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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: quoted-printable 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: MinabvoZEjpY7j9pT4LTZ3tN4dO6EwaH46lZGL2sMkcA7kcivDOIOdOUlCY4QtwMFz9b1OQmJEc9g7MT8ABXgBRRx1IgdKlMnGH2OlWOFZmyZI2eZOuUL9sYJFhx/d5RCCe4SbpDXqwRmzR3lXZiNW2tKcAxsd5e6FA5XzglnHsawZOwf4Br1VpocfID7lsVzP9eo9T48s9XDiCA1p5M6hNGAFvvHFLzdd9+7B3jzb0BeiCdWiTlDLjYZvXKCo6iueIpl3KSzbzRgtvZU7Ltep2o2FW0V1Wd/UZgsO3JxNUt0t7k2HPKY3duuWqagH83y/FJr9obx07K+WiSH8CCdjWyrtu1XMKMetYMeurpFTpHnaus+N7641VQsyZMMe7Wd/BbJ909JRtqDz9Keu2FdpbITQ2eW7nYnK/BXCC4D3IjOCgJXPssMGAsBIIANzVTofKZ6vITL4SKoJXtwt6l5huLqjKVcMMKWnvRQx6fZqJMO49VyPqWwelMzU2FULj1223GwmwgXkW0o7gZPpIQ7sTZKqrXjMITNku2oTi0xcn4Gw63/LRtrGDWbbnf1QTa8Bizb0w31d0YRVqqqwy9Z+OGo6wcvQBa0/YgEUcJOUqDUIGZrVxMuyhH5CPX9iiBJubhKNFSP6YyyexrUZ1NPHwXDaHWhR/DMfUE9U1Se6sdzWDCuD01HS9QlwpTWPyBxFe+cILjctHSx1r8JI34EQ== 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 Content-Type: text/plain; charset="utf-8" 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 =3D=3D 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 "=3D=3D 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; =20 roots_per_node =3D 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 =3D 1; + } =20 count =3D 0; node =3D 0; --=20 2.55.0 From nobody Mon Sep 28 05:43:07 2026 Received: from CH4PR04CU002.outbound.protection.outlook.com (mail-northcentralusazon11013039.outbound.protection.outlook.com [40.107.201.39]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A49A448F83E; Tue, 25 Aug 2026 21:48:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; 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Peter Anvin" , Ingo Molnar , "Mario Limonciello" , Thomas Gleixner , , Yazen Ghannam CC: Jason Andryuk , , Penny Zheng , , "Mario Limonciello (AMD)" Subject: [PATCH v3 2/2] x86/amd_node: Remove smn_exclusive Date: Tue, 25 Aug 2026 17:48:03 -0400 Message-ID: <20260825214805.39148-3-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: quoted-printable X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN2PEPF000044AB:EE_|CH3PR12MB9097:EE_ X-MS-Office365-Filtering-Correlation-Id: 486ddfc3-9471-499b-cbb1-08df02f29a15 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|36860700016|376014|1800799024|82310400026|6133799003|10067099003|56012099006|11063799006|22082099003|18002099003; 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:satlexmb08.amd.com;PTR:unknown-90-133.xilinx.com;CAT:NONE;SFS:(13230040)(23010399003)(36860700016)(376014)(1800799024)(82310400026)(6133799003)(10067099003)(56012099006)(11063799006)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: D3rSzBIBiCCktAN+QLT9Z6moT4RK/joKyVjRQsyqxfgJvfjUm0Y5qRJyWJ4cVXnR4VEylpITI5+J+YTu/qRy804ZML/5gRcOBS6Ad2D0SVmiJBkJeIwjov4zd3iUYsoJKDi98ZjQakKw89OZTyzBN5t5bLz9XuSo37sl1lIIiqjuf0ojmEFzjQRn/hA1J3dlRF3GRE3HsIANb2NF3qh2hZ8/pDa+Gts6S6H5MtnbtlCVxx3F/JQOErCgeA8/IiRn5u224d167uEveMh9Ek0qN/48w2eEUcI5L+wNwi5VF/2ZTOio6DVs64Qa2zolOn7GCDkLN7ZIWxw9peqMWK3fUjAofMYw5FhQX2Q7Gw3RdofbcBabQLpGRt1q764hVUxjdvi/TowvrSsljUgQauKAK4Z8DnRzntCJhhSiKkuySfUYlwbQgQOuDsDHBi9Xjg4+ X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Aug 2026 21:48:29.8596 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 486ddfc3-9471-499b-cbb1-08df02f29a15 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=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN2PEPF000044AB.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB9097 Content-Type: text/plain; charset="utf-8" amd_smn_read/write() are exported functions around __amd_smn_rw(), so they are always available even if amd_smn_init() fails. smn_exclusive would prevent access to __amd_smn_rw(), but it is placed too late. If amd_smn_init() failed, amd_roots is NULL and __amd_smn_rw() will fault over it. Replace smn_exclusive with directly checking amd_roots to avoid the NULL pointer dereference. commit 83518453074d ("x86/amd_node: Add SMN offsets to exclusive region access") added smn_exclusive which indicated the calls to pci_request_config_region_exclusive() succeeded to prevent userspace access. commit 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching") re-ordered initialization so pci_request_config_region_exclusive() is called earlier and a failure exits amd_smn_init() before allocating amd_roots. Setting smn_exclusive moved to the end of amd_smn_init(), after amd_roots is allocated. smn_exclusive became redundant to amd_roots and can be removed. Add a comment stating how amd_roots replaces smn_exclusive's purpose. Fixes: 77466b798d59 ("x86/amd_node: Remove dependency on AMD_NB") Cc: stable@vger.kernel.org Reviewed-by: Yazen Ghannam Reviewed-by: Mario Limonciello (AMD) Signed-off-by: Jason Andryuk --- Fixes is the introduction of amd_roots, which could be a NULL deref. v3: No change v2: R-b Yazen and Mario Add comment about amd_root taking smn_exclusive's purpose to indicate userspace access is prevented. Expand commit message --- arch/x86/kernel/amd_node.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c index 408b9fd48349..833e5eda5d91 100644 --- a/arch/x86/kernel/amd_node.c +++ b/arch/x86/kernel/amd_node.c @@ -38,7 +38,6 @@ static struct pci_dev **amd_roots; =20 /* Protect the PCI config register pairs used for SMN. */ static DEFINE_MUTEX(smn_mutex); -static bool smn_exclusive; =20 #define SMN_INDEX_OFFSET 0x60 #define SMN_DATA_OFFSET 0x64 @@ -91,11 +90,15 @@ static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u= 32 address, u32 *value, b if (node >=3D amd_num_nodes()) return err; =20 - root =3D amd_roots[node]; - if (!root) + /* + * non-NULL amd_roots indicates pci_request_config_region_exclusive() + * succeeded and userspace cannot access the registers. + */ + if (!amd_roots) return err; =20 - if (!smn_exclusive) + root =3D amd_roots[node]; + if (!root) return err; =20 guard(mutex)(&smn_mutex); @@ -313,8 +316,6 @@ static int __init amd_smn_init(void) debugfs_create_file("value", 0600, debugfs_dir, NULL, &smn_value_fops); } =20 - smn_exclusive =3D true; - return 0; } =20 --=20 2.55.0