On Mon, May 17, 2021 at 7:01 AM 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. This
> patch adds a helper function that to be shared between book3s and generic
> halt-polling loop.
>
> 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>
> ---
> v2 -> v3:
> * add a helper function
> v1 -> v2:
> * update patch description
>
> arch/powerpc/kvm/book3s_hv.c | 2 +-
> include/linux/kvm_host.h | 2 ++
> virt/kvm/kvm_main.c | 9 +++++++--
> 3 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 28a80d240b76..360165df345b 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -3936,7 +3936,7 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
> break;
> }
> cur = ktime_get();
> - } while (single_task_running() && ktime_before(cur, stop));
> + } while (kvm_vcpu_can_block(cur, stop));
>
> spin_lock(&vc->lock);
> vc->vcore_state = VCORE_INACTIVE;
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 2f34487e21f2..bf4fd60c4699 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1583,4 +1583,6 @@ static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
> /* Max number of entries allowed for each kvm dirty ring */
> #define KVM_DIRTY_RING_MAX_ENTRIES 65536
>
> +bool kvm_vcpu_can_block(ktime_t cur, ktime_t stop);
> +
> #endif
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 6b4feb92dc79..c81080667fd1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2945,6 +2945,12 @@ update_halt_poll_stats(struct kvm_vcpu *vcpu, u64 poll_ns, bool waited)
> vcpu->stat.halt_poll_success_ns += poll_ns;
> }
>
> +
> +bool kvm_vcpu_can_block(ktime_t cur, ktime_t stop)
> +{
> + return single_task_running() && !need_resched() && ktime_before(cur, stop);
> +}
> +
> /*
> * The vCPU has executed a HLT instruction with in-kernel mode enabled.
> */
> @@ -2973,8 +2979,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> goto out;
> }
> poll_end = cur = ktime_get();
> - } while (single_task_running() && !need_resched() &&
> - ktime_before(cur, stop));
> + } while (kvm_vcpu_can_block(cur, stop));
> }
>
> prepare_to_rcuwait(&vcpu->wait);
> --
> 2.25.1
>
Reviewed-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxxxx>
