Subject: Re: vm changes from linux-2.6.14 to linux-2.6.15

From: Benjamin Herrenschmidt <[email-masked]>
Date: Tue, 01 May 2007 10:00:19 +1000

> > Interesting - thanks for working that out.  Let's keep linux-mm on cc please.
> 
> You can't elide the update_mmu_cache() call on sun4c because that will
> miss some critical TLB setups which are performed there.
> 
> The sun4c TLB has two tiers of entries:
> 
> 1) segment maps, these hold ptes for a range of addresses
> 2) ptes, mapped into segment maps
> 
> update_mmu_cache() on sun4c take care of allocating and setting
> up the segment maps, so if you elide the call this never happens
> and we fault forever.

Maybe we can move that logic to ptep_set_access_flags()... in fact, the
tlb flush logic should be done there too imho.

There would still be the update_mmu_cache() that we don't want on
powerpc in all cases I suppose. That can be done by having
ptep_set_access_flags() return a boolean indicating wether
update_mmu_cache() shall be called or not ...

Ben.