On Fri, Nov 19, 2021 at 05:44:35AM +0000, Tian, Kevin wrote: > Well, the difference is just in literal. I don't know the background > why the existing iommu_attach_device() users want to do it this > way. But given the condition in iommu_attach_device() it could > in theory imply some unknown hardware-level side effect which > may break the desired functionality once the group size grows > beyond singleton. Is it a real case? I don't know... No, this must not be. Any device can have VFIO attached to it, and VFIO does the equivalent of iommu_attach_device(). We cannot have "unknown hardware-level side effects" to changing the domain's of multi device groups and also have working VFIO. If these HW problems exist they are a seperate issue and the iommu core should flag such groups as being unable to change their domains at all. Jason
