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

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Date:   Fri, 6 Jan 2023 10:29:55 -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 08:03:32PM -0500, Matthew Rosato wrote:
> On 1/5/23 7:32 PM, Jason Gunthorpe wrote:
> > 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.
> > 
> 
> If the core vfio code were to add logic to invoke kvm_put_kvm and
> kvm_get_kvm, won't this introduce a vfio dependency on kvm?  If I
> recall, we have the drivers handling the kvm reference today in
> order to avoid that..

Not in vfio, put it in kvm 'kvm_put_async()'

Jason