linux-kernel - Re: [PATCH 3/4] x86/asm: Add asm macros for static keys/jump labels

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Date:	Sat, 7 Nov 2015 12:20:59 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andy Lutomirski <luto@...nel.org>
cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 3/4] x86/asm: Add asm macros for static keys/jump
 labels

On Fri, 6 Nov 2015, Andy Lutomirski wrote:

> Unfortunately, these only work if HAVE_JUMP_LABEL.  In principle, we
> could do some serious surgery on the core jump label infrastructure
> to keep the patch infrastructure available on x86 on all builds, but
> that's probably not worth it.

No, but we can be smarter about it. There is nothing which that asm
entry code needs from linux/jump_label.h and asm/jump_label.h execpt
STATIC_KEY_INIT_NOP. Something like the patch below should do the
trick.

Thanks,

	tglx

Index: tip/arch/x86/entry/calling.h
===================================================================
--- tip.orig/arch/x86/entry/calling.h
+++ tip/arch/x86/entry/calling.h
@@ -232,3 +232,22 @@ For 32-bit we have the following convent
 
 #endif /* CONFIG_X86_64 */
 
+/* ASM jump label support */
+#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
+#include <asm/jump_label.h>
+
+	.macro STATIC_CALL_IF_ENABLED fun, key
+	1:
+	jmp.d32		2f
+	call		fun
+	.pushsection __jump_table, "aw"
+	_ASM_ALIGN
+	_ASM_PTR	1b, 2f, \key
+	.popsection
+	2:
+	.endm
+#else
+	.macro STATIC_CALL_IF_ENABLED fun, key
+	call		fun
+	.endm
+#endif
Index: tip/arch/x86/entry/entry_64.S
===================================================================
--- tip.orig/arch/x86/entry/entry_64.S
+++ tip/arch/x86/entry/entry_64.S
@@ -510,7 +510,7 @@ END(irq_entries_start)
 	 */
 	SWAPGS
 #ifdef CONFIG_CONTEXT_TRACKING
-	call enter_from_user_mode
+	STATIC_CALL_IF_ENABLED enter_from_user_mode, context_tracking_enabled
 #endif
 
 1:
@@ -1050,7 +1050,7 @@ ENTRY(error_entry)
 
 .Lerror_entry_from_usermode_after_swapgs:
 #ifdef CONFIG_CONTEXT_TRACKING
-	call enter_from_user_mode
+	STATIC_CALL_IF_ENABLED enter_from_user_mode, context_tracking_enabled
 #endif
 
 .Lerror_entry_done:
Index: tip/arch/x86/include/asm/jump_label.h
===================================================================
--- tip.orig/arch/x86/include/asm/jump_label.h
+++ tip/arch/x86/include/asm/jump_label.h
@@ -1,10 +1,6 @@
 #ifndef _ASM_X86_JUMP_LABEL_H
 #define _ASM_X86_JUMP_LABEL_H
 
-#ifndef __ASSEMBLY__
-
-#include <linux/stringify.h>
-#include <linux/types.h>
 #include <asm/nops.h>
 #include <asm/asm.h>
 
@@ -16,6 +12,11 @@
 # define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC
 #endif
 
+#ifndef __ASSEMBLY__
+
+#include <linux/stringify.h>
+#include <linux/types.h>
+
 static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
 	asm_volatile_goto("1:"


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