[Xen-devel] [PATCH RFC V3 6/8] jump_label: add arch_jump_label_transform_static() to optimise non-live code updates

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

When updating a newly loaded module, the code is definitely not yet
executing on any processor, so it can be updated with no need for any
heavyweight synchronization.

This patch adds arch_jump_label_static() which is implemented as
arch_jump_label_transform() by default, but architectures can override
it if it avoids, say, a call to stop_machine().

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 include/linux/jump_label.h |    2 ++
 kernel/jump_label.c        |   14 +++++++++++++-
 2 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 12e804e..56594e4 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -45,6 +45,8 @@ extern void jump_label_lock(void);
 extern void jump_label_unlock(void);
 extern void arch_jump_label_transform(struct jump_entry *entry,
                                      enum jump_label_type type);
+extern void arch_jump_label_transform_static(struct jump_entry *entry,
+                                            enum jump_label_type type);
 extern int jump_label_text_reserved(void *start, void *end);
 extern void jump_label_inc(struct jump_label_key *key);
 extern void jump_label_dec(struct jump_label_key *key);
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 059202d5..f0a9bef 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -104,6 +104,18 @@ static int __jump_label_text_reserved(struct jump_entry 
*iter_start,
        return 0;
 }
 
+/* 
+ * Update code which is definitely not currently executing.
+ * Architectures which need heavyweight synchronization to modify
+ * running code can override this to make the non-live update case
+ * cheaper.
+ */
+void __weak arch_jump_label_transform_static(struct jump_entry *entry,
+                                           enum jump_label_type type)
+{
+       arch_jump_label_transform(entry, type); 
+}
+
 static void __jump_label_update(struct jump_label_key *key,
                                struct jump_entry *entry,
                                struct jump_entry *stop, int enable)
@@ -208,7 +220,7 @@ void jump_label_apply_nops(struct module *mod)
                return;
 
        for (iter = iter_start; iter < iter_stop; iter++)
-               arch_jump_label_transform(iter, JUMP_LABEL_DISABLE);
+               arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 }
 
 static int jump_label_add_module(struct module *mod)
-- 
1.7.6.4


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