Yep, vm-memory needs pretty large changes to the crate itself but fortunately they're already in progress to add IOMMU support to the virtio and vhost crates. Probably there will be an API break but with old and new crates able to talk to each other so you don't need a flag day.

I am curious if you get to DMA before or after QEMU, and if before what your API will look like.

Very little free time unfortunately... Haven't spent many hours on this project.