linux-kernel - Re: [PATCH 3/4] iommu/of: Don't call iommu_ops->add

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Date:   Thu, 20 Dec 2018 16:42:17 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Joerg Roedel <jroedel@...e.de>,
        Sudeep Holla <sudeep.holla@....com>,
        Robin Murphy <robin.murphy@....com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH 3/4] iommu/of: Don't call iommu_ops->add_device directly

Hi Jörg,

On Wed, Dec 19, 2018 at 5:51 PM Joerg Roedel <joro@...tes.org> wrote:
> On Wed, Dec 19, 2018 at 10:54:18AM +0100, Marek Szyprowski wrote:
> > On 2018-12-11 16:05, Joerg Roedel wrote:
> > > From: Joerg Roedel <jroedel@...e.de>
> > >
> > > Make sure to invoke this call-back through the proper
> > > function of the IOMMU-API.
> > >
> > > Signed-off-by: Joerg Roedel <jroedel@...e.de>
> > > ---
> > >  drivers/iommu/of_iommu.c | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> > > index c5dd63072529..4d4847de727e 100644
> > > --- a/drivers/iommu/of_iommu.c
> > > +++ b/drivers/iommu/of_iommu.c
> > > @@ -218,10 +218,10 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
> > >             ops = dev->iommu_fwspec->ops;
> > >     /*
> > >      * If we have reason to believe the IOMMU driver missed the initial
> > > -    * add_device callback for dev, replay it to get things in order.
> > > +    * probe for dev, replay it to get things in order.
> > >      */
> > > -   if (ops && ops->add_device && dev->bus && !dev->iommu_group)
> > > -           err = ops->add_device(dev);
> > > +   if (dev->bus && !dev->iommu_group)
> > > +           err = iommu_probe_device(dev);
> >
> > This change removes a check for NULL ops, what causes NULL pointer
> > exception on first device without IOMMU.
>
> Bummer, this check was supposed to be in iommu_probe_device(), but
> apparently it got lost. Does the attached patch fix it?
>
> > I'm also not sure if this is a good idea to call iommu_probe_device(),
> > which comes from dev->bus->iommu_ops, which might be different from ops
> > from local variable.
>
> The local variable comes from dev->iommu_fwspec->ops, which should be
> exactly the same as dev->bus->iommu_ops. I'll leave that for now until
> it turns out to be a problem (which I don't expect).
>
>
> Regards,
>
>         Joerg
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index a2131751dcff..3ed4db334341 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -114,10 +114,14 @@ void iommu_device_unregister(struct iommu_device *iommu)
>  int iommu_probe_device(struct device *dev)
>  {
>         const struct iommu_ops *ops = dev->bus->iommu_ops;
> +       int ret = -EINVAL;
>
>         WARN_ON(dev->iommu_group);
>
> -       return ops->add_device(dev);
> +       if (ops)

Is this sufficient? The old code checked for ops->add_device != NULL,
too.

> +               ret = ops->add_device(dev);
> +
> +       return ret;
>  }
>
>  void iommu_release_device(struct device *dev)


Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds