linux-kernel - Re: [PATCH v5 12/15] KVM: s390: do not restore IAM immediately before SIE entry

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Message-Id: <0c05a099-199e-426f-93af-b8614a3f800e@linux.ibm.com>
Date:   Mon, 7 Jan 2019 18:53:23 +0100
From:   Michael Mueller <mimu@...ux.ibm.com>
To:     pmorel@...ux.ibm.com, KVM Mailing List <kvm@...r.kernel.org>
Cc:     Linux-S390 Mailing List <linux-s390@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        kvm390-list@...maker.boeblingen.de.ibm.com,
        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>,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH v5 12/15] KVM: s390: do not restore IAM immediately before
 SIE entry



On 03.01.19 16:00, Pierre Morel wrote:
> On 19/12/2018 20:17, Michael Mueller wrote:
>> The IAM shall no be restored when deliverable interruptions are
>> delivered to vcpus by means of the PSW swap mechanism. That would
>> trigger the GIB alert millicode although we know that SIE will be
>> able to handle the pending interruption on entry.
>>
>> Signed-off-by: Michael Mueller <mimu@...ux.ibm.com>
>> ---
>>   arch/s390/kvm/interrupt.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
>> index 8307717e3caf..48a93f5e5333 100644
>> --- a/arch/s390/kvm/interrupt.c
>> +++ b/arch/s390/kvm/interrupt.c
>> @@ -328,11 +328,11 @@ static unsigned long disable_iscs(struct 
>> kvm_vcpu *vcpu,
>>       return active_mask;
>>   }
>> -static unsigned long deliverable_irqs(struct kvm_vcpu *vcpu)
>> +static unsigned long deliverable_irqs(struct kvm_vcpu *vcpu, u16 
>> irq_flags)
>>   {
>>       unsigned long active_mask;
>> -    active_mask = pending_irqs(vcpu, IRQ_MASK_ALL);
>> +    active_mask = pending_irqs(vcpu, irq_flags);
>>       if (!active_mask)
>>           return 0;
>> @@ -1090,7 +1090,7 @@ int kvm_s390_ext_call_pending(struct kvm_vcpu 
>> *vcpu)
>>   int kvm_s390_vcpu_has_irq(struct kvm_vcpu *vcpu, int exclude_stop)
>>   {
>> -    if (deliverable_irqs(vcpu))
>> +    if (deliverable_irqs(vcpu, IRQ_MASK_ALL | IRQ_FLAG_IAM))
> 
> Why do we need to restore IAM here?


please see kvm_s390_handle_wait()

It calls kvm_arch_vcpu_runnable() / kvm_s390_vcpu_has_irq()

That's the place where we want the IAM to be restored when
no ISC is pending in the IPM anymore.

> 
> 
>