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Date:   Thu, 5 Jan 2023 19:34:30 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Alex Williamson <alex.williamson@redhat.com>
Cc:     Matthew Rosato <mjrosato@linux.ibm.com>, cohuck@redhat.com,
        borntraeger@linux.ibm.com, jjherne@linux.ibm.com,
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        intel-gfx@lists.freedesktop.org,
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        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Kevin Tian <kevin.tian@intel.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM
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References: <20220519183311.582380-1-mjrosato@linux.ibm.com>
 <20220519183311.582380-2-mjrosato@linux.ibm.com>
 <20230105150930.6ee65182.alex.williamson@redhat.com>
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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