quoted

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.