linux-kernel - Re: [PATCH v4 1/7] s390: ap: kvm: add PQAP interception for AQIC

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Date:   Fri, 1 Mar 2019 16:32:30 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Tony Krowiak <akrowiak@...ux.ibm.com>, alex.williamson@...hat.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, frankja@...ux.ibm.com, pasic@...ux.ibm.com,
        david@...hat.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, freude@...ux.ibm.com, mimu@...ux.ibm.com
Subject: Re: [PATCH v4 1/7] s390: ap: kvm: add PQAP interception for AQIC

On 01/03/2019 13:36, Cornelia Huck wrote:
> On Fri, 1 Mar 2019 13:05:54 +0100
> Christian Borntraeger <borntraeger@...ibm.com> wrote:
> 
>> On 01.03.2019 13:03, Pierre Morel wrote:
>>> On 28/02/2019 15:14, Pierre Morel wrote:
>>>> On 28/02/2019 14:52, Cornelia Huck wrote:
>>>>> On Thu, 28 Feb 2019 14:16:09 +0100
>>>>> Pierre Morel <pmorel@...ux.ibm.com> wrote:
>>>>>   
>>>>>> On 28/02/2019 12:22, Cornelia Huck wrote:
>>>>>   
>>>>>>> So, to summarize, the function should do:
>>>>>>> - Is userspace supposed to emulate everything (!ECA_APIE)? Return
>>>>>>>      -EOPNOTSUPP to hand control to it.
>>>>>>> - We are now interpreting the instruction in KVM. Do common checks
>>>>>>>      (PSTATE etc.) and inject exceptions, if needed.
>>>>>>> - Now look at the fc; if there's a handler for it, call that; if not
>>>>>>>      (case does not attempt to call a specific handler, or no handler
>>>>>>>      registered), inject a specification exception. (Do we want pre-checks
>>>>>>>      like for facility 65 here, or in the handler?)
>>>>>>>
>>>>>>> That response code 0x01 thingy probably needs to go into the specific
>>>>>>> handler function, if anywhere (don't know the semantics, sorry).
>>>>>>
>>>>>> What do you mean with specific handler function?
>>>>>>
>>>>>> If you mean a switch around the FC with static function's call, I agree,
>>>>>> if you mean a jump into a hook I do not agree.
>>>>>
>>>>> Ah, ok; so each case (that we want to handle) should call into a
>>>>> subhandler that does
>>>>> {
>>>>>      (... check things like facilities ...)
>>>>>      if (!specific_hook)
>>>>>          inject_specif_excp_and_return();
>>>>>      ret = specific_hook();
>>>>>      if (ret)
>>>>>          set_resp_code_0x01(); // or in specific_hook()?
>>>>> }
>>>>>
>>>>> ?
>>>>
>>>> Yes something in this direction.
>>>
>>> Sorry, after reflection, no, we do not want to change the previous behavior so we only handle the AQIC case.
>>
>> I think what you wanted to say is the following:
>> Today (without the patch set) we will answer PQAP with an exception.
>> With this patch set we want to handle FC==3, but nothing else. So for anything FC!=3 we
>> will continue to return an exception?
>>
>> Correct?

Yes correct.
Thanks for the much preciser explanation.

>>
> 
> That sounds reasonable; but I don't see how this conflicts with my
> proposal? Just don't introduce a subfunction for fc != 3...
> 

Correct too, it does not conflict, as you said it is just not introduce 
subfunctions.

Regards,
Pierre


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