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Peter Anvin" , Ingo Molnar , "Mario Limonciello" , Thomas Gleixner , , , Penny Zheng , References: <20260806160159.230453-1-jason.andryuk@amd.com> <20260806160159.230453-3-jason.andryuk@amd.com> <20260810144706.GC57095@yaz-khff2.amd.com> <20260811092107.37ef648b@pumpkin> Content-Language: en-US From: Jason Andryuk In-Reply-To: <20260811092107.37ef648b@pumpkin> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY4PEPF0000EE3A:EE_|SJ2PR12MB9140:EE_ X-MS-Office365-Filtering-Correlation-Id: 2c5ac8b2-eaeb-4850-7974-08def7eed90b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700016|376014|23010399003|1800799024|82310400026|6133799003|4143699003|10067099003|56012099006|11063799006|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)(36860700016)(376014)(23010399003)(1800799024)(82310400026)(6133799003)(4143699003)(10067099003)(56012099006)(11063799006)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: GDj2KAk3XXd1k5ENmUJJQm1I7LEYOvaHyA8wZYvrxnnA12xMsq3QKdfwXrkSAZyHJCvOQcXxIqreV8QCHtVC/KAzPPCqyelC7OPUxqczjHse6Ycx2L8VRHYzcHUO9bvMFe4J5M21tjmecSxUrOj1ffj9g9p8Qhld/wiH5xPd9S+NUGs8pEkSzdaPcCYHuYM3QEBR7Gq6T+T2amaqd5vRb8imfVUlu2ZP1JZ2orKMA0YS42+TBJtai3qpV+J8rmCmvJj9mftJqIfdXIsa85lnYks5k/wQaS8Q3Bzm/+REefKCTvAezxEqTUh02LEwh8mxkUzZfuZwn09yacuLAIoF6I/SwpqIvSVsCHeJjXXw1sTX1gJ13y/XlH0+kj2KZXb6qUjDwSK37P6HrlJL0dQxzPu60859h6nQNGxtNoW9408hZ+ASd6/vV/wNhFwH+q19 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Aug 2026 21:23:54.8010 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2c5ac8b2-eaeb-4850-7974-08def7eed90b 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: CY4PEPF0000EE3A.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB9140 On 2026-08-11 04:21, David Laight wrote: > On Mon, 10 Aug 2026 10:47:06 -0400 > Yazen Ghannam wrote: > >> On Thu, Aug 06, 2026 at 12:01:57PM -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) >>> >>> On a virtualized system, default the value to 1. The issue is seen with >>> Xen, but it could affect other systems. >>> >>> Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: Jason Andryuk >> >> I agree with the idea with some minor feedback below. >> >>> --- >>> 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 ea553267e5fa..c5025e5291b6 100644 >>> --- a/arch/x86/kernel/amd_node.c >>> +++ b/arch/x86/kernel/amd_node.c >>> @@ -286,6 +286,11 @@ static int __init amd_smn_init(void) >>> return -ENOMEM; >>> >>> roots_per_node = num_roots / num_nodes; >>> + if (roots_per_node == 0) { >> >> Can be '!roots_per_node'. >> >>> + if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR)) >>> + pr_err(FW_BUG "Error detecting roots per node.\n"); >>> + roots_per_node = 1; >>> + } >> >> I don't think this is necessarily a Firmware bug. >> >> Likewise, it can be a 'warning' rather than 'error'. I interpret 'error' >> as something known to be incorrect. This was my position before on this >> topic. But the various contrary reports changed my mind (even if they >> come from virtualization). >> >> Furthermore, I think 'warning' is more appropriate. It says "We found >> something unexpected. We're letting you (the user) know about it. And >> we'll mitigate it to avoid an error." >> >> Anyways, I just wanted to write out some thoughts since this topic has >> come up a few times. >> >> Possible rework for the above change: >> >> if (!roots_per_node && !cpu_feature_enabled(X86_FEATURE_HYPERVISOR) >> pr_warn("Expected at least 1 root per AMD node.\n"); >> >> roots_per_node = max(roots_per_node, 1); > > I'd not add the max(), just; > if (!roots_per_node) { > roots_per_node = 1; > if (cpu_feature_enabled(X86_FEATURE_HYPERVISOR) > pr_warn("Expected at least 1 root per AMD node.\n"); > } I prefer this because it puts the special handing inside the check. David, you dropped ! from X86_FEATURE_HYPERVISOR - did you mean that? The intent was to only warn if real hardware doesn't match the expectation. Really, I just want to get this fixed. Thanks, Jason