Re: [PATCH v2 16/30] KVM: s390: pci: enable host forwarding of Adapter Event Notifications

[Matthew Rosato]

On 1/17/22 12:38 PM, Pierre Morel wrote:
>
...
> > +static void aen_process_gait(u8 isc)
> > +{
> > +    bool found = false, first = true;
> > +    union zpci_sic_iib iib = {{0}};
> > +    unsigned long si, flags;
> > +
> > +    spin_lock_irqsave(&aift->gait_lock, flags);
> > +
> > +    if (!aift->gait) {
> > +        spin_unlock_irqrestore(&aift->gait_lock, flags);
> > +        return;
> > +    }
> > +
> > +    for (si = 0;;) {
> > +        /* Scan adapter summary indicator bit vector */
> > +        si = airq_iv_scan(aift->sbv, si, airq_iv_end(aift->sbv));
> > +        if (si == -1UL) {
> > +            if (first || found) {
> > +                /* Reenable interrupts. */
> > +                if (zpci_set_irq_ctrl(SIC_IRQ_MODE_SINGLE, isc,
> > +                              &iib))
> > +                    break;
>
> AFAIU this code is VFIO interpretation specific code and facility 12 is 
> a precondition for it, so I think this break will never occur.
> If I am right we should not test the return value which will make the 
> code clearer.

Yep, you are correct; we can just ignore the return value here.

> > +                first = found = false;
> > +            } else {
> > +                /* Interrupts on and all bits processed */
> > +                break;
> > +            }
>
> May be add a comment: "rescan after re-enabling interrupts"

OK

> > +            found = false;
> > +            si = 0;
> > +            continue;
> > +        }
> > +        found = true;
> > +        aen_host_forward(si);
> > +    }
> > +
> > +    spin_unlock_irqrestore(&aift->gait_lock, flags);
> > +}
> > +
> >   static void gib_alert_irq_handler(struct airq_struct *airq,
> >                     struct tpi_info *tpi_info)
> >   {
> > +    struct tpi_adapter_info *info = (struct tpi_adapter_info *)tpi_info;
> > +
> >       inc_irq_stat(IRQIO_GAL);
> > -    process_gib_alert_list();
> > +
> > +    if (IS_ENABLED(CONFIG_PCI) && (info->forward || info->error)) {
> > +        aen_process_gait(info->isc);
> > +        if (info->aism != 0)
> > +            process_gib_alert_list();
> > +    } else
> > +        process_gib_alert_list();
>
> NIT: I think we need braces around this statement

OK

> >   }
> >   static struct airq_struct gib_alert_irq = {
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index 01dc3f6883d0..ab8b56deed11 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -65,7 +65,8 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
> >       STATS_DESC_COUNTER(VM, inject_float_mchk),
> >       STATS_DESC_COUNTER(VM, inject_pfault_done),
> >       STATS_DESC_COUNTER(VM, inject_service_signal),
> > -    STATS_DESC_COUNTER(VM, inject_virtio)
> > +    STATS_DESC_COUNTER(VM, inject_virtio),
> > +    STATS_DESC_COUNTER(VM, aen_forward)
> >   };
> >   const struct kvm_stats_header kvm_vm_stats_header = {
> > diff --git a/arch/s390/kvm/pci.h b/arch/s390/kvm/pci.h
> > index b2000ed7b8c3..387b637863c9 100644
> > --- a/arch/s390/kvm/pci.h
> > +++ b/arch/s390/kvm/pci.h
> > @@ -12,6 +12,7 @@
> >   #include <linux/pci.h>
> >   #include <linux/mutex.h>
> > +#include <linux/kvm_host.h>
> >   #include <asm/airq.h>
> >   #include <asm/kvm_pci.h>
> > @@ -34,6 +35,14 @@ struct zpci_aift {
> >   extern struct zpci_aift *aift;
> > +static inline struct kvm *kvm_s390_pci_si_to_kvm(struct zpci_aift *aift,
> > +                         unsigned long si)
> > +{
> > +    if (!IS_ENABLED(CONFIG_PCI) || aift->kzdev == 0 || 
> > aift->kzdev[si] == 0)
>
> Shouldn't it be better CONFIG_VFIO_PCI ?

While it's true that we can't be doing interpretation without 
CONFIG_VFIO_PCI=y|m, the reason I'm using CONFIG_PCI here and elsewhere 
in the code is because CONFIG_PCI is what is being used to determine 
whether or not we build arch/s390/kvm/pci.o in patch 14 (and thus 
whether or not the aift exists) -- And the reason we use this is because 
this is where the code dependencies exist (examples include 
ZPCI_NR_DEVICES, the AEN pieces that must be preserved over KVM module 
remove/insert in patch 15)

If we for some reason have a case where CONFIG_KVM=y|m && CONFIG_PCI=y|m 
&& CONFIG_VFIO_PCI=n, this will still work:  aift and aift->kzdev will 
exist (kvm/pci.o is linked) but we will never actually drive this 
routine anyway because we'll never register a device for AEN forwarding 
without CONFIG_VFIO_PCI.