory
 Many warnings, undoubtedly many
problems to resolve after compilation
completes

17. Remaining Work
 Compile remaining files in arch
subdirectory
 Will involve substantial porting effort
 Resolve problems with final executable
 Port Linux guest OS to form dom0 and
domU, using ARM/Linux experience
acquired earlier

18. Anticipated Difficulties
 ARM has only two protection rings, not
four as is the case in x86 and IA64
 AMD64 only has two rings as well, perhaps we
can learn from their modifications
 ARM has fairly unique MMU architecture
 ARM does not provide a timestamp
counter, but the clocks Xen provides are
based upon such a counter