linux-kernel - Re: [PATCH v7 9/9] x86/startup_64: Drop global variables keeping track of LA57 state

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Message-ID: <20240301192017.GOZeIqcbI9S69zdBYW@fat_crate.local>
Date: Fri, 1 Mar 2024 20:20:17 +0100
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.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>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH v7 9/9] x86/startup_64: Drop global variables keeping
 track of LA57 state

On Tue, Feb 27, 2024 at 04:19:17PM +0100, Ard Biesheuvel wrote:
> +	asm(ALTERNATIVE_TERNARY(
> +		"movq %%cr4, %[reg] \n\t btl %[la57], %k[reg]" CC_SET(c),
> +		%P[feat], "stc", "clc")
> +		: [reg] "=&r" (r), CC_OUT(c) (ret)
> +		: [feat] "i"  (X86_FEATURE_LA57),
> +		  [la57] "i"  (X86_CR4_LA57_BIT)
> +		: "cc");
> +
> +	return ret;

Yeah, I said this is creative but an alternative here looks like an
overkill.

Can we use a RIP_REL_REF(global var) instead pls?

Thx.

-- 
Regards/Gruss,
    Boris.

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