Re: [RFC PATCH 11/45] KVM: arm/arm64: vgic-new: Implement kvm_vgic_vcpu_pending_irq

Christoffer Dall
2016-03-31T08:53:29Z

On Fri, Mar 25, 2016 at 02:04:34AM +0000, Andre Przywara wrote:
> From: Eric Auger <eric.auger@linaro.org>
>
> Tell KVM whether a particular VCPU has an IRQ that needs handling
> in the guest. This is used to decide whether a VCPU is runnable.
>
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
> include/kvm/vgic/vgic.h | 2 ++
> virt/kvm/arm/vgic/vgic.c | 22 ++++++++++++++++++++++
> 2 files changed, 24 insertions(+)
>
> diff --git a/include/kvm/vgic/vgic.h b/include/kvm/vgic/vgic.h
> index 986f23f..2ce9b4a 100644
> --- a/include/kvm/vgic/vgic.h
> +++ b/include/kvm/vgic/vgic.h
> @@ -181,6 +181,8 @@ struct vgic_cpu {
> int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int intid,
> bool level);
>
> +int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu);
> +
> #define irqchip_in_kernel(k) (!!((k)->arch.vgic.in_kernel))
> #define vgic_initialized(k) (false)
> #define vgic_ready(k) ((k)->arch.vgic.ready)
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 9eb031e8..d6c8c92 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -477,3 +477,25 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
> vgic_populate_lrs(vcpu);
> spin_unlock(&vcpu->arch.vgic_cpu.ap_list_lock);
> }
> +
> +int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu)
> +{
> + struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> + struct vgic_irq *irq;
> + bool pending = false;
> +
> + spin_lock(&vgic_cpu->ap_list_lock);
> +
> + list_for_each_entry(irq, &vgic_cpu->ap_list_head, ap_list) {
> + spin_lock(&irq->irq_lock);
> + pending = irq->pending && irq->enabled;
> + spin_unlock(&irq->irq_lock);
> +
> + if (pending)
> + break;
> + }
> +
> + spin_unlock(&vgic_cpu->ap_list_lock);
> +
> + return pending;
> +}

as long as we only call this in the wfi/wfe path, then it's fine. If we
start calling this in the critical path, I think we should check the
common case of list_empty(&vgic_cpu->ap_list) first.

Thanks,
-Christoffer