From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pierre Morel Subject: Re: [PATCH v5 05/13] s390: vfio-ap: register matrix device with VFIO mdev framework Date: Tue, 15 May 2018 16:17:01 +0200 Message-ID: <1f9117bd-ed14-bde4-fdbd-cb3733c8c633@linux.ibm.com> References: <1525705912-12815-1-git-send-email-akrowiak@linux.vnet.ibm.com> <1525705912-12815-6-git-send-email-akrowiak@linux.vnet.ibm.com> <5471b194-d7ca-c9c6-132e-fa9539fe44f0@linux.ibm.com> <4688078d-3e13-5201-582f-52576b25defa@linux.vnet.ibm.com> Reply-To: pmorel@linux.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <4688078d-3e13-5201-582f-52576b25defa@linux.vnet.ibm.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Tony Krowiak , Halil Pasic , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: freude@de.ibm.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, borntraeger@de.ibm.com, cohuck@redhat.com, kwankhede@nvidia.com, bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com, alex.williamson@redhat.com, pmorel@linux.vnet.ibm.com, alifm@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com, jjherne@linux.vnet.ibm.com, thuth@redhat.com, pasic@linux.vnet.ibm.com, berrange@redhat.com, fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com List-ID: 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 >>> + * >>> + */ >>> +#include >>> +#include >>> +#include >>> +#include >>> +#include >>> + >>> +#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. > >> >> >> Regards, >> Halil >> >>> + mdev_unregister_device(&ap_matrix->device); >>> +} > > -- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany