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

From: Peter Zijlstra
Date: Fri Jun 28 2019 - 09:36:25 EST


This allows architectures to have variable sized jumps.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
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;