Re: [PATCH] KVM: s390: Remove false WARN_ON_ONCE for the PQAP instruction

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 5 May 2020 10:27:16 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 05.05.20 10:04, David Hildenbrand wrote:
> > On 05.05.20 09:55, Christian Borntraeger wrote:  
> >>
> >>
> >> On 05.05.20 09:53, Cornelia Huck wrote:  
> >>> On Tue,  5 May 2020 09:35:25 +0200
> >>> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >>>  
> >>>> In LPAR we will only get an intercept for FC==3 for the PQAP
> >>>> instruction. Running nested under z/VM can result in other intercepts as
> >>>> well, for example PQAP(QCI). So the WARN_ON_ONCE is not right. Let
> >>>> us simply remove it.  
> >>>
> >>> While I agree with removing the WARN_ON_ONCE, I'm wondering why z/VM
> >>> gives us intercepts for those fcs... is that just a result of nesting
> >>> (or the z/VM implementation), or is there anything we might want to do?  
> >>
> >> Yes nesting. 
> >> The ECA bit for interpretion is an effective one. So if the ECA bit is off
> >> in z/VM (no crypto cards) our ECA bit is basically ignored as these bits
> >> are ANDed.
> >> I asked Tony to ask the z/VM team if that is the case here.
> >>  
> > 
> > So we can't detect if we have support for ECA_APIE, because there is no
> > explicit feature bit, right? Rings a bell. Still an ugly
> > hardware/firmware specification.  
> 
> Yes, no matter if this is the case here, we cannot rely on ECA_APIE to not
> trigger intercepts. So we must remove the WARN_ON. 
> 
> cc stable?

Agreed.

> 
> > 
> > Seems to be the right thing to do
> > 
> > Reviewed-by: David Hildenbrand <david@redhat.com>
> >   
>