> What sort of device exposes regions of memory in I/O space? When I think of
> hypervisors emulating devices, all their registers typically *do stuff*
> when you write to them.

Historically, video cards and network cards definitely had memory
buffers in what RISC-V would consider I/O space.  Yes, typical video
and networking hardware may work differently today, but can we be
certain there are absolutely no such devices any more of any kind that
we need to care about?  And will never be in the future, either?

I'd be fine if the answer is "yes", but I'm sure not willing to commit
to that answer solely on my own incomplete knowledge.

    - John Hauser