[RFC][PATCH 7/8] jump_label, x86: Introduce jump_entry_size()

[Peter Zijlstra <peterz@infradead.org>]

This allows architectures to have variable sized jumps.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/jump_label.h |    4 ++--
 arch/x86/kernel/jump_label.c      |    8 ++++++++
 include/linux/jump_label.h        |    9 +++++++++
 kernel/jump_label.c               |    2 +-
 4 files changed, 20 insertions(+), 3 deletions(-)

--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -4,8 +4,6 @@
 
 #define HAVE_JUMP_LABEL_BATCH
 
-#define JUMP_LABEL_NOP_SIZE 5
-
 #ifdef CONFIG_X86_64
 # define STATIC_KEY_NOP2 P6_NOP2
 # define STATIC_KEY_NOP5 P6_NOP5_ATOMIC
@@ -55,6 +53,8 @@ static __always_inline bool arch_static_
 	return true;
 }
 
+extern int arch_jump_entry_size(struct jump_entry *entry);
+
 #else	/* __ASSEMBLY__ */
 
 .macro STATIC_BRANCH_FALSE_LIKELY target, key
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -32,6 +32,14 @@ static inline bool __jump_disp_is_byte(s
 	return false;
 }
 
+int arch_jump_entry_size(struct jump_entry *entry)
+{
+	s32 disp = jump_entry_target(entry) - jump_entry_code(entry);
+	if (__jump_disp_is_byte(disp))
+		return JMP8_INSN_SIZE;
+	return JMP32_INSN_SIZE;
+}
+
 static int __jump_label_set_jump_code(struct jump_entry *entry,
 				      enum jump_label_type type,
 				      union jump_code_union *code,
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -176,6 +176,15 @@ static inline void jump_entry_set_init(s
 	entry->key |= 2;
 }
 
+static inline int jump_entry_size(struct jump_entry *entry)
+{
+#ifdef JUMP_LABEL_NOP_SIZE
+	return JUMP_LABEL_NOP_SIZE;
+#else
+	return arch_jump_entry_size(entry);
+#endif
+}
+
 #endif
 #endif
 
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -309,7 +309,7 @@ EXPORT_SYMBOL_GPL(jump_label_rate_limit)
 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 {
 	if (jump_entry_code(entry) <= (unsigned long)end &&
-	    jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
+	    jump_entry_code(entry) + jump_entry_size(entry) > (unsigned long)start)
 		return 1;
 
 	return 0;