linux-kernel - Re: AVIC related warning in enable_irq

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Message-ID: <dda0de57-b891-9e30-b2f1-561c5e04ca39@amd.com>
Date:   Mon, 4 May 2020 02:18:13 +0700
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     Maxim Levitsky <mlevitsk@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: AVIC related warning in enable_irq_window

Maxim / Paolo,

On 5/2/20 11:43 PM, Maxim Levitsky wrote:
> On Sat, 2020-05-02 at 18:42 +0200, 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?
>>
>> svm_set_vintr also has a rather silly
>>
>> static void svm_set_vintr(struct vcpu_svm *svm)
>> {
>>         set_intercept(svm, INTERCEPT_VINTR);
>>         if (is_intercept(svm, INTERCEPT_VINTR))
>>                 svm_enable_vintr(svm);
>> }
>>
>> so I'm thinking of just inlining svm_enable_vintr and renaming
>> svm_{set,clear}_vintr to svm_{enable,disable}_vintr_window.  Would you
>> like to send two patches for this, the first to remove the WARN_ON and
>> the second to do the cleanup?
> 
> Absolutely! I will send a patch very soon.

I have been debugging this and I have a patch that is supposed to fix this
(instead of removing the WARN ON). Please do not remove the warn on just yet.

Thanks,
Suravee