Re: [dpdk-dev] [PATCH v3] doc: Clarify IOMMU usage with "uio_pci_generic" kernel module

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Sep 19, 2018 at 07:44:36AM +0000, Tone Zhang (Arm Technology China) wrote:
> Hello Bruce, Luca, Rami and Stephen,
> 
> Could you please help to review the change? 
> 
> Any comments are welcome.
> 
> Thanks a lot!
> 
> Br,
> Tone
> 
> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of tone.zhang
> Sent: Wednesday, September 5, 2018 1:18 PM
> To: dev@dpdk.org
> Cc: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>; bruce.richardson@intel.com; bluca@debian.org; roszenrami@gmail.com; nd <nd@arm.com>
> Subject: [dpdk-dev] [PATCH v3] doc: Clarify IOMMU usage with "uio_pci_generic" kernel module
> 
> If the devices used for DPDK are bound to the "uio_pci_generic" kernel module, the IOMMU should be disabled in order not to break the IO transmission because of the virtual / physical address mapping.
> 
> The patch clarifies the IOMMU configurations on both x86_64 and arm64 systems.
> 
> Signed-off-by: tone.zhang <tone.zhang@arm.com>
> ---
>  doc/guides/linux_gsg/linux_drivers.rst | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/doc/guides/linux_gsg/linux_drivers.rst b/doc/guides/linux_gsg/linux_drivers.rst
> index 371a817..b46fc6a 100644
> --- a/doc/guides/linux_gsg/linux_drivers.rst
> +++ b/doc/guides/linux_gsg/linux_drivers.rst
> @@ -48,6 +48,13 @@ be loaded as shown below:
>     ``vfio-pci`` kernel module rather than ``igb_uio`` or ``uio_pci_generic``.
>     For more details see :ref:`linux_gsg_binding_kernel` 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. One can add ``intel_iommu=off`` or
> +   ``intel_iommu=pt`` or ``amd_iommu=off`` in GRUB command line on x86_64 systems,
> +   or add ``iommu.passthrough=1`` on arm64 system.
> +

I'm not really an expert in these IOMMU commands, but for the passthrough
option on my systems, I've always used "intel_iommu=on iommu=pt", rather
than "intel_iommu=pt". Can someone confirm that the latter works ok, as
documented here?

/Bruce