[xenpreview-dev] xen boot xp from pre-existing xp partition

[Charles Coffing]

On Thu, May 17, 2007 at 12:30 PM, Michael Brian Bentley <bentley at crenelle.com> wrote: 
> I installed Xen from Yast after installing SUSE 10.2 on a machine 
> with xp installed in /dev/sda1.
> 
> Is there something fundamentally wrong with trying to start Windows 
> xp in its /dev/sda1 partition under Xen, on a Core 2 Duo machine with 
> Full Virtualization turned on?

It's possible, but there are several caveats:

1. Point to the entire disk, not a single partition, since the virtualized BIOS expects to see a boot sector, etc.  However, since you are sharing this disk with the SUSE installation, this is inherently unsafe.  Windows could (theoretically) write to your SUSE partition and destroy your setup, so the tools won't let you do this.  (In general, the tools disallow giving multiple VMs writable access to the same disk.)  To disable this check and proceed anyway, change the "w" near the end of the "disk=" line to "w!".

2.  Windows may, in some cases, behave oddly when it is moved between a physical and a virtual machine.  Windows seems to store some hardware settings in the registry, and does not re-probe these settings at each boot.  Therefore, if you originally installed Windows on a physical machine and later booted it on a virtual machine, some settings might not match or make sense, and Windows might have problems.  (Notable example is the APIC; using it is not necessary on a 32 bit uniprocessor VM, and in fact is undesirable because emulating the APIC is quite slow.  But when installing Windows on physical hardware, use of the APIC is probably turned on in the registry.  So you may find that Windows would run faster if it were installed within the VM, rather than migrating from physical to virtual.)


I'll also note that SLES 10 SP1 and openSUSE 10.3 have updated versions of Xen and updated tools.  We've seen many HVM problems fixed, so you may want to watch for these releases.

 
> All the examples I see on the net involve creating a .img file, 
> either from copying it from an original install or from installing 
> into the .img file. But pointing to xp at /dev/sda1 or /dev/sda after 
> doing a regular SUSE 10.2 install that involves shrinking the 
> pre-existing xp partition, and doing an xm create, does not work (for 
> me). Shouldn't this thing just work if I get the .hvm configuration 
> file set up right?
>
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