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Date: Fri, 8 Sep 2017 14:44:37 +1000
From: Nicholas Piggin <npiggin@gmail.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: linuxppc-dev@lists.ozlabs.org, "Aneesh Kumar K . V"
 <aneesh.kumar@linux.vnet.ibm.com>, Anton Blanchard  <anton@samba.org>
Subject: Re: [RFC PATCH 8/8] powerpc/64s/radix: Only flush local TLB for
 spurious fault flushes
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On Fri, 08 Sep 2017 08:05:38 +1000
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> On Fri, 2017-09-08 at 00:51 +1000, Nicholas Piggin wrote:
> > When permissiveness is relaxed, or found to have been relaxed by
> > another thread, we flush that address out of the TLB to avoid a
> > future fault or micro-fault due to a stale TLB entry.
> > 
> > Currently for processes with TLBs on other CPUs, this flush is always
> > done with a global tlbie. Although that could reduce faults on remote
> > CPUs, a broadcast operation seems to be wasteful for something that
> > can be handled in-core by the remote CPU if it comes to it.
> > 
> > This is not benchmarked yet. It does seem cut some tlbie operations
> > from the bus.  
> 
> What happens with the nest MMU here ?

Good question, I'm not sure. I can't tell from the UM or not if the
agent and NMMU must discard cached translations if there is a
translation cached but it has a permission fault. It's not clear 
from that I've read that if it's relying on the host to send back a
tlbie.

I'll keep digging.

Thanks,
Nick