[SeaBIOS] [RFC] map 64-bit PCI devices after all possible RAM

Gerd Hoffmann kraxel at redhat.com
Wed Oct 9 15:12:08 CEST 2013

On Mi, 2013-10-09 at 14:23 +0200, Igor Mammedov wrote:
> I'm posting it to get an oppinion on one of possible approaches
> on where to map a hotplug memory.
> This patch assumes that a space for hotplug memory is located right
> after RamSizeOver4G region and QEMU will provide romfile to specify
> where it ends so that BIOS could know from what base to start
> 64-bit PCI devices mapping.

We should think about both pci hotplug and memory hotplug while being at

Today the 64bit pci window is mapped right above high memory and is
sized (in acpi tables) according to what is needed to map the devices
present at boot.

Effect is that there is no extra address space for 64bit bars of
hotplugged pci devices.  And the window is also in the way when it comes
to memory hotplug.

Given that some windows versions don't like the large 64bit windows we
should make the window size configurable.

The window location can either be made configurable too, or we simply
place it at the top of the address space, with "address space" being
what the cpu can address according to cpuinfo.

Current qemu reports this by default:

  $ cat /proc/cpuinfo 
  model name	: QEMU Virtual CPU version 1.5.3
  address sizes	: 40 bits physical, 48 bits virtual

40 address lines allow 1TB, so we would place the window just below 1TB.



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