From: Nicolin Chen nicolinc@nvidia.com Sent: Friday, February 10, 2023 5:13 AM
if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {if (list_empty(&hwpt->devices)) {iopt_table_remove_domain(&hwpt->ioas->iopt,hwpt->domain);list_del(&hwpt->hwpt_item);}I'm not sure how this can be fully shared between detach and replace. Here some work e.g. above needs to be done before calling iommu_group_replace_domain() while others can be done afterwards.
This iopt_table_remove_domain/list_del is supposed to be done in the hwpt's destroy() actually. We couldn't move it because it'd need the new domain_alloc_user op and its implementation in ARM driver. Overall, I think it should be safe to put it behind the iommu_group_replace_domain().
My confusion is that we have different flows between detach/attach and replace.
today with separate detach+attach we have following flow:
Remove device from current hwpt; if (last_device in hwpt) { Remove hwpt domain from current iopt; if (last_device in group) detach group from hwpt domain; }
if (first device in group) { attach group to new hwpt domain; if (first_device in hwpt) Add hwpt domain to new iopt; Add device to new hwpt;
but replace flow is different on the detach part:
if (first device in group) { replace group's domain from current hwpt to new hwpt; if (first_device in hwpt) Add hwpt domain to new iopt; }
Remove device from old hwpt; if (last_device in old hwpt) Remove hwpt domain from old iopt;
Add device to new hwpt;
I'm yet to figure out whether we have sufficient lock protection to prevent other paths from using old iopt/hwpt to find the device which is already attached to a different domain.