[PATCH 0/2] iommu: Remove iommu_sva_ops::mm_exit()

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

The IOMMU SVA API currently requires device drivers to implement an
mm_exit() callback, which stops device jobs that do DMA. This function
is called in the release() MMU notifier, when an address space that is
shared with a device exits.

It has been noted several time during discussions about SVA that
cancelling DMA jobs can be slow and complex, and doing it in the
release() notifier might cause synchronization issues (patch 2 has more
background). Device drivers must in any case call unbind() to remove
their bond, after stopping DMA from a more favorable context (release of
a file descriptor).

So after mm exits, rather than notifying device drivers, we can hold on
to the PASID until unbind(), ask IOMMU drivers to silently abort DMA and
Page Requests in the meantime. This change should relieve the mmput()
path.

Patch 1 removes the mm_exit() callback from the uacce module, and patch
2 removes it from the IOMMU API.

Jean-Philippe Brucker (2):
  uacce: Remove mm_exit() op
  iommu: Remove iommu_sva_ops::mm_exit()

 include/linux/iommu.h      |  30 -------
 include/linux/uacce.h      |  34 ++------
 drivers/iommu/iommu.c      |  11 ---
 drivers/misc/uacce/uacce.c | 171 +++++++++----------------------------
 4 files changed, 50 insertions(+), 196 deletions(-)

-- 
2.26.0

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