linux-kernel - Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the vfio

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Message-Id: <6cc5b478-4678-9a82-b902-cc9aed22becf@linux.ibm.com>
Date:   Tue, 19 Feb 2019 22:31:17 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>, borntraeger@...ibm.com
Cc:     cohuck@...hat.com, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, frankja@...ux.ibm.com,
        pasic@...ux.ibm.com, david@...hat.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, freude@...ux.ibm.com
Subject: Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the
 vfio_ap bus subsystem

On 19/02/2019 19:52, Tony Krowiak wrote:
> On 2/18/19 1:08 PM, Pierre Morel wrote:
>> Libudev relies on having a subsystem link for non-root devices. To
>> avoid libudev (and potentially other userspace tools) choking on the
>> matrix device let us introduce a vfio_ap bus and with that the vfio_ap
>> bus subsytem, and make the matrix device reside within it.
>>
>> Doing this we need to suppress the forced link from the matrix device to
>> the vfio_ap driver and we suppress the device_type we do not need
>> anymore.
>>
>> Since the associated matrix driver is not the vfio_ap driver any more,
>> we have to change the search for the devices on the vfio_ap driver in
>> the function vfio_ap_verify_queue_reserved.
>>
>> Reported-by: Marc Hartmayer <mhartmay@...ux.ibm.com>
>> Reported-by: Christian Borntraeger <borntraeger@...ibm.com>
>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>> ---
>>   drivers/s390/crypto/vfio_ap_drv.c     | 48 
>> +++++++++++++++++++++++++++++------
>>   drivers/s390/crypto/vfio_ap_ops.c     |  4 +--
>>   drivers/s390/crypto/vfio_ap_private.h |  1 +
>>   3 files changed, 43 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/s390/crypto/vfio_ap_drv.c 
>> b/drivers/s390/crypto/vfio_ap_drv.c
>> index 31c6c84..8e45559 100644
>> --- a/drivers/s390/crypto/vfio_ap_drv.c
>> +++ b/drivers/s390/crypto/vfio_ap_drv.c
>> @@ -24,10 +24,6 @@ MODULE_LICENSE("GPL v2");
>>   static struct ap_driver vfio_ap_drv;
>> -static struct device_type vfio_ap_dev_type = {
>> -    .name = VFIO_AP_DEV_TYPE_NAME,
>> -};
>> -
>>   struct ap_matrix_dev *matrix_dev;
>>   /* Only type 10 adapters (CEX4 and later) are supported
>> @@ -62,6 +58,27 @@ static void vfio_ap_matrix_dev_release(struct 
>> device *dev)
>>       kfree(matrix_dev);
>>   }
>> +static int matrix_bus_match(struct device *dev, struct device_driver 
>> *drv)
>> +{
>> +    return 1;
> 
> I think we should verify the following:
> 
> * dev == matrix_dev->device
> * drv == &matrix_driver
> 
> The model employed is for the matrix device to be a singleton, so I
> think we should verify that the matrix device and driver defined herein
> ought to be the only possible choices for a match. Of course, doing so
> will require some restructuring of this patch.

I think Conny already answered this question.

> 
>> +}
>> +
>> +static struct bus_type matrix_bus = {
>> +    .name = "vfio_ap",
>> +    .match = &matrix_bus_match,
>> +};
>> +
>> +static int matrix_probe(struct device *dev)
>> +{
>> +    return 0;
>> +}
>> +
>> +static struct device_driver matrix_driver = {
>> +    .name = "vfio_ap",
> 
> This is the same name used for the original device driver. I think
> this driver ought to have a different name to avoid confusion.
> How about vfio_ap_matrix or some other name to differentiate the
> two.

I would like too, but changing this will change the path to the mediated 
device supported type.


> 
>> +    .bus = &matrix_bus,
>> +    .probe = matrix_probe,
> 
> I would add:
>      .suppress_bind_attrs = true;
> 
> This will remove the sysfs bind/unbind interfaces. Since there is only
> one matrix device and it's lifecycle is controlled herein, there is no
> sense in allowing a root user to bind/unbind it.
> 

OTOH bind/unbind has no impact.
If no one else ask for this I will not change what has already been 
reviewed by Conny and Christian.

Regards,
Pierre


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany