Patch Detail
get:
Show a patch.
patch:
Update a patch.
put:
Update a patch.
GET /api/1.1/patches/2221530/?format=api
{ "id": 2221530, "url": "http://patchwork.ozlabs.org/api/1.1/patches/2221530/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-ppc/patch/20260409161042.55281-1-harshpb@linux.ibm.com/", "project": { "id": 69, "url": "http://patchwork.ozlabs.org/api/1.1/projects/69/?format=api", "name": "QEMU powerpc development", "link_name": "qemu-ppc", "list_id": "qemu-ppc.nongnu.org", "list_email": "qemu-ppc@nongnu.org", "web_url": "", "scm_url": "", "webscm_url": "" }, "msgid": "<20260409161042.55281-1-harshpb@linux.ibm.com>", "date": "2026-04-09T16:10:42", "name": "[for,11.0-rc3] accel/kvm: Fix BQL lock imbalance in kvm_cpu_exec", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "fab9819f1b42e65ca43977cceba6475c8421eacb", "submitter": { "id": 85411, "url": "http://patchwork.ozlabs.org/api/1.1/people/85411/?format=api", "name": "Harsh Prateek Bora", "email": "harshpb@linux.ibm.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/qemu-ppc/patch/20260409161042.55281-1-harshpb@linux.ibm.com/mbox/", "series": [ { "id": 499324, "url": "http://patchwork.ozlabs.org/api/1.1/series/499324/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-ppc/list/?series=499324", "date": "2026-04-09T16:10:42", "name": "[for,11.0-rc3] accel/kvm: Fix BQL lock imbalance in kvm_cpu_exec", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/499324/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2221530/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2221530/checks/", "tags": {}, "headers": { "Return-Path": "<qemu-ppc-bounces+incoming=patchwork.ozlabs.org@nongnu.org>", "X-Original-To": "incoming@patchwork.ozlabs.org", "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256\n header.s=pp1 header.b=VrKFslVR;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists.gnu.org;\n envelope-from=qemu-ppc-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)" ], "Received": [ "from lists.gnu.org (lists1p.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fs4gJ0Ch3z1yCv\n\tfor <incoming@patchwork.ozlabs.org>; Fri, 10 Apr 2026 02:11:22 +1000 (AEST)", "from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.90_1)\n\t(envelope-from <qemu-ppc-bounces@nongnu.org>)\n\tid 1wAryB-0006tr-21; Thu, 09 Apr 2026 12:11:04 -0400", "from eggs.gnu.org ([2001:470:142:3::10])\n by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <harshpb@linux.ibm.com>)\n id 1wAry7-0006r0-Tk; Thu, 09 Apr 2026 12:10:59 -0400", "from mx0b-001b2d01.pphosted.com ([148.163.158.5])\n by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <harshpb@linux.ibm.com>)\n id 1wAry6-0007oI-7Z; Thu, 09 Apr 2026 12:10:59 -0400", "from pps.filterd (m0353725.ppops.net [127.0.0.1])\n by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id\n 639EApJU2401288; Thu, 9 Apr 2026 16:10:54 GMT", "from ppma13.dal12v.mail.ibm.com\n (dd.9e.1632.ip4.static.sl-reverse.com [50.22.158.221])\n by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4dcn2hn0bp-1\n (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT);\n Thu, 09 Apr 2026 16:10:54 +0000 (GMT)", "from pps.filterd (ppma13.dal12v.mail.ibm.com [127.0.0.1])\n by ppma13.dal12v.mail.ibm.com (8.18.1.2/8.18.1.2) with ESMTP id\n 639CnqXK018946;\n Thu, 9 Apr 2026 16:10:53 GMT", "from smtprelay01.fra02v.mail.ibm.com ([9.218.2.227])\n by ppma13.dal12v.mail.ibm.com (PPS) with ESMTPS id 4dcme9mbax-1\n (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT);\n Thu, 09 Apr 2026 16:10:53 +0000", "from smtpav03.fra02v.mail.ibm.com (smtpav03.fra02v.mail.ibm.com\n [10.20.54.102])\n by smtprelay01.