Re: [Qemu-devel] [RFC PATCH v2 05/21][SeaBIOS] pciinit: Fix pcimem_start value

[Vasilis Liaskovitis]

On Thu, Jul 12, 2012 at 09:22:14AM +0200, Gerd Hoffmann wrote:
> On 07/11/12 18:45, Vasilis Liaskovitis wrote:
> > Hi,
> > 
> > On Wed, Jul 11, 2012 at 01:56:19PM +0200, Gerd Hoffmann wrote:
> >> On 07/11/12 12:31, Vasilis Liaskovitis wrote:
> >>> In order to hotplug memory between RamSize and BUILD_PCIMEM_START, the pci
> >>> window needs to start at BUILD_PCIMEM_START (0xe0000000).
> >>> Otherwise, the guest cannot online new dimms at those ranges due to 
> >>> pci_root
> >>> window conflicts. (workaround for linux guest is booting with pci=nocrs)
> >>
> >>>  static void pci_bios_map_devices(struct pci_bus *busses)
> >>>  {
> >>> -    pcimem_start = RamSize;
> >>> +    pcimem_start = BUILD_PCIMEM_START;
> >>
> >> It isn't that simple.  For the 32bit pci window it will work, but will
> >> leaves address space unused instead of assigning it to the 32bit pci
> >> window.  For the 64bit pci window it will not work.
> >>
> >> You have to walk the dimms and figure what the highest used address is,
> >> for both below-4g and above-4g.  Then fill two variable with it and make
> >> the pci init code use that instead of RamSize and RamSizeOver4G.
> > 
> > I see. I already have these values values computed in qemu-kvm, so I can 
> > pass
> > them in a paravirt struct, or infer them from the dimm/srat paravirt info 
> > that I
> > already pass to seabios. 
> 
> I'd suggest to infer from the dimm info, to limit the amout of
> information which needs to be passed from qemu to seabios.

ok.Currently dimm info is processed in bios_init_tables(), which is called after
pci_setup(). I 'll see if i can do the processing earlier.

> 
> > If i understand correctly, we would like the pcimem windows to use the 
> > maximum
> > possible address space (constrained by the exact dimms/ranges which are 
> > defined)
> > instead of leaving unused space.
> 
> Yes, for the 32bit pci window.
> 
> The 64bit pci window is mapped above all memory, and it must likewise
> consider defined+unfilled dimms so the start address doesn't collide
> with memory hot-plugged above 4G later on.

yes, understood.

thanks,

- Vasilis