Turns out that the mga module is no longer included as of kernel v4.9-rc1, as it is now hidden behind the CONFIG_DRM_LEGACY option: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d92d9c3a14488e5af9d7015189f50e02346950f2 Apparently xf86-video-mga has two ways of accessing the memory, either through the DRI1 module, or by direct access via libpciaccess/sysfs. The latter should still work if the X server is run as root, and it does on kernel v4.4, but not on v4.9 (thus, the bug you reported). The failure backtrace is: error in mmap called by pci_device_linux_sysfs_map_range_wc called by pci_device_linux_sysfs_map_range called by pci_device_map_range called by MGAMapMem