linux-kernel - Re: [PATCH v2] iommu: Check dev->iommu in iommu_dev

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Date:   Fri, 12 Feb 2021 16:38:33 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Cc:     "joro@...tes.org" <joro@...tes.org>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "will@...nel.org" <will@...nel.org>,
        "Zengtao (B)" <prime.zeng@...ilicon.com>,
        "linuxarm@...neuler.org" <linuxarm@...neuler.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@...wei.com]
>> Sent: 01 February 2021 12:41
>> To: linux-kernel@...r.kernel.org; iommu@...ts.linux-foundation.org
>> Cc: joro@...tes.org; robin.murphy@....com; jean-philippe@...aro.org;
>> will@...nel.org; Zengtao (B) <prime.zeng@...ilicon.com>;
>> linuxarm@...neuler.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@...wei.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?

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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