On Wed, May 25, 2022 at 02:04:49AM +0000, Tian, Kevin wrote:
> > From: Jean-Philippe Brucker <jean-phili...@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...@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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