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Reply-To: mimu@linux.ibm.com
Subject: Re: [PATCH v6 11/13] KVM: s390: add functions to (un)register GISC
 with GISA
To:     pmorel@linux.ibm.com, KVM Mailing List <kvm@vger.kernel.org>
Cc:     Linux-S390 Mailing List <linux-s390@vger.kernel.org>,
        linux-kernel@vger.kernel.org,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        David Hildenbrand <david@redhat.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Halil Pasic <pasic@linux.ibm.com>
References: <20190124125939.130763-1-mimu@linux.ibm.com>
 <20190124125939.130763-12-mimu@linux.ibm.com>
 <d9884098-9d2a-c47d-cca2-0266fa23be9c@linux.ibm.com>
From:   Michael Mueller <mimu@linux.ibm.com>
Organization: IBM
Date:   Mon, 28 Jan 2019 17:04:10 +0100
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On 28.01.19 16:45, Pierre Morel wrote:
> On 24/01/2019 13:59, Michael Mueller wrote:
>> Add the Interruption Alert Mask (IAM) to the architecture specific
>> kvm struct. This mask in the GISA is used to define for which ISC
>> a GIB alert will be issued.
>>
>> The functions kvm_s390_gisc_register() and kvm_s390_gisc_unregister()
>> are used to (un)register a GISC (guest ISC) with a virtual machine and
>> its GISA.
>>
>> Upon successful completion, kvm_s390_gisc_register() returns the
>> ISC to be used for GIB alert interruptions. A negative return code
>> indicates an error during registration.
>>
>> Theses functions will be used by other adapter types like AP and PCI to
>> request pass-through interruption support.
>>
>> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
>> ---
>>   arch/s390/include/asm/kvm_host.h |  13 +++++
>>   arch/s390/kvm/interrupt.c        | 117 
>> +++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 130 insertions(+)
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h 
>> b/arch/s390/include/asm/kvm_host.h
>> index 7077762ab460..2cfff617cb21 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -781,6 +781,9 @@ struct kvm_s390_gisa {
>>               u8  reserved03[11];
>>               u32 airq_count;
>>           } g1;
>> +        struct {
>> +            u64 word[4];
>> +        } u64;
>>       };
>>   };
>> @@ -813,8 +816,15 @@ struct kvm_s390_vsie {
>>       struct page *pages[KVM_MAX_VCPUS];
>>   };
>> +struct kvm_s390_gisa_iam {
>> +    u8 mask;
>> +    spinlock_t ref_lock;
>> +    u32 ref_count[MAX_ISC + 1];
>> +};
>> +
>>   struct kvm_s390_gisa_interrupt {
>>       struct kvm_s390_gisa *origin;
>> +    struct kvm_s390_gisa_iam alert;
>>   };
>>   struct kvm_arch{
>> @@ -885,6 +895,9 @@ void kvm_arch_crypto_set_masks(struct kvm *kvm, 
>> unsigned long *apm,
>>   extern int sie64a(struct kvm_s390_sie_block *, u64 *);
>>   extern char sie_exit;
>> +extern int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc);
>> +extern int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc);
>> +
>>   static inline void kvm_arch_hardware_disable(void) {}
>>   static inline void kvm_arch_check_processor_compat(void *rtn) {}
>>   static inline void kvm_arch_sync_events(struct kvm *kvm) {}
>> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
>> index 5efcd9e2cf8f..6bc9dab6d352 100644
>> --- a/arch/s390/kvm/interrupt.c
>> +++ b/arch/s390/kvm/interrupt.c
>> @@ -222,6 +222,33 @@ static inline u8 int_word_to_isc(u32 int_word)
>>    */
>>   #define IPM_BIT_OFFSET (offsetof(struct kvm_s390_gisa, ipm) * 
>> BITS_PER_BYTE)
>> +/**
>> + * gisa_set_iam - change the GISA interruption alert mask
>> + *
>> + * @gisa: gisa to operate on
>> + * @iam: new IAM value to use
>> + *
>> + * Change the IAM atomically with the next alert address and the IPM
>> + * of the GISA if the GISA is not part of the GIB alert list. All three
>> + * fields are located in the first long word of the GISA.
>> + *
>> + * Returns: 0 on success
>> + *          -EBUSY in case the gisa is part of the alert list
>> + */
>> +static inline int gisa_set_iam(struct kvm_s390_gisa *gisa, u8 iam)
>> +{
>> +    u64 word, _word;
>> +
>> +    do {
>> +        word = READ_ONCE(gisa->u64.word[0]);
>> +        if ((u64)gisa != word >> 32)
>> +            return -EBUSY;
>> +        _word = (word & ~0xffUL) | iam;
>> +    } while (cmpxchg(&gisa->u64.word[0], word, _word) != word);
>> +
>> +    return 0;
>> +}
>> +
>>   static inline void gisa_set_ipm_gisc(struct kvm_s390_gisa *gisa, u32 
>> gisc)
>>   {
>>       set_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
>> @@ -2911,6 +2938,8 @@ void kvm_s390_gisa_init(struct kvm *kvm)
>>       if (!css_general_characteristics.aiv)
>>           return;
>>       gi->origin = &kvm->arch.sie_page2->gisa;
>> +    gi->alert.mask = 0;
>> +    spin_lock_init(&gi->alert.ref_lock);
>>       kvm_s390_gisa_clear(kvm);
>>       VM_EVENT(kvm, 3, "gisa 0x%pK initialized", gi->origin);
>>   }
>> @@ -2920,6 +2949,94 @@ void kvm_s390_gisa_destroy(struct kvm *kvm)
>>       kvm->arch.gisa_int.origin = NULL;
>>   }
>> +/**
>> + * kvm_s390_gisc_register - register a guest ISC
>> + *
>> + * @kvm:  the kernel vm to work with
>> + * @gisc: the guest interruption sub class to register
>> + *
>> + * The function extends the vm specific alert mask to use.
>> + * The effectve IAM mask in the GISA is updated as well
>> + * in case the GISA is not part of the GIB alert list.
>> + * It will be updated latest when the IAM gets restored
>> + * by gisa_get_ipm_or_restore_iam().
>> + *
>> + * Returns: the nonspecific ISC (NISC) the gib alert mechanism
>> + *          has registered with the channel subsystem.
>> + *          -ENODEV in case the vm uses no GISA
>> + *          -ERANGE in case the guest ISC is invalid
>> + */
>> +int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc)
>> +{
>> +    struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
>> +    u8 alert_mask;
>> +
>> +    if (!gi->origin)
>> +        return -ENODEV;
>> +    if (gisc > MAX_ISC)
>> +        return -ERANGE;
>> +
>> +    spin_lock(&gi->alert.ref_lock);
>> +    if (gi->alert.ref_count[gisc] == 0) {
>> +        alert_mask = gi->alert.mask | 0x80 >> gisc;
>> +        WRITE_ONCE(gi->alert.mask, alert_mask);
> 
> not sure WRITE_ONCE is useful.

I dropped that in both routines.

> 
> 
> 
>> +    }
>> +    gi->alert.ref_count[gisc]++;
>> +    if (gi->alert.ref_count[gisc] == 1)
>> +        gisa_set_iam(gi->origin, alert_mask);
> 
> This will trigger a GAL interrupt on first AP interrupt in all cases.
> However setting the iam here is simple and the price is not so high.
> so... without the WRITE_ONCE in register and in unregister:


> 
> Acked-by: Pierre Morel<pmorel@linux.ibm.com>
> 
> Pierre
> 

Cheers,
Michael