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Mon, 24 Aug 2026 21:56:10 +0000 (GMT) Received: from li-4c4c4544-004d-4810-8043-b7c04f423534.ibm.com.com (unknown [9.61.96.163]) by smtpav05.wdc07v.mail.ibm.com (Postfix) with ESMTP; Mon, 24 Aug 2026 21:56:10 +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 v2 3/4] s390/vfio-ap: Fix unbounded loop in apq_reset_check() Date: Mon, 24 Aug 2026 17:56:02 -0400 Message-ID: <20260824215603.819379-4-akrowiak@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260824215603.819379-1-akrowiak@linux.ibm.com> References: <20260824215603.819379-1-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: fXA-4VpoV58SSSGvFE2dY0jJ4UaR3pYf X-Proofpoint-Spam-Info: AW1haW4tMjYwODI0MDE4MiBTYWx0ZWRfXzHhI1iOcNbi0 U4WAgWmUfmakwLw6yg++E7I2iklB+lcjsGCn9lamsptMw9Dbb4JgefODupCa4TTCheq363j7fXN l52izQdV3rLZ58hJjWCgxiZnjUmwPdY= X-Proofpoint-GUID: fXA-4VpoV58SSSGvFE2dY0jJ4UaR3pYf X-Authority-Analysis: v=2.4 cv=JZyMa0KV c=1 sm=1 tr=0 ts=6a8cbdff cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=y3d8e9OS9Gm2Uli4ifAA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODI0MDE4MiBTYWx0ZWRfXwVsJPukXNVtx txy8Hee8V11GpxiESY9Sq3/idECO7XSxhmTqzHq1NsIqS0yxWdmIxIBaIsnnZxOBbfdvRnEcJYK 4gXEAV7/Ez9RcKu2TJVcctnaJVf2SAoNOe5nqQVQ6+ttbUYcDlgNKEASD9tCXDTqGYYqoU9m2Tr QRshbyt9VLtoMA+g7fXIk5fjsEDJF4EL5C4FC1gN83d/SMgN3MqANXylV0LC80VySvIbzEC1ej3 fKlOdMwJk5lghXodz5mDqJJid7w0lFahU03/QPhbVvGoi8iIiL6o81Q36BYN8wk2DyPT21F29Eu f6Wl/FXxD7C61lHHP3bfKgWfP64NQKo596Ct8sHd3gGY608CurvF4hV8kqTrsEuqYolDEx/jjNS 7EradTVx/+ASNpwCG7d6CqH+h4/FN9jNhCZ8QRdgGS+bJP3OCsyOTCX53mEK6QY8eMZNIcXTBZW wI6FHhZy+xVUin6yaFA== 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_06,2026-08-24_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-2608240182 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_MAX_WAIT (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_MAX_WAIT (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 | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index 3f99b239fa95..7a9b5448e90a 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); @@ -1971,6 +1972,27 @@ 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. + * + * The AQIC resources associated with this queue - the pinned page + * containing the NIB and the registered guest ISC - cannot be freed + * here. The NIB is the active DMA target for AP interrupt delivery + * until the reset completes; freeing the pinned page while the + * hardware may still write to it would result in a use-after-free + * kernel crash. + * + * If the reset eventually completes, interrupts will be terminated + * and the pinned NIB page and ISC registration will be leaked. This + * is preferable to either a use-after-free or waiting indefinitely: + * apq_reset_check() holds the matrix_dev->mdevs_lock mutex, which + * serializes access to all mdev objects system-wide, so blocking + * here would stall all other guests using AP queues. + */ + memcpy(&q->reset_status, &status, sizeof(status)); + return; + } } else { if (q->reset_status.response_code == AP_RESPONSE_RESET_IN_PROGRESS || q->reset_status.response_code == AP_RESPONSE_BUSY || -- 2.53.0