[lxc-users] /proc/mtrr permissions inside container keep X from running inside LXC without root, but only for radeon?

[Dan Kegel]

Hey all,
I'm running X inside lxc containers on ubuntu 16.04.
The script I'm using to tweak lxc configuration to support X is
http://kegel.com/linux/lxc-opengl-demo/install-x.sh.txt
Seems to work fine for intel and nvidia, but for amd graphics (two
different systems so far), it complains
  Fatal server error: AddScreen/ScreenInit failed for driver 0
strace shows that X can't open /proc/mtrr.
Running startx as root works around the problem, but that shouldn't be needed.
Can I buy a clue here?   Thanks!
- Dan

p.s. To reproduce:

# Bring down X
host$ sudo systemctl start multi-user.target
# Create a container, add a user, give him sudo, start in foreground
host$ sudo lxc-create -n video -t download  -- --dist ubuntu --release
xenial --arch amd64
host$ wget http://kegel.com/linux/lxc-opengl-demo/install-x.sh
host$ sudo sh install-x.sh host video
host$ sudo lxc-start -n vdeo
host$ sudo lxc-attach -n video adduser fred
host$ sudo lxc-attach -n video vi /etc/group  # add fred to sudo group
# Restart the container in the foreground
host$ sudo lxc-stop -n vdeo
host$ sudo lxc-start -n video -F
# Log in to the guest as user fred, then:
video$ wget http://kegel.com/linux/lxc-opengl-demo/install-x.sh
# Alas, you have to run install-x.sh guest every time you start the
container, to recreate /dev stuff.
video$ sudo sh install-x.sh guest
# Only if you're using nvidia hardware: Install nvidia driver that
matches outer host.  Careful.  e.g.
#video$ sudo apt install nvidia-340
# Finally, start x in the container
video$ echo "exec xterm" > .xinitrc
video$ startx -- vt9

This should give you an xterm with working keyboard and mouse, capable
of running glxgears, etc.