KVM PCI Passthrough and Omni-Path » History » Revision 22
Revision 21 (Brian Smith, 08/09/2019 06:40 PM) → Revision 22/23 (Brian Smith, 09/11/2019 04:49 PM)
# KVM PCI Passthrough and Omni-Path
A KVM guest can use OPA hardware when configured for PCI passthrough. This document is OPA and Debian-centric, but the concepts should apply to other Linux host operating systems and PCI devices.
## BIOS Settings
1. Intel VT must be enabled.
2. Integrated IO / IntelVT must be enabled.
## Kernel Command Line
Add this to the host's kernel command line and reboot the host:
```
intel_iommu=on iommu=pt
```
When configured properly, ```/sys/kernel/iommu_groups/``` will contain many subdirectories. If that path is empty, IOMMU is not working.
## Install KVM
```
$ sudo apt install qemu-kvm libvirt-clients libvirt-daemon-system virtinst libosinfo-bin
```
## Disable hfi1 on host
The hfi1 driver must not be loaded on the host machine, in order to use PCI passthrough. In /etc/modprobe.d/hfi1.conf:
```
blacklist hfi1
```
Also, there is no reason to have IFS installed on the host. The host machine should have no OPA functionality enabled.
## Configure PCI Passthrough
The hfi1 device must be setup for PCI passthrough. Find the device's port in the output of lspci:
```
$ lspci -vnn | grep Omni | cut -f1 '-d '
```
For the scripts below, prepend the port with 0000:, like "0000:80:02.0".
Use the following script, replace PCI_PORT with the port of the hfi1:
```
#!/bin/bash
PCI_PORT=0000:80:02.0
DEV_VENDOR=8086
DEV_MODEL=24f0
rmmod vfio_pci
rmmod vfio
echo "$PCI_PORT" > /sys/bus/pci/devices/$PCI_PORT/driver/unbind
modprobe vfio
modprobe vfio_pci
echo $DEV_VENDOR $DEV_MODEL > /sys/bus/pci/drivers/vfio-pci/new_id
```
## Create Guest
While it is possible to manage guests for an unprivileged user, they get a non-functional network setup in the default config.
**Use virsh as root.**
```
$ systemctl start libvirtd
$ virt-install --name GUEST_NAME \
--vcpus=4 --virt-type kvm --cdrom $HOME/kvm-guest/debian-8.7.0-amd64-DVD-1.iso \
-v --os-variant debian8 \
--disk path=PATH_TO_CREATE_DISK,size=16 --memory 4096 --graphics vnc
```
Connect a VNC client to a tunneled connection to the host.
From the workstation:
```
$ ssh -L5910:localhost:5900 YOU@HOST
```
Now connect a VNC client to localhost:5910 and complete the install.
## Import Existing Disk to New Guest
To import an existing guest disk image, use the following command:
```
$ sudo virt-install --virt-type kvm --name GUEST_NAME \
--vcpus=4 --virt-type kvm --import \
-v --os-variant debian8 \
--disk PATH_TO_DISK_IMAGE,device=disk,bus=virtio --memory 4096 --graphics vnc
```
## Connect to Guest, Configure DNS
The default network for KVM is 192.168.122.0/24 and the guest should be assigned a DHCP address when it boots. Use the VNC connection to execute ```$ ip addr``. ssh should be able to connect to the guest from the host.
Unfortunately, dnsmasq doesn't appear to set the search domain properly. For Debian, configure a search domain in the guest's ```/etc/network/interfaces```.
```
allow-hotplug eth0
iface eth0 inet dhcp
dns-search MYDOMAIN
```
## Configure Guest for PCI Passthrough
Shutdown the guest if it is running.
```
$ virsh shutdown GUEST_NAME
```
Look for the PCI device in virsh. Look for a pci device that matches the port found via lspci.
```
$ virsh nodedev-list --tree
```
Detach the device. Use the child device of the one that matches the device you found via lspci.
```
$ virsh nodedev-detach pci_0000_81_00_0
```
Dump the device info.
```
$ virsh nodedev-dumpxml pci_0000_81_00_0
```
Convert bus, slot and function to hex. The printf utility may be used to do this.
```
$ printf %x VALUE
```
Edit the guest and add a hostdev section:
```
$ virsh edit GUEST_NAME
<hostdev mode='subsystem' type='pci' managed='yes'>
<source>
<address domain='0x0000' bus='0x81' slot='0x0' function='0x0'/>
</source>
</hostdev>
```
Boot the guest
```
$ virsh start GUEST_NAME
```
Upon booting the guest, the passthrough device should be present in the guest's lspci output. The passthrough device should be usable by the guest's kernel drivers.
**Note**: the PCI device may have different capabilities in the VM than it has on the physical host. Hopefully, the driver takes this into account. Refer to https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4c009af473b2026caaa26107e34d7cc68dad7756 for a patch that fixes one such problem in hfi1. Hope it helps.
## References
1. https://wiki.debian.org/KVM
2. https://jamielinux.com/docs/libvirt-networking-handbook/nat-based-network.html
3. https://www.linux-kvm.org/page/How_to_assign_devices_with_VT-d_in_KVM
4. https://wiki.archlinux.org/index.php/PCI_passthrough_via_OVMF
5. https://wiki.debian.org/VGAPassthrough
----
Brian T. Smith
Senior Technical Staff
System Fabric Works, Inc.
bsmith@systemfabricworks.com