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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.googlemail.com with ESMTPSA id f16-20020adff590000000b001f0122f63e1sm5754207wro.85.2022.03.02.10.36.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 02 Mar 2022 10:36:07 -0800 (PST) Message-ID: <43809107-cd8a-21f5-c45b-2f39c1bd037e@redhat.com> Date: Wed, 2 Mar 2022 19:36:04 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH v3 22/28] KVM: x86/mmu: Zap defunct roots via asynchronous worker Content-Language: en-US To: David Matlack , Sean Christopherson Cc: Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , David Hildenbrand , kvm list , LKML , Ben Gardon , Mingwei Zhang References: <20220226001546.360188-1-seanjc@google.com> <20220226001546.360188-23-seanjc@google.com> From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/2/22 19:33, David Matlack wrote: > On Wed, Mar 2, 2022 at 9:35 AM Sean Christopherson 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