I am interested in adding a new memory mapping option that establishes one identity-mapped region for all DMA_TO_DEVICE mappings and creates a new dynamic mapping for any DMA_FROM_DEVICE and DMA_BIDIRECTIONAL mappings. My thought is it should allow for a compromise between security and performance (in the case of networking) in that many of the server NICs drivers these days are running with mostly pinned or resused paged for Rx. By using an identity mapping for the Tx packets we should be able to significantly cut down on the IOMMU overhead for the device. The other advantage if this works is that we could use this to possibly do something like dirty page tracking in the case of a emulated version of the IOMMU.
I was originally thinking I could get away with just reusing the identity mapping code but it looks like that would end up merging everything into one domain if I am understanding correctly. Do I have that right? Would I be correct in assuming that I will need to have a separate domain per device, each domain containing the 1 TO_DEVICE identity mapped region, and then whatever other mappings are needed to handle the FROM and BIDIRECTIONAL mappings? Thanks. - Alex _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
