Xen FAQ Booting

Booting Xen

I get an error from Xen... (console output starting "(XEN)")

(XEN) Initial guest OS requires too much space
(XEN) (8MB is greater than 0MB limit)

Check that you are correctly specifying the dom0_mem command line option for starting Xen. Note that: dom0_mem=512M should work in recent versions while older versions such as 2.0.5 require the memory specification to be in kilobytes, e.g. dom0_mem=524288.

(Note: you need to leave some memory for Xen, so the above assumes you have more than 512M total in the system; if you still have problems, reduce the amount further).

How do I hide a pci device from dom0?

In Xen 2.x, you can add the physdev_dom0_hide parameter (see Xen Hypervisor Boot Options for more parameters) to hide one or more pci devices to Dom0, so you can affect them to domU.

Pci slots MUST be formatted like this:

• (nn:nn.n)

so

• (03:06.1) is correct
• (03:6.1) is NOT correct

You can get the pci bus address on a Linux system by using the lspci command (only the last bits are relevant):

lspci | grep Ethernet
0000:02:03.0 Ethernet controller: Intel Corp. 82546EB Gigabit Ethernet Controller (Copper) (rev 01)
0000:02:03.1 Ethernet controller: Intel Corp. 82546EB Gigabit Ethernet Controller (Copper) (rev 01)

Then:

• to hide the second network interface from dom0, you can then append physdev_dom0_hide=(02:03.1) to your kernel /boot/xen-2.0.gz.
• to hide multiple pci devices, simply concatenate all the pci slots address like this: physdev_dom0_hide=(02:03.0)(02:03.1)

If everything went ok, you should see the following lines after a reboot:

(XEN) Hiding PCI device 02:03.0 from DOM0
(XEN) Hiding PCI device 02:03.1 from DOM0

Error about root device still mounted when it's not mounted, zombie domU that can't be killed, domU hangs under heavy I/O (e.g disk) access

This is an unresolved problem with Xen 3.0.

You may try to pass nousb to dom0 kernel command line, or pass ignorebiostables, or try to disable software IRQ affinity for 1850/2850 systems.

• Discussion in xen-users mailing list