Subject: [PATCH v2 3/8] arm/arm64: KVM: vgic: Factor out level irq processing on guest exit

From: [email-masked] (Christoffer Dall)
Date: Mon, 14 Sep 2015 13:31:46 +0200

On Mon, Sep 07, 2015 at 05:32:35PM +0200, Eric Auger wrote:
> 
> 
> On 09/04/2015 09:40 PM, Christoffer Dall wrote:
> > Currently vgic_process_maintenance() processes dealing with a completed
> > level-triggered interrupt directly, but we are soon going to reuse this
> > logic for level-triggered mapped interrupts with the HW bit set, so
> > move this logic into a separate static function.
> > 
> > Probably the most scary part of this commit is convincing yourself that
> > the current flow is safe compared to the old one.  In the following I
> > try to list the changes and why they are harmless:
> > 
> >   Move vgic_irq_clear_queued after kvm_notify_acked_irq:
> >     Harmless because the effect of clearing the queued flag wrt.
> >     kvm_set_irq is only that vgic_update_irq_pending does not set the
> >     pending bit on the emulated CPU interface or in the pending_on_cpu
> >     bitmask,
> well actually the notifier calls vgic_update_irq_pending with level ==0
> so it does not reach the can_sample.
>  but we set this in __kvm_vgic_sync_hwstate later on if the

can the notifier never go through a flow where it calls the function
with level = 1 ?  For example if the interrupt hit in between?

In any case, it should still be functionally correct.

Thanks for the RB.

-Christoffer

> >     level is stil high.
> still
> 
> Reviewed-by: Eric Auger <[email-masked]>
> 
> Eric
> > 
> >   Move vgic_set_lr before kvm_notify_acked_irq:
> >     Also, harmless because the LR are cpu-local operations and
> >     kvm_notify_acked only affects the dist
> > 
> >   Move vgic_dist_irq_clear_soft_pend after kvm_notify_acked_irq:
> >     Also harmless because it's just a bit which is cleared and altering
> >     the line state does not affect this bit.
> > 
> > Reviewed-by: Marc Zyngier <[email-masked]>
> > Signed-off-by: Christoffer Dall <[email-masked]>
> > ---
> >  virt/kvm/arm/vgic.c | 88 ++++++++++++++++++++++++++++++-----------------------
> >  1 file changed, 50 insertions(+), 38 deletions(-)
> > 
> > diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> > index 6bd1c9b..fe0e5db 100644
> > --- a/virt/kvm/arm/vgic.c
> > +++ b/virt/kvm/arm/vgic.c
> > @@ -1322,12 +1322,56 @@ epilog:
> >  	}
> >  }
> >  
> > +static int process_level_irq(struct kvm_vcpu *vcpu, int lr, struct vgic_lr vlr)
> > +{
> > +	int level_pending = 0;
> > +
> > +	vlr.state = 0;
> > +	vlr.hwirq = 0;
> > +	vgic_set_lr(vcpu, lr, vlr);
> > +
> > +	/*
> > +	 * If the IRQ was EOIed (called from vgic_process_maintenance) or it
> > +	 * went from active to non-active (called from vgic_sync_hwirq) it was
> > +	 * also ACKed and we we therefore assume we can clear the soft pending
> > +	 * state (should it had been set) for this interrupt.
> > +	 *
> > +	 * Note: if the IRQ soft pending state was set after the IRQ was
> > +	 * acked, it actually shouldn't be cleared, but we have no way of
> > +	 * knowing that unless we start trapping ACKs when the soft-pending
> > +	 * state is set.
> > +	 */
> > +	vgic_dist_irq_clear_soft_pend(vcpu, vlr.irq);
> > +
> > +	/*
> > +	 * Tell the gic to start sampling the line of this interrupt again.
> > +	 */
> > +	vgic_irq_clear_queued(vcpu, vlr.irq);
> > +
> > +	/* Any additional pending interrupt? */
> > +	if (vgic_dist_irq_get_level(vcpu, vlr.irq)) {
> > +		vgic_cpu_irq_set(vcpu, vlr.irq);
> > +		level_pending = 1;
> > +	} else {
> > +		vgic_dist_irq_clear_pending(vcpu, vlr.irq);
> > +		vgic_cpu_irq_clear(vcpu, vlr.irq);
> > +	}
> > +
> > +	/*
> > +	 * Despite being EOIed, the LR may not have
> > +	 * been marked as empty.
> > +	 */
> > +	vgic_sync_lr_elrsr(vcpu, lr, vlr);
> > +
> > +	return level_pending;
> > +}
> > +
> >  static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
> >  {
> >  	u32 status = vgic_get_interrupt_status(vcpu);
> >  	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> > -	bool level_pending = false;
> >  	struct kvm *kvm = vcpu->kvm;
> > +	int level_pending = 0;
> >  
> >  	kvm_debug("STATUS = %08x\n", status);
> >  
> > @@ -1342,54 +1386,22 @@ static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
> >  
> >  		for_each_set_bit(lr, eisr_ptr, vgic->nr_lr) {
> >  			struct vgic_lr vlr = vgic_get_lr(vcpu, lr);
> > -			WARN_ON(vgic_irq_is_edge(vcpu, vlr.irq));
> >  
> > -			spin_lock(&dist->lock);
> > -			vgic_irq_clear_queued(vcpu, vlr.irq);
> > +			WARN_ON(vgic_irq_is_edge(vcpu, vlr.irq));
> >  			WARN_ON(vlr.state & LR_STATE_MASK);
> > -			vlr.state = 0;
> > -			vgic_set_lr(vcpu, lr, vlr);
> >  
> > -			/*
> > -			 * If the IRQ was EOIed it was also ACKed and we we
> > -			 * therefore assume we can clear the soft pending
> > -			 * state (should it had been set) for this interrupt.
> > -			 *
> > -			 * Note: if the IRQ soft pending state was set after
> > -			 * the IRQ was acked, it actually shouldn't be
> > -			 * cleared, but we have no way of knowing that unless
> > -			 * we start trapping ACKs when the soft-pending state
> > -			 * is set.
> > -			 */
> > -			vgic_dist_irq_clear_soft_pend(vcpu, vlr.irq);
> >  
> >  			/*
> >  			 * kvm_notify_acked_irq calls kvm_set_irq()
> > -			 * to reset the IRQ level. Need to release the
> > -			 * lock for kvm_set_irq to grab it.
> > +			 * to reset the IRQ level, which grabs the dist->lock
> > +			 * so we call this before taking the dist->lock.
> >  			 */
> > -			spin_unlock(&dist->lock);
> > -
> >  			kvm_notify_acked_irq(kvm, 0,
> >  					     vlr.irq - VGIC_NR_PRIVATE_IRQS);
> > -			spin_lock(&dist->lock);
> > -
> > -			/* Any additional pending interrupt? */
> > -			if (vgic_dist_irq_get_level(vcpu, vlr.irq)) {
> > -				vgic_cpu_irq_set(vcpu, vlr.irq);
> > -				level_pending = true;
> > -			} else {
> > -				vgic_dist_irq_clear_pending(vcpu, vlr.irq);
> > -				vgic_cpu_irq_clear(vcpu, vlr.irq);
> > -			}
> >  
> > +			spin_lock(&dist->lock);
> > +			level_pending |= process_level_irq(vcpu, lr, vlr);
> >  			spin_unlock(&dist->lock);
> > -
> > -			/*
> > -			 * Despite being EOIed, the LR may not have
> > -			 * been marked as empty.
> > -			 */
> > -			vgic_sync_lr_elrsr(vcpu, lr, vlr);
> >  		}
> >  	}
> >  
> > 
>