virt_to_page(phys_to_virt(masked_addr)) still works.  But the 460GX
sticks bits in the middle, so the free blows up.

I've tested the agp_allocate_memory() change on Intel 460GX.  I don't have
hardware to test the Intel MCH change, but it looks to me like the same
problem.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Dave Jones <davej@redhat.com>