5. Linux Drivers

Different PMDs may require different kernel drivers in order to work properly. Depending on the PMD being used, a corresponding kernel driver should be loaded, and network ports should be bound to that driver.

5.1. VFIO

VFIO is a robust and secure driver that relies on IOMMU protection. To make use of VFIO, the vfio-pci module must be loaded:

sudo modprobe vfio-pci

VFIO kernel is usually present by default in all distributions, however please consult your distributions documentation to make sure that is the case.

For DMA mapping of either external memory or hugepages, VFIO interface is used. VFIO does not support partial unmap of once mapped memory. Hence DPDK’s memory is mapped in hugepage granularity or system page granularity. Number of DMA mappings is limited by kernel with user locked memory limit of a process (rlimit) for system/hugepage memory. Another per-container overall limit applicable both for external memory and system memory was added in kernel 5.1 defined by VFIO module parameter dma_entry_limit with a default value of 64K. When application is out of DMA entries, these limits need to be adjusted to increase the allowed limit.

Since Linux version 5.7, the vfio-pci module supports the creation of virtual functions. After the PF is bound to vfio-pci module, the user can create the VFs using the sysfs interface, and these VFs will be bound to vfio-pci module automatically.

When the PF is bound to vfio-pci, by default it will have a randomly generated VF token. For security reasons, this token is write only, so the user cannot read it from the kernel directly. To access the VFs, the user needs to create a new token, and use it to initialize both VF and PF devices. The tokens are in UUID format, so any UUID generation tool can be used to create a new token.

This VF token can be passed to DPDK by using EAL parameter --vfio-vf-token. The token will be used for all PF and VF ports within the application.

  1. Generate the VF token by uuid command

    14d63f20-8445-11ea-8900-1f9ce7d5650d

  2. Load the vfio-pci module with enable_sriov parameter set

    sudo modprobe vfio-pci enable_sriov=1

    Alternatively, pass the enable_sriov parameter through the sysfs if the module is already loaded or is built-in:

    echo 1 | sudo tee /sys/module/vfio_pci/parameters/enable_sriov

  3. Bind the PCI devices to vfio-pci driver

    ./usertools/dpdk-devbind.py -b vfio-pci 0000:86:00.0

  4. Create the desired number of VF devices

    echo 2 > /sys/bus/pci/devices/0000:86:00.0/sriov_numvfs

  5. Start the DPDK application that will manage the PF device

    <build_dir>/app/dpdk-testpmd -l 22-25 -n 4 -a 86:00.0 \
--vfio-vf-token=14d63f20-8445-11ea-8900-1f9ce7d5650d --file-prefix=pf -- -i

  6. Start the DPDK application that will manage the VF device

    <build_dir>/app/dpdk-testpmd -l 26-29 -n 4 -a 86:02.0 \
--vfio-vf-token=14d63f20-8445-11ea-8900-1f9ce7d5650d --file-prefix=vf0 -- -i

To make use of full VFIO functionality, both kernel and BIOS must support and be configured to use IO virtualization (such as Intel® VT-d).

Note

Linux versions earlier than version 3.6 do not support VFIO.

Note

Linux versions earlier than version 5.7 do not support the creation of virtual functions within the VFIO framework.

Note

In most cases, specifying “iommu=on” as kernel parameter should be enough to configure the Linux kernel to use IOMMU.

For proper operation of VFIO when running DPDK applications as a non-privileged user, correct permissions should also be set up. For more information, please refer to Running DPDK Applications Without Root Privileges.

5.2. VFIO no-IOMMU mode

If there is no IOMMU available on the system, VFIO can still be used, but it has to be loaded with an additional module parameter:

modprobe vfio enable_unsafe_noiommu_mode=1

Alternatively, one can also enable this option in an already loaded kernel module:

echo 1 > /sys/module/vfio/parameters/enable_unsafe_noiommu_mode

After that, VFIO can be used with hardware devices as usual.

Note

It may be required to unload all VFIO related-modules before probing the module again with enable_unsafe_noiommu_mode=1 parameter.

Warning

Since no-IOMMU mode forgoes IOMMU protection, it is inherently unsafe. That said, it does make it possible for the user to keep the degree of device access and programming that VFIO has, in situations where IOMMU is not available.

5.3. UIO

In situations where using VFIO is not an option, there are alternative drivers one can use. In many cases, the standard uio_pci_generic module included in the Linux kernel can be used as a substitute for VFIO. This module can be loaded using the command:

sudo modprobe uio_pci_generic

Note

uio_pci_generic module doesn’t support the creation of virtual functions.

As an alternative to the uio_pci_generic, there is the igb_uio module which can be found in the repository dpdk-kmods. It can be loaded as shown below:

sudo modprobe uio
sudo insmod igb_uio.ko

Note

For some devices which lack support for legacy interrupts, e.g. virtual function (VF) devices, the igb_uio module may be needed in place of uio_pci_generic.

Note

If UEFI secure boot is enabled, the Linux kernel may disallow the use of UIO on the system. Therefore, devices for use by DPDK should be bound to the vfio-pci kernel module rather than any UIO-based module. For more details see Binding and Unbinding Network Ports to/from the Kernel Modules below.

