linux-kernel - Re: [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET

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Message-ID: <Y7dsJpudKGtM0kbl@nvidia.com>
Date:   Thu, 5 Jan 2023 20:32:38 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>, cohuck@...hat.com,
        borntraeger@...ux.ibm.com, jjherne@...ux.ibm.com,
        akrowiak@...ux.ibm.com, pasic@...ux.ibm.com,
        zhenyuw@...ux.intel.com, zhi.a.wang@...el.com, hch@...radead.org,
        intel-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kevin Tian <kevin.tian@...el.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

On Thu, Jan 05, 2023 at 07:16:37PM -0500, Matthew Rosato wrote:

> Yeah, this is also what I was thinking, replace the direct
> kvm_put_kvm calls with, say, schedule_delayed_work in each driver,
> where the delayed task just does the kvm_put_kvm (along with a brief
> comment explaining why we handle the put asynchronously).

Don't put that in every driver, do something like mmput_async() where
the core code has all of this.

> Other than that..  The goal of this patch originally was to get the
> kvm reference at first open_device and release it with the very last
> close_device, so the only other option I could think of would be to
> take the responsibility back from the vfio drivers and do the
> kvm_get_kvm and kvm_put_kvm directly in vfio_main after dropping the
> (but that would result in some ugly symbol linkage and would acquire
> kvm references that a driver maybe does not care about so I don't
> really like that idea)

And we still have the deadlock problem anyhow..

Jason