if debug message is not working correctly, you should change the /etc/default/grub, in which there "GRUB_CMDLINE_XEN" option line should be corrected to GRUB_CMDLINE_XEN="loglvl=all guest_loglvl=all sync_console console_to_ring". After that, grub2-mkconfig -o /boot/grub2/grub.cfg and reboot will be fine