[Qemu-devel] Re: [PATCH 15/15] xen: Add a Xen specific ACPI Implementation to target-xen

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Fri, 13 Aug 2010, Anthony Liguori wrote:
> On 08/13/2010 02:37 PM, Stefano Stabellini wrote:
> > On Fri, 13 Aug 2010, Anthony Liguori wrote:
> >    
> >> On 08/12/2010 09:10 AM, stefano.stabellini@eu.citrix.com wrote:
> >>      
> >>> From: Anthony PERARD<anthony.perard@citrix.com>
> >>>
> >>> Xen currently uses a different BIOS (hvmloader + rombios) therefore the
> >>> Qemu acpi_piix4 implementation wouldn't work correctly with Xen.
> >>> We plan on fixing this properly but at the moment we are just adding a
> >>> new Xen specific acpi_piix4 implementation.
> >>> This patch is optional; without it the VM boots but it cannot shutdown
> >>> properly or go to S3.
> >>>
> >>>        
> >> What's the long term plan?  Will Xen adopt SeaBIOS or will you adapt
> >> your BIOS to cope with our ACPI implementation?
> >>
> >>      
> > I think it shouldn't be too difficult to adapt our current BIOS, but
> > we'll need few xen specific hooks in acpi_piix4.
> > The price that we'll have to pay doing so is loosing live-migration
> > compatibility with older xen installations.
> >    
> 
> Does Xen migrate roms (like the BIOS) in such a way that the persist 
> after a reboot?
> 

No, I don't think so.
However it is common practice not to require any VM reboot on host
upgrade.


> I noticed there was only one machine type defined.  In our experience, 
> to preserve compatibility with migration, it's useful to have versioned 
> machine names.  We also have some special machine parameters to support 
> compatibility with qdev.
> 

Thanks for the tip, we'll look into it.
Knowing that we would have the BIOS problem mentioned above, we didn't
try yet any save/restore or migration compatibility between old qemu-xen
and new qemu.


> How does Xen handle hvm migration machine model compatibility?
> 
 
We use per-device save state versions and we tend to use always the same
set of devices.