OVMF

Tianocore / OVMF the Open-source community's project to enable EFI / UEFI for virtual machines. OVMF is integrated into Xen 4.4 release with essential patches upstreamed. However in 4.4 it is not built by default.

To build Xen with OVMF support, you would need to have --enable-ovmf when running configure. If you would like to have hypervisor log output you will need to manually edit OvmfPkg.dec, change PcdDebugIoPort to 0xe9 (which is the IO port used by Xen hypervisor logging facility) before building OVMF.

Then enable EFI for your Xen guest by adding bios='ovmf' to your xl.cfg file. See the example below for more information.

One thing to have in mind is Xen supports both its own QEMU fork called qemu-traditional and upstream QEMU called qemu-xen. OVMF only supports the latter. Xen 4.4 has upstream QEMU configured for all HVM guests by default, so it is fine to not specify which QEMU to use in guest config file. But if you have already configured qemu-traditional for your guest you would need to delete / comment out that line.

A typical guest config file looks like below. Nothing fancy, just the "bios=" option is important. Also read the comment in the example for disk specification.

builder = 'hvm'
name = 's0-efi'

vcpus = 2

memory = 1024
# memory = 6000

vif = ['bridge=xenbr0']

# This is a disk image with EFI guest installed, you can also use live CD if you prefer.
# You can either specify xvda or hda, QEMU will start with emulated IDE drive in both cases.
# But if you speficy sda then it might not boot as OVMF doesn't have the driver at the moment.
disk = [ '/data/s0-efi.qcow2,qcow2,xvda,w' ]

on_crash = 'preserve'

vnc=1
vnclisten='0.0.0.0'

serial='pty'
bios='ovmf' # if you don't have this line, seabios will be used

Debuging OVMF

Here we will describe the different ways one can enable the debug output of OVMF.

Log into a file

Simply add the following to your guest config file:

device_model_args_hvm = [
  # Debug OVMF
  '-chardev', 'file,id=debugcon,path=/var/log/xen/ovmf.log,',
  '-device', 'isa-debugcon,iobase=0x402,chardev=debugcon',
]

This will tell QEMU to save OVMF's debug output to /var/log/xen/ovmf.log.

(Checkout QEMU's help of -chardev for more options.)

Log via the guest console

The alternative is to recompile OVMF so that it would log its debug via the guest console.

Recompile OVMF with -D DEBUG_ON_SERIAL_PORT to enable the use of the console.

To recompile OVMF, you can edit xen.git:tools/firmware/ovmf-makefile and add -D DEBUG_ON_SERIAL_PORT to the OvmfPkg/build.sh command line before building OVMF via Xen build system. Or you can execute OvmfPkg/build.sh -a X64 -b DEBUG -n $(nproc) -D DEBUG_ON_SERIAL_PORT within the ovmf directory.