Re: [RFC PATCH] s390: vfio-ap: Register the vfio_ap module for the "ap" parent bus

[Thomas Huth]

On 01/12/2021 18.10, Harald Freudenberger wrote:
> On 01.12.21 15:11, Thomas Huth wrote:
> > The crypto devices that we can use with the vfio_ap module are sitting
> > on the "ap" bus, not on the "vfio_ap" bus that the module defines
> > itself. With this change, the vfio_ap module now gets automatically
> > loaded if a supported crypto adapter is available in the host.
> >
> > Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
> > ---
> >   Note: Marked as "RFC" since I'm not 100% sure about it ...
> >         please review carefully!
> >
> >   drivers/s390/crypto/vfio_ap_drv.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c
> > index 4d2556bc7fe5..5580e40608a4 100644
> > --- a/drivers/s390/crypto/vfio_ap_drv.c
> > +++ b/drivers/s390/crypto/vfio_ap_drv.c
> > @@ -39,7 +39,7 @@ static struct ap_device_id ap_queue_ids[] = {
> >   	{ /* end of sibling */ },
> >   };
> >   
> > -MODULE_DEVICE_TABLE(vfio_ap, ap_queue_ids);
> > +MODULE_DEVICE_TABLE(ap, ap_queue_ids);
> >   
> >   /**
> >    * vfio_ap_queue_dev_probe:
> Hello Thomas, interesting.
> Did you test this ? I mean did you build a kernel and have it run on a s390 with crypto cards available ?

Yes, I've tested it. Without the patch, the vfio_ap module does not get 
loaded automatically if a crypto card is available. With the patch applied, 
the vfio_ap module correctly gets loaded automatically on my system (similar 
to the vfio_ccw module).

> My strong feeling is that this will make the AP bus code stumble as the code silently assumes there are exact
> two types of ap devices attached to the ap bus: ap cards and ap queues.

This is only about getting the module loaded automatically once such a 
device is available ... AFAIK it does not grab any of the devices 
automatically, so there shouldn't be any problems?

 Thomas