Thanks Daniel for helping with this :)
# cat /proc/mounts
rootfs / rootfs rw 0 0
/dev/root / ext4 rw,noatime,data=ordered 0 0
devtmpfs /dev devtmpfs rw,relatime,size=1970508k,nr_inodes=492627,mode=755
0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,relatime 0 0
tmpfs /run tmpfs rw,relatime,mode=755 0 0
devpts /dev/pts devpts rw,relatime,gid=5,mode=620,ptmxmode=000 0 0
fusectl /sys/fs/fuse/connections fusectl rw,relatime 0 0
/dev/sda1 /media/oldslack ext4 rw,noatime,data=ordered 0 0
/dev/sdb1 /home ext4 rw,noatime,data=ordered 0 0
/dev/md0p1 /data ext4 rw,noatime,data=ordered 0 0
tmpfs /dev/shm tmpfs rw,relatime 0 0
gvfsd-fuse /home/poncez/.gvfs fuse.gvfsd-fuse
rw,nosuid,nodev,relatime,user_id=1000,group_id=100 0 0
cgroup /sys/fs/cgroup cgroup
rw,relatime,bfqio,hugetlb,perf_event,blkio,net_cls,freezer,devices,memory,cpuacct,cpu,cpuset,clone_children
0 0
if useful, also
# cat /etc/mtab
/dev/sda2 / ext4 rw,noatime 0 0
proc /proc proc rw 0 0
sysfs /sys sysfs rw 0 0
/dev/sda1 /media/oldslack ext4 rw,noatime 0 0
/dev/sdb1 /home ext4 rw,noatime 0 0
/dev/md0p1 /data ext4 rw,noatime 0 0
tmpfs /dev/shm tmpfs rw 0 0
gvfsd-fuse /home/poncez/.gvfs fuse.gvfsd-fuse rw,nosuid,nodev,user=poncez 0
0
cgroup /sys/fs/cgroup cgroup rw 0 0
in /etc/libvirt/qemu.conf I uncommented this line
cgroup_controllers = [ "cpu", "devices", "memory",
"blkio", "cpuset",
"cpuacct" ]
Matteo