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Date: Mon, 7 Aug 2017 08:54:45 -0700
From: Andi Kleen <ak@linux.intel.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Dave Hansen <dave.hansen@intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCHv3 13/13] x86/mm: Offset boot-time paging mode switching
 cost
Message-ID: <20170807155445.GG3946@tassilo.jf.intel.com>
References: <20170807141451.80934-1-kirill.shutemov@linux.intel.com>
 <20170807141451.80934-14-kirill.shutemov@linux.intel.com>
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> 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