On Mon, 16 May 2022 15:35:58 -0300 Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > On Mon, May 16, 2022 at 02:30:46PM -0400, Matthew Rosato wrote: > > > Conceptually I think this would work for QEMU anyway (it always sets the kvm > > before we open the device). I tried to test the idea quickly but couldn't > > get the following to apply on vfio-next or your vfio_group_locking -- but I > > understand what you're trying to do so I'll re-work and try it out. > > I created it on 8c9350e9bf43de1ebab3cc8a80703671e6495ab4 which is the > vfio_group_locking.. I can send you a github if it helps > https://github.com/jgunthorpe/linux/commits/vfio_group_lockin > > > @Alex can you think of any usecase/reason why we would need to be able to > > set the KVM sometime after the device was opened? Doing something like > > below would break that, as this introduces the assumption that the group is > > associated with the KVM before the device is opened (and if it's not, the > > device open fails). > > Keep in mind that GVT already hard requires this ordering to even > allow open_device to work - so it already sets a floor for what > userspace can do.. How is this going to work when vfio devices are exposed directly? We currently have a strict ordering through the group to get to the device, and it's therefore a reasonable requirement for userspace to register the group with kvm before opening the device. Is the notifier and async KVM registration necessary to support this dependency with direct device access? I don't have as clear a picture of the ordering with with direct access. Thanks, Alex
