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Peter Anvin" , Ingo Molnar , "Mario Limonciello" , Thomas Gleixner , , Yazen Ghannam CC: Jason Andryuk , , Penny Zheng , Subject: [PATCH v2 1/2] x86/amd_node: Avoid divide by zero on virtualized systems Date: Fri, 14 Aug 2026 17:42:52 -0400 Message-ID: <20260814214255.83127-2-jason.andryuk@amd.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260814214255.83127-1-jason.andryuk@amd.com> References: <20260814214255.83127-1-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: BN3PEPF0000B073:EE_|PH0PR12MB7814:EE_ X-MS-Office365-Filtering-Correlation-Id: 2bd3e272-1cc8-4c34-333a-08defa4d0f75 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|376014|36860700016|23010399003|1800799024|11063799006|10067099003|56012099006|22082099003|18002099003; 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)(82310400026)(376014)(36860700016)(23010399003)(1800799024)(11063799006)(10067099003)(56012099006)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: pCVt24Ugxk8i5dJXoBwB2L+TWX9y1qPCDqydsfV4KENH8mNdp/nHr1TRT0vWoj5+Dk/ibwhJagqeo9ADgE9xZsIh1BHOIWNFTQewYJm5hw+Q9LkeNeinEJfk+MHBL+8NiJsaL126xnXBQm1vUbXMcVvfg8woCSv7hfQPFMYi7DXnm38WMEEVltL3jsfvw+IMhspQIlDadyDBbDKUaChLFa5G/S6MvC6NKggTaO/ZQ/Bv+Ijn58HjiCQZb9HPTVkXUi4aakvwCPCi93vS0vDaw9VFHLH/gFlbUMl2GOGM3YS0toBs8FCTlB+XVSrls3P3772+8af5vEffhSqNrz1iPWl0bvpcpDrOvtF5n+ewJbea17tPC/v2zNfOZ9ffSZgdLnR/utq9pTB3AD2nqxF5BYw5I+nJ3MFA0mh1b1NZRCxEHSRvJC8PpyBpOEPvlP4M X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Aug 2026 21:43:21.1519 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2bd3e272-1cc8-4c34-333a-08defa4d0f75 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: BN3PEPF0000B073.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR12MB7814 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 Signed-off-by: Jason Andryuk --- 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..c3e214925d9c 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."); + roots_per_node = 1; + } count = 0; node = 0; -- 2.55.0