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Subject: Re: [for-4.8, 1/2] powerpc/mm: Switch user slb fault handling to
 translation enabled
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Nicholas Piggin <npiggin@gmail.com>, "Aneesh Kumar K.V"
 <aneesh.kumar@linux.vnet.ibm.com>
Cc: paulus@samba.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org
Date: Fri, 22 Jul 2016 23:40:43 +1000
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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.