linux-kernel - Re: [PATCH v4 04/11] x86/startup_64: Defer assignment of 5-level paging global variables

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Date: Wed, 21 Feb 2024 00:33:08 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, Kevin Loughlin <kevinloughlin@...gle.com>, 
	Tom Lendacky <thomas.lendacky@....com>, Dionna Glaze <dionnaglaze@...gle.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>, linux-arch@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: Re: [PATCH v4 04/11] x86/startup_64: Defer assignment of 5-level
 paging global variables

On Tue, 20 Feb 2024 at 19:45, Borislav Petkov <bp@...en8.de> wrote:
>
> On Tue, Feb 13, 2024 at 01:41:48PM +0100, Ard Biesheuvel wrote:
> > From: Ard Biesheuvel <ardb@...nel.org>
> >
> > Assigning the 5-level paging related global variables from the earliest
> > C code using explicit references that use the 1:1 translation of memory
> > is unnecessary, as the startup code itself does not rely on them to
> > create the initial page tables, and this is all it should be doing. So
> > defer these assignments to the primary C entry code that executes via
> > the ordinary kernel virtual mapping.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> > ---
> >  arch/x86/kernel/head64.c | 44 +++++++-------------
> >  1 file changed, 14 insertions(+), 30 deletions(-)
>
> Whoops:
>

Right, this is the same issue as in #11 - in both cases, the extern
declaration of __pgtable_l5_enabled needs to be visible regardless of
CONFIG_X86_5LEVEL.

I'll fix both cases for v5.

> arch/x86/kernel/head64.c: In function ‘x86_64_start_kernel’:
> arch/x86/kernel/head64.c:442:17: error: ‘__pgtable_l5_enabled’ undeclared (first use in this function); did you mean ‘pgtable_l5_enabled’?
>   442 |                 __pgtable_l5_enabled    = 1;
>       |                 ^~~~~~~~~~~~~~~~~~~~
>       |                 pgtable_l5_enabled
> arch/x86/kernel/head64.c:442:17: note: each undeclared identifier is reported only once for each function it appears in
> make[4]: *** [scripts/Makefile.build:243: arch/x86/kernel/head64.o] Error 1
> make[3]: *** [scripts/Makefile.build:481: arch/x86/kernel] Error 2
> make[2]: *** [scripts/Makefile.build:481: arch/x86] Error 2
> make[2]: *** Waiting for unfinished jobs....
> make[1]: *** [/mnt/kernel/kernel/2nd/linux/Makefile:1921: .] Error 2
> make: *** [Makefile:240: __sub-make] Error 2
>
>
> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette