OH NO!! The funmap system call will unmap the grant by default, but
we haven't necessarily created a grant with fmap, we may very well
just have given the pointer of a physical region!
This will fail!! Is this "abuse" of fmap bad? Do we keep the phys* functions instead? If no, how do we fix this? Do we make each kernel scheme responsible for clearing up the grants themselves?
Depends on syscall!57