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

Michael Mueller
2019-01-29T15:29:40Z

On 29.01.19 14:26, Halil Pasic wrote:
> On Thu, 24 Jan 2019 13:59:38 +0100
> Michael Mueller <mimu@linux.ibm.com> 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@linux.ibm.com>
> [..]
>> +/**
>> + * 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.

"relevant" refers to the ISCs handled by the GAL mechanism, i.e those
registered in the kvm->arch.gisa_int.alert.mask.

>
> [..]
>
>>
>> +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 */?

what is the difference here...

>
>> + 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.

I can break at out as I had before... ;)

>
>> 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 ;)

You know I will increase it to 1 ms together with the change that I
proposed. (gisa_get_ipm_or_restore_iam() in kvm_s390_handle_wait()).

>
>> + 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().

There will be no vcpus available anymore at this time, whence
none will be kicked by the timer function. Thus canceling the
timer will be sufficient after the loop.

I have addressed the message as well, but will write it into
the KVM trace.

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;
+ if (gi->alert.mask)
+ KVM_EVENT(3, "vm 0x%pK has unexpected iam 0x%02x",
+ kvm, gi->alert.mask);
+ while (gisa_in_alert_list(gi->origin))
+ cpu_relax();
+ hrtimer_cancel(&gi->timer);
+ gi->origin = NULL;
}

>
>> + 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@linux.ibm.com>
>

Michael