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

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Date:   Thu, 28 Feb 2019 15:14:13 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        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 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.

>   
>>>
>>> Question: Will the handlers for the individual fcs need to generate
>>> different exceptions on their own? I.e., do they need to do injections
>>> themselves, or should the calling function possibly inject an exception
>>> on error?
>>
>> There are some specificities.
> 
> Ok, should probably done in the subhandlers?
> 
> (I hope I don't muddy the waters too much; but basically, I'm poking
> around with a stick in the dark :)
> 

No problem, it is OK.
My first idea was to make only changes associated with PQAP/AQIC.
We already should have done it for all PQAP functions so it is decided 
that we will do it now as Christian proposed.

Regards,
Pierre


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