context overflow

[Paul Mackerras]

Dan Malek writes:

> Heh :-)....Right, but it will require a context, and active_mm is
> the proper place to store/retrieve it.  Doesn't the HIGHMEM option
> require we properly use a kernel context?  Or, do we just get lucky
> there, too :-).

The way we do things on 6xx/7xx, kernel accesses to addresses >=
0xc0000000 don't depend on active_mm or on the currently selected
context at all.  We can effectively choose a different context for
each 256MB segment of the address space, and we always choose context
0 for segments 0xc to 0xf.  Further, the hash_page routine looks in
swapper_pg_dir for linux PTEs for addresses >= 0xc0000000, rather than
in the page tables associated with current->active_mm or current->mm.

--
Paul Mackerras, Open Source Research Fellow, Linuxcare, Inc.
+61 2 6262 8990 tel, +61 2 6262 8991 fax
paulus at linuxcare.com.au, http://www.linuxcare.com.au/
Linuxcare.  Putting Open Source to work.

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