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

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Message-ID: <9efaf42c-417c-1fa1-7d1c-d31260966109@linux.ibm.com>
Date:   Tue, 18 Jan 2022 12:25:46 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Pierre Morel <pmorel@...ux.ibm.com>, linux-s390@...r.kernel.org
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        schnelle@...ux.ibm.com, farman@...ux.ibm.com,
        borntraeger@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        frankja@...ux.ibm.com, david@...hat.com, imbrenda@...ux.ibm.com,
        vneethv@...ux.ibm.com, oberpar@...ux.ibm.com, freude@...ux.ibm.com,
        thuth@...hat.com, pasic@...ux.ibm.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 16/30] KVM: s390: pci: enable host forwarding of
 Adapter Event Notifications

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.