Re: [PATCH v6 12/13] KVM: s390: add gib_alert_irq_handler()

[Halil Pasic]

On Thu, 24 Jan 2019 13:59:38 +0100
Michael Mueller <mimu@xxxxxxxxxxxxx> wrote:

> The patch implements a handler for GIB alert interruptions
> on the host. Its task is to alert guests that interrupts are
> pending for them.
> 
> A GIB alert interrupt statistic counter is added as well:
> 
> $ cat /proc/interrupts
>           CPU0       CPU1
>   ...
>   GAL:      23         37   [I/O] GIB Alert
>   ...
> 
> Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
[..]
> +/**
> + * gisa_get_ipm_or_restore_iam - return IPM or restore GISA IAM
> + *
> + * @gi: gisa interrupt struct to work on
> + *
> + * Atomically restores the interruption alert mask if none of the
> + * relevant ISCs are pending and return the IPM.

The word 'relevant' probably reflects some previous state. It does not
bother me too much.

[..]

>  
> +static void __airqs_kick_single_vcpu(struct kvm *kvm, u8 deliverable_mask)
> +{
> +	int vcpu_id, online_vcpus = atomic_read(&kvm->online_vcpus);
> +	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
> +	struct kvm_vcpu *vcpu;
> +
> +	for_each_set_bit(vcpu_id, kvm->arch.idle_mask, online_vcpus) {
> +		vcpu = kvm_get_vcpu(kvm, vcpu_id);
> +		if (psw_ioint_disabled(vcpu))
> +			continue;
> +		deliverable_mask &= (u8)(vcpu->arch.sie_block->gcr[6] >> 24);
> +		if (deliverable_mask) {
> +			/* lately kicked but not yet running */

How about /* was kicked but didn't run yet */?

> +			if (test_and_set_bit(vcpu_id, gi->kicked_mask))
> +				return;
> +			kvm_s390_vcpu_wakeup(vcpu);
> +			return;
> +		}
> +	}
> +}
> +

[..]

> +static void process_gib_alert_list(void)
> +{
> +	struct kvm_s390_gisa_interrupt *gi;
> +	struct kvm_s390_gisa *gisa;
> +	struct kvm *kvm;
> +	u32 final, origin = 0UL;
> +
> +	do {
> +		/*
> +		 * If the NONE_GISA_ADDR is still stored in the alert list
> +		 * origin, we will leave the outer loop. No further GISA has
> +		 * been added to the alert list by millicode while processing
> +		 * the current alert list.
> +		 */
> +		final = (origin & NONE_GISA_ADDR);
> +		/*
> +		 * Cut off the alert list and store the NONE_GISA_ADDR in the
> +		 * alert list origin to avoid further GAL interruptions.
> +		 * A new alert list can be build up by millicode in parallel
> +		 * for guests not in the yet cut-off alert list. When in the
> +		 * final loop, store the NULL_GISA_ADDR instead. This will re-
> +		 * enable GAL interruptions on the host again.
> +		 */
> +		origin = xchg(&gib->alert_list_origin,
> +			      (!final) ? NONE_GISA_ADDR : NULL_GISA_ADDR);
> +		/*
> +		 * Loop through the just cut-off alert list and start the
> +		 * gisa timers to kick idle vcpus to consume the pending
> +		 * interruptions asap.
> +		 */
> +		while (origin & GISA_ADDR_MASK) {
> +			gisa = (struct kvm_s390_gisa *)(u64)origin;
> +			origin = gisa->next_alert;
> +			gisa->next_alert = (u32)(u64)gisa;
> +			kvm = container_of(gisa, struct sie_page2, gisa)->kvm;
> +			gi = &kvm->arch.gisa_int;
> +			if (hrtimer_active(&gi->timer))
> +				hrtimer_cancel(&gi->timer);
> +			hrtimer_start(&gi->timer, 0, HRTIMER_MODE_REL);
> +		}
> +	} while (!final);
> +
> +}
> +
>  void kvm_s390_gisa_clear(struct kvm *kvm)
>  {
>  	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
>  
>  	if (!gi->origin)
>  		return;
> -	memset(gi->origin, 0, sizeof(struct kvm_s390_gisa));
> -	gi->origin->next_alert = (u32)(u64)gi->origin;
> +	gisa_clear_ipm(gi->origin);

This could be a separate patch. I would like little more explanation
to this.

>  	VM_EVENT(kvm, 3, "gisa 0x%pK cleared", gi->origin);
>  }
>  
> @@ -2940,13 +3078,25 @@ void kvm_s390_gisa_init(struct kvm *kvm)
>  	gi->origin = &kvm->arch.sie_page2->gisa;
>  	gi->alert.mask = 0;
>  	spin_lock_init(&gi->alert.ref_lock);
> -	kvm_s390_gisa_clear(kvm);
> +	gi->expires = 50 * 1000; /* 50 usec */

I blindly trust your choice here ;) 

> +	hrtimer_init(&gi->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +	gi->timer.function = gisa_vcpu_kicker;
> +	memset(gi->origin, 0, sizeof(struct kvm_s390_gisa));
> +	gi->origin->next_alert = (u32)(u64)gi->origin;
>  	VM_EVENT(kvm, 3, "gisa 0x%pK initialized", gi->origin);
>  }
>  
>  void kvm_s390_gisa_destroy(struct kvm *kvm)
>  {
> -	kvm->arch.gisa_int.origin = NULL;
> +	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
> +
> +	if (!gi->origin)
> +		return;
> +	hrtimer_cancel(&gi->timer);

I'm not sure this cancel here is sufficient. 

> +	WRITE_ONCE(gi->alert.mask, 0);
> +	while (gisa_in_alert_list(gi->origin))
> +		cpu_relax();

If you end up waiting here, I guess, it's likely that a new
timer is going to get set up right after we do
gisa->next_alert = (u32)(u64)gisa;
in  process_gib_alert_list().

> +	gi->origin = NULL;
>  }
>  
>  /**
> @@ -3037,11 +3187,23 @@ int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc)
>  }
>  EXPORT_SYMBOL_GPL(kvm_s390_gisc_unregister);
>  


Overall, there are couple of things I would prefer done differently,
but better something working today that something prefect in 6 months.
In that sense, provided my comment regarding destroy is addressed:

Acked-by: Halil Pasic <pasic@xxxxxxxxxxxxx>