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Mon, 04 May 2020 02:25:32 -0700 (PDT) Received: from [192.168.178.58] ([151.20.132.175]) by smtp.gmail.com with ESMTPSA id a8sm5031002wrg.85.2020.05.04.02.25.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 May 2020 02:25:32 -0700 (PDT) Subject: Re: AVIC related warning in enable_irq_window To: Maxim Levitsky , Suravee Suthikulpanit , kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org References: <9ce7bb5c4fb8bcc4ac21103f7534a6edfcbe195d.camel@redhat.com> <758b27a8-74c0-087d-d90b-d95faee2f561@redhat.com> <159382e7fdf0f9b50d79e29554842289e92e1ed7.camel@redhat.com> From: Paolo Bonzini Message-ID: Date: Mon, 4 May 2020 11:25:31 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <159382e7fdf0f9b50d79e29554842289e92e1ed7.camel@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 04/05/20 11:13, Maxim Levitsky wrote: > On Mon, 2020-05-04 at 15:46 +0700, Suravee Suthikulpanit wrote: >> Paolo / Maxim, >> >> On 5/2/20 11:42 PM, Paolo Bonzini wrote: >>> On 02/05/20 15:58, Maxim Levitsky wrote: >>>> The AVIC is disabled by svm_toggle_avic_for_irq_window, which calls >>>> kvm_request_apicv_update, which broadcasts the KVM_REQ_APICV_UPDATE vcpu request, >>>> however it doesn't broadcast it to CPU on which now we are running, which seems OK, >>>> because the code that handles that broadcast runs on each VCPU entry, thus >>>> when this CPU will enter guest mode it will notice and disable the AVIC. >>>> >>>> However later in svm_enable_vintr, there is test 'WARN_ON(kvm_vcpu_apicv_active(&svm->vcpu));' >>>> which is still true on current CPU because of the above. >>> >>> Good point! We can just remove the WARN_ON I think. Can you send a patch? >> >> Instead, as an alternative to remove the WARN_ON(), would it be better to just explicitly >> calling kvm_vcpu_update_apicv(vcpu) to update the apicv_active flag right after >> kvm_request_apicv_update()? >> > This should work IMHO, other that the fact kvm_vcpu_update_apicv will be called again, > when this vcpu is entered since the KVM_REQ_APICV_UPDATE will still be pending on it. > It shoudn't be a problem, and we can even add a check to do nothing when it is called > while avic is already in target enable state. I thought about that but I think it's a bit confusing. If we want to keep the WARN_ON, Maxim can add an equivalent one to svm_vcpu_run, which is even better because the invariant is clearer. WARN_ON((vmcb->control.int_ctl & (AVIC_ENABLE_MASK | V_IRQ_MASK)) == (AVIC_ENABLE_MASK | V_IRQ_MASK)); Paolo