ervin's blog

Tips and tricks to try before you strangle yourself with a wireless mouse

Fixing IOMMU issues on Ubuntu 14.04 Trusty

Installation of Ubuntu 14.04 (or any other distro really) on a configuration with an AMD 970 + SB950 chipset is not as straightforward as you may think. In my particular case, the motherboard is a Gigabyte GA-970A-DS3.

I will describe some workarounds I’ve found, while trying to make the penguins happy.

Tieing the shoolaces

The first issue arose when I created a bootable Ubuntu 14.04.1 USB with Universal USB Installer. Once the computer was at the Ubuntu loading screen, I noticed strange HDD activity. The activity light was blinking in suspiciously regular periods. Not much after this, I was greeted by a lovely message:

(initramfs) unable to find a live medium containing a live file system

My first thought was that the OS image on the USB stick was corrupted. I tried it in another computer and it was working fine. I had some issues with the IOMMU controller + Linux before, so I decided to see what’s the current setup of the BIOS. IOMMU was turned off. I turned it back on and gave the USB boot another shot. It worked! But not for long.

Hobbling to victory

Before the installation splash screen, a charming AMD-Vi: Completion-Wait loop timed out showed up. After about 10 seconds, it continued with the startup process and everything seemed to be working fine. The installation process had begun, which of course, froze at 29%. Let’s check out some IOMMU kernel flags.

I’ve seen people use pt (passthrough) in combination with 1 and soft. These effectively bypass the physical device. I had most success with the soft variant.

After a restart, right after the USB starts to boot, pressing any key (I prefer mashing “Space”) enters the Ubuntu installation menu. Scroll to the installation entry and press “F6”. This shows some additional installation options which can be ignored in this instance. What can’t be ignored, is the input line which shows up after this. Append iommu=soft here and press “Enter”. With that in place, the installation should succeed. Note that this option can also be added when the bootable USB is created but first you should be sure which options works for you.

Before you open a champaign, there’s possibly one more lemon to chew. After the first restart, you may encounter something funny. Based on my previous experiences with IOMMU error messages, AMD-Vi: Event logged [IO_PAGE_FAULT] isn’t a good thing to happen at the first boot of a freshly installed OS. Your EXT4 partition(s) used by the new Ubuntu installation can become corrupted. Actually, I found it to be a rule. To work around this, you have to edit the GRUB menu entry for Ubuntu. When you reboot the machine after the OS installation completes, boot from the hard disk which has Ubuntu installed on it. The GRUB menu will be shown with a countdown. Pressing “E” on the Ubuntu menu item will enter edit mode, where iommu=soft should be added to the end of the line which begins with linux. After this the OS should boot up fine.

This is a fun thing to do, but if you want to make the change permanent, you’ll have the edit GRUB’s configuration file. Run sudo vi /etc/default/grub and change the option shown below to include iommu=soft:

GRUB_LINUX_CMD_LINE="iommu=soft"

To let GRUB know about this change for future boots, execute sudo update-grub. Keep in mind that IOMMU is still enabled in the BIOS.

There are also some alternative solutions, which you might try.

You should also try this approach if you’re having freezing issues with Ubuntu.

Now let’s open that champaign!

Update (03-01-2017)

I was never fully satisfied with the solution above, and with each new kernel release, a new spark of hope arose. I found that other distros are having the exact same problems like Ubuntu Trusty.

A particular diff in kernel 4.8 was really promising. Once I’ve came around to try it, Fedora 25 was released, running kernel version 4.8, so I decided to give it a shot.

In short, this is probably the best distribution I’ve used. Everything is so streamlined and polished.

And the best part is, the freezing issues are comple

I’m kidding (but not completely)! The boot log still shows an issue with AMD-Vi, but apparently, the new kernel worked around the problem which caused the freezes. The installation actually froze at the very last second. Luckily, this happened after everything was set up. The OS booted and I ran an update, after which I rebooted the system.

To knock on the whole Amazon rainforest, everything is working as it should.

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