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

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

[Wanpeng Li]

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

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@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
>

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

[Wanpeng Li]

On Sat, 15 May 2021 at 05:21, David Matlack <dmatlack@google.com> wrote:
>
> 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.

Will do in the next version, thanks for review. :)

    Wanpeng