Re: [PATCH v3 52/59] KVM: arm/arm64: GICv4: Use the doorbell interrupt as an unblocking source

Christoffer Dall
2017-08-28T18:19:02Z

On Mon, Jul 31, 2017 at 06:26:30PM +0100, Marc Zyngier wrote:
> The doorbell interrupt is only useful if the vcpu is blocked on WFI.
> In all other cases, recieving a doorbell interrupt is just a waste
> of cycles.
>
> So let's only enable the doorbell if a vcpu is getting blocked,
> and disable it when it is unblocked. This is very similar to
> what we're doing for the background timer.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> include/kvm/arm_vgic.h | 3 +++
> virt/kvm/arm/arm.c | 2 ++
> virt/kvm/arm/vgic/vgic-v4.c | 32 +++++++++++++++++++++++++++++++-
> 3 files changed, 36 insertions(+), 1 deletion(-)
>
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index 050f78d4fb42..7b1cc7ff5b42 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -375,4 +375,7 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int irq,
> int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int irq,
> struct kvm_kernel_irq_routing_entry *irq_entry);
>
> +void kvm_vgic_v4_enable_doorbell(struct kvm_vcpu *vcpu);
> +void kvm_vgic_v4_disable_doorbell(struct kvm_vcpu *vcpu);
> +
> #endif /* __KVM_ARM_VGIC_H */
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 6803ea27c47d..5dbc8dc8fbf4 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -316,11 +316,13 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
> void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)
> {
> kvm_timer_schedule(vcpu);
> + kvm_vgic_v4_enable_doorbell(vcpu);
> }
>
> void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
> {
> kvm_timer_unschedule(vcpu);
> + kvm_vgic_v4_disable_doorbell(vcpu);
> }
>
> int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
> index 6af3cde6d7d4..50721c4e3da5 100644
> --- a/virt/kvm/arm/vgic/vgic-v4.c
> +++ b/virt/kvm/arm/vgic/vgic-v4.c
> @@ -16,6 +16,7 @@
> */
>
> #include <linux/interrupt.h>
> +#include <linux/irq.h>
> #include <linux/irqdomain.h>
> #include <linux/kvm_host.h>
>
> @@ -73,6 +74,14 @@ int vgic_v4_init(struct kvm *kvm)
> kvm_for_each_vcpu(i, vcpu, kvm) {
> int irq = dist->its_vm.vpes[i]->irq;
>
> + /*
> + * Don't automatically enable the doorbell, as we're
> + * flipping it back and forth when the vcpu gets
> + * blocked. Also disable the lazy disabling, as the
> + * doorbell could kick us out of the guest too
> + * early...
> + */
> + irq_set_status_flags(irq, IRQ_NOAUTOEN | IRQ_DISABLE_UNLAZY);
> ret = request_irq(irq, vgic_v4_doorbell_handler,
> 0, "vcpu", vcpu);
> if (ret) {
> @@ -98,7 +107,10 @@ void vgic_v4_teardown(struct kvm *kvm)
>
> for (i = 0; i < its_vm->nr_vpes; i++) {
> struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, i);
> - free_irq(its_vm->vpes[i]->irq, vcpu);
> + int irq = its_vm->vpes[i]->irq;
> +
> + irq_clear_status_flags(irq, IRQ_NOAUTOEN | IRQ_DISABLE_UNLAZY);
> + free_irq(irq, vcpu);
> }
>
> its_free_vcpu_irqs(its_vm);
> @@ -211,3 +223,21 @@ int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int virq,
> mutex_unlock(&its->its_lock);
> return ret;
> }
> +
> +void kvm_vgic_v4_enable_doorbell(struct kvm_vcpu *vcpu)
> +{
> + if (vgic_is_v4_capable(vcpu->kvm)) {
> + int irq = vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq;
> + if (irq)
> + enable_irq(irq);
> + }
> +}
> +
> +void kvm_vgic_v4_disable_doorbell(struct kvm_vcpu *vcpu)
> +{
> + if (vgic_is_v4_capable(vcpu->kvm)) {
> + int irq = vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq;
> + if (irq)
> + disable_irq(irq);
> + }
> +}
> --
> 2.11.0
>
Reviewed-by: Christoffer Dall <cdall@linaro.org>