Re: [PATCH] zcrypt: handle AP Info notification from CHSC SEI command

[Tony Krowiak]

On 2/1/19 9:35 AM, Cornelia Huck wrote:
> On Thu, 31 Jan 2019 18:50:57 -0500
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > On 1/31/19 4:55 AM, Cornelia Huck wrote:
> > > On Wed, 30 Jan 2019 12:48:46 -0500
> > > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > > Two questions:
> > > - Does the event cover _any_ change to the AP configuration, or can the
> > >     periodic scan detect changes that are not signaled?
> >
> > It can detect any change, such as a change to the CRYCB masks.
>
> Nice. I suppose we can not rely on those messages being generated,
> though, and therefore need to keep the periodic scan...

I don't know how the CRYCB can be changed dynamically on the host, but
hot plug for a guest changes it dynamically. Down the road, we may
send a CHSC SEI AP Configuration event to let the guest know. I don't 
know if there may be other AP config changes that can occur without this
event being posted, so it is probably a good idea to keep the scan. It
certainly doesn't hurt anything to do so.

> > > - Do we want to generate such an event in QEMU on plugging/unplugging
> > >     the vfio-ap device?
> >
> > We've discussed this quite a bit internally and decided not to implement
> > that at this time. We will address it as a future enhancement.
>
> Ok, but I think it would be nice to have.

Duly noted, but that discussion is outside of scope for this patch.

> > > > diff --git a/drivers/s390/cio/chsc.c b/drivers/s390/cio/chsc.c
> > > > index a0baee25134c..dccccc337078 100644
> > > > --- a/drivers/s390/cio/chsc.c
> > > > +++ b/drivers/s390/cio/chsc.c
> > > > @@ -586,6 +586,15 @@ static void chsc_process_sei_scm_avail(struct chsc_sei_nt0_area *sei_area)
> > > >    			      " failed (rc=%d).\n", ret);
> > > >    }
> > > >    
> > > > +static void chsc_process_sei_ap_cfg_chg(struct chsc_sei_nt0_area *sei_area)
> > > > +{
> > > > +	CIO_CRW_EVENT(3, "chsc: ap config changed\n");
> > > > +	if (sei_area->rs != 5)
> > > > +		return;
> > >
> > > I'm guessing that a reporting source of 5 means ap, right? (The code is
> > > silent on all those magic rs values :/)
> >
> > The 5 indicates the accessibility of one or more adjunct processors has
> > changed. The reason this gets called is because the CC sent with the
> > instruction indicates the AP configuration has changed, so the reporting
> > belongs where it is. There is only one RS associated with it.
>
> So if we'd ever get there anything but rs == 5, it would be a hardware
> or hypervisor bug? Then the code makes sense, I guess.

I have no idea if that is possible, but this follows the architecture.

> > > If so, should the debug logging be moved after the check?
> >
> > covered in the response above.
> >
> > >    
> > > > +
> > > > +	ap_bus_cfg_chg();
> > > > +}
> > > > +