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client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C Received: from satlexmb07.amd.com (165.204.84.17) by DS2PEPF00003442.mail.protection.outlook.com (10.167.17.69) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9587.10 via Frontend Transport; Tue, 3 Feb 2026 22:24:40 +0000 Received: from dryer.amd.com (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 15.2.2562.17; Tue, 3 Feb 2026 16:24:39 -0600 From: Kim Phillips To: , , , CC: Sean Christopherson , Paolo Bonzini , K Prateek Nayak , "Nikunj A Dadhania" , Tom Lendacky , "Michael Roth" , Borislav Petkov , Borislav Petkov , Naveen Rao , David Kaplan , Kim Phillips Subject: [PATCH v2 2/3] KVM: SEV: Add support for IBPB-on-Entry Date: Tue, 3 Feb 2026 16:24:04 -0600 Message-ID: <20260203222405.4065706-3-kim.phillips@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260203222405.4065706-1-kim.phillips@amd.com> References: <20260203222405.4065706-1-kim.phillips@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: DS2PEPF00003442:EE_|BL4PR12MB9533:EE_ X-MS-Office365-Filtering-Correlation-Id: 14969d09-187c-4944-3a26-08de637305e9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|36860700013|82310400026|13003099007; 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charset="utf-8" AMD EPYC 5th generation and above processors support IBPB-on-Entry for SNP guests. By invoking an Indirect Branch Prediction Barrier (IBPB) on VMRUN, old indirect branch predictions are prevented from influencing indirect branches within the guest. SNP guests may choose to enable IBPB-on-Entry by setting SEV_FEATURES bit 21 (IbpbOnEntry). Host support for IBPB on Entry is indicated by CPUID Fn8000_001F[IbpbOnEntry], bit 31. If supported, indicate support for IBPB on Entry in sev_supported_vmsa_features bit 23 (IbpbOnEntry). For more info, refer to page 615, Section 15.36.17 "Side-Channel Protection", AMD64 Architecture Programmer's Manual Volume 2: System Programming Part 2, Pub. 24593 Rev. 3.42 - March 2024 (see Link). Link: https://bugzilla.kernel.org/attachment.cgi?id=3D306250 Signed-off-by: Kim Phillips Reviewed-by: Tom Lendacky --- v2: Added Tom's Reviewed-by. v1: https://lore.kernel.org/kvm/20260126224205.1442196-3-kim.phillips@amd.c= om/ arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/include/asm/svm.h | 1 + arch/x86/kvm/svm/sev.c | 9 ++++++++- 3 files changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpuf= eatures.h index c01fdde465de..3ce5dff36f78 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -459,6 +459,7 @@ #define X86_FEATURE_ALLOWED_SEV_FEATURES (19*32+27) /* Allowed SEV Feature= s */ #define X86_FEATURE_SVSM (19*32+28) /* "svsm" SVSM present */ #define X86_FEATURE_HV_INUSE_WR_ALLOWED (19*32+30) /* Allow Write to in-us= e hypervisor-owned pages */ +#define X86_FEATURE_IBPB_ON_ENTRY (19*32+31) /* SEV-SNP IBPB on VM Entry */ =20 /* AMD-defined Extended Feature 2 EAX, CPUID level 0x80000021 (EAX), word = 20 */ #define X86_FEATURE_NO_NESTED_DATA_BP (20*32+ 0) /* No Nested Data Breakpo= ints */ diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h index edde36097ddc..eebc65ec948f 100644 --- a/arch/x86/include/asm/svm.h +++ b/arch/x86/include/asm/svm.h @@ -306,6 +306,7 @@ static_assert((X2AVIC_4K_MAX_PHYSICAL_ID & AVIC_PHYSICA= L_MAX_INDEX_MASK) =3D=3D X2AV #define SVM_SEV_FEAT_ALTERNATE_INJECTION BIT(4) #define SVM_SEV_FEAT_DEBUG_SWAP BIT(5) #define SVM_SEV_FEAT_SECURE_TSC BIT(9) +#define SVM_SEV_FEAT_IBPB_ON_ENTRY BIT(21) =20 #define VMCB_ALLOWED_SEV_FEATURES_VALID BIT_ULL(63) =20 diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index ea515cf41168..8a6d25db0c00 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -3165,8 +3165,15 @@ void __init sev_hardware_setup(void) cpu_feature_enabled(X86_FEATURE_NO_NESTED_DATA_BP)) sev_supported_vmsa_features |=3D SVM_SEV_FEAT_DEBUG_SWAP; =20 - if (sev_snp_enabled && tsc_khz && cpu_feature_enabled(X86_FEATURE_SNP_SEC= URE_TSC)) + if (!sev_snp_enabled) + return; + /* the following feature bit checks are SNP specific */ + + if (tsc_khz && cpu_feature_enabled(X86_FEATURE_SNP_SECURE_TSC)) sev_supported_vmsa_features |=3D SVM_SEV_FEAT_SECURE_TSC; + + if (cpu_feature_enabled(X86_FEATURE_IBPB_ON_ENTRY)) + sev_supported_vmsa_features |=3D SVM_SEV_FEAT_IBPB_ON_ENTRY; } =20 void sev_hardware_unsetup(void) --=20 2.43.0