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Subject: Re: [PATCH V5 1/6] mdev: class id support
To:     Alex Williamson <alex.williamson@redhat.com>
Cc:     kvm@vger.kernel.org, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
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        cohuck@redhat.com, maxime.coquelin@redhat.com,
        cunming.liang@intel.com, zhihong.wang@intel.com,
        rob.miller@broadcom.com, xiao.w.wang@intel.com,
        haotian.wang@sifive.com, zhenyuw@linux.intel.com,
        zhi.a.wang@intel.com, jani.nikula@linux.intel.com,
        joonas.lahtinen@linux.intel.com, rodrigo.vivi@intel.com,
        airlied@linux.ie, daniel@ffwll.ch, farman@linux.ibm.com,
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        christophe.de.dinechin@gmail.com, kevin.tian@intel.com,
        stefanha@redhat.com
References: <20191023130752.18980-1-jasowang@redhat.com>
 <20191023130752.18980-2-jasowang@redhat.com>
 <20191023154204.31d74866@x1.home>
 <38bdf762-524a-e0f1-6e9a-1102adfe8fb1@redhat.com>
 <20191024134636.253131c5@x1.home> <20191024141330.017a6480@x1.home>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <c8ab994e-8daa-926c-c91d-785e9d3c5044@redhat.com>
Date:   Fri, 25 Oct 2019 09:42:31 +0800
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On 2019/10/25 =E4=B8=8A=E5=8D=884:13, Alex Williamson wrote:
> On Thu, 24 Oct 2019 13:46:36 -0600
> Alex Williamson <alex.williamson@redhat.com> wrote:
>
>> On Thu, 24 Oct 2019 11:27:36 +0800
>> Jason Wang <jasowang@redhat.com> wrote:
>>
>>> On 2019/10/24 =E4=B8=8A=E5=8D=885:42, Alex Williamson wrote:
>>>> On Wed, 23 Oct 2019 21:07:47 +0800
>>>> Jason Wang <jasowang@redhat.com> wrote:
>>>>    =20
>>>>> Mdev bus only supports vfio driver right now, so it doesn't implement
>>>>> match method. But in the future, we may add drivers other than vfio,
>>>>> the first driver could be virtio-mdev. This means we need to add
>>>>> device class id support in bus match method to pair the mdev device
>>>>> and mdev driver correctly.
>>>>>
>>>>> So this patch adds id_table to mdev_driver and class_id for mdev
>>>>> device with the match method for mdev bus.
>>>>>
>>>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>>>>> ---
>>>>>    .../driver-api/vfio-mediated-device.rst       |  5 +++++
>>>>>    drivers/gpu/drm/i915/gvt/kvmgt.c              |  1 +
>>>>>    drivers/s390/cio/vfio_ccw_ops.c               |  1 +
>>>>>    drivers/s390/crypto/vfio_ap_ops.c             |  1 +
>>>>>    drivers/vfio/mdev/mdev_core.c                 | 18 +++++++++++++++
>>>>>    drivers/vfio/mdev/mdev_driver.c               | 22 +++++++++++++++=
++++
>>>>>    drivers/vfio/mdev/mdev_private.h              |  1 +
>>>>>    drivers/vfio/mdev/vfio_mdev.c                 |  6 +++++
>>>>>    include/linux/mdev.h                          |  8 +++++++
>>>>>    include/linux/mod_devicetable.h               |  8 +++++++
>>>>>    samples/vfio-mdev/mbochs.c                    |  1 +
>>>>>    samples/vfio-mdev/mdpy.c                      |  1 +
>>>>>    samples/vfio-mdev/mtty.c                      |  1 +
>>>>>    13 files changed, 74 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/driver-api/vfio-mediated-device.rst b/Docu=
mentation/driver-api/vfio-mediated-device.rst
>>>>> index 25eb7d5b834b..6709413bee29 100644
>>>>> --- a/Documentation/driver-api/vfio-mediated-device.rst
