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Peter Anvin" , , Subject: [PATCH v1 1/2] x86/amd_node: avoid divide-by-zero in amd_smn_init() under Xen dom0 Date: Wed, 6 May 2026 13:55:18 +0800 Message-ID: <20260506055528.476493-2-penny.zheng@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260506055528.476493-1-penny.zheng@amd.com> References: <20260506055528.476493-1-penny.zheng@amd.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 Content-Type: text/plain X-ClientProxiedBy: satlexmb08.amd.com (10.181.42.217) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN1PEPF00036F3F:EE_|SA5PPFD911547FB:EE_ X-MS-Office365-Filtering-Correlation-Id: 8b51d57d-91d4-4d7f-2040-08deab343453 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|36860700016|82310400026|56012099003|18002099003|22082099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(1800799024)(376014)(36860700016)(82310400026)(56012099003)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: ++9QBZu2qMm3vsjUnSr6e/ceM3c0R7gkHyjkPA3d39jAg4M4Pa7Qsqf233LskQMdMpJ55jhPitso3p9oVCLA3rOg68QI2Z/75Cps89DZL2FwE053LrUHxaQ4OiZZS0Gqv1rgtktWwkjn3uDLEcenMs5Z3jaGjEAQYaB/Qi392OueHGbE0JmpXmLAg4U21UNd/9Y2EKwUR5EHYaBG7fCPGDXFN04TwyoWlGyrZhj7vr1akeJOnni2JY6NqugsvmZNnKCfgomEU0QwTyess8jlgJvD+mWXIIVlhDBpPPMznA8qkIe7xIQ6tJM+MRt7cxHt0MpuC2y4lrAXtpwo74IggP4eyEr33IYWUVry2Gsxmqf2lt36dIIhebhGF6z7HlYbDiNNV+Xo4W+G+HMypvfagZGULW14DH5D+Yeza3FzAB+08/8fbqLqoXC+wStUWgQa X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2026 05:56:23.7040 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8b51d57d-91d4-4d7f-2040-08deab343453 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SN1PEPF00036F3F.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA5PPFD911547FB To prevent each dom0 vCPU from looking like an SMT sibling of another vCPU, Xen synthesizes guest x2APIC IDs as vcpu_index * 2. While the spacing every vCPU's APIC ID by 2 can therefore push the IDs past the package-field boundary, making Linux see more packages than the platform actually has. amd_num_nodes() inherits that inflated count, so num_nodes can exceed num_roots (the number of AMD root complexes discovered on the PCI bus). The subsequent roots_per_node = num_roots / num_nodes; ... count % roots_per_node ... then divides by zero in amd_smn_init(). Reject num_roots < num_nodes explicitly and bail out with -ENODEV. Signed-off-by: Penny Zheng --- arch/x86/kernel/amd_node.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c index 0be01725a2a4..c896060fe0df 100644 --- a/arch/x86/kernel/amd_node.c +++ b/arch/x86/kernel/amd_node.c @@ -282,6 +282,18 @@ static int __init amd_smn_init(void) return -ENODEV; num_nodes = amd_num_nodes(); + + /* + * Xen dom0's synthetic APIC IDs may imply more nodes than host + * bridges visible in PCI config space. Bail out to avoid a + * divide-by-zero when later computing roots_per_node. + */ + if (num_roots < num_nodes) { + pr_debug("AMD root count (%u) < node count (%u); skipping SMN init\n", + num_roots, num_nodes); + return -ENODEV; + } + amd_roots = kzalloc_objs(*amd_roots, num_nodes); if (!amd_roots) return -ENOMEM; -- 2.43.0