[PATCH 2/7] powerpc/mm: 64-bit 4k: use a PMD-based virtual page table

[Benjamin Herrenschmidt]

On Mon, 2011-05-23 at 18:31 -0500, Scott Wood wrote:
> On Tue, 24 May 2011 06:51:01 +1000
> Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:
> 
> > Is your linear mapping bolted ? If it is you may be able to cut out most
> > of the save/restore stuff (SRR0,1, ...) since with a normal walk you
> > won't take nested misses.
> 
> It is bolted -- we ignore anything we can't map with 16 entries.  The only
> semi-realistic case I can think of where we might bump into that (and thus
> want non-bolted memory), especially with more than negligible loss compared
> to the size of memory, is AMP with a non-zero start address where we have
> to stick with smaller pages due to alignment. Even so, 16 times the
> alignment of the start of RAM doesn't seem that unreasonable a limit.  The
> 32-bit limit of 3 entries for lowmem is a bit more troublesome there.

Ok so in this case, it might be worth doing a separate of TLB miss
handlers without all the context save/restore business... would also
make re-entrant CRITs and MCs easier to deal with.

Cheers,
Ben.