>>>>> +++ b/Documentation/driver-api/vfio-mediated-device.rst
>>>>> @@ -102,12 +102,14 @@ structure to represent a mediated device's driv=
er::
>>>>>          * @probe: called when new device created
>>>>>          * @remove: called when device removed
>>>>>          * @driver: device driver structure
>>>>> +      * @id_table: the ids serviced by this driver
>>>>>          */
>>>>>         struct mdev_driver {
>>>>>    =09     const char *name;
>>>>>    =09     int  (*probe)  (struct device *dev);
>>>>>    =09     void (*remove) (struct device *dev);
>>>>>    =09     struct device_driver    driver;
>>>>> +=09     const struct mdev_class_id *id_table;
>>>>>         };
>>>>>   =20
>>>>>    A mediated bus driver for mdev should use this structure in the fu=
nction calls
>>>>> @@ -170,6 +172,9 @@ that a driver should use to unregister itself wit=
h the mdev core driver::
>>>>>   =20
>>>>>    =09extern void mdev_unregister_device(struct device *dev);
>>>>>   =20
>>>>> +It is also required to specify the class_id in create() callback thr=
ough::
>>>>> +
>>>>> +=09int mdev_set_class(struct mdev_device *mdev, u16 id);
>>>>>   =20
>>>>>    Mediated Device Management Interface Through sysfs
>>>>>    =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D
>>>>> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/=
gvt/kvmgt.c
>>>>> index 343d79c1cb7e..6420f0dbd31b 100644
>>>>> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
>>>>> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
>>>>> @@ -678,6 +678,7 @@ static int intel_vgpu_create(struct kobject *kobj=
, struct mdev_device *mdev)
>>>>>    =09=09     dev_name(mdev_dev(mdev)));
>>>>>    =09ret =3D 0;
>>>>>   =20
>>>>> +=09mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
>>>>>    out:
>>>>>    =09return ret;
>>>>>    }
>>>>> diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_=
ccw_ops.c
>>>>> index f0d71ab77c50..cf2c013ae32f 100644
>>>>> --- a/drivers/s390/cio/vfio_ccw_ops.c
>>>>> +++ b/drivers/s390/cio/vfio_ccw_ops.c
>>>>> @@ -129,6 +129,7 @@ static int vfio_ccw_mdev_create(struct kobject *k=
obj, struct mdev_device *mdev)
>>>>>    =09=09=09   private->sch->schid.ssid,
>>>>>    =09=09=09   private->sch->schid.sch_no);
>>>>>   =20
>>>>> +=09mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
>>>>>    =09return 0;
>>>>>    }
>>>>>   =20
>>>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/=
vfio_ap_ops.c
>>>>> index 5c0f53c6dde7..07c31070afeb 100644
>>>>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>>>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>>>>> @@ -343,6 +343,7 @@ static int vfio_ap_mdev_create(struct kobject *ko=
bj, struct mdev_device *mdev)
>>>>>    =09list_add(&matrix_mdev->node, &matrix_dev->mdev_list);
>>>>>    =09mutex_unlock(&matrix_dev->lock);
>>>>>   =20
>>>>> +=09mdev_set_class(mdev, MDEV_CLASS_ID_VFIO);
>>>>>    =09return 0;
>>>>>    }
>>>>>   =20
>>>>> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_c=
ore.c
>>>>> index b558d4cfd082..3a9c52d71b4e 100644
>>>>> --- a/drivers/vfio/mdev/mdev_core.c
>>>>> +++ b/drivers/vfio/mdev/mdev_core.c
>>>>> @@ -45,6 +45,16 @@ void mdev_set_drvdata(struct mdev_device *mdev, vo=
id *data)
>>>>>    }
>>>>>    EXPORT_SYMBOL(mdev_set_drvdata);
>>>>>   =20
>>>>> +/* Specify the class for the mdev device, this must be called during
>>>>> + * create() callback.
