linux-kernel - Re: [PATCH v3 1/4] iommu: Check IOMMU_DEV_FEAT

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Date:   Thu, 30 Jul 2020 09:46:50 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v3 1/4] iommu: Check IOMMU_DEV_FEAT_AUX feature in aux
 api's

Hi Alex,

On 7/30/20 4:03 AM, Alex Williamson wrote:
> On Tue, 14 Jul 2020 13:57:00 +0800
> Lu Baolu <baolu.lu@...ux.intel.com> wrote:
> 
>> The iommu aux-domain api's work only when IOMMU_DEV_FEAT_AUX is enabled
>> for the device. Add this check to avoid misuse.
> 
> Shouldn't this really be the IOMMU driver's responsibility to test?  If
> nothing else, iommu_dev_feature_enabled() needs to get the iommu_ops
> from dev->bus->iommu_ops, which is presumably the same iommu_ops we're
> then calling from domain->ops to attach/detach the device, so it'd be
> more efficient for the IOMMU driver to error on devices that don't
> support aux.  Thanks,

Fair enough. The vendor iommu driver always knows the status of aux-
domain support. So this check is duplicated. I will drop this patch.

Best regards,
baolu

> 
> Alex
> 
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/iommu.c | 16 +++++++++-------
>>   1 file changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 1ed1e14a1f0c..e1fdd3531d65 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -2725,11 +2725,13 @@ EXPORT_SYMBOL_GPL(iommu_dev_feature_enabled);
>>    */
>>   int iommu_aux_attach_device(struct iommu_domain *domain, struct device *dev)
>>   {
>> -	int ret = -ENODEV;
>> +	int ret;
>>   
>> -	if (domain->ops->aux_attach_dev)
>> -		ret = domain->ops->aux_attach_dev(domain, dev);
>> +	if (!iommu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX) ||
>> +	    !domain->ops->aux_attach_dev)
>> +		return -ENODEV;
>>   
>> +	ret = domain->ops->aux_attach_dev(domain, dev);
>>   	if (!ret)
>>   		trace_attach_device_to_domain(dev);
>>   
>> @@ -2748,12 +2750,12 @@ EXPORT_SYMBOL_GPL(iommu_aux_detach_device);
>>   
>>   int iommu_aux_get_pasid(struct iommu_domain *domain, struct device *dev)
>>   {
>> -	int ret = -ENODEV;
>> +	if (!iommu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX) ||
>> +	    !domain->ops->aux_get_pasid)
>> +		return -ENODEV;
>>   
>> -	if (domain->ops->aux_get_pasid)
>> -		ret = domain->ops->aux_get_pasid(domain, dev);
>> +	return domain->ops->aux_get_pasid(domain, dev);
>>   
>> -	return ret;
>>   }
>>   EXPORT_SYMBOL_GPL(iommu_aux_get_pasid);
>>   
>