linux-kernel - Re: [PATCH v5 13/15] KVM: s390: add function process_gib_alert

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Date:   Wed, 9 Jan 2019 15:49:56 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     mimu@...ux.ibm.com, KVM Mailing List <kvm@...r.kernel.org>,
        Linux-S390 Mailing List <linux-s390@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: Re: [PATCH v5 13/15] KVM: s390: add function process_gib_alert_list()

On 09/01/2019 14:10, Halil Pasic wrote:
> On Wed, 9 Jan 2019 13:14:17 +0100
> Pierre Morel <pmorel@...ux.ibm.com> wrote:
> 
>> On 08/01/2019 16:21, Michael Mueller wrote:
>>>
>>>
>>> On 08.01.19 13:59, Halil Pasic wrote:
>>>> On Wed, 19 Dec 2018 20:17:54 +0100
>>>> Michael Mueller <mimu@...ux.ibm.com> wrote:
>>>>
>>>>> This function processes the Gib Alert List (GAL). It is required
>>>>> to run when either a gib alert interruption has been received or
>>>>> a gisa that is in the alert list is cleared or dropped.
>>>>>
>>>>> The GAL is build up by millicode, when the respective ISC bit is
>>>>> set in the Interruption Alert Mask (IAM) and an interruption of
>>>>> that class is observed.
>>>>>
>>>>> Signed-off-by: Michael Mueller <mimu@...ux.ibm.com>
>>>>> ---
>>>>>    arch/s390/kvm/interrupt.c | 140
>>>>> ++++++++++++++++++++++++++++++++++++++++++++++
>>>>>    1 file changed, 140 insertions(+)
>>>>>
>>>>> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
>>>>> index 48a93f5e5333..03e7ba4f215a 100644
>>>>> --- a/arch/s390/kvm/interrupt.c
>>>>> +++ b/arch/s390/kvm/interrupt.c
>>>>> @@ -2941,6 +2941,146 @@ int kvm_s390_get_irq_state(struct kvm_vcpu
>>>>> *vcpu, __u8 __user *buf, int len)
>>>>>        return n;
>>>>>    }
>>>>> +static int __try_airqs_kick(struct kvm *kvm, u8 ipm)
>>>>> +{
>>>>> +    struct kvm_s390_float_interrupt *fi = &kvm->arch.float_int;
>>>>> +    struct kvm_vcpu *vcpu = NULL, *kick_vcpu[MAX_ISC + 1];
>>>>> +    int online_vcpus = atomic_read(&kvm->online_vcpus);
>>>>> +    u8 ioint_mask, isc_mask, kick_mask = 0x00;
>>>>> +    int vcpu_id, kicked = 0;
>>>>> +
>>>>> +    /* Loop over vcpus in WAIT state. */
>>>>> +    for (vcpu_id = find_first_bit(fi->idle_mask, online_vcpus);
>>>>> +         /* Until all pending ISCs have a vcpu open for airqs. */
>>>>> +         (~kick_mask & ipm) && vcpu_id < online_vcpus;
>>>>> +         vcpu_id = find_next_bit(fi->idle_mask, online_vcpus,
>>>>> vcpu_id)) {
>>>>> +        vcpu = kvm_get_vcpu(kvm, vcpu_id);
>>>>> +        if (psw_ioint_disabled(vcpu))
>>>>> +            continue;
>>>>> +        ioint_mask = (u8)(vcpu->arch.sie_block->gcr[6] >> 24);
>>>>> +        for (isc_mask = 0x80; isc_mask; isc_mask >>= 1) {
>>>>> +            /* ISC pending in IPM ? */
>>>>> +            if (!(ipm & isc_mask))
>>>>> +                continue;
>>>>> +            /* vcpu for this ISC already found ? */
>>>>> +            if (kick_mask & isc_mask)
>>>>> +                continue;
>>>>> +            /* vcpu open for airq of this ISC ? */
>>>>> +            if (!(ioint_mask & isc_mask))
>>>>> +                continue;
>>>>> +            /* use this vcpu (for all ISCs in ioint_mask) */
>>>>> +            kick_mask |= ioint_mask;
>>>>> +            kick_vcpu[kicked++] = vcpu;
>>>>
>>>> Assuming that the vcpu can/will take all ISCs it's currently open for
>>>> does not seem right. We kind of rely on this assumption here, or?
>>
>> why does it not seem right?
>>
> 
> When an interrupt is delivered a psw-swap takes place. The new-psw
> may fence IO interrupts. Thus for example if we have the vcpu open for
> all ISCs and 0, 1 and 2 pending, we may end up only delivering 0, if the
> psw-swap corresponding to delivering 0 closes the vcpu for IO
> interrupts. After guest has control, we don't have control over the rest
> of the story.

OK I think I understand your concern, waking up a single waiting vCPU 
per ISC is not enough.
We must wake all vCPU in wait state having at least one matching ISC bit.

Regards,
Pierre


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany