Re: [dpdk-dev] [PATCH v3 4/4] doc: add VFIO troubleshooting section

[Kevin Traynor <ktraynor@redhat.com>]

On 19/11/2020 11:32, Anatoly Burakov wrote:
> There are common problems with VFIO that get asked over and over on the
> mailing list. Document common problems with VFIO and how to fix them or
> at least figure out what went wrong.
> 
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> ---
>  doc/guides/linux_gsg/linux_drivers.rst | 43 ++++++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/doc/guides/linux_gsg/linux_drivers.rst b/doc/guides/linux_gsg/linux_drivers.rst
> index 9c61850dbb..f3c06c68d1 100644
> --- a/doc/guides/linux_gsg/linux_drivers.rst
> +++ b/doc/guides/linux_gsg/linux_drivers.rst
> @@ -276,3 +276,46 @@ To restore device ``82:00.0`` to its original kernel binding:
>  .. code-block:: console
>  
>      ./usertools/dpdk-devbind.py --bind=ixgbe 82:00.0
> +
> +Troubleshooting VFIO
> +--------------------
> +
> +In certain situations, using ``dpdk-devbind.py`` script to bing a device to VFIO
> +driver may fail. The first place to check is the kernel messages:
> +
> +.. code-block:: console
> +
> +    # 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 couldn't 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:
> +
> +.. code-block:: console
> +
> +    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:
> +
> +.. code-block:: console
> +
> +    # 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.
> 

Good to have some debug hints and it avoids a backport ;-)

With Bruce's s/bing/bind/

Acked-by: Kevin Traynor <ktraynor@redhat.com>