linux-kernel - Re: AVIC related warning in enable_irq

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Message-ID: <c5c32371-4b4e-1382-c616-3830ba46bf85@amd.com>
Date:   Mon, 4 May 2020 15:46:35 +0700
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: AVIC related warning in enable_irq_window

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()?

Thanks,
Suravee