We have got some issues with 64bit PCI devices support under Windows guests. Windows fails to start any PCI devices with 64bit BARs when size exceeds 512MB with error code 12 (can't allocate resources). In other words it fails when the PCI memory region is located above 4GB.
I tried to investigate this problem and found document from Microsoft: http://msdn.microsoft.com/en-us/windows/hardware/gg462986
It states that the _DSM method must be implemented to support devices above 4GB.
Unfortunately I'm not familiar with ACPI code of seabios, so can't implement the _DSM method. May be you have other ideas what needs to be done to fix it? Any help is appreciated.