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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=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by DS2PEPF0000343C.mail.protection.outlook.com (10.167.18.39) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.7228.16 via Frontend Transport; Fri, 26 Jan 2024 04:47:04 +0000 Received: from localhost (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.34; Thu, 25 Jan 2024 22:47:04 -0600 From: Michael Roth To: CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Kim Phillips , Dave Hansen Subject: [PATCH v2 02/25] x86/speculation: Do not enable Automatic IBRS if SEV SNP is enabled Date: Thu, 25 Jan 2024 22:11:02 -0600 Message-ID: <20240126041126.1927228-3-michael.roth@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20240126041126.1927228-1-michael.roth@amd.com> References: <20240126041126.1927228-1-michael.roth@amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS2PEPF0000343C:EE_|BL1PR12MB5995:EE_ X-MS-Office365-Filtering-Correlation-Id: 75451af7-cfca-47bc-91bb-08dc1e29d834 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Jan 2024 04:47:04.8802 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 75451af7-cfca-47bc-91bb-08dc1e29d834 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=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: DS2PEPF0000343C.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5995 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1789127598877440605 X-GMAIL-MSGID: 1789127598877440605 From: Kim Phillips Without SEV-SNP, Automatic IBRS protects only the kernel. But when SEV-SNP is enabled, the Automatic IBRS protection umbrella widens to all host-side code, including userspace. This protection comes at a cost: reduced userspace indirect branch performance. To avoid this performance loss, don't use Automatic IBRS on SEV-SNP hosts. Fall back to retpolines instead. Signed-off-by: Kim Phillips Acked-by: Dave Hansen [mdr: squash in changes from review discussion] Signed-off-by: Michael Roth --- arch/x86/kernel/cpu/common.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 8f367d376520..6b253440ea72 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1355,8 +1355,13 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) /* * AMD's AutoIBRS is equivalent to Intel's eIBRS - use the Intel feature * flag and protect from vendor-specific bugs via the whitelist. + * + * Don't use AutoIBRS when SNP is enabled because it degrades host + * userspace indirect branch performance. */ - if ((ia32_cap & ARCH_CAP_IBRS_ALL) || cpu_has(c, X86_FEATURE_AUTOIBRS)) { + if ((ia32_cap & ARCH_CAP_IBRS_ALL) || + (cpu_has(c, X86_FEATURE_AUTOIBRS) && + !cpu_feature_enabled(X86_FEATURE_SEV_SNP))) { setup_force_cpu_cap(X86_FEATURE_IBRS_ENHANCED); if (!cpu_matches(cpu_vuln_whitelist, NO_EIBRS_PBRSB) && !(ia32_cap & ARCH_CAP_PBRSB_NO))