From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752647AbeEQHpD (ORCPT ); Thu, 17 May 2018 03:45:03 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:37402 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752348AbeEQHpB (ORCPT ); Thu, 17 May 2018 03:45:01 -0400 Date: Thu, 17 May 2018 09:44:54 +0200 From: Cornelia Huck To: Tony Krowiak Cc: Halil Pasic , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, freude@de.ibm.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, borntraeger@de.ibm.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 Subject: Re: [PATCH v5 05/13] s390: vfio-ap: register matrix device with VFIO mdev framework Message-ID: <20180517094454.6afae7ba.cohuck@redhat.com> In-Reply-To: <4688078d-3e13-5201-582f-52576b25defa@linux.vnet.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> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 14 May 2018 15:42:18 -0400 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. > >> +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".)