Re: [Xen-users] 32Bit PVM on 64Bit dom0?

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> I tried to start a 32Bit PVM system on a 64Bit dom0, and got the following
> error:
> Using config file "./VM1".
> Error: (2, 'Invalid kernel', 'xc_dom_compat_check: guest type
> xen-3.0-x86_32 not supported by xen kernel, sorry\n')

That is a non-PAE kernel, right?  If it were PAE, I'd expect the guest type to 
be "xen-3.0-x86_32p".  Only 32-bit PAE kernels will boot on 64-bit so you'd 
need to get a guest kernel with PAE enabled (either rebuild it or see if your 
distro has a PAE-enabled package).

> and it just did not started. Is ist just because of the different 32/64Bit
> of domU and dom0? The xen in the dom0 is configured to be backward
> compatible. The dom0 is a xen 3.1.0, the domU is a xen 3.0.3.

3.1 had backwards compatibility for 32-bit PAE domains on a 64-bit Xen, 
however, if I recall correctly the original 3.1.0 release didn't work with 
older 32-bit guest kernels (full backwards compatibility was implemented in a 
subsequent patch - it's probably in a later release in the 3.1 series).

So you *might* need a newer release of 3.1 to run your guest; I'm not sure on 
this, though because I never really looked into what the limitation was.

I think a few things (live migration / save-restore) were also not supported 
for domains of a different addressing mode to dom0 under 3.1 (e.g. can't 
save/restore/migrate 32-bit domUs if dom0 is 64-bit, or vice-versa) but the 
basic functionality of booting and running domains ought to work OK...

> When this is just not working, then I have to run the dom0 in 32Bit. Do I
> can then assign 4GB RAM to each domU, or will the dom0 be unable to handle
> that amount of memory? I assume I need a PAE enabled Xen kernel for the
> dom0? But will I need such a kernel then for the domU's too?

You can have 32-bit dom0 and still run 64-bit domUs, if your Xen itself is 
64-bit; you should be able to run 32-bit PAE domUs with > 4G of memory as 
well, I think.

Hope that helps,

Cheers,
Mark

> kind regards
> Sebastian
>
> Sorry if this mail hits the M/L twice, I sent the original yesterday
> afternoon, and still nothing on the list, therefore resending it now.
>
>
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> http://lists.xensource.com/xen-users



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