What is STUBDOM ?
Stubdoms are lightweight 'service' or 'driver' domains. The initial purpose was to offload qemu (for hvm guests) out of dom0. So with stubdoms you can run hvm guest qemu in a separate stubdom, which boosts performance and makes it more secure. stubdoms can also run for example pv-grub for pv guests, making it more secure compared to pygrub, which always runs in dom0.
Configure Example
/etc/xen/OVM_EL5U1_X86_HVM_4GB:
name = 'OVM_EL5U1_X86_HVM_4GB'
uuid = 'de0edfdc-c6f1-4d2b-a2a3-88c035208c79'
builder = 'hvm'
device_model = '/usr/lib/xen/bin/stubdom-dm'
kernel = '/usr/lib/xen/boot/hvmloader'
memory = '256'
vif = [ 'mac=00:16:3e:6b:66:d7,bridge=xenbr0', ]
disk = [ 'file:/share/vm/OVM_EL5U1_X86_HVM_4GB/system.img,hda,w!', ]
acpi = 1
apic = 1
pae = 1
vcpus = 1
sdl = 0
vnc = 1
vnclisten = '192.168.1.199'
on_crash = 'restart'
on_reboot = 'restart'
Note: you can comment the disk statement here; but if you want use pvhvm drivers, you should leave it uncommented.
/etc/xen/OVM_EL5U1_X86_HVM_4GB-dm:
disk = [ 'file:/share/vm/OVM_EL5U1_X86_HVM_4GB/system.img,hda,w!', ]
kernel = "/usr/lib/xen/boot/ioemu-stubdom.gz"
#vfb = [ 'type=sdl' ]
#vfb = [ 'type=vnc' ]
vif = [ 'ip=192.168.1.199', 'mac=00:16:3e:6b:66:d7,bridge=xenbr0', ]