Comment by tremon

I built that setup over a decade ago, when I virtualized my parents' WinXP installation and gave them Debian on the host.

  - transparent ethernet switch on the host (i.e. br0)
  - old disk copied into an LVM volume (to ease with later migrations and partition growth)
  - qemu instance managed by virt-manager (for autostart and managed shutdown)
  - tty5 linked to spice-client in its own X server (i.e. startx -- spice-client-gtk in inittab)

I considered my solution kinda hacky back then, it effectively ran the entire spice client as root. But it did what it needed to do, and I'm sure it would have been trivial to add a su call somewhere in the startup chain.

I'm sure that between systemd and virtd the same solution should be easier to build today, if it weren't for Wayland and logind complicating the hell out of single-app (think kiosk mode) display sessions.