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Date:   Fri, 1 Mar 2019 13:36:09 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     pmorel@...ux.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 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?
> 

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

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