Messages in this thread | | | Subject | Re: [PATCH v5 05/13] s390: vfio-ap: register matrix device with VFIO mdev framework | From | Tony Krowiak <> | Date | Tue, 22 May 2018 17:41:19 -0400 |
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On 05/22/2018 04:19 AM, Cornelia Huck wrote: > On Mon, 21 May 2018 11:13:58 -0400 > Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote: > >> On 05/17/2018 03:44 AM, Cornelia Huck wrote: >>> On Mon, 14 May 2018 15:42:18 -0400 >>> Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote: >>> >>>> On 05/11/2018 01:18 PM, Halil Pasic wrote: >>>>> On 05/07/2018 05:11 PM, Tony Krowiak wrote: >>>>>> Registers the matrix device created by the VFIO AP device >>>>>> driver with the VFIO mediated device framework. >>>>>> Registering the matrix device will create the sysfs >>>>>> structures needed to create mediated matrix devices >>>>>> each of which will be used to configure the AP matrix >>>>>> for a guest and connect it to the VFIO AP device driver. >>>>>> +static int vfio_ap_mdev_create(struct kobject *kobj, struct >>>>>> mdev_device *mdev) >>>>>> +{ >>>>>> + struct ap_matrix *ap_matrix = to_ap_matrix(mdev_parent_dev(mdev)); >>>>>> + >>>>>> + ap_matrix->available_instances--; >>>>>> + >>>>>> + return 0; >>>>>> +} >>>>>> + >>>>>> +static int vfio_ap_mdev_remove(struct mdev_device *mdev) >>>>>> +{ >>>>>> + struct ap_matrix *ap_matrix = to_ap_matrix(mdev_parent_dev(mdev)); >>>>>> + >>>>>> + ap_matrix->available_instances++; >>>>>> + >>>>>> + return 0; >>>>>> +} >>>>>> + >>>>> The above functions seem to be called with the lock of this >>>>> auto-generated >>>>> mdev parent device held. That's why we don't have to care about >>>>> synchronization >>>>> ourselves, right? >>>> I would assume as much. The comments for the 'struct mdev_parent_ops' in >>>> include/linux/mdev.h do not mention anything about synchronization, nor >>>> did I >>>> see any locking or synchronization in the vfio_ccw implementation after >>>> which >>>> I modeled my code, so frankly it is something I did not consider. >>>> >>>>> A small comment in the code could be helpful for mdev non-experts. >>>>> Hell, I would >>>>> even consider documenting it for all mdev -- took me some time to >>>>> figure out. >>>> You may want to bring this up with the VFIO mdev maintainers, but I'd be >>>> happy to >>>> include a comment in the functions in question if you think it important. >>> Important note: There's currently a patch on list that removes the mdev >>> parent mutex, and it seems there was never intended to be any >>> serialization in that place by the mdev core. (Look for "vfio/mdev: >>> Check globally for duplicate devices".) >> The patch on the list holds the mdev_list_lock during create and remove >> of an mdev device, so it looks like no synchronization is necessary on the >> part of the vendor code in the create/remove callbacks; does that sound >> about right? > v1/v2 did that; v3/v4 hold the list lock only while the device is added > to the mdev list. v4 also adds a note regarding locking to the > documentation.
I'll add some synchronization to the read/update of available instances.
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