linux-kernel - Re: [PATCH v2 37/43] KVM: SVM: Unconditionally mark AVIC as running on vCPU load (with APICv)

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Message-ID: <e9509fb0-54f3-ca86-57b7-8b6d5de240b7@redhat.com>
Date:   Mon, 25 Oct 2021 17:57:39 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Atish Patra <atish.patra@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: Re: [PATCH v2 37/43] KVM: SVM: Unconditionally mark AVIC as running
 on vCPU load (with APICv)

On 25/10/21 17:48, Sean Christopherson wrote:
> On Mon, Oct 25, 2021, Paolo Bonzini wrote:
>> On 09/10/21 04:12, Sean Christopherson wrote:
>>> +	/* TODO: Document why the unblocking path checks for updates. */
>>
>> Is that a riddle or what? :)
> 
> Yes?  I haven't been able to figure out why the unblocking path explicitly
> checks and handles an APICv update.
> 

Challenge accepted.  In the original code, it was because without it 
avic_vcpu_load would do nothing, and nothing would update the IS_RUNNING 
flag.

It shouldn't be necessary anymore since commit df7e4827c549 ("KVM: SVM: 
call avic_vcpu_load/avic_vcpu_put when enabling/disabling AVIC", 
2021-08-20), where svm_refresh_apicv_exec_ctrl takes care of the 
avic_vcpu_load on the next VMRUN.

Paolo