Re: [PATCH v4 07/10] KVM: s390: add function process_gib_alert_list()

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On Fri, 30 Nov 2018 15:32:12 +0100
Michael Mueller <mimu@xxxxxxxxxxxxx> wrote:

> This function processes the gib alert list. It is required to
> run when either a gib alert interruption has been received or
> a gisa that might be in the alert list is cleared or dropped.
> 
> The GIB alert list contains all GISAs that have pending
> adapter interruptions.

I'm not sure this last paragraph is 100% correct. If e.g. all vcpus
of a guest are in SIE we don't ask for alerting, and we would not get
alerted when an IPM bit is set in the GISA.

> 
> Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
> Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
> Reviewed-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> ---
>  arch/s390/kvm/interrupt.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index 251d01f1e9bf..37a5df4e8dac 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -2900,6 +2900,56 @@ static void nullify_gisa(struct kvm_s390_gisa *gisa)
>  	gisa->next_alert = (u32)(u64)gisa;
>  }
>  
> +#define NULL_GISA_ADDR 0x00000000UL
> +#define NONE_GISA_ADDR 0x00000001UL
> +#define GISA_ADDR_MASK 0xfffff000UL
> +
> +static void __maybe_unused process_gib_alert_list(void)
> +{
> +	u32 final, next_alert, origin = 0UL;
> +	struct kvm_s390_gisa *gisa;
> +	struct kvm_vcpu *vcpu;
> +	struct kvm *kvm;
> +
> +	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.
> +		 */
> +		for (origin = xchg(&gib->alert_list_origin,
> +				   (!final) ? NONE_GISA_ADDR : NULL_GISA_ADDR);
> +		     /* Loop through the just cut-off alert list. */
> +		     origin & GISA_ADDR_MASK;
> +		     origin = next_alert) {
> +			gisa = (struct kvm_s390_gisa *)(u64)origin;
> +			next_alert = gisa->next_alert;
> +			/* Unlink the GISA from the alert list. */
> +			gisa->next_alert = origin;
> +			if (!kvm_s390_gisa_get_ipm(gisa))
> +				continue;
> +			/*
> +			 * Wake-up an idle vcpu of the kvm this GISA
> +			 * belongs to if available.
> +			 */
> +			kvm = container_of(gisa, struct sie_page2, gisa)->kvm;
> +			vcpu = __find_vcpu_for_floating_irq(kvm);
> +			if (vcpu)
> +				kvm_s390_vcpu_wakeup(vcpu);

I don't quite understand the logic here. You seem to wake up the first
idle vcpu, or the next round-robin vcpu (I guess the rr one is actually
in SIE). What I would expect is making an attempt at delivering all irqs
in the IPM. Since vcpus can mask ISCs a scenario can be constructed where
more than one vcpu shuld be woken up.

Or am I misunderstanding something?

Regards,
Halil

> +		}
> +	} while (!final);
> +}
> +
>  void kvm_s390_gisa_clear(struct kvm *kvm)
>  {
>  	if (kvm->arch.gisa) {




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