linux-kernel - Re: [PATCH] kvm/vfio: Fix potential deadlock on vfio group

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: <Y9km+xezgD4ovjDX@nvidia.com>
Date:   Tue, 31 Jan 2023 10:34:35 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Anthony Krowiak <akrowiak@...ux.ibm.com>
Cc:     Yi Liu <yi.l.liu@...el.com>, alex.williamson@...hat.com,
        pbonzini@...hat.com, mjrosato@...ux.ibm.com, kevin.tian@...el.com,
        cohuck@...hat.com, farman@...ux.ibm.com, pmorel@...ux.ibm.com,
        borntraeger@...ux.ibm.com, frankja@...ux.ibm.com,
        imbrenda@...ux.ibm.com, david@...hat.com, jjherne@...ux.ibm.com,
        pasic@...ux.ibm.com, zhenyuw@...ux.intel.com, zhi.a.wang@...el.com,
        seanjc@...gle.com, linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm/vfio: Fix potential deadlock on vfio group_lock

On Tue, Jan 31, 2023 at 09:27:54AM -0500, Anthony Krowiak wrote:
> I encountered a lockdep splat while running some regression tests today (see
> below). I suspected it might be this patch so I reverted it, rebuilt the
> kernel and ran the regression tests again; this time, the test ran cleanly.
> It looks like this patch may not have fixed the problem for which it was
> intended. Here is the relevant dmesg output:

Well, it fixes the deadlock it intended to fix and created another one
:)

It means device drivers cannot obtain the kvm lock from their open
functions in this new model.

Why does ap need to touch kvm->lock? (via get_update_locks_for_kvm)

Maybe you should split that lock and have a dedicated apcb lock?

Jason