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

Nicolin Chen
2022-06-17T23:07:30Z

On Fri, Jun 17, 2022 at 02:53:13AM +0000, Tian, Kevin wrote:
> > > ...
> > > > - 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.
>
> Looks msi_cookie requirement is per platform (currently only
> for smmu. see arm_smmu_get_resv_regions()). If there is
> no mixed case then above check is not required.

Do you mean "reusing existing domain" for the "mixed case"?

> But let's hear whether Robin has a different thought here.

Yea, sure.

> > > > - 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?
>
> Perhaps detach_destroy() can return a Boolean to indicate whether
> a domain is destroyed.

It could be a solution but doesn't feel that common for a clean
function to have a return value indicating a special case. Maybe
passing in "&domain" so that we can check if it's NULL after?