linux-kernel - Re: [PATCH 04/44] KVM: Teardown VFIO ops earlier in kvm

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Date:   Thu, 03 Nov 2022 13:46:28 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Anup Patel <anup@...infault.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Eric Farman <farman@...ux.ibm.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Atish Patra <atishp@...shpatra.org>,
        David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        kvmarm@...ts.cs.columbia.edu, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Fabiano Rosas <farosas@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Chao Gao <chao.gao@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yuan Yao <yuan.yao@...el.com>
Subject: Re: [PATCH 04/44] KVM: Teardown VFIO ops earlier in kvm_exit()

On Wed, Nov 02 2022, Sean Christopherson <seanjc@...gle.com> wrote:

> Move the call to kvm_vfio_ops_exit() further up kvm_exit() to try and
> bring some amount of symmetry to the setup order in kvm_init(), and more
> importantly so that the arch hooks are invoked dead last by kvm_exit().
> This will allow arch code to move away from the arch hooks without any
> change in ordering between arch code and common code in kvm_exit().
>
> That kvm_vfio_ops_exit() is called last appears to be 100% arbitrary.  It
> was bolted on after the fact by commit 571ee1b68598 ("kvm: vfio: fix
> unregister kvm_device_ops of vfio").  The nullified kvm_device_ops_table
> is also local to kvm_main.c and is used only when there are active VMs,
> so unless arch code is doing something truly bizarre, nullifying the
> table earlier in kvm_exit() is little more than a nop.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  virt/kvm/kvm_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Looks safe to me.

Reviewed-by: Cornelia Huck <cohuck@...hat.com>