linux-kernel - Re: [PATCH] x86/fred: Fix early boot failures on SEV-ES/SNP guests

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Message-ID: <37d4fd07-02e4-4492-b5e0-3618208b5e5c@amd.com>
Date: Fri, 6 Feb 2026 09:01:59 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: kernel test robot <lkp@...el.com>, <linux-kernel@...r.kernel.org>,
	<kvm@...r.kernel.org>, <bp@...en8.de>, <thomas.lendacky@....com>
CC: <llvm@...ts.linux.dev>, <oe-kbuild-all@...ts.linux.dev>,
	<tglx@...nel.org>, <mingo@...hat.com>, <dave.hansen@...ux.intel.com>,
	<hpa@...or.com>, <xin@...or.com>, <seanjc@...gle.com>, <pbonzini@...hat.com>,
	<x86@...nel.org>, <jon.grimm@....com>, <stable@...r.kernel.org>
Subject: Re: [PATCH] x86/fred: Fix early boot failures on SEV-ES/SNP guests


On 2/5/2026 4:11 PM, kernel test robot wrote:
> Hi Nikunj,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on 3c2ca964f75460093a8aad6b314a6cd558e80e66]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Nikunj-A-Dadhania/x86-fred-Fix-early-boot-failures-on-SEV-ES-SNP-guests/20260205-131359
> base:   3c2ca964f75460093a8aad6b314a6cd558e80e66
> patch link:    https://lore.kernel.org/r/20260205051030.1225975-1-nikunj%40amd.com
> patch subject: [PATCH] x86/fred: Fix early boot failures on SEV-ES/SNP guests
> config: x86_64-kexec (https://download.01.org/0day-ci/archive/20260205/202602051859.vGTf24Nk-lkp@intel.com/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260205/202602051859.vGTf24Nk-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202602051859.vGTf24Nk-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>    arch/x86/entry/entry_fred.c:213:11: error: call to undeclared function 'user_exc_vmm_communication'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>      213 |                         return user_exc_vmm_communication(regs, error_code);
>          |                                ^
>>> arch/x86/entry/entry_fred.c:213:4: warning: void function 'fred_hwexc' should not return a value [-Wreturn-mismatch]
>      213 |                         return user_exc_vmm_communication(regs, error_code);
>          |                         ^      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    arch/x86/entry/entry_fred.c:215:11: error: call to undeclared function 'kernel_exc_vmm_communication'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>      215 |                         return kernel_exc_vmm_communication(regs, error_code);
>          |                                ^
>    arch/x86/entry/entry_fred.c:215:4: warning: void function 'fred_hwexc' should not return a value [-Wreturn-mismatch]
>      215 |                         return kernel_exc_vmm_communication(regs, error_code);
>          |                         ^      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    2 warnings and 2 errors generated.
> 
> 

Thanks for the report, below patch should solve the problem:

diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c
index 7a8659f19441..9946b9e96692 100644
--- a/arch/x86/entry/entry_fred.c
+++ b/arch/x86/entry/entry_fred.c
@@ -208,11 +208,15 @@ 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:
 		if (user_mode(regs))
 			return user_exc_vmm_communication(regs, error_code);
 		else
 			return kernel_exc_vmm_communication(regs, error_code);
+#endif
+
 	default: return fred_bad_type(regs, error_code);
 	}
 


Regards
Nikunj