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Date: Thu, 17 Dec 2015 16:09:17 +0100
From: Peter Zijlstra <peterz@infradead.org>
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Subject: Re: [Qemu-devel] [PATCH] virtio_ring: use smp_store_mb
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>, Will Deacon <will.deacon@arm.com>, qemu-devel@nongnu.org, Alexander Duyck <alexander.duyck@gmail.com>, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org

On Thu, Dec 17, 2015 at 04:34:57PM +0200, Michael S. Tsirkin wrote:
> On Thu, Dec 17, 2015 at 03:02:12PM +0100, Peter Zijlstra wrote:

> > > 	commit 9e1a27ea42691429e31f158cce6fc61bc79bb2e9
> > > 	Author: Alexander Duyck <alexander.h.duyck@redhat.com>
> > > 	Date:   Mon Apr 13 21:03:49 2015 +0930
> > > 
> > > 	    virtio_ring: Update weak barriers to use dma_wmb/rmb
> > 
> > That commit doesn't make any sense. dma_*mb() explicitly does _NOT_
> > cover the smp_*mb() part.
> > 
> > Again, look at the ARM definitions, the smp_*mb() primitives use the
> > inner coherence stuff, while the dma_*mb() primitives use the outer
> > coherent stuff.
> 
> Does outer coherent imply inner coherent?
> 
> > the *mb() primitives cover both.

I do not think so, but lets add Will, he dreams this stuff.