Extremely slow boot on VMWare with Opteron 2352 (acpi?)

[Ryan Stone]

256MB is correct.  The PCI standard allows for up to 256 buses, each
with up to 32 slots, and each slot can have up to 8 functions.  PCIe
devices have a full 4096 bytes worth of configuration registers.
Multiply all that and you get 256MB.

Also, keep in mind that it's not allocating 256MB of memory; it's
allocating 256MB of address space and memory-mapping the configuration
registers in that space.