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

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Date:   Fri, 1 Feb 2019 15:35:22 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        sebott@...ux.ibm.com, oberpar@...ux.ibm.com, freude@...ux.ibm.com,
        pmorel@...ux.ibm.com, pasic@...ux.ibm.com
Subject: Re: [PATCH] zcrypt: handle AP Info notification from CHSC SEI
 command

On Thu, 31 Jan 2019 18:50:57 -0500
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> On 1/31/19 4:55 AM, Cornelia Huck wrote:
> > On Wed, 30 Jan 2019 12:48:46 -0500
> > Tony Krowiak <akrowiak@...ux.ibm.com> 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...

> 
> > - 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.

> >> 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.

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