Re: [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

Jason Gunthorpe
2023-01-05T23:34:44Z

On Thu, Jan 05, 2023 at 03:09:30PM -0700, Alex Williamson wrote:
> On Thu, 19 May 2022 14:33:11 -0400
> Matthew Rosato <mjrosato@linux.ibm.com> wrote:
>
> > Rather than relying on a notifier for associating the KVM with
> > the group, let's assume that the association has already been
> > made prior to device_open. The first time a device is opened
> > associate the group KVM with the device.
> >
> > This fixes a user-triggerable oops in GVT.
>
> It seems this has traded an oops for a deadlock, which still exists
> today in both GVT-g and vfio-ap. These are the only vfio drivers that
> care about kvm, so they make use of kvm_{get,put}_kvm(), where the
> latter is called by their .close_device() callbacks.

Bleck

It is pretty common to run the final part of 'put' from a workqueue
specifically to avoid stuff like this, eg fput does it

Maybe that is the simplest?

Jason