Re: [PATCH 03/14] iommufd: Replace the hwpt->devices list with iommufd_group

Jason Gunthorpe
2023-03-08T19:00:10Z

On Wed, Mar 08, 2023 at 07:29:36AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Tuesday, March 7, 2023 9:53 PM
> >
> > On Tue, Mar 07, 2023 at 02:38:47AM +0000, Tian, Kevin wrote:
> > > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > > Sent: Tuesday, March 7, 2023 4:22 AM
> > > >
> > > > On Thu, Mar 02, 2023 at 08:01:00AM +0000, Tian, Kevin wrote:
> > > > > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > > > > Sent: Saturday, February 25, 2023 8:28 AM
> > > > > >
> > > > > > +struct iommufd_hw_pagetable *
> > > > > > +iommufd_hw_pagetable_detach(struct iommufd_device *idev)
> > > > > > {
> > > > > > - if (!iommufd_hw_pagetable_has_group(hwpt, idev->igroup))
> > > > > > + struct iommufd_hw_pagetable *hwpt = idev->igroup->hwpt;
> > > > > > +
> > > > > > + lockdep_assert_held(&idev->igroup->lock);
> > > > > > +
> > > > > > + idev->igroup->devices--;
> > > > > > + if (!idev->igroup->devices) {
> > > > > > iommu_detach_group(hwpt->domain, idev->igroup->group);
> > > > > > + idev->igroup->hwpt = NULL;
> > > > >
> > > > > hwpt->obj.users should be decremented here instead of leaving it
> > > > > in iommufd_device_detach().
> > > >
> > > > It is like this because eventually we can't call
> > > > iommufd_object_destroy_user() while holding the locks.
> > > >
> > > > So the lowest function returns the hwpt up the call chain and once
> > > > everything is unlocked then it calls iommufd_hw_pagetable_put()
> > >
> > > but don't we have unbalanced refcnt poke?
> >
> > Yes, the refcount should be incremented for every attached device
> >
>
> per device or per group?

per device

> Now it's igroup tracking attached hwpt and each device holds a reference
> on the igroup. Then why do we want to further poke the refcnt per attached
> device?

It simplified some things, so this is how I made v2..

Jason