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From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@elte.hu>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jason Baron <jbaron@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Frederic Weisbecker <fweisbec@gmail.com>
Subject: [PATCH 2/5] x86/jump-label: Do not bother updating nops if they are correct
Date: Fri, 27 Jan 2012 15:14:44 -0500	[thread overview]
Message-ID: <20120127202031.234193929@goodmis.org> (raw)
In-Reply-To: 20120127201442.080360013@goodmis.org

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From: Steven Rostedt <srostedt@redhat.com>

On boot up, the jump label init function scans all the jump label locations
and converts them to the best nop for the machine. If the nop is already
the ideal nop, do not bother with changing it.

Cc: Jason Baron <jbaron@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 arch/x86/kernel/jump_label.c |   20 +++++++++++++++++++-
 1 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index ea9d5f2f..0f4c6ba 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -53,7 +53,25 @@ void arch_jump_label_transform(struct jump_entry *entry,
 void arch_jump_label_transform_static(struct jump_entry *entry,
 				      enum jump_label_type type)
 {
-	__jump_label_transform(entry, type, text_poke_early);
+	static int once;
+	static int update;
+
+	/*
+	 * This function is called at boot up and when modules are
+	 * first loaded. Check if the default nop, the one that is
+	 * inserted at compile time, is the ideal nop. If it is, then
+	 * we do not need to update the nop, and we can leave it as is.
+	 * If it is not, then we need to update the nop to the ideal nop.
+	 */
+	if (!once) {
+		unsigned char default_nop[] = { JUMP_LABEL_INIT_NOP };
+		const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
+		once++;
+		if (memcmp(ideal_nop, default_nop, 5) != 0)
+			update = 1;
+	}
+	if (update)
+		__jump_label_transform(entry, type, text_poke_early);
 }
 
 #endif
-- 
1.7.8.3



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  parent reply	other threads:[~2012-01-27 20:20 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-27 20:14 [PATCH 0/5] [GIT PULL] x86/jump label: Paranoid checks and 2 or 5 byte nops Steven Rostedt
2012-01-27 20:14 ` [PATCH 1/5] x86/jump-label: Use best default nops for inital jump label calls Steven Rostedt
2012-01-27 20:27   ` H. Peter Anvin
2012-01-27 20:49     ` Steven Rostedt
2012-01-27 20:50       ` H. Peter Anvin
2012-01-27 21:00         ` Steven Rostedt
2012-01-30 21:05       ` Michal Marek
2012-01-27 20:14 ` Steven Rostedt [this message]
2012-01-27 20:34   ` [PATCH 2/5] x86/jump-label: Do not bother updating nops if they are correct Andrew Morton
2012-01-27 20:42     ` Steven Rostedt
2012-01-27 20:14 ` [PATCH 3/5] x86/jump-label: Add safety checks to jump label conversions Steven Rostedt
2012-01-27 20:14 ` [PATCH 4/5] jump labels: Add infrastructure to update jump labels at compile time Steven Rostedt
2012-01-27 20:14 ` [PATCH 5/5] jump labels/x86: Use etiher 5 byte or 2 byte jumps Steven Rostedt
2012-01-27 21:47   ` Steven Rostedt

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