RE: [PATCH v7 06/10] iommu/sva: Refactoring iommu_sva_bind/unbind_device()

Tian, Kevin
2022-05-25T02:04:58Z

> 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?