Moved from a two level 512/1024 entry setup mapping 32 (9/10/13) bits
respectively to a three level 1024/1024/1024 entry setup mapping 43
(10/10/10/13) bits. In 32-bit mode we waste about 1/12 pages mapping the high
11 bits. We also only manage 43 of the possible 44 bits of virtual address
space, wasting half of it. Oh well, maybe we'll do better next revision.
a465fdedc6