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Date:   Mon, 25 Oct 2021 17:57:39 +0200
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Subject: Re: [PATCH v2 37/43] KVM: SVM: Unconditionally mark AVIC as running
 on vCPU load (with APICv)
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To:     Sean Christopherson <seanjc@google.com>
Cc:     Marc Zyngier <maz@kernel.org>, Huacai Chen <chenhuacai@kernel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
        Paul Mackerras <paulus@ozlabs.org>,
        Anup Patel <anup.patel@wdc.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Atish Patra <atish.patra@wdc.com>,
        David Hildenbrand <david@redhat.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-mips@vger.kernel.org, kvm@vger.kernel.org,
        kvm-ppc@vger.kernel.org, kvm-riscv@lists.infradead.org,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        David Matlack <dmatlack@google.com>,
        Oliver Upton <oupton@google.com>,
        Jing Zhang <jingzhangos@google.com>
References: <20211009021236.4122790-1-seanjc@google.com>
 <20211009021236.4122790-38-seanjc@google.com>
 <acea3c6d-49f4-ab5e-d9fe-6c6a8a665a46@redhat.com>
 <YXbRyMQgMpHVQa3G@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <YXbRyMQgMpHVQa3G@google.com>
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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