From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from SN4PR2101CU001.outbound.protection.outlook.com (mail-southcentralusazon11012048.outbound.protection.outlook.com [40.93.195.48]) (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 E2BF13B5305; Wed, 26 Aug 2026 22:52:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.93.195.48 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787784763; cv=fail; b=J8MfHVKjenOObgaavDsGLNSiN/2gy/BgSDAtwmdqc0do/ff27a/bh8GMfO6Jj2n+Q2EioAThPn4uBImRSg0OW+MCvDG1rb1A6E59Uw0D8FcXBaR9SNFfN+68MtnGV4PjTu1+Z/7Aj1VRbgzOJbIwljwkK9FsMaHj0QS1jpvGzMM= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787784763; c=relaxed/simple; bh=ADB4JQxfzU5Dky3RxvOda6q3B3ryFlMj/GCsn3RuJns=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=XMSlnRM+LsYcR+9yi/B9T1q5fDvciC0X9tOClWZwr+8SfX0GsmbHpjK+Jye7PPWBBm//pEE9JUbdDZ68z5qLHqdRTtXp1fSkddhJRYwi73mUIOO244NVCvXb+zWsh3qhFiEt9e3BTuP7UiXUx46E479BNrReFtr9ijjtlQMfYdA= 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=Dms19mh4; arc=fail smtp.client-ip=40.93.195.48 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="Dms19mh4" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=CQ4dNgnMHBTR5xdf84YIgzd3Gy50mOB+INnpE3GJCmdh8vCXhG5iQaVgLCHahKGc7uwtCgDs/H5H035KNy2HNHsncgUJdg5Ot1HIEgq7NejL4V82/tflxOYwgHUUMLbjEHEzKn2Qq0zzknEwZB6SsGyAdvld4EAPWA+aoEu6G3JpKtl0vBN3aiyDECZgqqHes6U2mapd1SjGJ6Z/qKlhD18/dgFy0pvNRJVrPZQ9oRUKktH/3J/gffY563rl9WomSZHtF2Lth7FBgYTRx56PpsV3NiVafJVwmQtkP79zaw+O0QkQugpIbbb3IPtLiPNxnQEoJvYghiWzrtdnQVDkAg== 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=J0sbJO93B4X+/TTz9a/wUcXX6D2HvgNhA+mK6aJegzk=; b=ft3P0F5ZnOS7jWf9CmBNVfl8NvMBCwf6rVegUrlDBI3rwJroMMS9VGaZgnVSGxBZxtFArL5mF+awK1eDPYPjyuVfgCE/rgPJEd3X84wZHkMBtQPpF3SYD653ZpnxhAQd0S0q1UQQxDmzl4onYkvy9aOV+qltLhAYloi0bKIfVOm8PwxlhrRMvEMNnOMYyfDrgmmiN+X1Ru2yqpqzjN52T/l2tTWLt+fHNr7tLITkQUEsFO+a+QW+OED4EQKJYkzGBDLCRlvNvUL3jasJhBZSAgqcHvY+YPlA4h9PvHv4HqgF+1Xc59vzGSzRCaYo9ETBoEx8r9k8sEoZ9ObkmDBPqA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=temperror (sender ip is 149.199.90.133) smtp.rcpttodomain=alien8.de smtp.mailfrom=amd.com; dmarc=temperror action=none 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=J0sbJO93B4X+/TTz9a/wUcXX6D2HvgNhA+mK6aJegzk=; b=Dms19mh4FKnFqzCnRgZYAyoQGM2gpr6zuiCxROCTrm/kDCImtMA3Jqx1s2GZzwxnAi08kwFskrvlqdwo6JisIBDMATIH0hAUQRHJmi4MOYcy+nh0Ds8epa+KW1bZH+owrhiO9uxIdYnmQaTfTtBoXowElIxT/TbC/HisCUUC1XA= Received: from BN9PR03CA0567.namprd03.prod.outlook.com (2603:10b6:408:138::32) by MW4PR12MB7262.namprd12.prod.outlook.com (2603:10b6:303:228::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.360.6; Wed, 26 Aug 2026 22:52:36 +0000 Received: from BN3PEPF00022BDB.namprd03.prod.outlook.com (2603:10b6:408:138:cafe::57) by BN9PR03CA0567.outlook.office365.com (2603:10b6:408:138::32) with Microsoft SMTP Server (version=TLS1_3, cipher=TLS_AES_256_GCM_SHA384) id 15.21.339.12 via Frontend Transport; Wed, 26 Aug 2026 22:52:34 +0000 X-MS-Exchange-Authentication-Results: spf=temperror (sender IP is 149.199.90.133) smtp.mailfrom=amd.com; dkim=none (message not signed) header.d=none;dmarc=temperror action=none header.from=amd.com; Received-SPF: TempError (protection.outlook.com: error in processing during lookup of amd.com: DNS Timeout) Received: from satlexmb07.amd.com (149.199.90.133) by BN3PEPF00022BDB.mail.protection.outlook.com (10.167.248.106) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.360.3 via Frontend Transport; Wed, 26 Aug 2026 22:52:33 +0000 Received: from [10.236.30.85] (10.180.168.240) 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; Wed, 26 Aug 2026 17:52:28 -0500 Message-ID: Date: Wed, 26 Aug 2026 17:52:28 -0500 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 02/10] cpu/bugs: Allow forcing Automatic IBRS with SNP active using spectre_v2=eibrs To: Borislav Petkov CC: , , , , Sean Christopherson , Paolo Bonzini , K Prateek Nayak , Nikunj A Dadhania , Tom Lendacky , Michael Roth , Naveen Rao , David Kaplan , Pawan Gupta , Dave Hansen , , kernel test robot References: <20260804235611.4053375-1-kim.phillips@amd.com> <20260804235611.4053375-3-kim.phillips@amd.com> <20260818232204.GBaoTpHK8k7wD9mMk4@fat_crate.local> Content-Language: en-US From: Kim Phillips In-Reply-To: <20260818232204.GBaoTpHK8k7wD9mMk4@fat_crate.local> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit 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: BN3PEPF00022BDB:EE_|MW4PR12MB7262:EE_ X-MS-Office365-Filtering-Correlation-Id: 2c4d81e9-6071-4635-e931-08df03c4b732 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|82310400026|1800799024|23010399003|36860700016|13003099007|6133799003|10067099003|11063799006|5023799004|56012099006|4143699003|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:satlexmb07.amd.com;PTR:unknown-90-133.xilinx.com;CAT:NONE;SFS:(13230040)(7416014)(376014)(82310400026)(1800799024)(23010399003)(36860700016)(13003099007)(6133799003)(10067099003)(11063799006)(5023799004)(56012099006)(4143699003)(22082099003)(18002099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 8tZ5GS9Bxk8IHON5nNrAlg7rNGh5ukp/AJu/v0HBvbgbKj+qqzD6tJ2wL3N6jRH1V7+Ad3OCQ0kXhHdyv0J9DHi7u4nupbI7vTMCw1Lg9xYsrGsCvnq6AqffhIAvtfgRV1ewl5cKK+ZnKVEuelcNmmjxJIw7K1/A+5cotiZyAU1SnptucEpmdy81W+haCijihSoww4JnngpvVf3UmsB9qi/XlvxVhfp1NXBAMI9+A7TeBo8U/2zXBnObguB/dWhfAbz14xfLsd0r5NIlCGes8IIa4NthfDSKaL9H7wu3t2JUC70gA3mdz0I9W3wI74o8tecWEozFGkNBJ9I+ufWE1PMRD44RSOceNPbX3gnrvptpam2YN2Mlj6aeOJBz8SSft7orQpXO2wYYgkRDoogmhKgf2hc8hzL+FWz+x6v/I4oOr+jNzVqh7rkCUF1XCOBT X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Aug 2026 22:52:33.0155 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2c4d81e9-6071-4635-e931-08df03c4b732 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: BN3PEPF00022BDB.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR12MB7262 On 8/18/26 6:22 PM, Borislav Petkov wrote: > On Tue, Aug 04, 2026 at 06:56:03PM -0500, Kim Phillips wrote: > > Please fix all your subject prefixes: it should be "x86/bugs:" > > The tip tree preferred format for patch subject prefixes is > 'subsys/component:', e.g. 'x86/apic:', 'x86/mm/fault:', 'sched/fair:', > 'genirq/core:'. Please do not use file names or complete file paths as > prefix. 'git log path/to/file' should give you a reasonable hint in most > cases. > >> spectre_v2=eibrs currently enables retpolines when SNP is enabled, >> instead of AutoIBRS (EIBRS) because the commit that disabled >> AutoIBRS if SNP is enabled stopped short of enabling >> X86_FEATURE_IBRS_ENHANCED. >> >> Change the logic to enable X86_FEATURE_IBRS_ENHANCED, and move the >> decision to switch to retpolines in the default/"auto" case in >> spectre_v2_select_mitigation(). This allows the existing >> spectre_v2=eibrs logic to work as intended. > So this whole hoopla is just to be able to select =eibrs in SNP guests, *and*, > in doing so, cause a performance loss. I.e., shoot oneself in the foot. > > Or is there another, better reason which wants this? It's not in guests, it's in the hypervisor, and in addition to making spectre_v2=eibrs work as advertised, it also fixes emitting the misleading "EIBRS selected but CPU doesn't have Enhanced or Automatic IBRS." on AutoIBRS-capable CPUs. Shooting oneself in the foot is subjective depending on what performance users want and whether in userspace or not, esp. considering this series also enables spectre_v2=ibrs on SNP hosts. >> Fixes: acaa4b5c4c85 ("x86/speculation: Do not enable Automatic IBRS if SEV-SNP is enabled") >> Reported-by: Tom Lendacky >> Cc: Borislav Petkov (AMD) >> Cc: Pawan Gupta >> Cc: Dave Hansen >> Cc: Sean Christopherson >> Cc: stable@kernel.org > Definitely not stable material. If at all. >> Reported-by: kernel test robot >> Closes: https://lore.kernel.org/oe-kbuild-all/202603121136.bc8zNsHS-lkp@intel.com/ > It doesn't close that - that link points to something which is not upstream. > These get dropped in v5 - please switch to reviewing v5 now: https://lore.kernel.org/lkml/20260826223510.3669875-1-kim.phillips@amd.com/ Thanks, Kim