Re: [RFC][PATCH 1/5] mm: Rework {set,clear,mm}_tlb_flush_pending()

From: Peter Zijlstra
Date: Tue Aug 01 2017 - 12:48:47 EST

On Tue, Aug 01, 2017 at 05:44:14PM +0100, Will Deacon wrote:
> On Tue, Aug 01, 2017 at 06:39:03PM +0200, Peter Zijlstra wrote:
> > Still this is all rather unsatisfactory. Either we should define
> > flush_tlb*() to imply a barrier when its not a no-op (sparc64/ppc-hash)
> > or simply make clear_tlb_flush_pending() an smp_store_release().
> >
> > I prefer the latter option.
> >
> > Opinions?
> I prefer the latter option too, since I'd like to relax the arm64 TLB
> flushing to have weaker barriers for the local case. Granted, that doesn't
> break the NUMA migration code, but it would make the barrier semantics of
> the TLB invalidation routines even more subtle if we were to define them
> generally.

Another 'fun' question, is smp_mb() strong enough to order against the
TLB invalidate? Because we really want to clear this flag _after_.

PowerPC for example uses PTESYNC before the TBLIE, so does a SYNC after
work? Ben?