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Date:   Tue, 5 Dec 2017 15:04:21 +0100
From:   Cornelia Huck <>
To:     Harald Freudenberger <>
Cc:     Tony Krowiak <>,
        Christian Borntraeger <>,
        Martin Schwidefsky <>,,,,,
        Boris Fiuczynski <>,,,,,,,,,,,,
Subject: Re: [RFC 19/19] s390/facilities: enable AP facilities needed by

On Tue, 5 Dec 2017 08:52:57 +0100
Harald Freudenberger <> wrote:

> On 12/02/2017 02:30 AM, Tony Krowiak wrote:

> > I agree with your suggestion that defining a new CPU model feature is probably
> > the best way to resolve this issue. The question is, should we define a single
> > feature indicating whether AP instructions are installed and set features bits
> > for the guest based on whether or not they are set in the linux host, or should
> > we define additional CPU model features for turning features bits on and off?
> > I guess it boils down to what behavior is expected for the AP bus running on
> > the linux guest. Here is a rundown of the facilities bits associated with AP
> > and how they affect the behavior of the AP bus:
> >
> > * STFLE.12 indicates whether the AP query function is available. If this bit
> >   is not set, then the AP bus scan will only test domains 0-15. For example,
> >   if adapters 4, 5, and 6 and domains 12 and 71 (0x47) are installed, then AP
> >   queues 04.0047, 05.0047 and 06.0047 will not be made available.  
> STFLE 12 is the indication for Query AP Configuration Information (QCI) available.
> > * STFLE.15 indicates whether the AP facilities test function is available. If
> >   this bit is not set, then the CEX4, CEX5 and CEX6 device drivers discovered
> >   by the AP bus scan will not get bound to any AP device drivers. Since the
> >   AP matrix model supports only CEX4 and greater, no devices will be bound
> >   to any driver for a guest.  
> This T-Bit extension to the TAPQ subfunction is a must have. When kvm only
> supports CEX4 and upper then this bit could also act as the indicator for
> AP instructions available. Of course if you want to implement pure virtual
> full simulated AP without any real AP hardware on the host this bit can't
> be the indicator.

It would probably make sense to group these two together. Or is there
any advantage in supporting only a part of it?

> > * STFLE.65 indicates whether AP interrupts are available. If this bit is not
> >   set, then the AP bus will use polling instead of using interrupt handlers
> >   to process AP events.

So, does this indicate "adapter interrupts for AP" only? If so, we
should keep this separate and only enable it when we have the gisa etc.

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