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From:   David Matlack <dmatlack@google.com>
Date:   Fri, 14 May 2021 14:20:38 -0700
Message-ID: <CALzav=eTC3HhHyxndHvS3NyCfPiBL2Wb5NvU=-+UsxSoMfmqXA@mail.gmail.com>
Subject: Re: [PATCH v2 1/4] KVM: PPC: Book3S HV: exit halt polling on
 need_resched() as well
To:     Wanpeng Li <kernellwp@gmail.com>
Cc:     linux-kernel@vger.kernel.org, kvm list <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Ben Segall <bsegall@google.com>,
        Venkatesh Srinivas <venkateshs@chromium.org>,
        Paul Mackerras <paulus@ozlabs.org>,
        Suraj Jitindar Singh <sjitindarsingh@gmail.com>
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On Wed, May 12, 2021 at 6:58 PM Wanpeng Li <kernellwp@gmail.com> wrote:
>
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Inspired by commit 262de4102c7bb8 (kvm: exit halt polling on need_resched()
> as well), CFS_BANDWIDTH throttling will use resched_task() when there is just
> one task to get the task to block. It was likely allowing VMs to overrun their
> quota when halt polling. Due to PPC implements an arch specific halt polling
> logic, we should add the need_resched() checking there as well.
>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Venkatesh Srinivas <venkateshs@chromium.org>
> Cc: Jim Mattson <jmattson@google.com>
> Cc: David Matlack <dmatlack@google.com>
> Cc: Paul Mackerras <paulus@ozlabs.org>
> Cc: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> v1 -> v2:
>  * update patch description
>
>  arch/powerpc/kvm/book3s_hv.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 28a80d2..6199397 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -3936,7 +3936,8 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
>                                 break;
>                         }
>                         cur = ktime_get();
> -               } while (single_task_running() && ktime_before(cur, stop));
> +               } while (single_task_running() && !need_resched() &&
> +                        ktime_before(cur, stop));

Consider moving this condition to a helper function that can be shared
between book3s and the generic halt-polling loop.

>
>                 spin_lock(&vc->lock);
>                 vc->vcore_state = VCORE_INACTIVE;
> --
> 2.7.4
>