Note

If the devices used for DPDK are bound to the uio_pci_generic kernel module, please make sure that the IOMMU is disabled or is in passthrough mode. One can add intel_iommu=off or amd_iommu=off or intel_iommu=on iommu=pt in GRUB command line on x86_64 systems, or add iommu.passthrough=1 on aarch64 systems.

Note

Using UIO drivers is inherently unsafe due to this method lacking IOMMU protection, and can only be done by root user.

5.4. Bifurcated Driver

PMDs which use the bifurcated driver co-exists with the device kernel driver. On such model the NIC is controlled by the kernel, while the data path is performed by the PMD directly on top of the device.

Such model has the following benefits:

  • It is secure and robust, as the memory management and isolation is done by the kernel.
  • It enables the user to use legacy linux tools such as ethtool or ifconfig while running DPDK application on the same network ports.
  • It enables the DPDK application to filter only part of the traffic, while the rest will be directed and handled by the kernel driver. The flow bifurcation is performed by the NIC hardware. As an example, using Flow isolated mode allows to choose strictly what is received in DPDK.

More about the bifurcated driver can be found in Mellanox Bifurcated DPDK PMD.

5.5. Binding and Unbinding Network Ports to/from the Kernel Modules

Note

PMDs which use the bifurcated driver should not be unbound from their kernel drivers. This section is for PMDs which use the UIO or VFIO drivers.

As of release 1.4, DPDK applications no longer automatically unbind all supported network ports from the kernel driver in use. Instead, in case the PMD being used use the VFIO or UIO drivers, all ports that are to be used by a DPDK application must be bound to the vfio-pci, uio_pci_generic, or igb_uio module before the application is run. For such PMDs, any network ports under Linux* control will be ignored and cannot be used by the application.

To bind ports to the vfio-pci, uio_pci_generic or igb_uio module for DPDK use, or to return ports to Linux control, a utility script called dpdk-devbind.py is provided in the usertools subdirectory. This utility can be used to provide a view of the current state of the network ports on the system, and to bind and unbind those ports from the different kernel modules, including the VFIO and UIO modules. The following are some examples of how the script can be used. A full description of the script and its parameters can be obtained by calling the script with the --help or --usage options. Note that the UIO or VFIO kernel modules to be used, should be loaded into the kernel before running the dpdk-devbind.py script.

Warning

Due to the way VFIO works, there are certain limitations to which devices can be used with VFIO. Mainly it comes down to how IOMMU groups work. Any Virtual Function device can usually be used with VFIO on its own, but physical devices may require either all ports bound to VFIO, or some of them bound to VFIO while others not being bound to anything at all.

If your device is behind a PCI-to-PCI bridge, the bridge will then be part of the IOMMU group in which your device is in. Therefore, the bridge driver should also be unbound from the bridge PCI device for VFIO to work with devices behind the bridge.

Warning

While any user can run the dpdk-devbind.py script to view the status of the network ports, binding or unbinding network ports requires root privileges.

To see the status of all network ports on the system:

./usertools/dpdk-devbind.py --status

Network devices using DPDK-compatible driver
============================================
0000:82:00.0 '82599EB 10-GbE NIC' drv=uio_pci_generic unused=ixgbe
0000:82:00.1 '82599EB 10-GbE NIC' drv=uio_pci_generic unused=ixgbe

Network devices using kernel driver
===================================
0000:04:00.0 'I350 1-GbE NIC' if=em0  drv=igb unused=uio_pci_generic *Active*
0000:04:00.1 'I350 1-GbE NIC' if=eth1 drv=igb unused=uio_pci_generic
0000:04:00.2 'I350 1-GbE NIC' if=eth2 drv=igb unused=uio_pci_generic
0000:04:00.3 'I350 1-GbE NIC' if=eth3 drv=igb unused=uio_pci_generic

Other network devices
=====================
<none>

To bind device eth1,``04:00.1``, to the uio_pci_generic driver:

./usertools/dpdk-devbind.py --bind=uio_pci_generic 04:00.1

or, alternatively,

./usertools/dpdk-devbind.py --bind=uio_pci_generic eth1

To restore device 82:00.0 to its original kernel binding:

./usertools/dpdk-devbind.py --bind=ixgbe 82:00.0

5.6. Troubleshooting VFIO

In certain situations, using dpdk-devbind.py script to bind a device to VFIO driver may fail. The first place to check is the kernel messages:

dmesg | tail
...
[ 1297.875090] vfio-pci: probe of 0000:31:00.0 failed with error -22
...

In most cases, the error -22 indicates that the VFIO subsystem could not be enabled because there is no IOMMU support.

To check whether the kernel has been booted with correct parameters, one can check the kernel command-line:

cat /proc/cmdline

Please refer to earlier sections on how to configure kernel parameters correctly for your system.

If the kernel is configured correctly, one also has to make sure that the BIOS configuration has virtualization features (such as Intel® VT-d). There is no standard way to check if the platform is configured correctly, so please check with your platform documentation to see if it has such features, and how to enable them.

In certain distributions, default kernel configuration is such that the no-IOMMU mode is disabled altogether at compile time. This can be checked in the boot configuration of your system:

cat /boot/config-$(uname -r) | grep NOIOMMU
# CONFIG_VFIO_NOIOMMU is not set

If CONFIG_VFIO_NOIOMMU is not enabled in the kernel configuration, VFIO driver will not support the no-IOMMU mode, and other alternatives (such as UIO drivers) will have to be used.