VirtIO MMIO for amd64

I've been working on a NetBSD-based unikernel and trying to make it 
compatible with the Firecracker VMM. Seeing as Firecracker only supports 
the MMIO transport method for VirtIO, I wanted to implement MMIO support 
for my unikernel.

I've seen that newer versions of NetBSD than what my source code was 
using have code for MMIO and specifically that Virtio MMIO support was 
implemented for ARM in NetBSD 9.0. So, what I want to ask is there 
similar support for amd64 also and if not are there some basics I could 
imitate from how it was implemented for ARM to get it working for amd64 
also? Alternatively, is there any reading material you can suggest that 
explains how the device system works in NetBSD, so that I might possibly 
understand what changes would be needed by myself?

I don't know if this is the most suitable mailing list for this 
question, but if you think there is a better place to ask, I'd be glad 
to do so.

--
George Gkanas