Re: [PATCH v3 2/4] s390x: kvm: topology: interception of PTF instruction

[Pierre Morel]

On 10/13/21 09:25, Thomas Huth wrote:
> On 16/09/2021 15.50, Pierre Morel wrote:
> > When the host supports the CPU topology facility, the PTF
> > instruction with function code 2 is interpreted by the SIE,
> > provided that the userland hypervizor activates the interpretation
> > by using the KVM_CAP_S390_CPU_TOPOLOGY KVM extension.
> >
> > The PTF instructions with function code 0 and 1 are intercepted
> > and must be emulated by the userland hypervizor.
> >
> > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> > ---
> >   hw/s390x/s390-virtio-ccw.c         | 36 ++++++++++++++++++++++++++++++
> >   include/hw/s390x/s390-virtio-ccw.h |  6 +++++
> >   target/s390x/kvm/kvm.c             | 15 +++++++++++++
> >   3 files changed, 57 insertions(+)
> >
> > diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> > index 61aeccb163..894f013139 100644
> > --- a/hw/s390x/s390-virtio-ccw.c
> > +++ b/hw/s390x/s390-virtio-ccw.c
> > @@ -404,6 +404,42 @@ static void 
> > s390_pv_prepare_reset(S390CcwMachineState *ms)
> >       s390_pv_prep_reset();
> >   }
>
> Could you please add a comment in front of this function, with some 
> explanations? If I've got that right, it's currently rather only a 
> "dummy" function, rejecting FC 0 and 1, and FC 2 is always handled by 
> the SIE, right?

I just saw I did not answer this question.

Yes function code 2 is handled by the SIE but it is not really a dummy 
function as without it PTF 0 or 1 would trigger a program check.

I will add a comment basically:

"We assume horizontal topology, the only one supported currently by 
Linux consequently we answer to function code 0 requesting horizontal 
polarization that it is already the current polarization and reject 
vertical polarization request without further explanation."


regards,
Pierre

--
Pierre Morel
IBM Lab Boeblingen