Messages in this thread | | | Date | Wed, 25 May 2022 08:29:49 +0100 | From | Jean-Philippe Brucker <> | Subject | Re: [PATCH v7 06/10] iommu/sva: Refactoring iommu_sva_bind/unbind_device() |
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On Wed, May 25, 2022 at 02:04:49AM +0000, Tian, Kevin wrote: > > From: Jean-Philippe Brucker <jean-philippe@linaro.org> > > Sent: Tuesday, May 24, 2022 6:58 PM > > > > 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. > > > > Is it clearer to have a sva_bond_get/put() pair instead of calling > bind() multiple times here?
I don't think it's clearer, and it would force device drivers to keep track of {dev, mm} pairs, when the IOMMU subsystem already does that. At the moment a device driver calls
bond = iommu_sva_bind_device(dev, mm)
for each ADI that it wants to assign to userspace. If a process happens to want multiple ADIs on one device, then the {dev, mm} parameters are the same and bind() returns the same bond. Since the IOMMU driver needs to track these anyway, it might as well refcount them.
Thanks, Jean
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