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Peter Anvin" , Ingo Molnar , "Mario Limonciello" , Thomas Gleixner , , Yazen Ghannam CC: Jason Andryuk , , Penny Zheng , Subject: [PATCH v3 1/2] x86/amd_node: Avoid divide by zero on virtualized systems Date: Tue, 25 Aug 2026 17:48:02 -0400 Message-ID: <20260825214805.39148-2-jason.andryuk@amd.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260825214805.39148-1-jason.andryuk@amd.com> References: <20260825214805.39148-1-jason.andryuk@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-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SA2PEPF00003AE9:EE_|DS0PR12MB7630:EE_ X-MS-Office365-Filtering-Correlation-Id: 98d2726a-4bc0-4186-909e-08df02f295cb X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|82310400026|1800799024|36860700016|23010399003|10067099003|11063799006|56012099006|18002099003|22082099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:149.199.90.133;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:unknown-90-133.xilinx.com;CAT:NONE;SFS:(13230040)(376014)(82310400026)(1800799024)(36860700016)(23010399003)(10067099003)(11063799006)(56012099006)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: Ts/G2O4ot1+fd3M12XB++z0GYjBXssvxh00ewYbTyoYPL8noBj8um7TGEDe//UX4Urtqg5LW+FNq6KcRCxaMc0RI5Rb2oAssH3oY/4+Dq7/LHMizHkZuBQJtTtkmQJ4d/+mzg6BccODzBiUj2TvIA09fh/WuejOm3kD2TbiuO5CRwOU585m/q2A9X+2toiLbWOnEBEVO2mga3fV8L8+8zvZ8Tbm2880WrePlvHy3T7rdOaQZvwRTchMnPcaT65Okn67NZ2ZmBK+nBOFAu9m0OB+kHRCGfPNKLTK9SvqHs7ZaEupCu0tQG7OjHGHw0eJzuzHEJ6r4LkMPoXBcucg4siISFPFa989qtUf0Retj114GK2q3NFjuloK3qud0clCe7tkJbXM9FjP3DYtTHf1/TZSlddVTZ5VDIP/MU6XtOe+G0MC1Dd7t85ybtQcEhZcw X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Aug 2026 21:48:22.7165 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 98d2726a-4bc0-4186-909e-08df02f295cb X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[149.199.90.133];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SA2PEPF00003AE9.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB7630 On a virtualized system, the number of nodes does not have a relationship to the number of roots. A Xen PVH dom0 can calculate roots_per_node as 0, which crashes with a divide by zero in: if (count++ % roots_per_node) The issue is seen with Xen, but it could affect other systems. Change roots_per_node == 0 to 1 to allow the system to boot. Print a warning when this is performed for non-virtualized systems. Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching") Cc: stable@vger.kernel.org Suggested-by: Borislav Petkov Reviewed-by: Yazen Ghannam Signed-off-by: Jason Andryuk --- v3: Add newline to warning. R-b: Yazen v2: Print as a warning instead of error Use "!" instead of "== 0". X86_FEATURE_XENPV is only for PV, but this is observed with a PVH dom0. --- arch/x86/kernel/amd_node.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c index 0be01725a2a4..408b9fd48349 100644 --- a/arch/x86/kernel/amd_node.c +++ b/arch/x86/kernel/amd_node.c @@ -287,6 +287,11 @@ static int __init amd_smn_init(void) return -ENOMEM; roots_per_node = num_roots / num_nodes; + if (!roots_per_node) { + if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR)) + pr_warn(FW_BUG "Error detecting roots per node.\n"); + roots_per_node = 1; + } count = 0; node = 0; -- 2.55.0