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Re: [Xen-devel] Multi-bridged PCIe devices (Was: Re: iommuu/vt-d issues with LSI MegaSAS (PERC5i))

 >>> On 11.09.13 at 13:44, Gordan Bobic <gordan@xxxxxxxxxx> wrote:
> This got me thinking - if the problem is broken IOMMU implementation,
>  is the IOMMU _actually_ required for PCI passthrough to HVM
>  guests if all the memory holes and BARs are made exactly the same
>  in dom0 and domU? If vBAR=pBAR, then surely there is no memory
>  range remapping to be done anyway - which means that there
>  is no need for the strict IOMMU requirements (over and above
>  the requirements and caveats of PV domUs).

But with this you ignore the need to handle device bus mastering
activities. In order to work without IOMMU, the guest's memory
addresses would also require guest-physical = machine-physical.


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