Re: [Qemu-devel] [PATCH 13/13] iommu: Add a memory barrier to DMA RW function

[Benjamin Herrenschmidt]

On Thu, 2012-05-17 at 07:10 +1000, Benjamin Herrenschmidt wrote:

> I have a long experience with dealing with ordering issues on large SMP
> systems and believe me, anything "fine grained" is really really hard to
> generally get right, and the resulting bugs are really nasty to track
> down and even identify. So I have a strong bias toward the big hammer
> approach that is guaranteed to avoid the problem for anything using the
> right DMA accessors.

BTW, this is going to also hurt SMP ARMs ... ARM is getting increasingly
out of order as well.

Cheers,
Ben.