Re: [PATCH 1/2] iommu: Consolidate pasid dma ownership check

[tina.zhang <tina.zhang@intel.com>]

Hi,

On 8/1/23 15:43, Baolu Lu wrote:
> On 2023/8/1 15:03, Tian, Kevin wrote:
>>>   /**
>>>    * iommu_device_use_default_domain() - Device driver wants to handle
>>> device
>>>    *                                     DMA through the kernel DMA API.
>>> @@ -3052,14 +3063,14 @@ int iommu_device_use_default_domain(struct
>>> device *dev)
>>>
>>>       mutex_lock(&group->mutex);
>>>       if (group->owner_cnt) {
>>> -        if (group->owner || !iommu_is_default_domain(group) ||
>>> -            !xa_empty(&group->pasid_array)) {
>>> +        if (group->owner || !iommu_is_default_domain(group)) {
>>>               ret = -EBUSY;
>>>               goto unlock_out;
>>>           }
>>>       }
>>>
>>>       group->owner_cnt++;
>>> +    assert_pasid_dma_ownership(group);
>> Old code returns error if pasid_xrrary is not empty.
>>
>> New code continues to take ownership with a warning.
>>
>> this is a functional change. Is it intended or not?
> 
> If iommu_device_use_default_domain() is called with pasid_array not
> empty, there must be a bug somewhere in the device driver. We should
> WARN it instead of returning an error. Probably this is a functional
> change? If so, I can add this in the commit message.
I think in case of a bug, returning error is still expected by callers. 
Otherwise, the callers might think everything is just fine, as the 
return value tells success.

Regards,
-Tina
> 
> Best regards,
> baolu
>