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I'll have to rebase that > > > anyway, so merging this as-is is absolutely fine! > > > > This might help your effort - after this series and this below there > > are no 'bus' users of iommu_capable left at all. > > Thanks, but I still need a device for the iommu_domain_alloc() as well, so > at that point the interrupt check is OK to stay where it is. It is a simple enough change that could avoid introducing the device_iommu_capable() at all perhaps. > I figured out a locking strategy per my original idea that seems > pretty clean, it just needs vfio_group_viable() to go away first: I think this should be more like: struct vfio_device *vdev; mutex_lock(&group->device_lock); vdev = list_first_entry(group->device_list, struct vfio_device, group_next); ret = driver->ops->attach_group(data, group->iommu_group, group->type, vdev->dev); mutex_unlock(&group->device_lock); Then don't do the iommu_group_for_each_dev() at all. The problem with iommu_group_for_each_dev() is that it may select a struct device that does not have a vfio_device bound to it, so we would be using a random struct device that is not protected by any VFIO device_driver. However, this creates an oddball situation where the vfio_device and it's struct device could become unplugged from the system while the domain that the struct device spawned continues to exist and remains attached to other devices in the same group. ie the iommu driver has to be careful not to retain the struct device input.. I suppose that is inevitable to have sharing of domains across devices, so the iommu drivers will have to accommodate this. Jason