[PATCH v2] eal/linux: force iova-mode va without pa available

[Christian Ehrhardt]

On Fri, Nov 24, 2023 at 11:29 AM Dmitry Kozlyuk <dmitry.kozliuk at gmail.com>
wrote:

> 2023-11-24 11:09 (UTC+0100), christian.ehrhardt at canonical.com:
> [...]
> > diff --git a/lib/eal/linux/eal.c b/lib/eal/linux/eal.c
> > index 57da058cec..2f1fce3c54 100644
> > --- a/lib/eal/linux/eal.c
> > +++ b/lib/eal/linux/eal.c
> > @@ -1067,6 +1067,16 @@ rte_eal_init(int argc, char **argv)
> >
> >       phys_addrs = rte_eal_using_phys_addrs() != 0;
> >
> > +     if (!phys_addrs) {
> > +             /* if we have no access to physical addresses, pick IOVA
> as VA mode. */
> > +             if (internal_conf->iova_mode == RTE_IOVA_PA)
> > +                     RTE_LOG(WARNING, EAL, "WARNING: --iova-mode=pa,
> but Physical addresses are unavailable, selecting IOVA as VA mode.\n");
>
> If an impossible combination of options is requested,
> initialization should fail instead.
>

You are absolutely right Dmitry.
In fact I was only trying to rebase an old patch that we used to carry.
But the more I look at and think about it the less I like the approach.

A production setup has an admin that should do this consciously.
What we actually should change is not the behavior of EAL, but just the
test automation to work on no-huge ppc64.
That is simpler and has much less impact and therefore probably is the
right solution.

Consider this patch here withdrawn.
I'll submit the fix to the tests in a few seconds.


> > +             else
> > +                     RTE_LOG(DEBUG, EAL, "Physical addresses are
> unavailable, selecting IOVA as VA mode.\n");
> > +             internal_conf->iova_mode = RTE_IOVA_VA;
> > +             rte_eal_get_configuration()->iova_mode =
> internal_conf->iova_mode;
> > +     }
> > +
> >       /* if no EAL option "--iova-mode=<pa|va>", use bus IOVA scheme */
> >       if (internal_conf->iova_mode == RTE_IOVA_DC) {
> >               /* autodetect the IOVA mapping mode */
>
> What do you think about keeping the existing code structure:
>
> if (--iova-mode not specified) {
>         iova_mode = VA if !phys_addrs or !RTE_IOVA_IN_MBUF (with logs)
>         if (iova_mode == DC) {
>                 // autodetect from bus requirements and IOMMU (with logs)
>         }
>         rte_eal_get_configuration()->iova_mode = iova_mode;
> } else {
>         rte_eal_get_configuration()->iova_mode =
>                 internal_conf->iova_mode;
> }
> // verify rte_eal_get_configuration()->iova_mode
>
> Note: the logic should be consistent across OS when possible.
>
>

-- 
Christian Ehrhardt
Director of Engineering, Ubuntu Server
Canonical Ltd
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