linux-kernel - Re: [PATCHv3 13/13] x86/mm: Offset boot-time paging mode switching cost

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Date:   Mon, 7 Aug 2017 08:54:45 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 13/13] x86/mm: Offset boot-time paging mode switching
 cost

> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 077e8b45784c..6f92e61d35ac 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -274,7 +274,7 @@ return_from_SYSCALL_64:
>  	 * depending on paging mode) in the address.
>  	 */
>  #ifdef CONFIG_X86_5LEVEL
> -	testl	$1, p4d_folded(%rip)
> +	testl	$1, __p4d_folded(%rip)
>  	jnz	1f


You can use

	ALTERNATIVE "", "jmp 1f", X86_FEATURE_LA57

to do the patching.

-Andi