Re: [PATCH 1/3] powerpc: implement barrier primitives

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On Wed, 2015-06-17 at 11:15 +0100, Will Deacon wrote:
> On Wed, Jun 17, 2015 at 10:43:48AM +0100, Andre Przywara wrote:
> > Instead of referring to the Linux header including the barrier
> > macros, copy over the rather simple implementation for the PowerPC
> > barrier instructions kvmtool uses. This fixes build for powerpc.
> > 
> > Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> > ---
> > Hi,
> > 
> > I just took what kvmtool seems to have used before, I actually have
> > no idea if "sync" is the right instruction or "lwsync" would do.
> > Would be nice if some people with PowerPC knowledge could comment.
> 
> I *think* we can use lwsync for rmb and wmb, but would want confirmation
> from a ppc guy before making that change!

Ugh, memory barriers :)

You probably can use lwsync, assuming you're only ordering cacheable vs
cacheable.

But, lwsync has given us pain in the past[1], so I'd be happier if you just used
sync.

cheers

[1]: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=51d7d5205d3389a32859f9939f1093f267409929


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