linux-kernel - Re: [PATCH v2 00/43] KVM: Halt-polling and x86 APICv overhaul

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Date:   Wed, 27 Oct 2021 17:37:47 +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 00/43] KVM: Halt-polling and x86 APICv overhaul

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