[Fedora-xen] 32 bit domU, 64 bit dom0?

[Chris Lalancette]

Tom Horsley wrote:
> I tried to follow the instructions in the FC6 Xen fedoraproject wiki
> page and tried installing 32 bit FC6 guest while booted in x86_64 dom0,
> the virt-manager tells me invalid argument and the xend-debug.log
> file says ERROR: Kernel not a Xen-compatible Elf image.
> 
> Does this mean it is, in fact, impossible to run a 32bit guest
> (x86 architecture) on a 64 bit x86_64 host?
> 
> Or does it just mean virt-manager isn't prepared to try doing an
> install from a 32 bit fedora install tree?
> 
> Installing an x86_64 guest seems to be working fine, by the way.
> 
> (I can't ever seem to find a plain statement about 32 versus 64
> bit compatibility under Xen, though I have seen plain statements
> that I can't run a 64 bit guest under and 32 bit host, which
> sort of implies by omission that maybe I can run a 32 bit guest
> under a 64 bit host as long as we are talking x86 architecture
> in general).
> 
> --
> Fedora-xen mailing list
> Fedora-xen at redhat.com
> https://www.redhat.com/mailman/listinfo/fedora-xen

No, this isn't a limitation of virt-manager; it's a limitation of Xen.  The problem with a clear statement is that things are always moving :).  As far as I know, it currently stands like this (where domU is paravirtualized domains and HVM is fully-virtualized domains):

Hypervisor	dom0		domU 		HVM
-------------------------------------------------------------
32-bit		32-bit		32-bit		32-bit
32-bit PAE	32-bit PAE	32-bit PAE	32-bit PAE
64-bit		64-bit		64-bit		32- or 64-bit

There is ongoing work upstream to allow 32-bit domU's to run on 64-bit hypervisors, but that doesn't work right now.

Chris Lalancette