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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: quoted-printable 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 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 Signed-off-by: Jason Andryuk Reviewed-by: Yazen Ghannam --- 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..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; =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."); + roots_per_node =3D 1; + } =20 count =3D 0; node =3D 0; --=20 2.55.0 From nobody Mon Sep 28 23:55:26 2026 Received: from SN4PR2101CU001.outbound.protection.outlook.com (mail-southcentralusazon11012045.outbound.protection.outlook.com [40.93.195.45]) (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 16ED83EC689; Fri, 14 Aug 2026 21:43:34 +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 v2 2/2] x86/amd_node: Remove smn_exclusive Date: Fri, 14 Aug 2026 17:42:53 -0400 Message-ID: <20260814214255.83127-3-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: quoted-printable X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN3PEPF0000B072:EE_|SJ2PR12MB9113:EE_ X-MS-Office365-Filtering-Correlation-Id: d1840b14-65a7-42ef-774a-08defa4d122b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|82310400026|36860700016|376014|22082099003|18002099003|11063799006|6133799003|56012099006|10067099003; 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)(1800799024)(23010399003)(82310400026)(36860700016)(376014)(22082099003)(18002099003)(11063799006)(6133799003)(56012099006)(10067099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: jGzkZRg8AaoUUwdIKvpxejFX08/6RlQLeOABeqHshxR8YT6JYqy8g2rfe0OfHPMSqWh/lZo+QK+KWAT0gfhj6MPm8QZ1om2/4rkjsh06VTWgdRrKK8rcWhQHl5A8ipAXKggnnmXfmr6A4e37nh34Dgdbzl+MuJy/jJhdo6n3Od46m0gt+r95QtmSu+AO4UquM61m4LfqpbiR4K6N/moyc+geZwyUGXtG7i/z6ny7Wsz6U/+PI7lWdG/whSkxV+nZY5pUVM6gVylsqiz3+s5WDyv1yx1V2XLAV7P3QLv8cM6nF7+dMZfnlMaXUvWdq2c2dD36ZePDCVo/ZYLh8oINdlvCK6In4fef7BFAa8FQRc/nH4zhgZyBdaeAG0OQz8hzM7TVqJ3QTnbBMxAKqeVgonYL44Dq5ynvsl5vc2e3ybbredd+LBLO2BtatXRovOTQ X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Aug 2026 21:43:25.7029 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d1840b14-65a7-42ef-774a-08defa4d122b 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: BN3PEPF0000B072.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB9113 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. 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 c3e214925d9c..14104f8c5d64 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