On 12/24/21 10:50 AM, Jason Gunthorpe wrote:
We don't need _USER anymore because iommu_group_set_dma_owner() always
does detatch, and iommu_replace_group_domain() avoids ever reassigning
default_domain. The sepecial USER behavior falls out automatically.
This means we will grow more group-centric interfaces. My understanding
is the opposite that we should hide the concept of group in IOMMU
subsystem, and the device drivers only faces device specific interfaces.
Ideally group interfaces would be reduced, but in this case VFIO needs
the group. It has sort of a fundamental problem with its uAPI that
expects the container is fully setup with a domain at the moment the
group is attached. So deferring domain setup to when the device is
available becomes a user visible artifact - and if this is important
or not is a whole research question that isn't really that important
for this series.
We also can't just pull a device out of thin air, a device that hasn't
been probed() hasn't even had dma_configure called! Let alone the
lifetime and locking problems with that kind of idea.
So.. leaving it as a group interface makes the most sense,
particularly for this series which is really about fixing the sharing
model in the iommu core and deleting the BUG_ONs.
I feel it makes more sense if we leave the attach_device/group
refactoring patches into a separated series. I will come up with this
new series so that people can review and comment on the real code.
Best regards,
baolu
