RE: [Xen-users] 32bit domU in 64 bit dom0

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

Mark Williamson wrote:
> [*] I think it's a shame we don't support 32-bit non-PAE 
> guests on 64-bit Xen.  
> I'm told most of the machinery should be there already.  As 
> far as I'm aware, 
> only the Linux port supports PAE, although I may be behind on this 
> information.

The main reason for this is that the 64-bit hypervisor uses 4-level
pagetables, and 32-bit PAE uses 3-level page-tables. Both 4- and 3-level
page-tables use 64-bit entries in the table. However, 32-bit non-PAE
uses 32-bit page-table entries. I don't think it's quite so easy to
switch to 32-bit non-PAE page-tables when running a 64-bit hypervisor -
it's probably POSSIBLE, but it makes life a lot harder.  Since we're
talking about PV-guests in the first place, it's not too much to ask
that the guest is compiled for PAE mode rather than non-PAE - it would
be different if it was HVM guest that don't necessarily have easy access
to source-code... 

--
Mats



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