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Date:   Wed, 2 Mar 2022 17:35:35 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Christian Borntraeger <borntraeger@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        David Hildenbrand <david@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, David Matlack <dmatlack@google.com>,
        Ben Gardon <bgardon@google.com>,
        Mingwei Zhang <mizhang@google.com>
Subject: Re: [PATCH v3 22/28] KVM: x86/mmu: Zap defunct roots via
 asynchronous worker
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 <b9270432-4ee8-be8e-8aa1-4b09992f82b8@redhat.com>
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On Wed, Mar 02, 2022, Paolo Bonzini wrote:
> However, I think we now need a module_get/module_put when creating/destroying
> a VM; the workers can outlive kvm_vm_release and therefore any reference
> automatically taken by VFS's fops_get/fops_put.

Haven't read the rest of the patch, but this caught my eye.  We _already_ need
to handle this scenario.  As you noted, any worker, i.e. anything that takes a
reference via kvm_get_kvm() without any additional guarantee that the module can't
be unloaded is suspect. x86 is mostly fine, though kvm_setup_async_pf() is likely
affected, and other architectures seem to have bugs.

Google has an internal patch that addresses this.  I believe David is going to post
the fix... David?