On Wed, May 20, 2015 at 03:15:59PM -0400, Mark Hounschell wrote:
> On 05/20/2015 01:30 PM, William Davis wrote:
> >In an IOMMU environment, the DMA ops would be one of the IOMMU
> >implementations, so these APIs would create a mapping for the peer device
> >resource, even if it's on the same bus. Would a transaction targeting that
> >mapping be forwarded upstream until it hits an IOMMU, which would then send
> >the translated request back downstream? Or is my understanding of this
> >configuration incorrect?
> >
>
> It's my understanding of the IOMMU that is lacking here. I have no
> idea if that is actually what would happen. Does it?
On the x86 side at least the IOMMU drivers enable ACS when available,
forcing all perr-to-peer DMA between PCIe devices to go through the
IOMMU. This only works when the peers are in different iommu groups,
though.
Joerg
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