Re: [Qemu-devel] Re: [PATCH 2/3] qemu: make cirrus init value pci spec compliant

[Michael S. Tsirkin]

On Thu, Oct 08, 2009 at 07:40:12PM +0100, Jamie Lokier wrote:
> Avi Kivity wrote:
> > On 10/08/2009 06:06 PM, Michael S. Tsirkin wrote:
> > >On Thu, Oct 08, 2009 at 05:29:29PM +0200, Avi Kivity wrote:
> > >   
> > >>On 10/08/2009 04:52 PM, Michael S. Tsirkin wrote:
> > >>     
> > >>>PCI memory should be disabled at reset, otherwise
> > >>>we might claim transactions at address 0.
> > >>>I/O should also be disabled, although for cirrus
> > >>>it is harmless to enable it as we do not
> > >>>have I/O bar.
> > >>>
> > >>>Note: need bios fix for this patch to work:
> > >>>currently pc-bios incorrently assumes that it does not
> > >>>need to enable i/o unless device has i/o bar.
> > >>>
> > >>>Signed-off-by: Michael S. Tsirkin<address@hidden>
> > >>
> > >>This needs to be conditional on the machine type.  Old machines must
> > >>retain this code for live migration to work (we need to live migrate the
> > >>bios, so we can't assume the bios fix is in during live migration from
> > >>older qemus).
> > >>     
> > >No, if you migrate from older qemu you will be fine as command
> > >is enabled there on init.
> > >   
> > 
> > Right.
> 
> No, I think Avi was right the first time.
> 
> Migrating from an older qemu will be fine at first, but at the next
> reset _following_ migration, it'll be running the old BIOS on a new
> qemu and fail.
> 
> -- Jamie

So after discussion with Gleb, it seems that what will happen
after migration to new qemu, old BIOS is shadowed, but memory
is already enabled.  After reset, new BIOS will be shadowed
and it will enable memory. Makes sense?

-- 
MST