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Peter Anvin" , Ingo Molnar , Mario Limonciello , Thomas Gleixner , , Yazen Ghannam , , Penny Zheng , References: <20260825214805.39148-1-jason.andryuk@amd.com> <20260825214805.39148-2-jason.andryuk@amd.com> <20260826044518.GBao5vXvWQx9_a9RzF@fat_crate.local> Content-Language: en-US From: Jason Andryuk In-Reply-To: <20260826044518.GBao5vXvWQx9_a9RzF@fat_crate.local> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN1PEPF00004684:EE_|SJ0PR12MB5636:EE_ X-MS-Office365-Filtering-Correlation-Id: 8557457d-d9cc-4f6d-a1a2-08df036bc57e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|376014|82310400026|1800799024|36860700016|56012099006|10067099003|22082099003|18002099003|4143699003|11063799006; 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)(23010399003)(376014)(82310400026)(1800799024)(36860700016)(56012099006)(10067099003)(22082099003)(18002099003)(4143699003)(11063799006);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 4FF2PPCzHck3mVP45dPJYY0mMbmv2rMS3+17RCRiyjgjQhZImw+cmxDNmVTHjKxJElOJ5+Y2SrGsXFprCPwyH4tKb014BU2PlzFrac8Rn46T+cRScSkP4paM7cTYkXggtjDo0tIq+Pf1YpnT1W7zdLV+EpdP6seRQOWaFiA5cqtY0PpayZ17n2D5rjU/7ohZa87zXERj4H4qYsEEEzjmFjvupVo8BMXGsAFckSSqOLPtOX1zOmMAIPQkg6Iab+eppno5ORWXFWBwzjITKoko9viw9JvAzT2TWWl6Dr9lHAnMrpQwVR+tNeE+00jAszufNZx7lhdp4okZjUyf1KXEl9r21/XXoLeLXv7V9qZFX/ht9twtJc/kXcgHqoI2rXd0kglpgETdvHroLf0E4cZ2QCE+75tEAWHDbMEjZmSugN0LomWsufN2Dga1qfVyjEpq X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Aug 2026 12:15:51.7942 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8557457d-d9cc-4f6d-a1a2-08df036bc57e 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: BN1PEPF00004684.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR12MB5636 On 2026-08-26 00:45, Borislav Petkov wrote: > On Tue, Aug 25, 2026 at 05:48:02PM -0400, 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 >> 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; > > Hold on - the only way this is fixing something on Xen - and you say that > roots_per_node becomes 0 - which means that num_roots is 0. > > But a couple of lines above, we have > > if (!num_roots) > return -ENODEV; > > So we would've exited already. > > num_nodes can't be 0 because you'd explode even with this patch. > > What am I missing? num_roots is 1, but num_nodes is 2. Integer division gives 0 for roots_per_node. Regards, Jason