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

From: Borislav Petkov <bp@alien8.de>
To: Ard Biesheuvel <ardb+git@google.com>
Cc: linux-kernel@vger.kernel.org, Ard Biesheuvel <ardb@kernel.org>,
	Kevin Loughlin <kevinloughlin@google.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Dionna Glaze <dionnaglaze@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Justin Stitt <justinstitt@google.com>,
	Kees Cook <keescook@chromium.org>,
	Brian Gerst <brgerst@gmail.com>,
	linux-arch@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH v4 04/11] x86/startup_64: Defer assignment of 5-level paging global variables
Date: Tue, 20 Feb 2024 19:45:13 +0100	[thread overview]
Message-ID: <20240220184513.GAZdTzOQN33Nccwkno@fat_crate.local> (raw)
In-Reply-To: <20240213124143.1484862-17-ardb+git@google.com>

On Tue, Feb 13, 2024 at 01:41:48PM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.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@kernel.org>
> ---
>  arch/x86/kernel/head64.c | 44 +++++++-------------
>  1 file changed, 14 insertions(+), 30 deletions(-)

Whoops:

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