Changing physmem from an int to a physaddr_t should fix the
memory-size problem. knowing Jason he probably caught that one already.
No idea where else sign extension will bite.

But does this machine really have 4GB - 96 Mbytes? 96Mbytes of
physical address space doesn't sound like a lot for PCI memory devices
(frame grabbers, linear-mode video cards), etc.  Or is it?