Enable pci passthrough for QEMU/KVM

I have a couple older HP ProLiant DL360 Gen 6 and Gen 7 Server I want to use as virtual machine hosts with some PCIe devices mapped through to the guests running there, let’s say so they can directly access the Fibre Channel ports on the host or whatnot. Here’s how to do it (running Ubuntu 14.04 LTS that is, YMMV with other distributions):

1. Edit your /etc/default/grub and add the intel_iommu=on boot option, it should look something like this (serial console for ILO enabled as well)

   GRUB_CMDLINE_LINUX="console=tty0 console=ttyS1,115200n8 intel_iommu=on"

2. Add the vfio module to the list in /etc/modules

   # /etc/modules: kernel modules to load at boot time.
   #
   # This file contains the names of kernel modules that should be loaded
   # at boot time, one per line. Lines beginning with "#" are ignored.
   # Parameters can be specified after the module name.
   lp
   rtc
   vfio

3. Create a file like /etc/modprobe.d/vfio.conf setting the allow_unsafe_interrupts option for the vfio module.

   options vfio_iommu_type1 allow_unsafe_interrupts=1

   Otherwise you’ll get an error when trying to start a VM with a PCI device passed through: “failed to set iommu for container: Operation not permitted”
   Apparently the IOMMU interrupt remapping is kinda broken on this platform.

4. Reboot your server and create a VM with one of your PCIe adapters passed through – it should show up just like if was a native device on a real, physical server.