[PATCH 6.19 241/342] x86/fred: Fix early boot failures on SEV-ES/SNP guests

Greg Kroah-Hartman
2026-03-31T16:41:38Z

From: Nikunj A Dadhania <nikunj@amd.com>

commit 3645eb7e3915990a149460c151a00894cb586253 upstream.

FRED-enabled SEV-(ES,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

* Early FRED #VC exceptions attempt to use uninitialized per-CPU GHCBs
instead of boot_ghcb

Add X86_TRAP_VC case to fred_hwexc() with a new exc_vmm_communication()
function that provides the unified entry point FRED requires, dispatching
to existing user/kernel handlers based on privilege level. The function is
already declared via DECLARE_IDTENTRY_VC().

Fix early GHCB access by falling back to boot_ghcb in
__sev_{get,put}_ghcb() when per-CPU GHCBs are not yet initialized.

Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: <stable@kernel.org> # 6.12+
Link: https://patch.msgid.link/20260318075654.1792916-4-nikunj@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/coco/sev/noinstr.c | 6 ++++++
arch/x86/entry/entry_fred.c | 14 ++++++++++++++
2 files changed, 20 insertions(+)

--- a/arch/x86/coco/sev/noinstr.c
+++ b/arch/x86/coco/sev/noinstr.c
@@ -120,6 +120,9 @@ noinstr struct ghcb *__sev_get_ghcb(stru

WARN_ON(!irqs_disabled());

+ if (!sev_cfg.ghcbs_initialized)
+ return boot_ghcb;
+
data = this_cpu_read(runtime_data);
ghcb = &data->ghcb_page;

@@ -163,6 +166,9 @@ noinstr void __sev_put_ghcb(struct ghcb_

WARN_ON(!irqs_disabled());

+ if (!sev_cfg.ghcbs_initialized)
+ return;
+
data = this_cpu_read(runtime_data);
ghcb = &data->ghcb_page;

--- a/arch/x86/entry/entry_fred.c
+++ b/arch/x86/entry/entry_fred.c
@@ -176,6 +176,16 @@ static noinstr void fred_extint(struct p
}
}

+#ifdef CONFIG_AMD_MEM_ENCRYPT
+noinstr void exc_vmm_communication(struct pt_regs *regs, unsigned long error_code)
+{
+ if (user_mode(regs))
+ return user_exc_vmm_communication(regs, error_code);
+ else
+ return kernel_exc_vmm_communication(regs, error_code);
+}
+#endif
+
static noinstr void fred_hwexc(struct pt_regs *regs, unsigned long error_code)
{
/* Optimize for #PF. That's the only exception which matters performance wise */
@@ -206,6 +216,10 @@ static noinstr void fred_hwexc(struct pt
#ifdef CONFIG_X86_CET
case X86_TRAP_CP: return exc_control_protection(regs, error_code);
#endif
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+ case X86_TRAP_VC: return exc_vmm_communication(regs, error_code);
+#endif
+
default: return fred_bad_type(regs, error_code);
}