linux-kernel - Re: [PATCH v3 22/28] KVM: x86/mmu: Zap defunct roots via asynchronous worker

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Message-ID: <43809107-cd8a-21f5-c45b-2f39c1bd037e@redhat.com>
Date:   Wed, 2 Mar 2022 19:36:04 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Matlack <dmatlack@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        David Hildenbrand <david@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ben Gardon <bgardon@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH v3 22/28] KVM: x86/mmu: Zap defunct roots via asynchronous
 worker

On 3/2/22 19:33, David Matlack wrote:
> On Wed, Mar 2, 2022 at 9:35 AM Sean Christopherson <seanjc@...gle.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.

Thanks!

Paolo