Share host memory with a guest running no operating system

[John Ramsden]

I'm attempting to share host memory with a guest running no operating system 
using `-object 
memory-backend-file,id=mem0,size=4G,mem-path=/dev/shm/qemu,share=on`. When I 
try this using a guest with an operating system such as Ubuntu, I see my object 
mem0 in `info mtree`, and I'm able to write to `/dev/shm/qemu` on the host and 
read the changed memory on the VM - similar to this blog post (I am not the 
author) https://blog.reds.ch/?p=1379. This doesn't seem to work when I have a 
guest without an operating system, there is no `mem0` device. In case it's 
relevant I am using an arm64 guest.

Do I need a guest operating system to use this feature?