Re: [Qemu-devel] [SeaBIOS] [PATCH] acpi: hide 64-bit PCI hole for Windows XP

[Michael S. Tsirkin]

On Thu, Aug 08, 2013 at 10:51:59AM +0200, Gerd Hoffmann wrote:
> On 08/08/13 10:22, Michael S. Tsirkin wrote:
> > On Thu, Aug 08, 2013 at 09:57:39AM +0200, Gerd Hoffmann wrote:
> >>   Hi,
> >>
> >>>> Huh?  The 32bit window is sized according to the installed memory.
> >>>> That
> >>>> logic is in seabios and you'll try to move it to qemu, using pci-info.
> >>>> It wasn't in qemu before ...
> >>>
> >>> The logic is in hw/i386/pc_piix.c and always was.
> >>
> >> What exactly you are refering to?
> > 
> > pc_init1 which picks addresses and passes them on to
> > i440fx_init.
> 
> Yep.  qemu figured where it wants map memory.  The unused 32bit address
> space goes into the pci hole.  cmos memory size is set accordingly.
> seabios gets the memory size from cmos, then it knows where the pci hole
> starts.  seabios rounds it up (i.e. may leave some of it unused) to be
> able to cover the complete hole with a single mtrr entry, but that isn't
> a issue and can be changed if needed.  The mtrr thing is more or less
> cosmetical anyway in a virtual machine.
> 
> >> Memory configuration is in the cmos, firmware can figure where it can
> >> place pci devices from that.  There is no need for a new interface.
> > 
> > The assumption being that whatever is not memory is PCI?
> > I'm not sure that's right.
> 
> Maybe not in general, but I'm pretty sure for the x86 chipsets we are
> emulating it is.

I think this is the basic question.

Speaking about PIIX:
http://download.intel.com/design/chipsets/datashts/29054901.pdf
it only supported 1G RAM and 32 bit PCI.

What happened with RAM below 1G is this:
 top of RAM to 0xfec00000 is PCI - this is emulated correctly
 fec10000 to ffe00000 is PCI - this is not emulated correctly

What happens with RAM >1G is all PV, it doesn't exist
on real hardware.

Re-adding qemu-devel. Can you please keep it Cc'd?

-- 
MST