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

[Luca Boccassi <bluca@debian.org>]

On Wed, 2018-09-19 at 12:33 +0100, Bruce Richardson wrote:
> 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.richa
> > rdson@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

Whops you are right, just checked and we use iommu=pt

-- 
Kind regards,
Luca Boccassi