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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d0e55400-d749-23a2-c88f-a2272723bc65@linux.ibm.com>
Date:   Thu, 5 Jan 2023 20:03:32 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Jason Gunthorpe <jgg@...dia.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 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..

>> 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..

Looks like I never finished my sentence here -- I meant call kvm_put_kvm directly in vfio_main after dropping the group lock (e.g. when we set device->kvm = NULL;). But I think we'd still have the kvm dependency issue