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Mon, 24 Aug 2026 13:58:57 +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 13:58:57 +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 3/4] s390/vfio-ap: Fix unbounded loop in apq_reset_check() Date: Mon, 24 Aug 2026 09:58:49 -0400 Message-ID: <20260824135850.503728-4-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: VU5VNhRIiXafo0sYIdv1UTAFMIRjWb8M X-Proofpoint-Spam-Info: AW1haW4tMjYwODI0MDExNCBTYWx0ZWRfX5hkmW1n+CZtQ IjBtsrYELkfPxsVIujarHC3uFHdSL8pJ90hXJNauxYZexN6FtVlV0kT957/TJB+zez1ywGNbHfJ Ry7Tqn1vFE1deYIEJsUIHfuIS7CuAWg= X-Proofpoint-GUID: VU5VNhRIiXafo0sYIdv1UTAFMIRjWb8M X-Authority-Analysis: v=2.4 cv=JZyMa0KV c=1 sm=1 tr=0 ts=6a8c4e25 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=KD7G0zD2dsexTIroXy8A:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODI0MDExNCBTYWx0ZWRfXxizVBYhFKV9o FwwiYxOfDYvl5IkpVqeRlGP3HkHXXZb/tg+BIHEzDzfXpF3U4zFv3lGxKnh1YZb7ZfvuhXaEBhh 6ovJRD/ODZnSRP+rwDR91l248/Y1ShKZOSwEU+SKWAXF0sMZyeeyp3DHFZUodoUFKS2cg1yWXAi 2p/DuRDeRdYlMz7X76eVoq4BTbTMFNyX90K09+8/sUVKJzWnNdvK/Hxb+aXWJlK0Yi8gqBKm8BC pQ/ruHRUih9aeNogsBaIMMVBLflfvjeXU//4sNxV0Nvkgbo7Isy2dny89Pt3c6RHhKrPSlsFJO9 XrXwkdsRNP/q5TYi97sKUrrBnH/UGIW30YEhaa3uGhbNkim/CnHG1fIfvIPF8k1prmlTZDhwzZk Ip8d6kvrcvDrQIYTP5eeZIi+Wdxs48BQzSvl38agoGeBkz80eEEFs3YmT1ESxXdL8cVUMmd546a /WjZ8JySgcr+zQPndRg== 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 The apq_reset_check() worker polls ap_tapq() in a while(true) loop waiting for a queue reset to complete. When ap_tapq() returns AP_RESPONSE_BUSY or AP_RESPONSE_RESET_IN_PROGRESS, apq_status_check() returns -EBUSY and the loop continues after sleeping AP_RESET_INTERVAL (20ms). There is no upper bound on how many times the loop iterates, so if the hardware continuously returns a busy response the worker runs indefinitely. This is particularly harmful because several callers of vfio_ap_mdev_reset_queues() and vfio_ap_mdev_reset_qlist() call flush_work() on each queue's reset_work while holding one or more of the global matrix_dev locks (guests_lock, mdevs_lock) or the KVM lock. An indefinitely spinning worker permanently blocks all of those locks, hanging mdev removal, KVM guest teardown, and the VFIO_DEVICE_RESET ioctl path. Fix this by introducing AP_RESET_TIMEOUT (2000ms) and breaking out of the poll loop when elapsed time reaches that threshold. On timeout the final busy status is written back to q->reset_status so that callers inspecting reset_status.response_code after flush_work() see a non-zero value and can return an appropriate error. vfio_ap_free_aqic_resources() is called before returning to release any KVM ISC registration and pinned NIB page, consistent with all other early-exit paths in the function. Fixes: dd174833e44e ("s390/vfio-ap: remove upper limit on wait for queue reset to complete") Cc: stable@vger.kernel.org Signed-off-by: Anthony Krowiak --- drivers/s390/crypto/vfio_ap_ops.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index 6e4569d6b975..c7eebbd0ed40 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -31,6 +31,7 @@ #define AP_QUEUE_IN_USE "in use" #define AP_RESET_INTERVAL 20 /* Reset sleep interval (20ms) */ +#define AP_RESET_MAX_WAIT 2000 /* Maximum wait for reset (2000ms) */ static int vfio_ap_mdev_reset_queues(struct ap_matrix_mdev *matrix_mdev); static int vfio_ap_mdev_reset_qlist(struct list_head *qlist); @@ -1973,6 +1974,12 @@ static void apq_reset_check(struct work_struct *reset_work) status.response_code, status.queue_empty, status.irq_enabled); + if (elapsed >= AP_RESET_MAX_WAIT) { + /* Timed out waiting for reset to complete */ + memcpy(&q->reset_status, &status, sizeof(status)); + vfio_ap_free_aqic_resources(q); + return; + } } else { if (q->reset_status.response_code == AP_RESPONSE_RESET_IN_PROGRESS || q->reset_status.response_code == AP_RESPONSE_BUSY || -- 2.53.0