Re: [RFC/PATCH] mm: Pass virtual address to [__]p{te,ud,md}_free_tlb()

On Wed, 2009-07-15 at 15:56 +0200, Nick Piggin wrote:

On Wed, Jul 15, 2009 at 05:49:47PM +1000, Benjamin Herrenschmidt wrote:

quoted

Upcoming paches to support the new 64-bit "BookE" powerpc architecture
will need to have the virtual address corresponding to PTE page when
freeing it, due to the way the HW table walker works.

Basically, the TLB can be loaded with "large" pages that cover the whole
virtual space (well, sort-of, half of it actually) represented by a PTE
page, and which contain an "indirect" bit indicating that this TLB entry
RPN points to an array of PTEs from which the TLB can then create direct
entries.

RPN is PFN in ppc speak, right?

Ah right, real page number in ppc slang :-)

quoted

Thus, in order to invalidate those when PTE pages are deleted,
we need the virtual address to pass to tlbilx or tlbivax instructions.

Interesting arrangement. So are these last level ptes modifieable
from userspace or something? If not, I wonder if you could manage
them as another level of pointers with the existing pagetable
functions?

I don't understand what you mean. Basically, the TLB contains PMD's.
There's nothing to change to the existing page table layout :-) But
because they appear as large page TLB entries that cover the virtual
space covered by a PMD, they need to be invalidated using virtual
addresses when PMDs are removed.

quoted

The old trick of sticking it somewhere in the PTE page struct page sucks
too much, the address is almost readily available in all call sites and
almost everybody implemets these as macros, so we may as well add the
argument everywhere. I added it to the pmd and pud variants for consistency.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

I would like to merge the new support that depends on this in 2.6.32,
so unless there's major objections, I'd like this to go in early during
the merge window. We can sort out separately how to carry the patch
around in -next until then since the powerpc tree will have a dependency
on it.

Can't see any problem with that.

Thanks, can I get an Ack then ? :-)

Cheers,
Ben.