linux-kernel - Re: [RFC PATCH] s390: vfio-ap: Register the vfio

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Date:   Thu, 2 Dec 2021 08:13:35 +0100
From:   Thomas Huth <thuth@...hat.com>
To:     Harald Freudenberger <freude@...ux.ibm.com>,
        linux-s390@...r.kernel.org, Tony Krowiak <akrowiak@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Jason Herne <jjherne@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [RFC PATCH] s390: vfio-ap: Register the vfio_ap module for the
 "ap" parent bus

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@...hat.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