linux-kernel - [PATCH v5 1/2] x86_64: remove not needed clear_page for init_level4

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Message-ID: <1433842921-18055-2-git-send-email-alpopov@ptsecurity.com>
Date:	Tue, 9 Jun 2015 12:42:00 +0300
From:	Alexander Popov <alpopov@...ecurity.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Andy Lutomirski <luto@...nel.org>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Borislav Petkov" <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Kees Cook <keescook@...omium.org>,
	Alexander Popov <alpopov@...ecurity.com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v5 1/2] x86_64: remove not needed clear_page for init_level4_page

From: Andrey Ryabinin <a.ryabinin@...sung.com>

Commit 8170e6bed465 ("x86, 64bit: Use a #PF handler to materialize
early mappings on demand") introduced clear_page(init_level4_pgt);
call in x86_64_start_kernel(). However, this clear_page is useless
because init_level4_page already filled with zeroes in head_64.S

Commit message in 8170e6bed465 says that this clear_page() was
dropped in v7, but it accidentally reappeared in later versions
of that patchset.

Signed-off-by: Andrey Ryabinin <a.ryabinin@...sung.com>
---
 arch/x86/kernel/head64.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 5a46681..6a6eefd 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -177,7 +177,6 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 	 */
 	load_ucode_bsp();
 
-	clear_page(init_level4_pgt);
 	/* set init_level4_pgt kernel high mapping*/
 	init_level4_pgt[511] = early_level4_pgt[511];
 
-- 
1.9.1

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