🚀 go-pugleaf

>So this is quite an old trick, and not really that difficult to do.  I would
>assume that current Unix/workstation systems do something similar.

Well, it's what Suns do.  Suns with "Sun-style" static RAM MMUs use the
MMU as a bus map - addresses on the I/O bus get run through the MMU
(after having, e.g. 0xFF stuck in as the top byte) to get the physical
address to which they refer.  Some, perhaps all, Suns with
in-memory-page-table MMUs have separate "I/O MMUs" for that purpose (the
3/80 and 3/4xx, which used the 68030's MMU as the main MMU, did, as do
the SPARC Reference MMU machines, or at least the Sun-4m machines; dunno
about the 386i).

Other UNIX boxes may or may not do that.