PCIe Passthrough with crosvm

Enabling PCIe Devices for VFIO with driverctl

As with other passthroughs, first, we need to set the target device to use VFIO driver. This can be done manually or by using the driverctl tool as below.

export BUS="0000:01:00.0"
driverctl --nosave set-override ${BUS} vfio-pci

Let’s consider the example of starting crosvm.

In some cases, crosvm may need privileged permissions to work properly. This applies specially for passthrough hardware devices as vfio devices are generally owned by the root user or the vfio group. For simplicity, it may be easier to run crosvm as the root user but it is be possible to set up correct permissions so that running as root is not needed.

Crosvm expects the device’s system path as its --vfio argument. The device identifier is different when comparing how passthrough devices are refrenced in QEMU. Using the guest-address option is not strictly required by the source documentation but it gives a bit more control for handling the passthrough device on the guest side.

export BUS="0000:01:00.0"
export GUESTBUS="00:08.0"
./target/debug/crosvm run \
        --mem=8192 \
        --block ./ubuntu-22.10.img \
        -i /boot/initrd.img-5.19.0-31-generic /boot/vmlinuz-5.19.0-31-generic \
        -p "root=/dev/vda2 loglevel=8 earlycon earlyprintk debug" \
        --vfio /sys/bus/pci/devices/${BUS},guest-address=${GUESTBUS},iommu=viommu

Reseting Driver to Original State Afterwards

The driverctl tool can reset the original device driver afterward:

export BUS="0000:01:00.0"
driverctl unset-override ${BUS}