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id\n 639GAnv159572632\n (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK);\n Thu, 9 Apr 2026 16:10:49 GMT", "from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1])\n by IMSVA (Postfix) with ESMTP id 7AE2520043;\n Thu, 9 Apr 2026 16:10:49 +0000 (GMT)", "from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1])\n by IMSVA (Postfix) with ESMTP id 7460E20040;\n Thu, 9 Apr 2026 16:10:47 +0000 (GMT)", "from localhost.localdomain (unknown [9.39.24.136])\n by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP;\n Thu, 9 Apr 2026 16:10:47 +0000 (GMT)" ], "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc\n :content-transfer-encoding:date:from:message-id:mime-version\n :subject:to; s=pp1; bh=pMxwQeZ4ev4mCAV9Ck0oKLFAv7ZIKhndqQKrvJsvl\n 6Y=; b=VrKFslVRPBWpbRQWJRLSZ+d/eEvAWKaSM7hMBkaV+k7HfJDNmqD63p7cU\n hpLW9ck+N5wO5ERIPSipLw/KTloxQuTOTWWKapRcSkQKzoa++8Tmv7ooMK1UIc6w\n dFO/8sFdEdgtiRODALnBw18K1O3DpxAd1m+1CbUR1oaPYoTWUjo4QNJhTOxyvstQ\n /4wZBToeVpflL6mJW5LCMkQGZIPGNmjWyg+Z191TOZdDWMiGW+eWoXBLSTzBFJ2x\n Th/iTtPVuq6IaVU71V7NwJXZn8NovigElWc+dmrnIUb22Or1y4UPX4Sl0JpR2JRM\n 6VNR8eVTfVaKff2mbGrPbNswtWKTg==", "From": "Harsh Prateek Bora <harshpb@linux.ibm.com>", "To": "qemu-devel@nongnu.org, qemu-ppc@nongnu.org", "Cc": "anisinha@redhat.com, pbonzini@redhat.com, npiggin@gmail.com,\n misanjum@linux.ibm.com, gautam@linux.ibm.com, peter.maydell@linaro.org", "Subject": "[PATCH for 11.0-rc3] accel/kvm: Fix BQL lock imbalance in\n kvm_cpu_exec", "Date": "Thu, 9 Apr 2026 21:40:42 +0530", "Message-ID": "<20260409161042.55281-1-harshpb@linux.ibm.com>", "X-Mailer": "git-send-email 2.52.0", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "X-TM-AS-GCONF": "00", "X-Proofpoint-Reinject": "loops=2 maxloops=12", "X-Proofpoint-Spam-Details-Enc": "AW1haW4tMjYwNDA5MDE0NSBTYWx0ZWRfX14lecYEXauIs\n VGw3irFbeq8+f045DWTY80qEW0Kptvd+8cwdgkUmr50MkIXWeqjTe6w0zBhT56aEY6HKnf632qu\n R7tTLpDmx0nZtgmqeH5BpnzCqlNLP+zyjHhgsGId6dYZobrOZWRhRrf6lF6Ikk9UguoN7FVXknz\n aKqHCGSvySvnoTiZtEs/83Rfh27/uchUHB676KkjE2J326O16WwiH2nswytVzGjM1/aPJJMWdu8\n cEzBDTBXu3YlAiTKgEbvrzJNB/pavgK0C5DaZifoiz1C10F7Wqa4mYYWcErtLFvAg2CD9z3SRCb\n sDbRXKUPjh451gxoeQcHd3e79mdkM7aUCfkccmMQD/IjeqzMwMZC5vwfX45ll06ZmnR7i52QHK/\n c0dwCfLYqmpnVQoDTBlRKpl/hJaIu5csiW1iGojgeXcksjwhU9OTuWoYKVb22BWR0E0Ehm0uqkb\n X+XO8Q0i63AEB2v3t/g==", "X-Proofpoint-GUID": "mB8bpi-nAlk1Q2GS0Bo8tnBoTzVVH4Ph", "X-Authority-Analysis": "v=2.4 cv=a/wAM0SF c=1 sm=1 tr=0 ts=69d7cf8e cx=c_pps\n a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17\n a=A5OVakUREuEA:10 a=f7IdgyKtn90A:10 a=VkNPw1HP01LnGYTKEx00:22\n a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8\n a=J3LV9hoIG5fqms1vbrYA:9 a=O8hF6Hzn-FEA:10", "X-Proofpoint-ORIG-GUID": "S9AEwKEdiqit0oF60W46EMXD0qU6EZUR", "X-Proofpoint-Virus-Version": "vendor=baseguard\n engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49\n definitions=2026-04-09_04,2026-04-09_02,2025-10-01_01", "X-Proofpoint-Spam-Details": "rule=outbound_notspam policy=outbound score=0\n bulkscore=0 clxscore=1015 spamscore=0 impostorscore=0 priorityscore=1501\n phishscore=0 lowpriorityscore=0 adultscore=0 malwarescore=0 suspectscore=0\n classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0\n reason=mlx scancount=1 engine=8.22.0-2604010000 definitions=main-2604090145", "Received-SPF": "pass client-ip=148.163.158.5;\n envelope-from=harshpb@linux.ibm.com;\n helo=mx0b-001b2d01.pphosted.com", "X-Spam_score_int": "-26", "X-Spam_score": "-2.7", "X-Spam_bar": "--", "X-Spam_report": "(-2.