pmap_enter() masked off the page offset bits, pmap_kenter() did not.
This (I believe) is the cause of the XFree86 startup and/or mptable(8)
panics when programs were reading from /dev/mem at non-page-aligned
offsets. The offsets were being converted into random page flags in the
page tables. :-( (including PG_PS = 4MB page size)