Re: [PATCH v3 3/5] iommu: Add iommu_get_domain_for_dev_locked() helper

Nicolin Chen
2025-08-21T14:42:21Z

On Thu, Aug 21, 2025 at 08:07:01AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: Saturday, August 16, 2025 2:45 AM
> >
> > On Fri, Aug 15, 2025 at 08:55:28AM +0000, Tian, Kevin wrote:
> > > > From: Nicolin Chen <nicolinc@nvidia.com>
> > > > Sent: Tuesday, August 12, 2025 6:59 AM
> > > > So, iommu_get_domain_for_dev() should check the gdev flag and return
> > the
> > > > blocked domain if the flag is set. But the caller of this API could hold
> > > > the group->mutex already or not, making it difficult to add the lock.
> > > >
> > > > Introduce a new iommu_get_domain_for_dev_locked() helper to be used
> > by
> > > > those drivers in a context that is already under the protection of the
> > > > group->mutex, e.g. those attach_dev callback functions. And roll out the
> > > > new helper to all the existing IOMMU drivers.
> > >
> > > iommu_get_domain_for_dev() is also called outside of attach_dev
> > > callback functions, e.g. malidp_get_pgsize_bitmap(). and the returned
> > > info according to the attached domain might be saved in static
> > > structures, e.g.:
> > >
> > > ms->mmu_prefetch_pgsize = malidp_get_pgsize_bitmap(mp);
> > >
> > > would that cause weird issues when blocking domain is returned
> > > though one may not expect reset to happen at that point?
> >
> > We aren't changing the iommu_get_domain_for_dev(). So, it should
> > be used exclusively for functions that are outside group->mutex,
> > like this one, i.e. they should still get the group->domain v.s.
> > the blocked domain.
> >
>
> Usually the difference between func() and func_locked() is only about
> whether the caller holds a lock. If they mean to return different
> domains, may need better naming (though I don't have a good option
> now)...

Yea, naming is tricky here :)

Perhaps it could follow a different pattern:
iommu_dev_get_domain_for_driver(struct device *dev);

With a simple note highlighting to be used by IOMMU drivers in the
iommu callback functions like attach_dev.

Nicolin