Re: vfio: missing patch in linux 3.6

["Roedel, Joerg" <Joerg.Roedel@amd.com>]

On Thu, Oct 04, 2012 at 10:28:00AM -0600, Alex Williamson wrote:
> There are a couple questions in the link above.  Since the devices don't
> expose a PCIe capability, we probably need to add a check to look at the
> upstream device and verify we're not on a legacy bus where ACS can't be
> enforced.

You can certainly do that, but for existing hardware (with an AMD IOMMU)
this check would never be true. These devices are always on a seperate
south-bridge chip which is connected to the north-bridge via PCIe. So
the topology where you find these devices is always the same in an AMD
IOMMU system.

> Then there's the general question of whether the confirmation
> of no peer-to-peer applies to every case where we might see this device
> (some of them seem to have history that pre-dates this specific package
> implementation) or do we need to try to identify specific package
> properties in addition to just a device ID?

The device ids are kept the same to maintain compatability with older
software. Besides that, my statement about the peer-2-peer safety is
true for all south-bridges that you can find in an AMD IOMMU capable
system.

Regards,

	Joerg

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