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1,\n DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7,\n RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001,\n RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001,\n SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no", "X-Spam_action": "no action", "X-BeenThere": "qemu-ppc@nongnu.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "<qemu-ppc.nongnu.org>", "List-Unsubscribe": "<https://lists.nongnu.org/mailman/options/qemu-ppc>,\n <mailto:qemu-ppc-request@nongnu.org?subject=unsubscribe>", "List-Archive": "<https://lists.nongnu.org/archive/html/qemu-ppc>", "List-Post": "<mailto:qemu-ppc@nongnu.org>", "List-Help": "<mailto:qemu-ppc-request@nongnu.org?subject=help>", "List-Subscribe": "<https://lists.nongnu.org/mailman/listinfo/qemu-ppc>,\n <mailto:qemu-ppc-request@nongnu.org?subject=subscribe>", "Errors-To": "qemu-ppc-bounces+incoming=patchwork.ozlabs.org@nongnu.org", "Sender": "qemu-ppc-bounces+incoming=patchwork.ozlabs.org@nongnu.org" }, "content": "When kvm_cpu_exec() returns EXCP_HLT due to kvm_arch_process_async_events()\nreturning true, it was returning before releasing the BQL (Big QEMU Lock).\nThis caused a lock imbalance where the vCPU thread would loop back to\nkvm_cpu_exec() while still holding the BQL, leading to deadlocks.\n\nThe issue manifests as boot hangs on PowerPC pseries machines with multiple\nvCPUs, where secondary vCPUs with start-powered-off=true remain halted and\nrepeatedly call kvm_cpu_exec() which returns EXCP_HLT. Each iteration held\nthe BQL, preventing other operations from proceeding.\n\nThe fix has two parts:\n\n1. In kvm_cpu_exec() (kvm-all.c):\n Release the BQL before returning EXCP_HLT in the early return path,\n matching the behavior of the normal execution path where bql_unlock()\n is called before entering the main KVM execution loop.\n\n2. In kvm_vcpu_thread_fn() (kvm-accel-ops.c):\n Re-acquire the BQL after kvm_cpu_exec() returns EXCP_HLT, since the\n loop expects to hold the BQL when calling kvm_cpu_exec() again.\n\nThis ensures proper BQL lock/unlock pairing:\n- kvm_vcpu_thread_fn() holds BQL before calling kvm_cpu_exec()\n- kvm_cpu_exec() releases BQL before returning (for EXCP_HLT)\n- kvm_vcpu_thread_fn() re-acquires BQL if EXCP_HLT was returned\n- Next iteration has BQL held as expected\n\nThis is a regression introduced by commit 98884e0cc1 (\"accel/kvm: add\nchanges required to support KVM VM file descriptor change\") which\nrefactored kvm_irqchip_create() and changed the initialization timing,\nexposing this lock imbalance issue.\n\nFixes: 98884e0cc1 (\"accel/kvm: add changes required to support KVM VM file descriptor change\")\nReported-by: Misbah Anjum N <misanjum@linux.ibm.com>\nReported-by: Gautam Menghani <gautam@linux.ibm.com>\nSigned-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>\n---\n accel/kvm/kvm-accel-ops.c | 4 ++++\n accel/kvm/kvm-all.c | 1 +\n 2 files changed, 5 insertions(+)", "diff": "diff --git a/accel/kvm/kvm-accel-ops.c b/accel/kvm/kvm-accel-ops.c\nindex 6d9140e549..d684fd0840 100644\n--- a/accel/kvm/kvm-accel-ops.c\n+++ b/accel/kvm/kvm-accel-ops.c\n@@ -52,6 +52,10 @@ static void *kvm_vcpu_thread_fn(void *arg)\n \n if (cpu_can_run(cpu)) {\n r = kvm_cpu_exec(cpu);\n+ if (r == EXCP_HLT) {\n+ /* kvm_cpu_exec() released BQL, re-acquire for next iteration */\n+ bql_lock();\n+ }\n if (r == EXCP_DEBUG) {\n cpu_handle_guest_debug(cpu);\n }\ndiff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c\nindex 774499d34f..00b8018664 100644\n--- a/accel/kvm/kvm-all.c\n+++ b/accel/kvm/kvm-all.c\n@@ -3439,6 +3439,7 @@ int kvm_cpu_exec(CPUState *cpu)\n trace_kvm_cpu_exec();\n \n if (kvm_arch_process_async_events(cpu)) {\n+ bql_unlock();\n return EXCP_HLT;\n }\n \n", "prefixes": [ "for", "11.0-rc3" ] }