linux-kernel - Re: sev_es_trampoline_start undefined symbol referenced errors during kunit run

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Message-ID: <20250414230047.GHZ_2Tnysv9zCD6-tX@fat_crate.local>
Date: Tue, 15 Apr 2025 01:00:47 +0200
From: Borislav Petkov <bp@...en8.de>
To: Shuah Khan <skhan@...uxfoundation.org>
Cc: thomas.lendacky@....com, David Gow <davidgow@...gle.com>,
	"x86@...nel.org" <x86@...nel.org>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: sev_es_trampoline_start undefined symbol referenced errors
 during kunit run

On Mon, Apr 14, 2025 at 04:28:44PM -0600, Shuah Khan wrote:
> Hi Tom,
> 
> I have been seeing sev_es_trampoline_start undefined symbol referenced errors
> during the following kunit test runs.
> 
> ./tools/testing/kunit/kunit.py run --arch x86_64
> ./tools/testing/kunit/kunit.py run --alltests --arch x86_64
> 
> The error is here:
> 
> ERROR:root:ld:arch/x86/realmode/rm/realmode.lds:236: undefined symbol `sev_es_trampoline_start' referenced in expression
> make[6]: *** [../arch/x86/realmode/rm/Makefile:49: arch/x86/realmode/rm/realmode.elf] Error 1
> make[5]: *** [../arch/x86/realmode/Makefile:22: arch/x86/realmode/rm/realmode.bin] Error 2
> make[4]: *** [../scripts/Makefile.build:461: arch/x86/realmode] Error 2
> 
> I made time to look into this error.
> 
> sev_es_trampoline_start is referenced in arch/x86/coco/sev/core.c twice:
> 
> - To override start_ip in  wakeup_cpu_via_vmgexit()
> - In sev_es_setup_ap_jump_table() to compute startup_ip
> 
> sev_es_trampoline_start is defined if CONFIG_AMD_MEM_ENCRYPT is enabled
> and all other references to it are under ifdef CONFIG_AMD_MEM_ENCRYPT
> conditional except the two in arch/x86/coco/sev/core.c
> 
> git grep sev_es_trampoline_start
> arch/x86/coco/sev/core.c:       start_ip = real_mode_header->sev_es_trampoline_start;
> arch/x86/coco/sev/core.c:       startup_ip = (u16)(rmh->sev_es_trampoline_start -
> arch/x86/include/asm/realmode.h:        u32     sev_es_trampoline_start;
> arch/x86/realmode/rm/header.S:  .long   pa_sev_es_trampoline_start
> arch/x86/realmode/rm/trampoline_64.S:SYM_CODE_START(sev_es_trampoline_start)
> arch/x86/realmode/rm/trampoline_64.S:SYM_CODE_END(sev_es_trampoline_start)
> 
> Why are these references not under ifdef CONFIG_AMD_MEM_ENCRYPT conditional?

obj-$(CONFIG_AMD_MEM_ENCRYPT)   += sev/

in arch/x86/coco/Makefile

The real problem looks like that pasyms.h thing which gets included at the end
of realmode.lds and which contains that symbol.

How exactly can this be reproduced? Exact steps please.

Thx.

-- 
Regards/Gruss,
    Boris.

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