Fedora upgrade broke Xorg… SOLVED!

A few of us here at work are using Fedora 12, two of the guys upgraded Fedora to find X not starting, seemingly a broken nvidia driver. Because they had issues I was careful about updates. But the inevitable happened.. I updated killing my Xorg.

I decided I’d do a bit of research into what was actually happening.. the fix the others used at work was to install the free nvidia driver or use a driver without proper 3D support, I didn’t like this so I started by checking my logs and then some google-fu.

The Xorg log file showed (/var/log/Xorg.0.log):

(II) May 11 11:18:49 NVIDIA: Using 768.00 MB of virtual memory for indirect framebuffer
(II) May 11 11:18:49 NVIDIA: access.
(II) May 11 11:18:49 NVIDIA(0): Initialized GPU GART.
(II) May 11 11:18:52 NVIDIA(0): Setting mode
(II) May 11 11:18:52 NVIDIA(0): "DFP-0:nvidia-auto-select+0+0,DFP-1:nvidia-auto-select+1680+0"
(EE) May 11 11:18:56 NVIDIA(0): WAIT: (E, 0, 0x827d, 0)

Notice it seemed to hang on a wait.

So I checked the kernel log (/var/log/messages) and found a lot of repeating entries:

May 11 11:19:55 localhost kernel: DMAR:[DMA Read] Request device [01:00.0] fault addr 22d226000
May 11 11:19:55 localhost kernel: DMAR:[fault reason 01] Present bit in root entry is clear
May 11 11:19:55 localhost kernel: DRHD: handling fault status reg 2

These repeated hundreds of times.
OK so time to start googling, it turns out these errors seem to point to the PCI bridge or something related to that, the device [01:00.0] turns out to be the address of my video card.

Some google hits talked about a bios issue and recommend adding “intel_iommut=off” to the kernel line, I also found mention in a kernel mailing list post about “intel_iommu=off”, as my PCI bus was made by Intel I thought I’d give it a go.
To check your PCI Bus you can use the “lspci” command.

For the keen observers you’ll notice intel_iommut and intel_iommu, I didn’t know if one had a typo so I added them both to my kernel line and booted.. and SUCCESS, Xorg started!

Updated Note: Thanks to Chris the only option you need is “intel_iommu=off”.

For those who don’t know how to add the extra stuff to your kernel command line permanently, then edit /boot/grub/menu.lst.

In this file there should be an entry for each kernel and operating system you have installed, each new entry starts with a “title” line, under which is a root, kernel and initrd line, just append the new option(s) to the end of the kernel line for the entry/kernel you want. e.g:

title Fedora (
root (hd0,0)
kernel /vmlinuz- ro root=/dev/mapper/system-fedora noiswmd LANG=en_AU.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us rhgb quiet nouveau.modeset=0 vga=0×318 intel_iommu=off
initrd /initramfs-

NOTE: The kernel line above is actually wrapping to a new line in, but should actually be all on the same line.
So there you go.