Re: [PATCH v2 1/4] KVM: PPC: Book3S HV: exit halt polling on need_resched() as well

[David Matlack]

On Wed, May 12, 2021 at 6:58 PM Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
>
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Cc: Venkatesh Srinivas <venkateshs@xxxxxxxxxxxx>
> Cc: Jim Mattson <jmattson@xxxxxxxxxx>
> Cc: David Matlack <dmatlack@xxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxxx>
> Cc: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
> 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
>