>>>>> + */
>>>>> +void mdev_set_class(struct mdev_device *mdev, u16 id)
>>>>> +{
>>>>> +=09WARN_ON(mdev->class_id);
>>>>> +=09mdev->class_id =3D id;
>>>>> +}
>>>>> +EXPORT_SYMBOL(mdev_set_class);
>>>>> +
>>>>>    struct device *mdev_dev(struct mdev_device *mdev)
>>>>>    {
>>>>>    =09return &mdev->dev;
>>>>> @@ -135,6 +145,7 @@ static int mdev_device_remove_cb(struct device *d=
ev, void *data)
>>>>>     * mdev_register_device : Register a device
>>>>>     * @dev: device structure representing parent device.
>>>>>     * @ops: Parent device operation structure to be registered.
>>>>> + * @id: class id.
>>>>>     *
>>>>>     * Add device to list of registered parent devices.
>>>>>     * Returns a negative value on error, otherwise 0.
>>>>> @@ -324,6 +335,13 @@ int mdev_device_create(struct kobject *kobj,
>>>>>    =09if (ret)
>>>>>    =09=09goto ops_create_fail;
>>>>>   =20
>>>>> +=09if (!mdev->class_id) {
>>>>> +=09=09ret =3D -EINVAL;
>>>>> +=09=09WARN(1, "class id must be specified for device %s\n",
>>>>> +=09=09     dev_name(dev));
>>>> Nit, dev_warn(dev, "mdev vendor driver failed to specify device class\=
n");
>>>
>>> Will fix.
>>>
>>>   =20
>>>>    =20
>>>>> +=09=09goto add_fail;
>>>>> +=09}
>>>>> +
>>>>>    =09ret =3D device_add(&mdev->dev);
>>>>>    =09if (ret)
>>>>>    =09=09goto add_fail;
>>>>> diff --git a/drivers/vfio/mdev/mdev_driver.c b/drivers/vfio/mdev/mdev=
_driver.c
>>>>> index 0d3223aee20b..319d886ffaf7 100644
>>>>> --- a/drivers/vfio/mdev/mdev_driver.c
>>>>> +++ b/drivers/vfio/mdev/mdev_driver.c
>>>>> @@ -69,8 +69,30 @@ static int mdev_remove(struct device *dev)
>>>>>    =09return 0;
>>>>>    }
>>>>>   =20
>>>>> +static int mdev_match(struct device *dev, struct device_driver *drv)
>>>>> +{
>>>>> +=09unsigned int i;
>>>>> +=09struct mdev_device *mdev =3D to_mdev_device(dev);
>>>>> +=09struct mdev_driver *mdrv =3D to_mdev_driver(drv);
>>>>> +=09const struct mdev_class_id *ids =3D mdrv->id_table;
>>>>> +
>>>> Nit, as we start to allow new mdev bus drivers, mdev-core might want t=
o
>>>> protect itself from a NULL id_table, by either failing the
>>>> mdev_register_driver() or failing the match here.  I think such a
>>>> condition would segfault as written here, but clearly we don't have
>>>> such external drivers yet.  Thanks,
>>>
>>> I'm not sure I get the point here. My understanding is that mdev-core
>>> won't try to be matched here since it was not a complete mdev device.
>> The parent driver failing to set a type vs the parent driver failing to
> Correction, the second half of this should be in reference to the mdev
> bus driver.
>
>> register with a struct mdev_driver where id_table is not null are
>> different issues.  I agree that if a vendor driver was not updated for
>> this series that they'd never successfully create a device because the
>> mdev-core would reject it for not setting a class, but mdev_match() is
>> called for devices that might be created by other vendor drivers, so
>> loading a parent driver with a null id_table potentially breaks
>> matching for everyone.  Thanks,
> The point is still valid though, for example if vfio-mdev registered
> with a null id_table it would break matching for virtio-mdev depending
> on the order we iterate through drivers as we call mdev_match().
> Thanks,
>
> Alex


I see the point, so I can check the existence of id_table before trying=20
to do the match here.

Thanks