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Peter Anvin" , Ingo Molnar , "Mario Limonciello" , Thomas Gleixner , , Yazen Ghannam CC: , Penny Zheng , References: <20260814214255.83127-1-jason.andryuk@amd.com> <20260814214255.83127-2-jason.andryuk@amd.com> Content-Language: en-US From: Jason Andryuk In-Reply-To: <20260814214255.83127-2-jason.andryuk@amd.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SA2PEPF00003AE9:EE_|CY1PR12MB9649:EE_ X-MS-Office365-Filtering-Correlation-Id: 3fdc147b-bd2d-4941-e7ac-08df021b1664 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|82310400026|23010399003|36860700016|376014|10067099003|56012099006|18002099003|22082099003|11063799006|4143699003; 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:satlexmb08.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(1800799024)(82310400026)(23010399003)(36860700016)(376014)(10067099003)(56012099006)(18002099003)(22082099003)(11063799006)(4143699003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: bQA/xESZX9EdjEpMJ4GxAByOHCGd7z6GIC3r4sNouxKOk/LOUst3nTadK2BFyILeS8RCdKb7pH2ZqgqG3IHiUr2lt9ZB0Y4gXOqYl7UDHBM2N/Z8Ct11OFajxCHe8fZ0FNCC8U0RLj0tDo3CkvXadc+kj9wHg7Fj0jTpWfsq/IdAZBa3ymlnZAon1qn/lBXjLq2gcYEYEx32jhWt1nqrXdquJ8nHcC5rD3fP5H4jY9cWTI/joWf0GkBU5DYRF3UrULnTt1cJABWKA8ZoViveWuBsM1bPrH58ClQXCS2K0F4ULiQu0SW6pugksvMIyf6LwzLrClWSJGnW1x/JJn65Pm5IvTl2tRJBafc9wsnubNsY1fnls1vav+acwZTzuFUuaxZ3hFpOrQrJVTjAovv1ha6LoJpiBVvVvE5oPu7kOdlJTpx8s0mMw8QJfy3cu9P7 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Aug 2026 20:05:47.2560 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 3fdc147b-bd2d-4941-e7ac-08df021b1664 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=[satlexmb08.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: CY1PR12MB9649 Hi, On 2026-08-14 17:42, Jason Andryuk wrote: > 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 Any feedback here? Thanks, Jason > --- > 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;