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

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: Robin Murphy [mailto:robin.murphy@arm.com]
> Sent: 12 February 2021 16:39
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
> linux-kernel@vger.kernel.org; iommu@lists.linux-foundation.org
> Cc: joro@8bytes.org; jean-philippe@linaro.org; will@kernel.org; Zengtao (B)
> <prime.zeng@hisilicon.com>; linuxarm@openeuler.org
> Subject: Re: [PATCH v2] iommu: Check dev->iommu in iommu_dev_xxx functions
> 
> On 2021-02-12 14:54, Shameerali Kolothum Thodi wrote:
> > Hi Robin/Joerg,
> >
> >> -----Original Message-----
> >> From: Shameer Kolothum [mailto:shameerali.kolothum.thodi@huawei.com]
> >> Sent: 01 February 2021 12:41
> >> To: linux-kernel@vger.kernel.org; iommu@lists.linux-foundation.org
> >> Cc: joro@8bytes.org; robin.murphy@arm.com; jean-philippe@linaro.org;
> >> will@kernel.org; Zengtao (B) <prime.zeng@hisilicon.com>;
> >> linuxarm@openeuler.org
> >> 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@huawei.com>
> >> ---
> >> 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?
> 

TBH, nothing I can think of now. That was mainly the way I interpreted your suggestion
from the v1.  Now it looks like you didn’t mean it :). I am Ok to rework it to dereference
it from iommu_dev. Please let me know.

Thanks,
Shameer

> 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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