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

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Date:   Tue, 1 Aug 2023 07:03:31 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.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:     "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

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, August 1, 2023 2:31 PM
>
> When switching device DMA ownership, it is required that all the device's
> pasid DMA be disabled. This is done by checking if the pasid array of the
> group is empty. Consolidate all the open code into a single helper. No
> intentional functionality change.

...

>  /**
>   * 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?