On Mo, 2014-01-20 at 13:23 +0200, Michael S. Tsirkin wrote:
> On Tue, Dec 17, 2013 at 06:56:06PM +0100, Gerd Hoffmann wrote:
> > > I merged your patch but split it: q35 is separate and piix
> > > is separate. Would you like me to drop the q35 part then?
> >
> > If you are fine with q35 having only 2G lowmem keep it. It's safe.
> >
> > We can sort the mmconfig setup afterwards, then check if (and how) we'll
> > transition to 3G lowmem. Maybe we simply don't after all, with the
> > world moving to 64bit it doesn't matter that much whenever memory is
> > mapped above or below 4g. And for old 32bit guests there is always the
> > option to stick with piix which continues to offers up to 3.5G lowmem.
> >
> > cheers,
> > Gerd
> >
>
> Any update here?
No time to investigate yet, still playing catch-up after xmas holidays &
being sick.
> I'm worried 2G lowmem is a bit too aggressive, PAE still exists.
piix (with up to 3.5g lowmem) exists too ;)
> If we want to support old bios, one way would be to add
> a new register to enable 3g lowmem.
Do we really want do this (allow guest change RAM mapping)?
I think we should:
(1) reserve mmconf xbar as motherboard ressource, so it can live within
PCI0._CRS
(2) make PCI0._CRS start at end of lowmem, like it does on piix
Then maybe:
(3) update seabios to place xbar somewhere else
(4) adjust memory layout.
(1)+(2) are useful anyway. (3)+(4) would allow for 3g lowmem, and
obviously have some compatibility issues: doing (4) requires a seabios
update.
cheers,
Gerd
