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helo=lists.xenproject.org; Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C From: Penny Zheng To: CC: , , , Penny Zheng , "Mario Limonciello" , Yazen Ghannam , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , , Subject: [PATCH v1 1/2] x86/amd_node: avoid divide-by-zero in amd_smn_init() under Xen dom0 Date: Wed, 6 May 2026 13:55:18 +0800 Message-ID: <20260506055528.476493-2-penny.zheng@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260506055528.476493-1-penny.zheng@amd.com> References: <20260506055528.476493-1-penny.zheng@amd.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: satlexmb08.amd.com (10.181.42.217) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN1PEPF00036F3F:EE_|SA5PPFD911547FB:EE_ X-MS-Office365-Filtering-Correlation-Id: 8b51d57d-91d4-4d7f-2040-08deab343453 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|36860700016|82310400026|56012099003|18002099003|22082099003; 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)(376014)(36860700016)(82310400026)(56012099003)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: ++9QBZu2qMm3vsjUnSr6e/ceM3c0R7gkHyjkPA3d39jAg4M4Pa7Qsqf233LskQMdMpJ55jhPitso3p9oVCLA3rOg68QI2Z/75Cps89DZL2FwE053LrUHxaQ4OiZZS0Gqv1rgtktWwkjn3uDLEcenMs5Z3jaGjEAQYaB/Qi392OueHGbE0JmpXmLAg4U21UNd/9Y2EKwUR5EHYaBG7fCPGDXFN04TwyoWlGyrZhj7vr1akeJOnni2JY6NqugsvmZNnKCfgomEU0QwTyess8jlgJvD+mWXIIVlhDBpPPMznA8qkIe7xIQ6tJM+MRt7cxHt0MpuC2y4lrAXtpwo74IggP4eyEr33IYWUVry2Gsxmqf2lt36dIIhebhGF6z7HlYbDiNNV+Xo4W+G+HMypvfagZGULW14DH5D+Yeza3FzAB+08/8fbqLqoXC+wStUWgQa X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2026 05:56:23.7040 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8b51d57d-91d4-4d7f-2040-08deab343453 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: SN1PEPF00036F3F.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA5PPFD911547FB X-purgate-ID: tlsNG-720697/1778046989-83961161-0B5678D3/0/0 X-purgate-type: clean X-purgate-size: 1563 X-ZohoMail-DKIM: pass (identity @amd.com) X-ZM-MESSAGEID: 1778047025960154100 Content-Type: text/plain; charset="utf-8" To prevent each dom0 vCPU from looking like an SMT sibling of another vCPU, Xen synthesizes guest x2APIC IDs as vcpu_index * 2. While the spacing every vCPU's APIC ID by 2 can therefore push the IDs past the package-field boundary, making Linux see more packages than the platform actually has. amd_num_nodes() inherits that inflated count, so num_nodes can exceed num_roots (the number of AMD root complexes discovered on the PCI bus). The subsequent roots_per_node =3D num_roots / num_nodes; ... count % roots_per_node ... then divides by zero in amd_smn_init(). Reject num_roots < num_nodes explicitly and bail out with -ENODEV. Signed-off-by: Penny Zheng --- arch/x86/kernel/amd_node.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c index 0be01725a2a4..c896060fe0df 100644 --- a/arch/x86/kernel/amd_node.c +++ b/arch/x86/kernel/amd_node.c @@ -282,6 +282,18 @@ static int __init amd_smn_init(void) return -ENODEV; =20 num_nodes =3D amd_num_nodes(); + + /* + * Xen dom0's synthetic APIC IDs may imply more nodes than host + * bridges visible in PCI config space. Bail out to avoid a + * divide-by-zero when later computing roots_per_node. + */ + if (num_roots < num_nodes) { + pr_debug("AMD root count (%u) < node count (%u); skipping SMN init\n", + num_roots, num_nodes); + return -ENODEV; + } + amd_roots =3D kzalloc_objs(*amd_roots, num_nodes); if (!amd_roots) return -ENOMEM; --=20 2.43.0 From nobody Mon May 25 00:58:14 2026 Received: from CH4PR04CU002.outbound.protection.outlook.com (mail-northcentralusazon11013059.outbound.protection.outlook.com [40.107.201.59]) (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 6BC65306B31 for ; Wed, 6 May 2026 05:56:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.201.59 ARC-Seal: i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778046991; cv=fail; b=QpPxeN31jlKFlvRiWIH+EbQxP/5s+bElfKV+1wKcx5PJUPgsnAVbJNDDviwv2rY0wC5ljleIuMaO99Pvs8l0M3XIcKz5yjlihPKvKzuiBBC29HvIPKRfeH/Am6dQjlSp3iOtb7QpLZPYsTlkIQF0aLE8o+Aefum11Q3/jaL35TI= ARC-Message-Signature: i=2; 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Peter Anvin" , , Subject: [PATCH v1 2/2] x86/amd_node: reject SMN access when amd_smn_init() did not complete Date: Wed, 6 May 2026 13:55:19 +0800 Message-ID: <20260506055528.476493-3-penny.zheng@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260506055528.476493-1-penny.zheng@amd.com> References: <20260506055528.476493-1-penny.zheng@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-ClientProxiedBy: satlexmb08.amd.com (10.181.42.217) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN1PEPF00036F3F:EE_|DS0PR12MB7947:EE_ X-MS-Office365-Filtering-Correlation-Id: 4b19c043-6684-4e11-fa26-08deab3434d1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|1800799024|36860700016|376014|22082099003|56012099003|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)(1800799024)(36860700016)(376014)(22082099003)(56012099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: mXlVNtNoo1kzNJh+imVuy1XCt55xpUiuUDxjjkMAl8pFT9/CRKPgt1GQRf/r9cBPnpteeU83OnlPkexoYYHuoyoXhpCSA1GVDnt9A3oiMtwz35sRv1XOlAdkLXTGZOH0b42+qZuSpy77jjNRbJ6kYRl4sW+ht86bNLSYR0WdAjeTLZeE2Ppr/axbgyxZQ0jRfvoN3AkIKyNeIROrCvqmp0nfTV8BjGcuzvTVW7jmHWENvOjcPvILp32Ugs9sLim4E8WlTOebbQchJddVJD9c7rKKg0Le3aIkstFutYHxDBfrja/VcZeofuF02gjI5bRxL1CCQMifEBdrFbv2NcP8ObmmFL+WdxF/YHnkaCUT8BSNqWufN4FeRbwMY1a3wqXP5kZQuhS9+7Mx04hBQcJRdGiVL7/EAY63PtI5steD0dMCSvTalNSdig/3tugytaRL X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2026 05:56:24.5348 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 4b19c043-6684-4e11-fa26-08deab3434d1 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: SN1PEPF00036F3F.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB7947 Content-Type: text/plain; charset="utf-8" amd_smn_init() can fail early (e.g. -ENODEV when num_roots < num_nodes, -ENOMEM from kcalloc) without setting smn_exclusive. In that case amd_roots stays NULL, but the existing __amd_smn_rw() ordering dereferenced amd_roots[node] before the smn_exclusive guard. The first SMN consumer (e.g. amd_pmc_probe -> amd_smn_read) then hit a NULL pointer dereference instead of getting -ENODEV. Move the smn_exclusive check to the very beginning of __amd_smn_rw() so a failed init is rejected before any deref. Also zero *value in amd_smn_read() on the error path so callers never read uninitialized data via the subsequent PCI_POSSIBLE_ERROR() check. Signed-off-by: Penny Zheng --- arch/x86/kernel/amd_node.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c index c896060fe0df..cb9ed022c53c 100644 --- a/arch/x86/kernel/amd_node.c +++ b/arch/x86/kernel/amd_node.c @@ -88,6 +88,9 @@ static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32= address, u32 *value, b struct pci_dev *root; int err =3D -ENODEV; =20 + if (!smn_exclusive) + return err; + if (node >=3D amd_num_nodes()) return err; =20 @@ -95,9 +98,6 @@ static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32= address, u32 *value, b if (!root) return err; =20 - if (!smn_exclusive) - return err; - guard(mutex)(&smn_mutex); =20 err =3D pci_write_config_dword(root, i_off, address); @@ -116,6 +116,11 @@ int __must_check amd_smn_read(u16 node, u32 address, u= 32 *value) { int err =3D __amd_smn_rw(SMN_INDEX_OFFSET, SMN_DATA_OFFSET, node, address= , value, false); =20 + if (err) { + *value =3D 0; + return err; + } + if (PCI_POSSIBLE_ERROR(*value)) { err =3D -ENODEV; *value =3D 0; --=20 2.43.0