[XEN-IOMMU] Proposal of DMA protection/isolation support

["Wei Wang2" <wei.wang2@amd.com>]

hi list,
I am considering adding DMA protection/isolation support for iommu
machine:  Below are the suggested approaches to be discussed:

1) Para-virtualized IOMMU
If it is possible to integrate IOMMU driver into guest kernel, we can
just implement a set of para-virtualized interface to forward hardware
operations from guest to HV. Guest kernel will allocation IO page table
for itself, but IO-PTE updating is verified by HV through hypercall.

2) IOMMU-aware dma layer.
Currently, driver domain utilizes swiotlb to get dma_address below 4G,
which is an additional overhead to IOMMU machine. For IOMMU machine, we
can implement a new dma layer which takes "guest_domain-id",
"device_bdf", and "guest_page" information as parameters and returns
virtual io address to guest OS. Guest OS only have very limited
knowledge/control to IOMMU. In this case, HV will allocate and update IO
page table for guest domain.

3) Hooking guest memory changes
No guest OS modification is needed in this approach.  All we need is to
update IO page table when guest physical memory changes triggered by
domain initialization, ballooning, and grant reference mapping...

Thanks for any comments, ideas, corrections... to this thread.

-Wei