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Date:   Wed, 27 Oct 2021 17:37:47 +0200
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Subject: Re: [PATCH v2 00/43] KVM: Halt-polling and x86 APICv overhaul
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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>,
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        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
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        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>
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From:   Paolo Bonzini <pbonzini@redhat.com>
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On 27/10/21 17:28, Sean Christopherson wrote:
> On Wed, Oct 27, 2021, Paolo Bonzini wrote:
>> On 27/10/21 16:41, Sean Christopherson wrote:
>>> The other thing I don't like about having the WARN in the loop is that it suggests
>>> that something other than the vCPU can modify the NDST and SN fields, which is
>>> wrong and confusing (for me).
>>
>> Yeah, I can agree with that.  Can you add it in a comment above the cmpxchg
>> loop, it can be as simple as
>>
>> 	/* The processor can set ON concurrently.  */
>>
>> when you respin patch 21 and the rest of the series?
> 
> I can definitely add a comment, but I think that comment is incorrect.

It's completely backwards indeed.  I first had "the hardware" and then 
shut down my brain for a second to replace it.

> So something like this?
> 
> 	/* ON can be set concurrently by a different vCPU or by hardware. */

Yes, of course.

Paolo