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

Tian, Kevin
2022-06-16T07:08:20Z

> From: Nicolin Chen
> Sent: Thursday, June 16, 2022 8:03 AM
>
> Un-inline the domain specific logic from the attach/detach_group ops into
> two paired functions vfio_iommu_alloc_attach_domain() and
> vfio_iommu_detach_destroy_domain() that strictly deal with creating and
> destroying struct vfio_domains.
>
> Add the logic to check for EMEDIUMTYPE return code of
> iommu_attach_group()
> and avoid the extra domain allocations and attach/detach sequences of the
> old code. This allows properly detecting an actual attach error, like
> -ENOMEM, vs treating all attach errors as an incompatible domain.
>
> Co-developed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 298 +++++++++++++++++---------------
> 1 file changed, 163 insertions(+), 135 deletions(-)
>

...
> +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.

...
> - 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.

...
> - 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.