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

["Tone Zhang (Arm Technology China)" <Tone.Zhang@arm.com>]

-----Original Message-----
From: Luca Boccassi <bluca@debian.org> 
Sent: Tuesday, September 4, 2018 6:15 PM
To: Bruce Richardson <bruce.richardson@intel.com>; Tone Zhang (Arm Technology China) <Tone.Zhang@arm.com>
Cc: dev@dpdk.org; nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH] doc: Clarify IOMMU usage with "uio-pci" kernel module

On Tue, 2018-09-04 at 11:06 +0100, Bruce Richardson wrote:
> On Tue, Sep 04, 2018 at 04:59:07PM +0800, tone.zhang wrote:
> > When binding the devices used by DPDK to the "uio-pci" 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 configuration 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..8f9ec8f 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 for used DPDK bound to the ``uio-pci`` kernel
> > module, please make
> > +   sure that the IOMMU is disabled. We can add ``intel_iommu=off``
> > or ``amd_iommu=off``
> > +   in ``GRUB_CMDLINE_LINUX`` in grub on x86_64 systems, or add
> > ``iommu.passthrough=1``
> > +   on arm64 system.
> > +
> 
> I think passthrough mode should work on x86 too. I remember running 
> with iommu=pt setting in the kernel in the past.
> 
> /Bruce

It does, can confirm.

--
Kind regards,
Luca Boccassi


@Luca, @Bruce, 
Thanks  for the comments. I will update the change and push V2. Thanks!

Br,
Tone