> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Monday, February 6, 2023 9:25 PM > > On Mon, Feb 06, 2023 at 06:57:35AM +0000, Tian, Kevin wrote: > > > From: Jason Gunthorpe <jgg@xxxxxxxxxx> > > > Sent: Friday, February 3, 2023 11:03 PM > > > > > > On Fri, Feb 03, 2023 at 08:26:44AM +0000, Tian, Kevin wrote: > > > > > From: Nicolin Chen <nicolinc@xxxxxxxxxx> > > > > > Sent: Thursday, February 2, 2023 3:05 PM > > > > > > > > > > All drivers are already required to support changing between active > > > > > UNMANAGED domains when using their attach_dev ops. > > > > > > > > All drivers which don't have *broken* UNMANAGED domain? > > > > > > No, all drivers.. It has always been used by VFIO. > > > > existing iommu_attach_group() doesn't support changing between > > two UNMANAGED domains. only from default->unmanaged or > > blocking->unmanaged. > > Yes, but before we added the blocking domains VFIO was changing > between unmanaged domains. Blocking domains are so new that no driver > could have suddenly started to depend on this. In legacy VFIO unmanaged domain was 1:1 associated with vfio container. I didn't say how a group can switch between two containers w/o going through transition to/from the default domain, i.e. detach from 1st container and then attach to the 2nd. > > btw looking at the code __iommu_group_set_domain(): > > > > * Note that this is called in error unwind paths, attaching to a > > * domain that has already been attached cannot fail. > > */ > > ret = __iommu_group_for_each_dev(group, new_domain, > > iommu_group_do_attach_device); > > > > with that we don't need fall back to core domain in above error > > unwinding per this comment. > > That does make some sense. > > I tried to make a patch to consolidate all this error handling once, > that would be the better way to approach this. that would be good. > > > > In this case the API cannot retain a hidden reference to the new > > > domain, so it must be purged, one way or another. > > > > Could you elaborate where the hidden reference is retained? > > Inside the driver, it can keep track of the domain pointer if > attach_dev succeeds > Are you referring to no error unwinding in __iommu_group_for_each_dev() so if it is failed some devices may have attach_dev succeeds then simply recovering group->domain in __iommu_attach_group() is insufficient?
