linux-kernel - [tip:x86/mm] x86/boot/32: Flip the logic in test_wp

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Message-ID: <tip-952a6c2c094f4eda295f20c42e6e2d73735950fa@git.kernel.org>
Date:   Fri, 31 Mar 2017 03:07:48 -0700
From:   tip-bot for Borislav Petkov <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, bp@...en8.de, jpoimboe@...hat.com,
        hpa@...or.com, mingo@...nel.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, dvlasenk@...hat.com,
        tglx@...utronix.de, brgerst@...il.com, bp@...e.de, luto@...nel.org
Subject: [tip:x86/mm] x86/boot/32: Flip the logic in test_wp_bit()

Commit-ID:  952a6c2c094f4eda295f20c42e6e2d73735950fa
Gitweb:     http://git.kernel.org/tip/952a6c2c094f4eda295f20c42e6e2d73735950fa
Author:     Borislav Petkov <bp@...e.de>
AuthorDate: Thu, 30 Mar 2017 09:44:05 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 31 Mar 2017 08:08:31 +0200

x86/boot/32: Flip the logic in test_wp_bit()

... to have a natural "likely()" in the code flow and thus have the
success case with a branch 99.999% of the times non-taken and function
return code following it instead of jumping to it each time.

This puts the panic() call at the end of the function - it is going to
be practically unreachable anyway.

The C code is a bit more readable too.

No functionality change.

Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: boris.ostrovsky@...cle.com
Cc: jgross@...e.com
Cc: thgarnie@...gle.com
Link: http://lkml.kernel.org/r/20170330080101.ywsf5rg6ilzu4itk@pd.tnic
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/mm/init_32.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 097089a..601b8e0 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -726,19 +726,18 @@ static void __init test_wp_bit(void)
 {
 	char z = 0;
 
-	printk(KERN_INFO
-  "Checking if this processor honours the WP bit even in supervisor mode...");
+	printk(KERN_INFO "Checking if this processor honours the WP bit even in supervisor mode...");
 
 	__set_fixmap(FIX_WP_TEST, __pa_symbol(empty_zero_page), PAGE_KERNEL_RO);
 
-	if (probe_kernel_write((char *)fix_to_virt(FIX_WP_TEST), &z, 1) == 0) {
-		printk(KERN_CONT "No.\n");
-		panic("Linux doesn't support CPUs with broken WP.");
+	if (probe_kernel_write((char *)fix_to_virt(FIX_WP_TEST), &z, 1)) {
+		clear_fixmap(FIX_WP_TEST);
+		printk(KERN_CONT "Ok.\n");
+		return;
 	}
 
-	clear_fixmap(FIX_WP_TEST);
-
-	printk(KERN_CONT "Ok.\n");
+	printk(KERN_CONT "No.\n");
+	panic("Linux doesn't support CPUs with broken WP.");
 }
 
 void __init mem_init(void)