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

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Date:   Tue, 1 Aug 2023 15:43:56 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Nicolin Chen <nicolinc@...dia.com>
Cc:     baolu.lu@...ux.intel.com, "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] iommu: Consolidate pasid dma ownership check

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.

Best regards,
baolu