From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from SN4PR0501CU005.outbound.protection.outlook.com (mail-southcentralusazon11011034.outbound.protection.outlook.com [40.93.194.34]) (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 460903A5456; Tue, 25 Aug 2026 04:22:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.93.194.34 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787631753; cv=fail; b=R8wv7ns5RgyM/k7dbE1A8sgnUEwG4qcyKZEuGhU/0hPDvKSvTYTCA6PRD3BAW0ueE+apFyWvybNnKtMFbFsTzIlgsjD2uCU3Q/Fp3OOd7Wjk4WFXdeCRFVZ/4QpM9i3PXZMAXAOh/3LDv25i98ov8DcbRDVJG6jX7EQisln98T4= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787631753; c=relaxed/simple; bh=mk1MG7waA2lGn3tit8PaFcz+zel6fPgL8foD07CYqWM=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=VnM8UtNDroxM6jHsxjCOZjTChs3qMhVg9pCR3/Nwmp4FAKH3TbA6Ug11v9go0uGmJuy6IGnOrxt44IxiXf+hZZfP/+GdN8x+QSTQwYXxEzvM9j1Oacg/kcrDAXmsMM+Coqt6TAIK0g8syvg+CwOEnt/P1IH0gQWUoog7EXGDGfg= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com; spf=fail smtp.mailfrom=amd.com; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b=Itf66Ej6; arc=fail smtp.client-ip=40.93.194.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=amd.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b="Itf66Ej6" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=oVpIbh9xU4XrIWsG2KwgyVRXvCl74R4bE5CV/NYF5rawOuHBC5vr9GNgjI+h8FyoDKYpo69fFFc6RghWhdei/7qg4+ZqFCSoECxB0Ur6pceXF+1Q/fSnefUK557/KJKGZUV4BndPRY/I2JaQzTeiCy0BQCGif5KSaDqLsjANm6J4OPEU500ZzJ6u2MjiYY8weejZWfwEMLnaX5Zic7tx5Yk9/k7uUa8HEjS77bp7HTPWH1afT2ZrduZAMbbEpwLZE+JGaDxMcsqoxDeXZsFk7KeoQ0FmePxa92gDA+wAlkBKnl1HIv5xoQ3f8+jYm9SPVb51zhOFGYj/OazbURFO2w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=j5AlrA+0ftlKlJkE8Q7L41s1BR6Db2eJfx/ENO1ZcEk=; b=TPjCQwgvhUu7qD99kwzVAiSymEU2Wky+gRiNq2FoE07ugteSqzNyOJQCyDmsAa2EAsn0dBOVZ/5zNWSt3cFDct490PuYhmVJuRcTuhsdvYqnGhJDOuWndFtOyHWcP9zFBoJkN5sPZ8XBQo7YclGEgQUUiYOn0OVnYdsGBsXvAiSHt6zy37wbU3yo+QyAa2bmWoaYnaQ2mdQcFzqVxN7aW+6y8Ll87Mjqhw3Ac9I9ff0pc3MXjD524//OOs+UqPVNTwnV/4CbJRqqD9PJiPH1SMwO3PEIk1RDJSw2kuupuz+6/NCQkTGfZJCTAOUfdNFDKaOjEYp41AnQxiCb8PiXqg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=softfail (sender ip is 149.199.90.133) smtp.rcpttodomain=alien8.de smtp.mailfrom=amd.com; dmarc=fail (p=quarantine sp=quarantine pct=100) action=quarantine header.from=amd.com; dkim=none (message not signed); arc=none (0) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amd.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=j5AlrA+0ftlKlJkE8Q7L41s1BR6Db2eJfx/ENO1ZcEk=; b=Itf66Ej6kKUhqMv+3p/uGBabzCrOv5iRb/Qq6WxQCOYEBTCOvGa2pQsd7k3DRj2ssEkMmJW3hHTKPq4Jk5nBVSjjGLEhJF15qmbs4R4mnSoB1qFsHfclRdlsEH0qbGEZg6bQ8exML2OGIddAhEUAUeI+sf4E2Zf9uVvjr81M0ag= Received: from SA1P222CA0060.NAMP222.PROD.OUTLOOK.COM (2603:10b6:806:2c1::10) by SA3PR12MB9129.namprd12.prod.outlook.com (2603:10b6:806:397::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.339.12; Tue, 25 Aug 2026 04:22:28 +0000 Received: from SN1PEPF0002BA4E.namprd03.prod.outlook.com (2603:10b6:806:2c1:cafe::8b) by SA1P222CA0060.outlook.office365.com (2603:10b6:806:2c1::10) with Microsoft SMTP Server (version=TLS1_3, cipher=TLS_AES_256_GCM_SHA384) id 15.21.339.12 via Frontend Transport; Tue, 25 Aug 2026 04:22:28 +0000 X-MS-Exchange-Authentication-Results: spf=softfail (sender IP is 149.199.90.133) smtp.mailfrom=amd.com; dkim=none (message not signed) header.d=none;dmarc=fail action=quarantine