Messages in this thread | | | Subject | Re: [PATCH v5 05/13] s390: vfio-ap: register matrix device with VFIO mdev framework | From | Halil Pasic <> | Date | Tue, 15 May 2018 17:48:37 +0200 |
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On 05/15/2018 05:16 PM, Tony Krowiak wrote: > On 05/15/2018 10:17 AM, Pierre Morel wrote: >> On 14/05/2018 21:42, Tony Krowiak 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. >>>>> >>>> [..] >>>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c >>>>> new file mode 100644 >>>>> index 0000000..d7d36fb >>>>> --- /dev/null >>>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c >>>>> @@ -0,0 +1,106 @@ >>>>> +// SPDX-License-Identifier: GPL-2.0+ >>>>> +/* >>>>> + * Adjunct processor matrix VFIO device driver callbacks. >>>>> + * >>>>> + * Copyright IBM Corp. 2017 >>>>> + * Author(s): Tony Krowiak <akrowiak@linux.vnet.ibm.com> >>>>> + * >>>>> + */ >>>>> +#include <linux/string.h> >>>>> +#include <linux/vfio.h> >>>>> +#include <linux/device.h> >>>>> +#include <linux/list.h> >>>>> +#include <linux/ctype.h> >>>>> + >>>>> +#include "vfio_ap_private.h" >>>>> + >>>>> +#define VFOP_AP_MDEV_TYPE_HWVIRT "passthrough" >>>>> +#define VFIO_AP_MDEV_NAME_HWVIRT "VFIO AP Passthrough Device" >>>>> + >>>>> +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. >>> >>>> >>>> >>>> [..] >>>> >>>> >>>>> +int vfio_ap_mdev_register(struct ap_matrix *ap_matrix) >>>>> +{ >>>>> + int ret; >>>>> + >>>>> + ret = mdev_register_device(&ap_matrix->device, &vfio_ap_matrix_ops); >>>>> + if (ret) >>>>> + return ret; >>>>> + >>>>> + ap_matrix->available_instances = AP_MATRIX_MAX_AVAILABLE_INSTANCES; >>>>> + >>>>> + return 0; >>>>> +} >>>>> + >>>>> +void vfio_ap_mdev_unregister(struct ap_matrix *ap_matrix) >>>>> +{ >>>>> + ap_matrix->available_instances--; >>>> >>>> What is this for? I don't understand. >>> >>> To control the number of mediated devices one can create for the matrix device. >>> Once the max is reached, the mdev framework will not allow creation of another >>> mediated device until one is removed. This counter keeps track of the number >>> of instances that can be created. This is documented with the mediated >>> framework. You may want to take a look at: >>> >>> Documentation/vfio-mediated-device.txt >>> Documentation/vfio.txt >>> Documentation/virtual/kvm/devices/vfio.txt >> >> This is what you do in create/remove. >> But here in unregister I agree with Halil, it does not seem to be usefull. > > If that is in fact what Halil was asking, then I misinterpreted his question; I > thought he was asking what the available_instances was used for. You are > correct, this does not belong here although it makes little difference given > this is called only when the driver, which creates the matrix device, is unloaded. > It is necessary in the register function to initialize its value, but I'll > remove it from here. >
I questioned the dubious usage of ap_matrix->available_instances rather than asking what is the variable for.
If I've had this deemed damaging I would have asked if it's damaging in a way I think it is. For example take my comment on 'KVM: s390: interfaces to manage guest's AP matrix'.
Regards, Halil
>> >> >>> >>>> >>>> >>>> Regards, >>>> Halil >>>> >>>>> + mdev_unregister_device(&ap_matrix->device); >>>>> +} >>> >>> >> >
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