tlb flushing on Power

[Benjamin Herrenschmidt]

> You can look at https://lkml.org/lkml/2012/1/9/389 in zsmalloc-main.c,
> zs_[un]map_object() functions for the currently uses of set_pte() and
> __flush_tlb_one().
> 
> > set_pte() is long gone on all archs really (or if it's still there it's
> > not meant to be used as is), use set_pte_at().
> 
> Problem with set_pte_at() for us is that we don't have an mm_struct to pass
> because the mapping is not for a userspace process but for the kernel itself.

Then use init_mm

> However, I do think this is the portable function we need to be using. Just
> need to figure out what to pass in for the mm_struct param.
> 
> > __flush_tlb_one() doesn't mean anything as an arch independent
> > functionality. We have a local_flush_tlb_page() that -might- do what you
> > want but why in hell is that patch not using proper existing
> > interfaces ?
> 
> flush_tlb_page() is the portable function we should be using.  However,
> again, it requires a vma_area_struct.  I'm not sure what we should be
> passing there.

Do you need this to be CPU local flush or global ? In the later, 
flush_tlb_kernel_range() is the right API.

If you want per-cpu, we'll have to add a new arch hook.

Cheers,
Ben.