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x86/fred: Fix early boot failures on SEV-ES/SNP guests

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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: 14619d912b ("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
This commit is contained in:
Nikunj A Dadhania
2026-03-18 07:56:54 +00:00
committed by Borislav Petkov (AMD)
parent 411df123c0
commit 3645eb7e39
2 changed files with 20 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
arch/x86/coco/sev/noinstr.c
View File

@@ -121,6 +121,9 @@ noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state)
WARN_ON(!irqs_disabled());
if (!sev_cfg.ghcbs_initialized)
return boot_ghcb;
data = this_cpu_read(runtime_data);
ghcb = &data->ghcb_page;
@@ -164,6 +167,9 @@ noinstr void __sev_put_ghcb(struct ghcb_state *state)
WARN_ON(!irqs_disabled());
if (!sev_cfg.ghcbs_initialized)
return;
data = this_cpu_read(runtime_data);
ghcb = &data->ghcb_page;

14
arch/x86/entry/entry_fred.c
View File

@@ -177,6 +177,16 @@ static noinstr void fred_extint(struct pt_regs *regs)
}
}
#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 */
@@ -207,6 +217,10 @@ static noinstr void fred_hwexc(struct pt_regs *regs, unsigned long error_code)
#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);
}