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

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