linux-kernel - Re: [RFC][PATCH 1/5] mm: Rework {set,clear,mm}_tlb_flush

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Date:   Wed, 02 Aug 2017 11:23:12 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>
Cc:     torvalds@...ux-foundation.org, oleg@...hat.com,
        paulmck@...ux.vnet.ibm.com, mpe@...erman.id.au, npiggin@...il.com,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        stern@...land.harvard.edu, Mel Gorman <mgorman@...e.de>,
        Rik van Riel <riel@...hat.com>
Subject: Re: [RFC][PATCH 1/5] mm: Rework {set,clear,mm}_tlb_flush_pending()

On Wed, 2017-08-02 at 00:59 +0200, Peter Zijlstra wrote:
> > PowerPC for example uses PTESYNC before the TBLIE, so does a SYNC after
> > work? Ben?
> > From what I gather it is not. You have TLBSYNC for it. So the good news

tlbsync is pretty much a nop these days. ptesync is a strict superset
of sync and we have it after every tlbie.

> is that PPC-radix does all that and is fully serialized on the tlb
> flush. Not sure for the PPC-hash case.
> 
> At the same time, smp_mb() is not sufficient on ARM either, they need a
> DSB barrier on both ends.
> 
> So are we going to mandate tlb flush implementations are completely
> ordered ?

Cheers,
Ben.