Subject: Re: [for-4.8, 1/2] powerpc/mm: Switch user slb fault handling to translation enabled

From: Benjamin Herrenschmidt <[email-masked]>
Date: Fri, 22 Jul 2016 23:40:43 +1000

On Fri, 2016-07-22 at 22:37 +1000, Nicholas Piggin wrote:
> > We also handle fault with proper stack initialized. This enable us
> to
> > callout to C in fault handling routines. We don't do this for
> kernel
> > mapping, because of the possibility of taking recursive fault if
> > kernel stack in not yet mapped by an slb entry.
> > 
> > This enable us to handle Power9 slb fault better. We will add
> bolted
> > entries for the entire kernel mapping in segment table and user slb
> > entries we take fault and insert on demand. With translation on, we
> > should be able to access segment table from fault handler.
> 
> What does this cost on P8? Is that a problem? Might need to do
> feature bits.

Also what is the need ?

The segment table is only for Nest MMU clients, we should probably
handle it separately.

Cheers,
Ben.