[SeaBIOS] [Qemu-devel] [RFC] map 64-bit PCI devices after all possible RAM
imammedo at redhat.com
Thu Oct 10 15:17:58 CEST 2013
On Thu, 10 Oct 2013 15:21:32 +0300
"Michael S. Tsirkin" <mst at redhat.com> wrote:
> On Thu, Oct 10, 2013 at 02:14:16PM +0200, Gerd Hoffmann wrote:
> > Hi,
> > > I think the simplest way to do all this is simply to tell seabios
> > > that we have more memory. seabios already programs 64 bit BARs
> > > higher than memory.
> > Hmm? As I understand Igor just wants some address space for memory
> > hotplug. So there wouldn't be memory there (yet). And telling seabios
> > there is although there isn't will make seabios place wrong info into
> > the e820 tables. Not going to fly.
> True. Maybe we should get some smbios stuff from qemu too.
> > > I think the issue is with legacy guests.
> > > E.g. if VCPU claims to support 50 bit of memory
> > > do we put high PCI memory at 1 << 50?
> > > If yes old guests which expect at most 40 bit
> > > will not be able to use it.
> > Hmm. Sure such guests exist?
> I wouldn't be surprised. At least some windows
> guests crash if you try to tell them your system
> has too much physical memory (e.g. 2^48).
confirmed, the same happened when memory device was mapped too high,
can't recall windows version tough.
> > Note this is physical address lines, not
> > virtual address space (where you might need an additional level of
> > pagetables to fully use it, which is not something we could expect old
> > guests being able to handle).
> > cheers,
> > Gerd
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