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

On Tue, Jul 21, 2009 at 10:02:26AM +1000, Benjamin Herrenschmidt wrote:

On Mon, 2009-07-20 at 12:38 +0200, Nick Piggin wrote:

quoted

On Mon, Jul 20, 2009 at 08:00:41PM +1000, Benjamin Herrenschmidt wrote:

quoted

On Mon, 2009-07-20 at 10:10 +0200, Nick Piggin wrote:

quoted

Maybe I don't understand your description correctly. The TLB contains
PMDs, but you say the HW still logically performs another translation
step using entries in the PMD pages? If I understand that correctly,
then generic mm does not actually care and would logically fit better
if those entries were "linux ptes". 

They are :-)

quoted

The pte invalidation routines
give the virtual address, which you could use to invalidate the TLB.

For PTEs, yes, but not for those PMD entries. IE. I need the virtual
address when destroying PMDs so that I can invalidate those "indirect"
pages. PTEs are already taken care of by existing mechanisms.

Hmm, so even after having invalidated all the pte translations
then you still need to invalidate the empty indirect page? (or
maybe you don't even invalidate the ptes if they're not cached
in a TLB).

The PTEs are cached in the TLB (ie, they turn into normal TLB entries). 

We need to invalidate the indirect entries when the PMD value change
(ie, when the PTE page is freed) or the TLB would potentially continue
loading PTEs from a stale PTE page :-)

Hence my patch adding the virtual address to pte_free_tlb() which is the
freeing of a PTE page. I'm adding it to the pmd/pud variants too for
consistency and because I believe there's no cost.

Yes I think we're on the same page now. So as I said, the
patch is quite OK with me.