Re: kvm PCI assignment & VFIO ramblings

Joerg Roedel
2011-08-04T10:41:05Z

On Mon, Aug 01, 2011 at 02:27:36PM -0600, Alex Williamson wrote:
> It's not clear to me how we could skip it. With VT-d, we'd have to
> implement an emulated interrupt remapper and hope that the guest picks
> unused indexes in the host interrupt remapping table before it could do
> anything useful with direct access to the MSI-X table. Maybe AMD IOMMU
> makes this easier?

AMD IOMMU provides remapping tables per-device, and not a global one.
But that does not make direct guest-access to the MSI-X table safe. The
table contains the table contains the interrupt-type and the vector
which is used as an index into the remapping table by the IOMMU. So when
the guest writes into its MSI-X table the remapping-table in the host
needs to be updated too.

Joerg