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Re: A few patches for 2.4.x for Alpha...

Sorry for jumping in a bit late...

On Tuesday,  7 Aug, Andrea Arcangeli wrote:
> On Wed, Aug 01, 2001 at 06:53:17PM -0400, Daniel Potts wrote:
> > It appears to me that the self-mapping entry in each task page table is
> > somehow getting corrupted, causing user mode permission bits to be set. I
> > don't even know why we have this mapping because a running kernel does not
> > use it. While the patch does make it go away, I'm still concerned that
> > something just happened to trash that memory. This one needs to be examined
> > closer.
> > 
> > Line 63 of linux-2.4.7/arch/alpha/mm/init.c
> I think the problem is that that is an entry in the pgd, it's not a pte,
> so it's a kind of corrupted entry in first place. I also don't know how
> can it be useful so I like your patch.

I always thought that the self-mapping entry was used by PALcode to
quickly handle TLB misses.  When the appropriate entries of page table
self-mapping are not cached in DTBs, PALcode has to descend through page
tables.  I don't remember what happens if the self-mapping is not provided
at all - if things are still working, it means that PALcode has to go the
"slow" way for every TLB miss.


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