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

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Date:   Wed, 2 Aug 2023 11:20:06 +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 2023/8/2 9:39, Tian, Kevin wrote:
>> From: Baolu Lu<baolu.lu@...ux.intel.com>
>> Sent: Tuesday, August 1, 2023 3:44 PM
>>
>> 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.
>>
> IMHO we should WARN*and*  return an error.

Okay, fine to me. Will make this in the next version.

Best regards,
baolu