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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 BN2PEPF000055DF.mail.protection.outlook.com (10.167.245.9) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9587.0 via Frontend Transport; Thu, 5 Feb 2026 05:10:50 +0000 Received: from gomati.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; Wed, 4 Feb 2026 23:10:46 -0600 From: Nikunj A Dadhania To: , , , CC: , , , , , , , , , , Subject: [PATCH] x86/fred: Fix early boot failures on SEV-ES/SNP guests Date: Thu, 5 Feb 2026 05:10:30 +0000 Message-ID: <20260205051030.1225975-1-nikunj@amd.com> X-Mailer: git-send-email 2.48.1 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: BN2PEPF000055DF:EE_|DS0PR12MB6463:EE_ X-MS-Office365-Filtering-Correlation-Id: 6be46e69-9e2f-4c89-6252-08de6474ee2c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|82310400026|1800799024|7416014|376014; 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charset="utf-8" FRED enabled SEV-ES and SNP guests fail to boot due to the following issues in the early boot sequence: * FRED does not have a #VC exception handler in the dispatch logic * For secondary CPUs, FRED is enabled before setting up the FRED MSRs, and console output triggers a #VC which cannot be handled * Early FRED #VC exceptions should use boot_ghcb until per-CPU GHCBs are initialized Fix these issues to ensure SEV-ES/SNP guests can handle #VC exceptions correctly during early boot when FRED is enabled. Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code") Cc: stable@vger.kernel.org # 6.9+ Signed-off-by: Nikunj A Dadhania --- Reason to add stable tag: With FRED support for SVM here=20 https://lore.kernel.org/kvm/20260129063653.3553076-1-shivansh.dhiman@amd.co= m, SVM and SEV guests running 6.9 and later kernels will support FRED. However, *SEV-ES and SNP guests cannot support FRED* and will fail to boot with the following error: [ 0.005144] Using GB pages for direct mapping [ 0.008402] Initialize FRED on CPU0 qemu-system-x86_64: cpus are not resettable, terminating Three problems were identified as detailed in the commit message above and is fixed with this patch. I would like the patch to be backported to the LTS kernels (6.12 and 6.18) = to ensure SEV-ES and SNP guests running these stable kernel versions can boot with FRED enabled on FRED-enabled hypervisors. --- arch/x86/coco/sev/noinstr.c | 6 ++++++ arch/x86/entry/entry_fred.c | 5 +++++ arch/x86/kernel/fred.c | 14 +++++++++++--- 3 files changed, 22 insertions(+), 3 deletions(-) diff --git a/arch/x86/coco/sev/noinstr.c b/arch/x86/coco/sev/noinstr.c index 9d94aca4a698..5afd663a1c21 100644 --- a/arch/x86/coco/sev/noinstr.c +++ b/arch/x86/coco/sev/noinstr.c @@ -121,6 +121,9 @@ noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *= state) =20 WARN_ON(!irqs_disabled()); =20 + if (!sev_cfg.ghcbs_initialized) + return boot_ghcb; + data =3D this_cpu_read(runtime_data); ghcb =3D &data->ghcb_page; =20 @@ -164,6 +167,9 @@ noinstr void __sev_put_ghcb(struct ghcb_state *state) =20 WARN_ON(!irqs_disabled()); =20 + if (!sev_cfg.ghcbs_initialized) + return; + data =3D this_cpu_read(runtime_data); ghcb =3D &data->ghcb_page; =20 diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c index a9b72997103d..7a8659f19441 100644 --- a/arch/x86/entry/entry_fred.c +++ b/arch/x86/entry/entry_fred.c @@ -208,6 +208,11 @@ static noinstr void fred_hwexc(struct pt_regs *regs, u= nsigned long error_code) #ifdef CONFIG_X86_CET case X86_TRAP_CP: return exc_control_protection(regs, error_code); #endif + case X86_TRAP_VC: + if (user_mode(regs)) + return user_exc_vmm_communication(regs, error_code); + else + return kernel_exc_vmm_communication(regs, error_code); default: return fred_bad_type(regs, error_code); } =20 diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c index e736b19e18de..8cf4da546a8e 100644 --- a/arch/x86/kernel/fred.c +++ b/arch/x86/kernel/fred.c @@ -27,9 +27,6 @@ EXPORT_PER_CPU_SYMBOL(fred_rsp0); =20 void cpu_init_fred_exceptions(void) { - /* When FRED is enabled by default, remove this log message */ - pr_info("Initialize FRED on CPU%d\n", smp_processor_id()); - /* * If a kernel event is delivered before a CPU goes to user level for * the first time, its SS is NULL thus NULL is pushed into the SS field @@ -70,6 +67,17 @@ void cpu_init_fred_exceptions(void) /* Use int $0x80 for 32-bit system calls in FRED mode */ setup_clear_cpu_cap(X86_FEATURE_SYSFAST32); setup_clear_cpu_cap(X86_FEATURE_SYSCALL32); + + /* + * For secondary processors, FRED bit in CR4 gets enabled in cr4_init() + * and FRED MSRs are not configured till the end of this function. For + * SEV-ES and SNP guests, any console write before the FRED MSRs are + * setup will cause a #VC and cannot be handled. Move the pr_info to + * the end of this function. + * + * When FRED is enabled by default, remove this log message + */ + pr_info("Initialized FRED on CPU%d\n", smp_processor_id()); } =20 /* Must be called after setup_cpu_entry_areas() */ base-commit: 3c2ca964f75460093a8aad6b314a6cd558e80e66 --=20 2.48.1