[PATCH v2 0/3] iommufd: Remove iommufd_hw_pagetable_has_group

Nicolin Chen
2023-01-28T21:19:06Z

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(-)

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2.39.1