Re: [PATCH v2 1/1] s390: vfio_ap: link the vfio_ap devices to the vfio_ap bus subsystem

[Pierre Morel]

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@xxxxxxxxxxxxx>
> > Reported-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > ---
> > Â drivers/s390/crypto/vfio_ap_drv.cÂÂÂÂ | 48 
> > +++++++++++++++++++++++++++++------
> > Â drivers/s390/crypto/vfio_ap_ops.cÂÂÂÂ |Â 4 +--
> > Â drivers/s390/crypto/vfio_ap_private.h |Â 1 +
> > Â 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");
> > Â static struct ap_driver vfio_ap_drv;
> > -static struct device_type vfio_ap_dev_type = {
> > -ÂÂÂ .name = VFIO_AP_DEV_TYPE_NAME,
> > -};
> > -
> > Â struct ap_matrix_dev *matrix_dev;
> > Â /* Only type 10 adapters (CEX4 and later) are supported
> > @@ -62,6 +58,27 @@ static void vfio_ap_matrix_dev_release(struct 
> > device *dev)
> > ÂÂÂÂÂ kfree(matrix_dev);
> > Â }
> > +static int matrix_bus_match(struct device *dev, struct device_driver 
> > *drv)
> > +{
> > +ÂÂÂ 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 = {
> > +ÂÂÂ .name = "vfio_ap",
> > +ÂÂÂ .match = &matrix_bus_match,
> > +};
> > +
> > +static int matrix_probe(struct device *dev)
> > +{
> > +ÂÂÂ return 0;
> > +}
> > +
> > +static struct device_driver matrix_driver = {
> > +ÂÂÂ .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.


> > +ÂÂÂ .bus = &matrix_bus,
> > +ÂÂÂ .probe = matrix_probe,
>
> I would add:
>  ÂÂÂÂ.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 BÃblingen - Germany