On Wed, 5 Apr 2023 08:01:49 +0000 "Liu, Yi L" <yi.l.liu@xxxxxxxxx> wrote: > > From: Liu, Yi L <yi.l.liu@xxxxxxxxx> > > Sent: Wednesday, April 5, 2023 3:55 PM > > > > > > > Therefore, I think as written, the singleton dev_set hot-reset is > > > enabled for iommufd and (unintentionally?) for the group path, while > > > also negating a requirement for a group fd or that a provided group fd > > > actually matches the device in this latter case. The null-array > > > approach is not however extended to groups for more general use. > > > Additionally, limiting no-iommu hot-reset to singleton dev_sets > > > provides only a marginal functional difference vs VFIO_DEVICE_RESET. > > > > I think the singletion dev_set hot-reset is for iommufd (or more accurately > > for the noiommu case in cdev path). > > but actually, singleton dev_set hot-reset can work for group path as well. > Based on this, I'm also wondering do we really want to have singleton dev_set > hot-reset only for cdev noiommu case? or we allow it generally or just > don't support it as it is equivalent with VFIO_DEVICE_RESET? I think you're taking the potential that VFIO_DEVICE_RESET and hot-reset could do the same thing too far. The former is more likely to do an FLR, or even a PM reset. QEMU even tries to guess what reset VFIO_DEVICE_RESET might use in order to choose to do a hot-reset if it seems like the device might only support a PM reset otherwise. Changing the reset method of a device requires privilege, which is maybe something we'd compromise on for no-iommu, but the general expectation is that VFIO_DEVICE_RESET provides a device level scope and hot-reset provides a... hot-reset, and sometimes those are the same thing, but that doesn't mean we can lean on the former. > If we don't support singletion dev_set hot-reset, noiommu devices in cdev > path shall fail the hot-reset if empty-fd array is provided. But we may just > document that empty-fd array does not work for noiommu. User should > use the device fd array. I don't see any replies to my comment on 08/12 where I again question why we need an empty array option. It's causing all sorts of headaches and I don't see the justification for it beyond some hand waving that it reduces complexity for the user. This singleton dev-set notion seems equally unjustified. Do we just need to deal with hot-reset being unsupported for no-iommu devices with iommufd? Thanks, Alex
