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Mon, 24 Aug 2026 13:58:55 +0000 (GMT) Received: from li-4c4c4544-004d-4810-8043-b7c04f423534.ibm.com.com (unknown [9.61.96.163]) by smtpav06.wdc07v.mail.ibm.com (Postfix) with ESMTP; Mon, 24 Aug 2026 13:58:55 +0000 (GMT) From: Anthony Krowiak To: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: jjherne@linux.ibm.com, borntraeger@de.ibm.com, mjrosato@linux.ibm.com, pasic@linux.ibm.com, alex@shazbot.org, kwankhede@nvidia.com, fiuczy@linux.ibm.com, pbonzini@redhat.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com, agordeev@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, stable@vger.kernel.org Subject: [PATCH 2/4] s390/vfio-ap: Fix failure to release IRQ notification eventfd contexts Date: Mon, 24 Aug 2026 09:58:48 -0400 Message-ID: <20260824135850.503728-3-akrowiak@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260824135850.503728-1-akrowiak@linux.ibm.com> References: <20260824135850.503728-1-akrowiak@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: t4EHuisXsMPHO_LB4vUtA5UHP2mBjE28 X-Proofpoint-Spam-Info: AW1haW4tMjYwODI0MDExNCBTYWx0ZWRfXxcwXronxS+wc pbvWNYfI5MrfwFGEiJXssqzayU/PdUDse2w/12sZXOJcr7i+HukpWdkU0VVsUH3dX+dLX2teg/r reA9ObLOBt2SetpplDx1f0pr+YVcKDc= X-Proofpoint-GUID: t4EHuisXsMPHO_LB4vUtA5UHP2mBjE28 X-Authority-Analysis: v=2.4 cv=JZyMa0KV c=1 sm=1 tr=0 ts=6a8c4e23 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=fxeDLeT5AZ2qCvnLJ4gA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODI0MDExNCBTYWx0ZWRfX+fj7riCi2qda nTWHSyJmnntyhjHbqXKLz/SBmKDPfInIRFBIl32irwBrcmoSEQZT7w58T0TkcK99trjlmBYagoK JZmWLBQOhSBh/Pf7e0lEMzAB24yW0jBzy6fXm3T+thpalNZEy+IeH1VepAm6MFhmOEZXiSaCDI3 t32L1PwWmYBP9pajxsN9u5bgqbcjsPplKThKqt17wJze9yt2EmLEm076x7JWme/AnFbv0wLuCio KZxlV1mJP6Th0QuUjdIdaGltNQK28LcAHjB74FJ5ipMmr8d8jQ1y7bPrJ2YSFYhttrIbQW1sV+V zmmThk5uVV9KqyT0qlcG85iKHMb/M4yj6d/YKSpRZi+kZt8XMPFhIB39M9wRWpvDNMPpUmXjEwu 2mlpZv5qwO005aTucDlNLV69+2dhYFPAdY4zTdhvudbL83aYQW5AGs0pZQk9Ui0CJysoe3Hxxrv TXLhE9p6QZ76iMFsKRg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-24_04,2026-08-24_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 clxscore=1015 adultscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 bulkscore=0 lowpriorityscore=0 suspectscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608240114 When userspace registers IRQ notification eventfds via the VFIO_DEVICE_SET_IRQS ioctl, vfio_ap_set_request_irq() and vfio_ap_set_cfg_change_irq() each call eventfd_ctx_fdget(), which takes a reference on the eventfd_ctx and stores it in matrix_mdev->req_trigger and matrix_mdev->cfg_chg_trigger respectively. These references are dropped only when userspace explicitly replaces or clears them via a subsequent SET_IRQS call. If the device is closed without that explicit teardown - because the guest exits, the VM process crashes, or the device file is simply closed - neither vfio_ap_mdev_close_device() nor the remove path releases these references. The eventfd_ctx backing objects and their associated file references therefore leak for the lifetime of the kernel. Fix this by introducing vfio_ap_mdev_release_eventfds() and calling it from vfio_ap_mdev_close_device() after vfio_ap_mdev_unset_kvm(). The VFIO core guarantees that close_device is called before vfio_unregister_group_dev() returns in the remove path, so fixing close_device is sufficient to cover both teardown paths. Note: ~~~~ The matrix_dev->mdevs lock must be held during the call to vfio_ap_mdev_release_eventfds(). There is a small window between the calls to vfio_ap_mdev_unset_kvm() which gets and releases the update locks and the acquisition of the matrix_dev->mdevs_lock mutex during which it is possible - although highly unlikely during normal operation - whereby a concurrent SET_IRQS call can get in. Taking matrix_dev->mdevs_lock around vfio_ap_mdev_release_eventfds() is sufficient to make this race-free. The SET_IRQS ioctl path writes req_trigger and cfg_chg_trigger only from vfio_ap_mdev_ioctl(), which holds mdevs_lock for its entire duration and always calls eventfd_ctx_put() on the previous value before storing the new one. Any number of concurrent SET_IRQS calls during the window between vfio_ap_mdev_unset_kvm() and the acquisition of mdevs_lock are therefore safe: each ioctl invocation puts the reference it found and installs a new one, leaving exactly one live reference in the field when it releases the lock. When release_eventfds subsequently acquires mdevs_lock it finds that single surviving reference and puts it. Conversely, a SET_IRQS call that loses the race and blocks on mdevs_lock will find the field NULL after release_eventfds finishes, take ownership of the reference it just created, and install it into a field that will never be read again - a transient leak. To close that final case, callers must ensure no new SET_IRQS ioctls can be issued after close_device() is called, which the VFIO core guarantees by releasing the device file before invoking close_device(). Fixes: bf48961f6f48e ("s390/vfio-ap: realize the VFIO_DEVICE_SET_IRQS ioctl") Cc: stable@vger.kernel.org Signed-off-by: Anthony Krowiak --- drivers/s390/crypto/vfio_ap_ops.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index a46bf381ab72..6e4569d6b975 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -2066,12 +2066,28 @@ static int vfio_ap_mdev_open_device(struct vfio_device *vdev) return vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm); } +static void vfio_ap_mdev_release_eventfds(struct ap_matrix_mdev *matrix_mdev) +{ + if (matrix_mdev->req_trigger) { + eventfd_ctx_put(matrix_mdev->req_trigger); + matrix_mdev->req_trigger = NULL; + } + if (matrix_mdev->cfg_chg_trigger) { + eventfd_ctx_put(matrix_mdev->cfg_chg_trigger); + matrix_mdev->cfg_chg_trigger = NULL; + } +} + static void vfio_ap_mdev_close_device(struct vfio_device *vdev) { struct ap_matrix_mdev *matrix_mdev = container_of(vdev, struct ap_matrix_mdev, vdev); vfio_ap_mdev_unset_kvm(matrix_mdev); + + mutex_lock(&matrix_dev->mdevs_lock); + vfio_ap_mdev_release_eventfds(matrix_mdev); + mutex_unlock(&matrix_dev->mdevs_lock); } static void vfio_ap_mdev_request(struct vfio_device *vdev, unsigned int count) -- 2.53.0