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

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Message-ID: <BN9PR11MB5276B0865C9D8DC9060BF1A08C0BA@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 2 Aug 2023 01:39:01 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <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: 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.