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From:   David Matlack <dmatlack@google.com>
Date:   Wed, 2 Mar 2022 10:33:22 -0800
Message-ID: <CALzav=dzqOp-css8kgqHhCLJnbUrUZt+e_YStCj2HFy0oD+vGg@mail.gmail.com>
Subject: Re: [PATCH v3 22/28] KVM: x86/mmu: Zap defunct roots via asynchronous worker
To:     Sean Christopherson <seanjc@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        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 list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ben Gardon <bgardon@google.com>,
        Mingwei Zhang <mizhang@google.com>
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On Wed, Mar 2, 2022 at 9:35 AM Sean Christopherson <seanjc@google.com> wrote:
>
> 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?

This was towards the back of my queue but I can bump it to the front.
I'll have the patches out this week.