Re: [PATCH v2] iommu: Check dev->iommu in iommu_dev_xxx functions

[Robin Murphy]

On 2021-02-12 14:54, Shameerali Kolothum Thodi wrote:
> Hi Robin/Joerg,
>
> > -----Original Message-----
> > From: Shameer Kolothum [mailto:shameerali.kolothum.thodi@xxxxxxxxxx]
> > Sent: 01 February 2021 12:41
> > To: linux-kernel@xxxxxxxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
> > Cc: joro@xxxxxxxxxx; robin.murphy@xxxxxxx; jean-philippe@xxxxxxxxxx;
> > will@xxxxxxxxxx; Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>;
> > linuxarm@xxxxxxxxxxxxx
> > Subject: [Linuxarm] [PATCH v2] iommu: Check dev->iommu in iommu_dev_xxx
> > functions
> >
> > The device iommu probe/attach might have failed leaving dev->iommu
> > to NULL and device drivers may still invoke these functions resulting
> > in a crash in iommu vendor driver code. Hence make sure we check that.
> >
> > Also added iommu_ops to the "struct dev_iommu" and set it if the dev
> > is successfully associated with an iommu.
> >
> > Fixes: a3a195929d40 ("iommu: Add APIs for multiple domains per device")
> > Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
> > ---
> > v1 --> v2:
> >   -Added iommu_ops to struct dev_iommu based on the discussion with Robin.
> >   -Rebased against iommu-tree core branch.
>
> A gentle ping on this...

Is there a convincing justification for maintaining yet another copy of 
the ops pointer rather than simply dereferencing iommu_dev->ops at point 
of use?

Robin.

> Thanks,
> Shameer
>
> > ---
> >   drivers/iommu/iommu.c | 19 +++++++------------
> >   include/linux/iommu.h |  2 ++
> >   2 files changed, 9 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index fd76e2f579fe..6023d0b7c542 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -217,6 +217,7 @@ static int __iommu_probe_device(struct device *dev,
> > struct list_head *group_list
> >   	}
> >
> >   	dev->iommu->iommu_dev = iommu_dev;
> > +	dev->iommu->ops = iommu_dev->ops;
> >
> >   	group = iommu_group_get_for_dev(dev);
> >   	if (IS_ERR(group)) {
> > @@ -2865,10 +2866,8 @@ EXPORT_SYMBOL_GPL(iommu_fwspec_add_ids);
> >    */
> >   int iommu_dev_enable_feature(struct device *dev, enum
> > iommu_dev_features feat)
> >   {
> > -	const struct iommu_ops *ops = dev->bus->iommu_ops;
> > -
> > -	if (ops && ops->dev_enable_feat)
> > -		return ops->dev_enable_feat(dev, feat);
> > +	if (dev->iommu && dev->iommu->ops->dev_enable_feat)
> > +		return dev->iommu->ops->dev_enable_feat(dev, feat);
> >
> >   	return -ENODEV;
> >   }
> > @@ -2881,10 +2880,8 @@
> > EXPORT_SYMBOL_GPL(iommu_dev_enable_feature);
> >    */
> >   int iommu_dev_disable_feature(struct device *dev, enum
> > iommu_dev_features feat)
> >   {
> > -	const struct iommu_ops *ops = dev->bus->iommu_ops;
> > -
> > -	if (ops && ops->dev_disable_feat)
> > -		return ops->dev_disable_feat(dev, feat);
> > +	if (dev->iommu && dev->iommu->ops->dev_disable_feat)
> > +		return dev->iommu->ops->dev_disable_feat(dev, feat);
> >
> >   	return -EBUSY;
> >   }
> > @@ -2892,10 +2889,8 @@
> > EXPORT_SYMBOL_GPL(iommu_dev_disable_feature);
> >
> >   bool iommu_dev_feature_enabled(struct device *dev, enum
> > iommu_dev_features feat)
> >   {
> > -	const struct iommu_ops *ops = dev->bus->iommu_ops;
> > -
> > -	if (ops && ops->dev_feat_enabled)
> > -		return ops->dev_feat_enabled(dev, feat);
> > +	if (dev->iommu && dev->iommu->ops->dev_feat_enabled)
> > +		return dev->iommu->ops->dev_feat_enabled(dev, feat);
> >
> >   	return false;
> >   }
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 524ffc2ff64f..ff0c76bdfb67 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -354,6 +354,7 @@ struct iommu_fault_param {
> >    * @fault_param: IOMMU detected device fault reporting data
> >    * @fwspec:	 IOMMU fwspec data
> >    * @iommu_dev:	 IOMMU device this device is linked to
> > + * @ops:	 iommu-ops for talking to the iommu_dev
> >    * @priv:	 IOMMU Driver private data
> >    *
> >    * TODO: migrate other per device data pointers under iommu_dev_data,
> > e.g.
> > @@ -364,6 +365,7 @@ struct dev_iommu {
> >   	struct iommu_fault_param	*fault_param;
> >   	struct iommu_fwspec		*fwspec;
> >   	struct iommu_device		*iommu_dev;
> > +	const struct iommu_ops		*ops;
> >   	void				*priv;
> >   };
> >
> > --
> > 2.17.1
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