Re: [PATCH v7 06/10] iommu/sva: Refactoring iommu_sva_bind/unbind_device() - Jean-Philippe Brucker

From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: "Tian, Kevin" <kevin.tian@intel.com>
Cc: "Jiang, Dave" <dave.jiang@intel.com>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	Robin Murphy <robin.murphy@arm.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Christoph Hellwig <hch@infradead.org>,
	Jean-Philippe Brucker <jean-philippe@linaro.com>,
	Vinod Koul <vkoul@kernel.org>,
	"Pan, Jacob jun" <jacob.jun.pan@intel.com>,
	Jason Gunthorpe <jgg@nvidia.com>, Will Deacon <will@kernel.org>
Subject: Re: [PATCH v7 06/10] iommu/sva: Refactoring iommu_sva_bind/unbind_device()
Date: Tue, 24 May 2022 11:57:59 +0100	[thread overview]
Message-ID: <Yoy6NxroLLZup0sE@myrica> (raw)
In-Reply-To: <BN9PR11MB5276E462E3B32DDE54DD66418CD79@BN9PR11MB5276.namprd11.prod.outlook.com>

On Tue, May 24, 2022 at 10:22:28AM +0000, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@linux.intel.com>
> > Sent: Thursday, May 19, 2022 3:21 PM
> > 
> > The existing iommu SVA interfaces are implemented by calling the SVA
> > specific iommu ops provided by the IOMMU drivers. There's no need for
> > any SVA specific ops in iommu_ops vector anymore as we can achieve
> > this through the generic attach/detach_dev_pasid domain ops.
> 
> set/block_pasid_dev, to be consistent.
> 
> > +
> > +	mutex_lock(&iommu_sva_lock);
> > +	/* Search for an existing domain. */
> > +	domain = iommu_get_domain_for_dev_pasid(dev, mm->pasid);
> > +	if (domain) {
> > +		sva_domain = to_sva_domain(domain);
> > +		refcount_inc(&sva_domain->bond.users);
> > +		goto out_success;
> > +	}
> > +
> 
> why would one device/pasid be bound to a mm more than once?

Device drivers can call bind() multiple times for the same device and mm,
for example if one process wants to open multiple accelerator queues.

Thanks,
Jean
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