Re: [Xen-users] Xen 3.4.1-rc10: Cannot restore/migrate 32-bit HVM domU (W2K3 Server) on 64-bit dom0

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Jul 31, 2009 at 02:51:09PM +0530, Sreeharsha Totakura wrote:
> 
> 
> xen-users-bounces@xxxxxxxxxxxxxxxxxxx wrote on 07/31/2009 01:55:09 PM:
> 
> > Pasi Kärkkäinen <pasik@xxxxxx>
> >
> > Subject
> >
> > Re: [Xen-users] Xen 3.4.1-rc10: Cannot restore/migrate 32-bit HVM
> > domU (W2K3 Server) on 64-bit dom0
> >
> > On Fri, Jul 31, 2009 at 10:19:04AM +0300, Pasi Kärkkäinen wrote:
> > > On Thu, Jul 30, 2009 at 08:00:21PM -0400, Joshua West wrote:
> > > > Hey all,
> > > >
> > > > I've been attempting to get 'xm restore' (and thus 'xm migrate') to
> work
> > > > for a 32-bit HVM domU on a 64-bit dom0 running Xen 3.4.1-rc10.  Has
> > > > anyone else been able to do so?  I can boot the VM and work within it
> > > > just fine.  The 'xm save' command also functions properly; issue is
> just
> > > > with 'restore' and therefore 'migrate'.
> 
> I too am attempting to live migrate a 32bit Guest from a 64 bit Dom-0 to a
> 32bit Dom-0 and haven't succeeded yet. Is this possible?
> 

I'm not sure if that's possible.

> From the logs I found that there is a problem in restoring the virtual
> machine on the 32 bit Dom-0.
> 
> > > What dom0 kernel you are running?
> > >
> > > If something else than linux-2.6.18-xen.hg please try with that
> instead.
> > >
> 
> I am running the kernel ( 2.6.18-128.el5xen) which came with RHEL5.3
> 

Xen 3.4.x uses linux-2.6.18-xen.hg as a default dom0 kernel, ie. Xen is tested
and developed using that kernel. 

So you should try running that to see if the problem is in your RHEL5.3 kernel.

Btw RHEL 5.4 beta xen and kernel-xen has a lot of fixes for 32-on-64, live
migrations etc.

> > Also if you can reproduce this problem running linux-2.6.18-xen on dom0,
> > then please send an email to xen-devel about this. Keir wants to release
> Xen
> > 3.4.1 final early next week, and this sounds like something that might be
> > good to check before the release.
> >
> > If this problem happens running for example Debian lenny 2.6.26-xen
> > kernel in dom0,
> > or some other 2.6.27, 2.6.29, 2.6.30 dom0 kernel then it _could_ be a bug
> in
> > them, and not in Xen.
> >
> > -- Pasi
> >
> > >
> > > > When I watch the system via "xm top" during the restoration process,
> I
> > > > do notice the memory allocation for the VM increase all the way to
> about
> > > > 1024MB.  Suddenly, the amount of memory allocated to the VM decreases
> by
> > > > a bit, and then finally the VM disappears.
> > > >
> > > > It may be of interest that I don't have issues
> > > > saving/restoring/migrating 32-bit PV domU's on this same set of
> 64-bit
> > > > dom0's.  This seems to be an issue only with HVM domU's.
> 
> May be true, I too have observed this on my 64bit Dom-0 where I am running
> 32bit Dom-U's. I guess they are running under HVM. Little clarification is
> needed here.. Can we run 32 Dom-U's under PV on 64 bit Dom-0 ?
> 

Yes, 32-on-64 is supported also for PV guests. 
32bit PV guests need to be PAE though.

-- Pasi

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