I wrote in my last post about how I upgraded from Linux Mint 16 to 17.1. I thought everything went smoothly, but it turns out one feature did break: VGA passthrough via Xen. For the past year or so I’ve had a Windows 8.1 gaming VM with direct access to my video card. It’s worked out nicely in Linux Mint 16 but broke completely in 17.1.
I followed the advice of powerhouse on the Linux Mint forums on how to get things up and running, but it wasn’t quite enough. After much banging of my head against the wall I read on the Xen mailing list that there was a regression in VGA passthrough functionality with Xen 4.4.1, which is the version of Xen Mint 17.1 uses.
I finally came to a solution to my problem today – upgrade to Xen 4.5. I couldn’t find any pre-built packages for Ubuntu 14.04 (the base of Mint 17.1) so I ended up compiling Xen 4.5 from source. Below is what I did to make it all work.
Fix broken symlink for /usr/lib/xen-default
sudo rm /usr/lib/xen-default
sudo ln -s /usr/lib/xen-4.4/ /usr/lib/xen-default
Update the DomU CFG file
A couple things needed tweaking. Here is my working cfg:
memory = '8192'
name = 'win8.1'
vif = [ 'mac=3a:82:47:2a:51:20,bridge=xenbr0,model=virtio' ]
disk = [ 'phy:/dev/mapper/desktop--xen-Win8.1,xvda,w' ]
device_model_version = 'qemu-xen-traditional'
pci=[ '01:00.0', '01:00.1' , '00:1d.0' ]
on_xend_stop = "shutdown"
For some, that’s all they had to do. For me, I had to do a few more things.
Compile Xen 4.5
This step was thanks to two different sites, this one and this one.
Install necessary packages
sudo apt-get install build-essential bcc bin86 gawk bridge-utils iproute libcurl3 libcurl4-openssl-dev bzip2 module-init-tools transfig tgif texinfo texlive-latex-base texlive-latex-recommended texlive-fonts-extra texlive-fonts-recommended pciutils-dev mercurial libjpeg-dev make gcc libc6-dev-i386 zlib1g-dev python python-dev python-twisted libncurses5-dev patch libvncserver-dev libsdl-dev libpixman-1-dev iasl libbz2-dev e2fslibs-dev git-core uuid-dev ocaml ocaml-findlib libx11-dev bison flex xz-utils libyajl-dev gettext markdown libaio-dev pandoc
Checkout Xen source
git clone git://xenbits.xen.org/xen.git xen-4.5.0
git checkout RELEASE-4.5.0
Build from source
make world -j8
When I tried this the make failed with this error:
/usr/include/linux/errno.h:1:23: fatal error: asm/errno.h: No such file or directory
The fix (thanks to askubuntu) was to install linux-libc-dev and make a symlink for it:
sudo apt-get install linux-libc-dev
sudo ln -s /usr/include/asm-generic /usr/include/asm
It then compiled successfully.
Install freshly compiled Xen 4.5
sudo make install
sudo update-rc.d xencommons defaults
sudo update-rc.d xendomains defaults
Set grub to boot from new Xen kernel
sudo vim /etc/default/grub
Edit GRUB_DEFAULT to match wherever update-grub put your new Xen kernel (in my case it was the second entry, so my GRUB_DEFAULT=1), then run update-grub again
Success at last. Enjoy your VM gaming once more with Xen 4.5.