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

[Tony Krowiak]

On 12/13/21 10:44, 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:
> I had a chance to check this now.
> First I have to apologize about the dispute with vfio devices appearing on the ap bus.
> That's not the case with this patch. As Connie states the MODULE_DEVICE_TABLE() does not
> change the parent of a device and vfio_ap_drv is a driver for ap devices and thus
> belongs to the ap bus anyway.
> So what's left is that with this change the vfio_ap kernel module is automatically loaded
> when an ap device type 10-13 is recognized by the ap bus. So the intention of the patch
> is fulfilled.
> Yet another kernel module which may occupy memory but will never get used by most customers.
> This may not be a problem but I had a glance at the list of kernel modules loaded on my
> LPAR with and without the patch and the difference is:
> ...
> kvm                   512000  1 vfio_ap
> vfio_ap                28672  0
> ...
> So the vfio_ap module has a dependency to the biggest kernel module ever - kvm.
> Do I need to say something more?
>
> If this dependency is removed then I would not hesitate to accept this patch. However
> this is up to Tony as he is the maintainer of the vfio ap device driver.

Since the vfio_ccw module also needs the kvm module and is automatically 
loaded,
I see no problem with automatically loading the vfio_ap module. I tested 
this patch by
running all of my regression tests successfully.

>