linux-kernel - Re: [PATCH 1/3] KVM: PPC: Book3S HV: exit halt polling on need

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Date:   Wed, 12 May 2021 08:02:02 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Paul Mackerras <paulus@...abs.org>,
        Ben Segall <bsegall@...gle.com>,
        Venkatesh Srinivas <venkateshs@...omium.org>,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH 1/3] KVM: PPC: Book3S HV: exit halt polling on
 need_resched() as well

Cc more guys,
On Sat, 8 May 2021 at 17:32, Wanpeng Li <kernellwp@...il.com> wrote:
>
> From: Wanpeng Li <wanpengli@...cent.com>
>
> Inspired by commit 262de4102c7bb8 (kvm: exit halt polling on need_resched()
> as well), due to PPC implements an arch specific halt polling logic, we should
> add the need_resched() checking there as well.
>

Update the patch description:

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: Paul Mackerras <paulus@...abs.org>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
>  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));
>
>                 spin_lock(&vc->lock);
>                 vc->vcore_state = VCORE_INACTIVE;
> --
> 2.7.4
>