[PATCH v2 0/3] iommufd: Remove iommufd_hw_pagetable_has_group

[Nicolin Chen <nicolinc@nvidia.com>]

The iommufd_hw_pagetable_has_group is not a device-centric API and has
been a bit of a hack. And it needs to keep tracking an attached device
list on the hw_pagetable, and a device lock to protect the device list.

However, the coming domain replacement series can overcomplicate this
list/lock solution, especially to handle nested hw_pagetable use cases.
So, as a preparatory series, remove the device list/lock and also fix
the iommufd_hw_pagetable_has_group hack.

The iommufd_hw_pagetable_has_group() using the device list could be
replaced with a domain-pointer comparison between the hwpt->domain and
iommu_get_domain_for_dev(). The piece of dependency on list_empty() of
the device list can be also replaced with a refcount. Yet, the removal
of the device lock might introduce a race condition, so the ioas mutex
can be moved as an alternative protection.

You can also find this series on Github:
https://github.com/nicolinc/iommufd/commits/remove_iommufd_hw_pagetable_has_group

Changelog
v1->v2:
 * Fixed a copy-n-paste mistake at a lockdep_assert_held() line

Thanks
Nicolin Chen

Nicolin Chen (2):
  iommufd/device: Make hwpt_list list_add/del symmetric
  iommufd/device: Change iommufd_hw_pagetable_has_group to device
    centric

Yi Liu (1):
  iommufd: Add devices_users to track the hw_pagetable usage by device

 drivers/iommu/iommufd/device.c          | 72 ++++++++++---------------
 drivers/iommu/iommufd/hw_pagetable.c    | 16 ++++--
 drivers/iommu/iommufd/iommufd_private.h |  3 +-
 3 files changed, 40 insertions(+), 51 deletions(-)

-- 
2.39.1