Xen users - Mar 2007 - Mixing architectures--64bit master, 32bit clients?

Has anyone successfully run the 64-bit Xen hypervisor (open source 
version) with
32-bit xen virtual machines? If so, are there any pointers to a
how-to of what to do, and things you should avoid?

Thanks

Steve Timm


-- 
------------------------------------------------------------------
Steven C. Timm, Ph.D  (630) 840-8525
timm@fnal.gov  http://home.fnal.gov/~timm/
Fermilab Computing Division, Scientific Computing Facilities,
Grid Facilities Department, FermiGrid Services Group, Assistant Group Leader.

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> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of 
> Steven Timm
> Sent: 13 March 2007 18:09
> To: xen-users@lists.xensource.com
> Subject: [Xen-users] Mixing architectures--64bit master, 
> 32bit clients?
> 
> 
> Has anyone successfully run the 64-bit Xen hypervisor (open source 
> version) with
> 32-bit xen virtual machines? If so, are there any pointers to a
> how-to of what to do, and things you should avoid?
This works fine in HVM (full virtualization) in any recent release of
Xen (e.g. 3.0.4 or 3.0.3).

Para-virtual model doesn''t allow mix of hypervisor and guest modes, so
hypervisor and all guests (Dom0 and others) will have to be the same,
either 64-bit, 32-bit PAE or 32-bit non-PAE. This is being worked on in
xen-unstable, where you should be able to run 32-bit PAE on 64-bit
(32-bit non-PAE is a bit more complicated because the page-tables are
different between 32-bit non-PAE and 64-bit, whilst 32-bit PAE uses the
same page-table format). 

3.0.5 should have 32-bit PAE on 64-bit working (fingers crossed). 

Of course, for many purposes, 64-bit guests will run 32-bit apps
perfectly fine (just like it does on "bare-metal 64-bit systems").
There
are exceptions, but if you''re not running particularly unusual setups
in
your guests, you may want to try that as an approach. Some people,
reportedly, even install 32-bit distributions and just upgrade the
kernel itself to 64-bit with good results [although this is not what I
would recommend]. 

--
Mats
> 
> Thanks
> 
> Steve Timm
> 
> 
> -- 
> ------------------------------------------------------------------
> Steven C. Timm, Ph.D  (630) 840-8525
> timm@fnal.gov  http://home.fnal.gov/~timm/
> Fermilab Computing Division, Scientific Computing Facilities,
> Grid Facilities Department, FermiGrid Services Group, 
> Assistant Group Leader.
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 
> 


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> Has anyone successfully run the 64-bit Xen hypervisor (open source
> version) with
> 32-bit xen virtual machines? If so, are there any pointers to a
> how-to of what to do, and things you should avoid?
This ought to work for HVM virtual machines just fine (you can run 32-bit PAE 
or non-PAE guests just fine).

For paravirtualised guests, 3.0.4 requires them to have the same paging model 
(i.e. 64-bit / 32-bit, and for the latter PAE or non PAE).

xen-unstable has (I believe) support for mixing paravirtualised 32-bit PAE 
guests and 64-bit paravirtualised guests on a 64-bit Xen.  Dom0 can also be 
32-bit in this scenario.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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On Tue, 13 Mar 2007, Mark Williamson wrote:
>> Has anyone successfully run the 64-bit Xen hypervisor (open source
>> version) with
>> 32-bit xen virtual machines? If so, are there any pointers to a
>> how-to of what to do, and things you should avoid?
>
> This ought to work for HVM virtual machines just fine (you can run 32-bit
PAE
> or non-PAE guests just fine).
Sorry for the real newbie questions here, but how can I look at my 
existing
xen 3.0.2 installation (installed by someone else before I took over)
and tell which kind of client I''ve got now, HVM or PAE or non-PAE?
And is there a basic howto that will define some of these acronyms?

Also, when upgrading from Xen 3.0.2 to xen 3.0.4 (kernel 
2.6.16-xen3_86.1_rhel4.1 to 2.16.16.33-)
is there any order that should be followed, i.e. should you
do the master first or the clients first, or does it matter?

Thanks

Steve timm


>
> For paravirtualised guests, 3.0.4 requires them to have the same paging
model
> (i.e. 64-bit / 32-bit, and for the latter PAE or non PAE).
>
> xen-unstable has (I believe) support for mixing paravirtualised 32-bit PAE
> guests and 64-bit paravirtualised guests on a 64-bit Xen.  Dom0 can also be
> 32-bit in this scenario.
>
> Cheers,
> Mark
>
>
-- 
------------------------------------------------------------------
Steven C. Timm, Ph.D  (630) 840-8525
timm@fnal.gov  http://home.fnal.gov/~timm/
Fermilab Computing Division, Scientific Computing Facilities,
Grid Facilities Department, FermiGrid Services Group, Assistant Group Leader.

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http://lists.xensource.com/xen-users

> Sorry for the real newbie questions here, but how can I look at my
> existing
> xen 3.0.2 installation (installed by someone else before I took over)
> and tell which kind of client I''ve got now, HVM or PAE or non-PAE?
> And is there a basic howto that will define some of these acronyms?
HVM is full virtualisation.  PAE is the mode of x86-32 which supports large 
memory systems, non-PAE is limited at 4Gig of physical address space (which 
in practice means a bit less than 4Gig ram maximum).

PAE and non-PAE are the standard ways of doing 32-bit guests (they support the 
same userspace, it''s just the kernel that''s different).

If your guests are Xen-aware then they''re not HVM.  If they''re
running
standard native installs and are fully virtualised, that''s HVM.

If you run xm info it''ll tell you what kind of guests your hardware
supports.
> Also, when upgrading from Xen 3.0.2 to xen 3.0.4 (kernel
> 2.6.16-xen3_86.1_rhel4.1 to 2.16.16.33-)
> is there any order that should be followed, i.e. should you
> do the master first or the clients first, or does it matter?
Doesn''t necessarily matter...  if the guests are compiled with support
for
compatibility with older Xen either way should probably work.  If you upgrade 
the master stuff (Xen, dom0 stuff, etc) first then the unprivileged clients 
will definitely continue to work.

Regarding dom0 stuff: The versions of Xen and the toolset must match. 
There''s
no longer the requirement in 3.0.4 that the dom0 kernel matches too so you 
may not need to upgrade this immediately... (I''m not sure if
that''ll work,
but you could try it and upgrade the kernel later if necessary).

As always, keep a known-good native kernel handy in case you need to boot and 
fix anything!

Cheers,
Mark
> Thanks
>
> Steve timm
>
> > For paravirtualised guests, 3.0.4 requires them to have the same
paging
> > model (i.e. 64-bit / 32-bit, and for the latter PAE or non PAE).
> >
> > xen-unstable has (I believe) support for mixing paravirtualised 32-bit
> > PAE guests and 64-bit paravirtualised guests on a 64-bit Xen.  Dom0
can
> > also be 32-bit in this scenario.
> >
> > Cheers,
> > Mark
-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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