[Source](https://superuser.com/a/628381)
Add
```
-virtfs local,path=/path/to/share,mount_tag=host0,security_model=passthrough,id=host0
```
to the `qemu-system` invocation and add
```
host0 /wherever 9p trans=virtio,version=9p2000.L 0 0
```
to the `/etc/fstab`.