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

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Date:   Fri, 1 Mar 2019 13:05:54 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     pmorel@...ux.ibm.com, Cornelia Huck <cohuck@...hat.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 13:03, 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?