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Date: Wed, 7 Feb 2024 14:29:22 +0100
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 v3 06/19] x86/startup_64: Drop global variables keeping
 track of LA57 state
Message-ID: <20240207132922.GSZcOFspSGaVluJo92@fat_crate.local>
References: <20240129180502.4069817-21-ardb+git@google.com>
 <20240129180502.4069817-27-ardb+git@google.com>
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On Mon, Jan 29, 2024 at 07:05:09PM +0100, Ard Biesheuvel wrote:
>  static inline bool pgtable_l5_enabled(void)
>  {
>  	return __pgtable_l5_enabled;
>  }
>  #else
> -#define pgtable_l5_enabled() cpu_feature_enabled(X86_FEATURE_LA57)
> +#define pgtable_l5_enabled() !!(native_read_cr4() & X86_CR4_LA57)
>  #endif /* USE_EARLY_PGTABLE_L5 */

Can we drop this ifdeffery and simply have __pgtable_l5_enabled always
present and contain the correct value?

So that we don't have an expensive CR4 read hidden in
pgtable_l5_enabled()?

For the sake of simplicity, pgtable_l5_enabled() can be defined outside
of CONFIG_X86_5LEVEL and since both vendors support 5level now, might as
well start dropping the CONFIG ifdeffery slowly...

Other than that - a nice cleanup!

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette