Re: [qemu-s390x] [RFC 19/19] s390/facilities: enable AP facilities needed by guest

[Pierre Morel]

On 05/12/2017 15:30, Cornelia Huck wrote:
> On Tue, 5 Dec 2017 15:23:50 +0100
> Pierre Morel <address@hidden> wrote:
>
> > On 05/12/2017 15:04, Cornelia Huck wrote:
> > > On Tue, 5 Dec 2017 08:52:57 +0100
> > > Harald Freudenberger <address@hidden> 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.
> > > ready.
> > >    
> >
> > Yes, STFLE 65, it is for AP only.
> >
> > QCI, STFLE 12, is no present on older systems, in this case AP uses TAPQ
> > to retrieve information for each AP
>
> Dumb question: How old? Machines that are still supported?

No idea which machine are supported or not, will ask.

What I can say is that I have here a Lpar which does not support QCI.
It seems to be a zEC12.2.
z13 support it.

> > So for my point of view, it make sense to separate the three facilities
> > to enable migration on older systems.
>
> OK, if STFLE 12 might not be present (pending my question above), but
> STFLE 15 is indeed a must-have, we should split this up.



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