From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pierre Morel Subject: Re: [PATCH v6 2/7] s390: ap: new vfio_ap_queue structure Date: Thu, 28 Mar 2019 13:53:25 +0100 Message-ID: References: <1553265828-27823-1-git-send-email-pmorel@linux.ibm.com> <1553265828-27823-3-git-send-email-pmorel@linux.ibm.com> <169eec34-6397-3150-27df-9985c9e711b8@linux.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 Cc: alex.williamson@redhat.com, cohuck@redhat.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, frankja@linux.ibm.com, pasic@linux.ibm.com, david@redhat.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, mimu@linux.ibm.com To: Harald Freudenberger , Tony Krowiak , borntraeger@de.ibm.com Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 27/03/2019 12:00, Harald Freudenberger wrote: > On 26.03.19 21:45, Tony Krowiak wrote: >> On 3/22/19 10:43 AM, Pierre Morel wrote: >>> The AP interruptions are assigned on a queue basis and ...snip... >>> +static void vfio_ap_free_queue(int apqn, struct ap_matrix_mdev *matrix_mdev) >>> +{ >>> +    struct vfio_ap_queue *q; >>> + >>> +    q = vfio_ap_get_queue(apqn, &matrix_mdev->qlist); >>> +    if (!q) >>> +        return; >>> +    q->matrix_mdev = NULL; >>> +    vfio_ap_mdev_reset_queue(q); >> >> I'm wondering if it's necessary to reset the queue here. The only time >> a queue is used is when a guest using the mdev device is started. When >> that guest is terminated, the fd for the mdev device is closed and the >> mdev device's release callback is invoked. The release callback resets >> the queues assigned to the mdev device. Is it really necessary to >> reset the queue again when it is unassigned even if there would have >> been no subsequent activity? > When I understand this here right this code is called when a queue goes > away from the guest but is still reserved for use by the vfio dd. So it is > possible to assign the queue now to another guest. But then it makes > sense to clear all the entries in the millicode queue because a pending > reply could be "received" by the wrong guest. > > If this function is just called on remove of a queue device where the > device goes back to the AP bus, a reset is not needed. You are right Harald, the function is called when un-assigning a queue from a mediated device, so it must be reset before to assign it to another. Regards, Pierre -- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany