[RFC PATCH 4/4] KVM: arm/arm64: Provide a vgic interrupt line level sample function

[Christoffer Dall]

On Sat, Sep 02, 2017 at 12:20:34PM +0100, Marc Zyngier wrote:
> On Tue, Aug 29 2017 at 11:39:02 am BST, Christoffer Dall <cdall at linaro.org> wrote:
> > The GIC sometimes need to sample the physical line of a mapped
> > interrupt.  As we know this to be notoriously slow, provide a callback
> > function for devices (such as the timer) which can do this much faster
> > than talking to the distributor, for example by comparing a few
> > in-memory values.  Fall back to the good old method of poking the
> > physical GIC if no callback is provided.
> >
> > Signed-off-by: Christoffer Dall <cdall at linaro.org>
> > ---
> >  include/kvm/arm_vgic.h    | 13 ++++++++++++-
> >  virt/kvm/arm/arch_timer.c | 16 +++++++++++++++-
> >  virt/kvm/arm/vgic/vgic.c  |  7 ++++++-
> >  3 files changed, 33 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> > index 53f631b..a52990b 100644
> > --- a/include/kvm/arm_vgic.h
> > +++ b/include/kvm/arm_vgic.h
> > @@ -125,6 +125,17 @@ struct vgic_irq {
> >  	u8 priority;
> >  	enum vgic_irq_config config;	/* Level or edge */
> >  
> > +	/*
> > +	 * Callback function pointer to in-kernel devices that can tell us the
> > +	 * state of the input level of mapped level-triggered IRQ faster than
> > +	 * peaking into the physical GIC.
> > +	 *
> > +	 * Always called in non-preemptible section and the functions can use
> > +	 * kvm_arm_get_running_vcpu() to get the vcpu pointer for private
> > +	 * IRQs.
> > +	 */
> > +	bool (*get_input_level)(int vintid);
> > +
> >  	void *owner;			/* Opaque pointer to reserve an interrupt
> >  					   for in-kernel devices. */
> >  };
> > @@ -309,7 +320,7 @@ void kvm_vgic_init_cpu_hardware(void);
> >  int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int intid,
> >  			bool level, void *owner);
> >  int kvm_vgic_map_phys_irq(struct kvm_vcpu *vcpu, unsigned int host_irq,
> > -			  u32 vintid);
> > +			  u32 vintid, bool (*callback)(int vindid));
> >  int kvm_vgic_unmap_phys_irq(struct kvm_vcpu *vcpu, unsigned int vintid);
> >  bool kvm_vgic_map_is_active(struct kvm_vcpu *vcpu, unsigned int vintid);
> >  
> > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> > index b24e2f7..82169ef 100644
> > --- a/virt/kvm/arm/arch_timer.c
> > +++ b/virt/kvm/arm/arch_timer.c
> > @@ -643,6 +643,19 @@ static bool timer_irqs_are_valid(struct kvm_vcpu *vcpu)
> >  	return true;
> >  }
> >  
> > +static bool timer_get_input_level(int vintid)
> > +{
> > +	struct kvm_vcpu *vcpu = kvm_arm_get_running_vcpu();
> > +	struct arch_timer_context *timer;
> > +
> > +	if (vintid == vcpu_vtimer(vcpu)->irq.irq)
> > +		timer = vcpu_vtimer(vcpu);
> > +	else
> > +		BUG(); /* We only map the vtimer so far */
> > +
> > +	return kvm_timer_should_fire(timer);
> > +}
> > +
> >  int kvm_timer_enable(struct kvm_vcpu *vcpu)
> >  {
> >  	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> > @@ -664,7 +677,8 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu)
> >  		return -EINVAL;
> >  	}
> >  
> > -	ret = kvm_vgic_map_phys_irq(vcpu, host_vtimer_irq, vtimer->irq.irq);
> > +	ret = kvm_vgic_map_phys_irq(vcpu, host_vtimer_irq, vtimer->irq.irq,
> > +				    &timer_get_input_level);
> 
> nit: no need for a & here.
> 
> >  	if (ret)
> >  		return ret;
> >  
> > diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> > index e3ce2fa..0466c10 100644
> > --- a/virt/kvm/arm/vgic/vgic.c
> > +++ b/virt/kvm/arm/vgic/vgic.c
> > @@ -147,6 +147,9 @@ bool vgic_irq_line_level(struct vgic_irq *irq)
> >  
> >  	BUG_ON(!irq->hw);
> >  
> > +	if (irq->get_input_level)
> > +		return irq->get_input_level(irq->intid);
> > +
> >  	WARN_ON(irq_get_irqchip_state(irq->host_irq,
> >  				      IRQCHIP_STATE_PENDING,
> >  				      &line_level));
> > @@ -429,7 +432,7 @@ int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int intid,
> >  }
> >  
> >  int kvm_vgic_map_phys_irq(struct kvm_vcpu *vcpu, unsigned int host_irq,
> > -			  u32 vintid)
> > +			  u32 vintid, bool (*callback)(int vindid))
> 
> nit #2: "callback" is a very non-descriptive name for a callback... ;-)
> How about calling it "get_input_level", matching the vgic_irq field?

Yeah, totally.

> 
> >  {
> >  	struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, vintid);
> >  	struct irq_desc *desc;
> > @@ -456,6 +459,7 @@ int kvm_vgic_map_phys_irq(struct kvm_vcpu *vcpu, unsigned int host_irq,
> >  	irq->hw = true;
> >  	irq->host_irq = host_irq;
> >  	irq->hwintid = data->hwirq;
> > +	irq->get_input_level = callback;
> >  
> >  out:
> >  	spin_unlock(&irq->irq_lock);
> > @@ -476,6 +480,7 @@ int kvm_vgic_unmap_phys_irq(struct kvm_vcpu *vcpu, unsigned int vintid)
> >  	spin_lock(&irq->irq_lock);
> >  	irq->hw = false;
> >  	irq->hwintid = 0;
> > +	irq->get_input_level = NULL;
> >  	spin_unlock(&irq->irq_lock);
> >  	vgic_put_irq(vcpu->kvm, irq);
> 
> Reviewed-by: Marc Zyngier <marc.zyngier at arm.com>
> 
Thanks!
-Christoffer