Re: [Qemu-devel] [PATCH 4/9] s390x: refactor error handling for SSCH and RSCH

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 6 Sep 2017 14:25:13 +0200
Halil Pasic <pasic@linux.vnet.ibm.com> wrote:

> We have basically two possibilities/options which ask for different
> handling:
> 1) EFAULT is due to a bug in the vfio-ccw implementation
> (can be QEMU or kernel).
> 2) EFAULT is due to buggy channel program.
> 
> Option 2) is basically to be handled with a channel-program check and
> setting primary secondary and alert status. For reference see PoP page
> 15-59 ("Designation of Storage Area").  An exception may be an invalid
> channel program address in the ORB. There the channel-program check ain't
> explicitly stated (although) I would expect one. It may be implied by the
> things on page 15-59 though.
> 
> Option 1) is however very similar to other we have figured out that the
> implementation is broken situations and should be handled consequently.
> The current state of the discussion is with a unit exception.
> 
> Does that make sense?

I think the situation is slightly different here, though. For the orb
flags, we reject something out of hand because we have not implemented
it, and for that, unit exception sounds like a good fit. Processing
errors, however, are more similar to errors in the hardware, and as
such can probably be reported via something like equipment check.

> 
> Now, Dong Jia, I need your help to figure out do we have option 1 or
> option 2 here? After quick look at the kernel code, it appears to me that
> I've seen both option 1 and option 2 (I'm afraid) -- but my assessment
> was really very superficial.
> 
> I would expect option 2 to be handled differently (kernel provides the
> SCSW) though.
> 
> Regards,
> Halil
>