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

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Message-ID: <20190228145254.2909425e.cohuck@redhat.com>
Date:   Thu, 28 Feb 2019 14:52:54 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Pierre Morel <pmorel@...ux.ibm.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 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()?
}

?
 
> > 
> > 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 :)