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    SubjectRe: [RFC PATCH] s390: vfio-ap: Register the vfio_ap module for the "ap" parent bus
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    On 12/13/21 11:11, Cornelia Huck wrote:
    > On Mon, Dec 13 2021, Harald Freudenberger <freude@linux.ibm.com> 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@redhat.com>
    >>> ---
    >>> 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.
    > I don't think you can drop the kvm reference, as the code in vfio-ap
    > obviously depends on it...
    >
    > One possibility is simply blocking autoload of the module in userspace by
    > default, and only allow it to be loaded automatically when e.g. qemu-kvm
    > is installed on the system. This is obviously something that needs to be
    > decided by the distros.
    >
    > (kvm might actually be autoloaded already, so autoloading vfio-ap would
    > not really make it worse.)

    The vfio_ccw module, which is automatically loaded, also requires the
    kvm module,
    so autoloading vfio_ap will not make much difference.

    >

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