> This is a vm bug in 1.2 and 1.3.  The pmap should allocate
> pde's when needed; it doesn't, rather the trap() code does.
> So, if you have a case where pages are wired (for raw access),
> you do not go thru trap() and do not create the pde's and you
> lose.
> Hints: Use a smaller bs, that way you are much less likely
> crossing over into vm w/o an allocate pde.  (A pde spans 4Meg.)

This can apparently be run into in the procfs/ptreace() code, as well,
in certain circumstances.  (I think Mark Brinicombe knows them better
than I; i've cc'd him in case he's on port-i386.)

(There was/is a problem with it on arm32, as well, that required a
gross hack to the procfs code which hasn't (yet?) gone back into the
master sources.  The same problem.)