Re: [PATCH v2 5/5] vfio/iommu_type1: Simplify group attachment

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Jun 16, 2022 at 07:08:10AM +0000, Tian, Kevin wrote:
> ...
> > +static struct vfio_domain *
> > +vfio_iommu_alloc_attach_domain(struct bus_type *bus, struct vfio_iommu
> > *iommu,
> > +                            struct vfio_iommu_group *group)
> > +{
> > +     struct iommu_domain *new_domain;
> > +     struct vfio_domain *domain;
> > +     int ret = 0;
> > +
> > +     /* Try to match an existing compatible domain */
> > +     list_for_each_entry (domain, &iommu->domain_list, next) {
> > +             ret = iommu_attach_group(domain->domain, group-
> > >iommu_group);
> > +             if (ret == -EMEDIUMTYPE)
> > +                     continue;
> 
> Probably good to add one line comment here for what EMEDIUMTYPE
> represents. It's not a widely-used retry type like EAGAIN. A comment
> can save the time of digging out the fact by jumping to iommu file.

Sure. I can add that.

> ...
> > -     if (resv_msi) {
> > +     if (resv_msi && !domain->msi_cookie) {
> >               ret = iommu_get_msi_cookie(domain->domain,
> > resv_msi_base);
> >               if (ret && ret != -ENODEV)
> >                       goto out_detach;
> > +             domain->msi_cookie = true;
> >       }
> 
> why not moving to alloc_attach_domain() then no need for the new
> domain field? It's required only when a new domain is allocated.

When reusing an existing domain that doesn't have an msi_cookie,
we can do iommu_get_msi_cookie() if resv_msi is found. So it is
not limited to a new domain.

> ...
> > -             if (list_empty(&domain->group_list)) {
> > -                     if (list_is_singular(&iommu->domain_list)) {
> > -                             if (list_empty(&iommu-
> > >emulated_iommu_groups)) {
> > -                                     WARN_ON(iommu->notifier.head);
> > -
> >       vfio_iommu_unmap_unpin_all(iommu);
> > -                             } else {
> > -
> >       vfio_iommu_unmap_unpin_reaccount(iommu);
> > -                             }
> > -                     }
> > -                     iommu_domain_free(domain->domain);
> > -                     list_del(&domain->next);
> > -                     kfree(domain);
> > -                     vfio_iommu_aper_expand(iommu, &iova_copy);
> 
> Previously the aperture is adjusted when a domain is freed...
> 
> > -                     vfio_update_pgsize_bitmap(iommu);
> > -             }
> > -             /*
> > -              * Removal of a group without dirty tracking may allow
> > -              * the iommu scope to be promoted.
> > -              */
> > -             if (!group->pinned_page_dirty_scope) {
> > -                     iommu->num_non_pinned_groups--;
> > -                     if (iommu->dirty_page_tracking)
> > -                             vfio_iommu_populate_bitmap_full(iommu);
> > -             }
> > +             vfio_iommu_detach_destroy_domain(domain, iommu,
> > group);
> >               kfree(group);
> >               break;
> >       }
> >
> > +     vfio_iommu_aper_expand(iommu, &iova_copy);
> 
> but now it's done for every group detach. The aperture is decided
> by domain geometry which is not affected by attached groups.

Yea, I've noticed this part. Actually Jason did this change for
simplicity, and I think it'd be safe to do so?