🚀 go-pugleaf

Kristoffer Eriksson <ske@pkmab.se> writes in message <1251@pkmab.se>
>
> How can the OS and MMU provide any protection, if they don't care what
> program is using what memory?

Imagine the Unix OS where each program has its own addressing space. Every
program then has its virtual pages mapped either onto disk, or onto some
scattered chunks of physical memory. Each program therefore has its own
translation table which maps a virtual addressing range starting at 0.

On a single addressing space OS, you have the exact same thing, except that
rather than having the virtual addresses start at 0, they start at arbitrary
and exclusive locations.

This is not the ideal implementation, but it is the best one the 68851 can
offer. If I were allowed to design my own MMU, I would use a single translation
table, where each page descriptor entry would also contain an "owner" field.
This owner field would then be compared to the current task ID, and thus the
access priviledge would be determined. Easy thing to design, but since the
68030 & 68040 have 68851-like MMUs already built in, this would be a waisted
effort.

Valentin
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