powerpc: Add jump label support

This patch adds support for the new "jump label" feature.

Unlike x86 and sparc we just merrily patch the code with no locks etc,
as far as I know this is safe, but I'm not really sure what the x86/sparc
code is protecting against so maybe it's not.

I also don't see any reason for us to implement the poke_early() routine,
even though sparc does.

[BenH: Updated the patch to upstream generic changes]

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/Kconfig

@@ -134,6 +134,7 @@ config PPC
 	select GENERIC_IRQ_SHOW_LEVEL
 	select HAVE_RCU_TABLE_FREE if SMP
 	select HAVE_SYSCALL_TRACEPOINTS
+	select HAVE_ARCH_JUMP_LABEL
 
 config EARLY_PRINTK
 	bool

arch/powerpc/include/asm/jump_label.h

@@ -0,0 +1,47 @@
+#ifndef _ASM_POWERPC_JUMP_LABEL_H
+#define _ASM_POWERPC_JUMP_LABEL_H
+
+/*
+ * Copyright 2010 Michael Ellerman, IBM Corp.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/types.h>
+
+#include <asm/feature-fixups.h>
+
+#define JUMP_ENTRY_TYPE		stringify_in_c(FTR_ENTRY_LONG)
+#define JUMP_LABEL_NOP_SIZE	4
+
+static __always_inline bool arch_static_branch(struct jump_label_key *key)
+{
+	asm goto("1:\n\t"
+		 "nop\n\t"
+		 ".pushsection __jump_table,  \"aw\"\n\t"
+		 ".align 4\n\t"
+		 JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
+		 ".popsection \n\t"
+		 : :  "i" (key) : : l_yes);
+	return false;
+l_yes:
+	return true;
+}
+
+#ifdef CONFIG_PPC64
+typedef u64 jump_label_t;
+#else
+typedef u32 jump_label_t;
+#endif
+
+struct jump_entry {
+	jump_label_t code;
+	jump_label_t target;
+	jump_label_t key;
+	jump_label_t pad;
+};
+
+#endif /* _ASM_POWERPC_JUMP_LABEL_H */

arch/powerpc/kernel/Makefile

@@ -76,6 +76,7 @@ obj-$(CONFIG_MODULES)		+= module.o module_$(CONFIG_WORD_SIZE).o
 obj-$(CONFIG_44x)		+= cpu_setup_44x.o
 obj-$(CONFIG_PPC_FSL_BOOK3E)	+= cpu_setup_fsl_booke.o dbell.o
 obj-$(CONFIG_PPC_BOOK3E_64)	+= dbell.o
+obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
 
 extra-y				:= head_$(CONFIG_WORD_SIZE).o
 extra-$(CONFIG_40x)		:= head_40x.o

arch/powerpc/kernel/jump_label.c

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010 Michael Ellerman, IBM Corp.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/jump_label.h>
+#include <asm/code-patching.h>
+
+void arch_jump_label_transform(struct jump_entry *entry,
+			       enum jump_label_type type)
+{
+	u32 *addr = (u32 *)(unsigned long)entry->code;
+
+	if (type == JUMP_LABEL_ENABLE)
+		patch_branch(addr, entry->target, 0);
+	else
+		patch_instruction(addr, PPC_INST_NOP);
+}