Re: [PATCH 1/1] vfio-ccw: Enable transparent CCW IPL from DASD

[Halil Pasic]

On Mon, 20 Apr 2020 14:13:17 +0200
Cornelia Huck <cohuck@xxxxxxxxxx> wrote:

> > Remove the explicit prefetch check when using vfio-ccw devices.
> > This check is not needed as all Linux channel programs are intended
> > to use prefetch and will be executed in the same way regardless.  
> 
> Hm... my understanding is that we have the reasonable expectation that
> our guests will always issue channel programs that work fine with
> prefetch even if the bit is not set in the orb (including CCW IPL, in
> the way it is implemented in the s390-ccw QEMU bios), and therefore
> this patch is just making things less complicated.

AFAIR the problem is not s390-ccw QEMU bios. We could easily fix that.
The practical problem is some channel programs generated by zipl that
simply fail to set the bit (although they could). That is a perfectly
legit thing to do, because the prefetch bit was originally about
performance.

Sorry I missed your mail, so complained about the same
issues.

Regards,
Halil