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

[Pierre Morel]

On 01/03/2019 13:36, Cornelia Huck wrote:
> On Fri, 1 Mar 2019 13:05:54 +0100
> Christian Borntraeger <borntraeger@xxxxxxxxxx> 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@xxxxxxxxxxxxx> 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
> > > > > > >  ÂÂÂ -EOPNOTSUPP to hand control to it.
> > > > > > > - We are now interpreting the instruction in KVM. Do common checks
> > > > > > >  ÂÂÂ (PSTATE etc.) and inject exceptions, if needed.
> > > > > > > - Now look at the fc; if there's a handler for it, call that; if not
> > > > > > >  ÂÂÂ (case does not attempt to call a specific handler, or no handler
> > > > > > >  ÂÂÂ registered), inject a specification exception. (Do we want pre-checks
> > > > > > >  ÂÂÂ 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
> > > > > {
> > > > >  ÂÂÂÂ(... check things like facilities ...)
> > > > >  ÂÂÂÂif (!specific_hook)
> > > > >  ÂÂÂÂÂÂÂ inject_specif_excp_and_return();
> > > > >  ÂÂÂÂret = specific_hook();
> > > > >  ÂÂÂÂif (ret)
> > > > >  ÂÂÂÂÂÂÂ 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 BÃblingen - Germany