header.from=amd.com; Received-SPF: SoftFail (protection.outlook.com: domain of transitioning amd.com discourages use of 149.199.90.133 as permitted sender) Received: from satlexmb07.amd.com (149.199.90.133) by SN1PEPF0002BA4E.mail.protection.outlook.com (10.167.242.71) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.360.3 via Frontend Transport; Tue, 25 Aug 2026 04:22:28 +0000 Received: from satlexmb08.amd.com (10.181.42.217) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.45; Mon, 24 Aug 2026 19:04:50 -0500 Received: from [192.168.19.2] (10.180.168.240) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server id 15.2.2562.45 via Frontend Transport; Mon, 24 Aug 2026 19:04:49 -0500 Message-ID: Date: Mon, 24 Aug 2026 20:02:51 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] x86/amd_node: Avoid divide by zero on virtualized systems To: Yazen Ghannam CC: Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Ingo Molnar , "Mario Limonciello" , Thomas Gleixner , , , Penny Zheng , References: <20260814214255.83127-1-jason.andryuk@amd.com> <20260814214255.83127-2-jason.andryuk@amd.com> <49f2616d-e37c-4420-9d8c-81f978386ce6@amd.com> <20260824210411.GA1500179@yaz-khff2.amd.com> Content-Language: en-US From: Jason Andryuk In-Reply-To: <20260824210411.GA1500179@yaz-khff2.amd.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN1PEPF0002BA4E:EE_|SA3PR12MB9129:EE_ X-MS-Office365-Filtering-Correlation-Id: 1249e7c8-39fa-447a-8041-08df02607925 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|36860700016|376014|82310400026|23010399003|4143699003|22082099003|18002099003|11063799006|56012099006|10067099003; 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)(1800799024)(36860700016)(376014)(82310400026)(23010399003)(4143699003)(22082099003)(18002099003)(11063799006)(56012099006)(10067099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: CAvFTqBtnu0Zd6TgvArwSCCayFRIA8BlZBET3Vx67T6bjlJ9XoD9o870pZuSEsoEvr7V3JLMiOCy508bLilj1+8ZnFa1o7r8ZI4N7mitlIPfJWd7KUKpJbrhipJhy5+mQhP1ku5EX3HTQlJpd8Vuu/x1pokS4m3qk7kVKVbVaaidJGEdggSvSnyWrWtIXU4st09eg1h7BJHcCkUKsNnvh+GATORO0385ny71nBwEwB9iggaBCkoxE0IgLuvBqiBfmxdIIpT1CE/r+RIw7erpBz446h3GQRwHgJVf/VkjRJ1Ec9TyllN+qEdW7OTZXhCbnGLZnx7xhPDv0e6TivxKrRHygeGEh1722Mi153diJqDHNot2zPr6ChiFirVbMkviYUdRQSEbAVKAmw30jAE+WQK4B/sPMmPbXNyApJVs7+Gj9Jr7MGOPB3ew8zlZs3Do X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Aug 2026 04:22:28.1581 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 1249e7c8-39fa-447a-8041-08df02607925 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: SN1PEPF0002BA4E.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA3PR12MB9129 On 2026-08-24 17:04, Yazen Ghannam wrote: > On Mon, Aug 24, 2026 at 04:05:40PM -0400, Jason Andryuk wrote: >> Hi, >> >> On 2026-08-14 17:42, 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 >>> Signed-off-by: Jason Andryuk >> >> Any feedback here? >> >> Thanks, >> Jason >> >>> --- >>> 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..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; >>> roots_per_node = 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 = 1; >>> + } > > Minor nit: add a newline after the closing brace. There is an existing newline that is preserved here in the original posting. It seems when I replied in Thunderbird the context here was corrupted. >>> count = 0; >>> node = 0; >> > > Overall, looks good to me. > > Reviewed-by: Yazen Ghannam Thank you. Jason