Re: [Qemu-devel] [PATCH v2 0/6] x86: Physical address limit patches

[Michael S. Tsirkin]

On Tue, Jul 05, 2016 at 12:59:42PM +0200, Paolo Bonzini wrote:
> 
> 
> On 05/07/2016 12:06, Michael S. Tsirkin wrote:
> > >      -m 2G,slots=16,maxmem=2T
> > > 
> > > On a host with a 39bit physaddress limit do you error
> > > on that or not?  I think oVirt is currently doing something
> > > similar to that, but I'm trying to get confirmation.
> > 
> > That would only be a problem since pci is allocated above
> > maxmem so 64 bit pci addresses aren't accessible.
> > With my proposal we can actually force firmware to avoid
> > using 64 bit memory for that config.
> > Will work better than today.
> 
> So you would remove completely the 64-bit _CRS in this case?

Yes.

> How do you handle migration in the above scenario from say 46bit host to
> 39bit host, where the firmware has mapped (while running on the source)
> a 64-bit BAR above the destination's maximum physical address?
> 
> Thanks,
> 
> Paolo

Again management would specify how much 64 bit pci space firmware should use.
If more is specified than host can support we can error out.

-- 
MST