Re: [dpdk-dev] [PATCH v3 0/3] force IOVA to a particular mode

[Alejandro Lucero <alejandro.lucero@netronome.com>]

On Tue, Oct 30, 2018 at 1:48 PM Burakov, Anatoly <anatoly.burakov@intel.com>
wrote:

> On 30-Oct-18 12:02 PM, Alejandro Lucero wrote:
> >
> >
> > On Sun, Oct 28, 2018 at 11:04 PM Thomas Monjalon <thomas@monjalon.net
> > <mailto:thomas@monjalon.net>> wrote:
> >
> >     11/10/2018 12:08, Thomas Monjalon:
> >      > +Cc more maintainers in order to collect more reviews
> >      >
> >      > 04/10/2018 11:19, Burakov, Anatoly:
> >      > > On 03-Oct-18 9:53 PM, eric zhang wrote:
> >      > > > This patchset introduces an EAL command line option
> "--iova-mode"
> >      > > > to give the user a facility to force IOVA mode to a special
> >     value.
> >      > > >
> >      > > > Auto detection of the IOVA mode, based on probing the bus and
> >     IOMMU
> >      > > > configuration, may not report the desired addressing mode
> >     when virtual
> >      > > > devices that are not directly attached to the bus are present.
> >      > > > The EAL command line option "--iova-mode" can be used to
> >     select either
> >      > > > physical addressing('pa') or virtual addressing('va').
> >      > >
> >      > > Acked-by: Anatoly Burakov <anatoly.burakov@intel.com
> >     <mailto:anatoly.burakov@intel.com>>
> >
> >     Rebased and applied, thanks
> >
> >
> >
> > Could not this lead to a problem if a device can not wok with the mode
> set?
> > For example, IOVA mode set to VA and IOMMU hw with less bits than those
> > required for the virtual addresses?
> >
> > IMO any device should be attached to a bus, and a bus should have a
> > function for setting IOVA mode and the --iova-mode option just allowed
> > with supported IOVA modes within the bus.
>
> I don't think it should work that way. It should warn the user that an
> incompatible IOVA mode was selected, but the user has specified an IOVA
> mode for a reason - it probably implies he really means it, so let him :)
>
>
Yes, that's true, but setting IOVA VA when a device has problems with it,
it is a bad idea and it could lead to a system crash.
My concern is not with the user knowing what he is doing but with the user
that "uhmm, what is this for, let's try this option".


> --
> Thanks,
> Anatoly
>