Messages in this thread |  | | Date | Thu, 27 Jan 2022 09:23:53 -0500 | Subject | Re: [RFC PATCH] s390: vfio-ap: Register the vfio_ap module for the "ap" parent bus | From | Tony Krowiak <> |
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On 12/2/21 03:33, Harald Freudenberger wrote: > On 02.12.21 08:13, Thomas Huth wrote: >> 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@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: >>> 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 >> > Yes, of course for the automatic module load works this way. But you understand that now > the vfio devices are childs of the ap bus and thus are siblings of the ap queue and ap card > devices. As I wrote the ap bus code is not prepared to deal with a 3th type of devices > dangling on the ap bus. So you should test what happens when there are real vfio ap devices > in use together with 'regular' ap card and queue devices. > > However, I am still not sure if it is preferable to have the vfio ap module loaded automatically. The majority > of customers will never use vfio ap devices - this is specific to kvm hosts only. I think this has to be > decided by Tony and maybe some kvm architect. If there is an agreement, I will try to rework the > ap code to be able to deal with foreign devices attached to the ap bus.
Can you please explain how foreign devices can get attached to the bus if the vfio_ap device driver is automatically loaded because the MODULE_DEVICE_TABLE specification is changed?
Regards, Tony Krowiak
> > So thanks for your investigations. Let's wait for Tony and see how we proceed. > > Harald > Harald
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