Other than implementation objections, so far the two main arguments
against this reduce to:
1. If you allow UIO ioctl then it opens an API hook for all the crap out
of tree UIO drivers to do what they want.
2. If you allow UIO MSI-X then you are expanding the usage of userspace
device access in an insecure manner.
Another alternative which I explored was making a version of VFIO that
works without IOMMU. It solves #1 but actually increases the likely negative
response to arguent #2. This would keep same API, and avoid having to
modify UIO. But we would still have the same (if not more resistance)
from IOMMU developers who believe all systems have to be secure against
root.
