Hi all,
I think I just found an answer:
2.11 Configuration Space
This BKDG chapter suggest that there is a MSR which can be used to do MMIO accesses.
MSRC001_0058 MMIO Configuration Base Address Register
Note that all cores should have this addr. Also it seems that this is what\ it should be used in ACPI instead of the NB MCFG aperture.
Rudolf