linux-kernel - Re: [PATCH] svm: Fix improper check when deactivate AVIC

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Message-ID: <a845d403-be02-ef43-2673-01b265e77fb3@amd.com>
Date:   Mon, 4 Feb 2019 16:05:59 +0000
From:   "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "joro@...tes.org" <joro@...tes.org>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>
Subject: Re: [PATCH] svm: Fix improper check when deactivate AVIC

Paolo,

On 2/1/19 6:01 PM, Suravee Suthikulpanit wrote:
> Paolo,
> 
> On 1/30/19 11:22 PM, Paolo Bonzini wrote:
>> On 29/01/19 09:09, Suthikulpanit, Suravee wrote:
>>> The function svm_refresh_apicv_exec_ctrl() always returning prematurely
>>> as kvm_vcpu_apicv_active() always return false when calling from
>>> the function arch/x86/kvm/x86.c:kvm_vcpu_deactivate_apicv().
>>> This is because the apicv_active is set to false just before calling
>>> refresh_apicv_exec_ctrl().
>>>
>>> Also, we need to mark VMCB_AVIC bit as dirty instead of VMCB_INTR.
>>>
>>> So, fix svm_refresh_apicv_exec_ctrl() to properly deactivate AVIC.
>>>
>>> Fixes: 67034bb9dd5e ('KVM: SVM: Add irqchip_split() checks before enabling AVIC')
>>
>> Having the lapic_in_kernel check in your code is a bit ugly - the caller
>> should check it.  And actually, even though it doesn't check it right
>> now, svm_refresh_apicv_exec_ctrl is only reachable if lapic_in_kernel
>> returns true; see the KVM_CAP_HYPERV_SYNIC case of
>> kvm_vcpu_ioctl_enable_cap.
>>
>> What about this simpler patch:
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 01b66bbcdd7a..74ceda470eae 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -5122,11 +5122,11 @@ static void svm_refresh_apicv_exec_ctrl(
>>       struct vcpu_svm *svm = to_svm(vcpu);
>>       struct vmcb *vmcb = svm->vmcb;
>>
>> -    if (!kvm_vcpu_apicv_active(&svm->vcpu))
>> -        return;
>> -
>> -    vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
>> -    mark_dirty(vmcb, VMCB_INTR);
>> +    if (kvm_vcpu_apicv_active(vcpu))
>> +        vmcb->control.int_ctl |= AVIC_ENABLE_MASK;
>> +    else
>> +        vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
>> +    mark_dirty(vmcb, VMCB_AVIC);
>>   }
>>
>>   static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64
>> *eoi_exit_bitmap)
>>
>> ?
>>
>> Thanks,
>>
>> Paolo
>>
> 
> Yes, this would work.
> 
> This patch is actually a precursor of a patch series that I am working on
> to allow AVIC enabling/disabling during run-time. I will send out a series
> for RFC soon.
> 
> Thanks,
> Suravee

Not sure if you have already applied this change. Anyhow, I just want to let
you know that I have included the change you suggested as patch 1/8 of
the RFC series

"KVM: x86: svm: Enabling AVIC with in kernel irqchip"

Thanks,
Suravee