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From:   Paolo Bonzini <pbonzini@redhat.com>
Date:   Mon, 27 Sep 2021 19:24:52 +0200
Message-ID: <CABgObfYtS6wiQe=BhF3t5usr7J6q4PWE4=rwZMMukfC9wT_6fA@mail.gmail.com>
Subject: Re: disabling halt polling broken? (was Re: [PATCH 00/14] KVM:
 Halt-polling fixes, cleanups and a new stat)
To:     Christian Borntraeger <borntraeger@de.ibm.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        David Matlack <dmatlack@google.com>,
        Jon Cargille <jcargill@google.com>,
        Jim Mattson <jmattson@google.com>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.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>,
        Joerg Roedel <joro@8bytes.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        KVM ARM <kvmarm@lists.cs.columbia.edu>,
        "open list:MIPS" <linux-mips@vger.kernel.org>,
        kvm <kvm@vger.kernel.org>, kvm-ppc <kvm-ppc@vger.kernel.org>,
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        Jing Zhang <jingzhangos@google.com>,
        Marc Zyngier <maz@kernel.org>,
        Huacai Chen <chenhuacai@kernel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
        Paul Mackerras <paulus@ozlabs.org>,
        Janosch Frank <frankja@linux.ibm.com>
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On Mon, Sep 27, 2021 at 5:17 PM Christian Borntraeger
<borntraeger@de.ibm.com> wrote:
> > So I think there are two possibilities that makes sense:
> >
> > * track what is using KVM_CAP_HALT_POLL, and make writes to halt_poll_ns follow that
>
> what about using halt_poll_ns for those VMs that did not uses KVM_CAP_HALT_POLL and the private number for those that did.

Yes, that's what I meant.  David pointed out that doesn't allow you to
disable halt polling altogether, but for that you can always ask each
VM's userspace one by one, or just not use KVM_CAP_HALT_POLL. (Also, I
don't know about Google's usecase, but mine was actually more about
using KVM_CAP_HALT_POLL to *disable* halt polling on some VMs!).

Paolo