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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Jan 2026 22:42:34.3956 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5f16bdb5-6ecb-4ce5-0fb4-08de5d2c32bd 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: BN2PEPF00004FC1.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB8016 Content-Type: text/plain; charset="utf-8" The SEV-SNP IBPB-on-Entry feature does not require a guest-side implementation. The feature was added in Zen5 h/w, after the first SNP Zen implementation, and thus was not accounted for when the initial set of SNP features were added to the kernel. In its abundant precaution, commit 8c29f0165405 ("x86/sev: Add SEV-SNP guest feature negotiation support") included SEV_STATUS' IBPB-on-Entry bit as a reserved bit, thereby masking guests from using the feature. Unmask the bit, to allow guests to take advantage of the feature on hypervisor kernel versions that support it: Amend the SEV_STATUS MSR SNP_RESERVED_MASK to exclude bit 23 (IbpbOnEntry). Fixes: 8c29f0165405 ("x86/sev: Add SEV-SNP guest feature negotiation suppor= t") Cc: Nikunj A Dadhania Cc: Tom Lendacky CC: Borislav Petkov (AMD) CC: Michael Roth Cc: stable@kernel.org Signed-off-by: Kim Phillips Reviewed-by: Nikunj A Dadhania Reviewed-by: Tom Lendacky --- arch/x86/boot/compressed/sev.c | 1 + arch/x86/coco/sev/core.c | 1 + arch/x86/include/asm/msr-index.h | 5 ++++- 3 files changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c index c8c1464b3a56..2b639703b8dd 100644 --- a/arch/x86/boot/compressed/sev.c +++ b/arch/x86/boot/compressed/sev.c @@ -188,6 +188,7 @@ bool sev_es_check_ghcb_fault(unsigned long address) MSR_AMD64_SNP_RESERVED_BIT13 | \ MSR_AMD64_SNP_RESERVED_BIT15 | \ MSR_AMD64_SNP_SECURE_AVIC | \ + MSR_AMD64_SNP_RESERVED_BITS19_22 | \ MSR_AMD64_SNP_RESERVED_MASK) =20 #ifdef CONFIG_AMD_SECURE_AVIC diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c index 9ae3b11754e6..13f608117411 100644 --- a/arch/x86/coco/sev/core.c +++ b/arch/x86/coco/sev/core.c @@ -122,6 +122,7 @@ static const char * const sev_status_feat_names[] =3D { [MSR_AMD64_SNP_VMSA_REG_PROT_BIT] =3D "VMSARegProt", [MSR_AMD64_SNP_SMT_PROT_BIT] =3D "SMTProt", [MSR_AMD64_SNP_SECURE_AVIC_BIT] =3D "SecureAVIC", + [MSR_AMD64_SNP_IBPB_ON_ENTRY_BIT] =3D "IBPBOnEntry", }; =20 /* diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-in= dex.h index 4d3566bb1a93..9016a6b00bc7 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -735,7 +735,10 @@ #define MSR_AMD64_SNP_SMT_PROT BIT_ULL(MSR_AMD64_SNP_SMT_PROT_BIT) #define MSR_AMD64_SNP_SECURE_AVIC_BIT 18 #define MSR_AMD64_SNP_SECURE_AVIC BIT_ULL(MSR_AMD64_SNP_SECURE_AVIC_BIT) -#define MSR_AMD64_SNP_RESV_BIT 19 +#define MSR_AMD64_SNP_RESERVED_BITS19_22 GENMASK_ULL(22, 19) +#define MSR_AMD64_SNP_IBPB_ON_ENTRY_BIT 23 +#define MSR_AMD64_SNP_IBPB_ON_ENTRY BIT_ULL(MSR_AMD64_SNP_IBPB_ON_ENTRY_BI= T) +#define MSR_AMD64_SNP_RESV_BIT 24 #define MSR_AMD64_SNP_RESERVED_MASK GENMASK_ULL(63, MSR_AMD64_SNP_RESV_BIT) #define MSR_AMD64_SAVIC_CONTROL 0xc0010138 #define MSR_AMD64_SAVIC_EN_BIT 0 --=20 2.43.0 From nobody Sat Feb 7 12:19:29 2026 Received: from CY7PR03CU001.outbound.protection.outlook.com (mail-westcentralusazon11010062.outbound.protection.outlook.com [40.93.198.62]) (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 031DA30AACD; 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Mon, 26 Jan 2026 16:42:45 -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 2/2] KVM: SEV: Add support for IBPB-on-Entry Date: Mon, 26 Jan 2026 16:42:05 -0600 Message-ID: <20260126224205.1442196-3-kim.phillips@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260126224205.1442196-1-kim.phillips@amd.com> References: <20260126224205.1442196-1-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: BN2PEPF00004FBF:EE_|DM4PR12MB6206:EE_ X-MS-Office365-Filtering-Correlation-Id: 56da80d3-1738-4f8a-69c1-08de5d2c3ad1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|82310400026|36860700013|13003099007; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Jan 2026 22:42:47.9511 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 56da80d3-1738-4f8a-69c1-08de5d2c3ad1 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: BN2PEPF00004FBF.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB6206 Content-Type: text/plain; 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 --- 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