[PATCH v8 2/6] init_on_alloc: Optimize static branches

[Kees Cook]

The state of CONFIG_INIT_ON_ALLOC_DEFAULT_ON (and ...ON_FREE...) did not
change the assembly ordering of the static branches: they were always out
of line. Use the new jump_label macros to check the CONFIG settings to
default to the "expected" state, which slightly optimizes the resulting
assembly code.

Reviewed-by: Alexander Potapenko <glider at google.com>
Link: https://lore.kernel.org/lkml/CAG_fn=X0DVwqLaHJTO6Jw7TGcMSm77GKHinrd0m_6y0SzWOrFA@mail.gmail.com/
Acked-by: Vlastimil Babka <vbabka at suse.cz>
Link: https://lore.kernel.org/lkml/5d626b9b-5355-be94-e8e2-1be47f880f30@suse.cz
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 include/linux/mm.h | 10 ++++++----
 mm/page_alloc.c    |  4 ++--
 mm/slab.h          |  6 ++++--
 3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 77e64e3eac80..2ccd856ac0d1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2871,18 +2871,20 @@ static inline void kernel_poison_pages(struct page *page, int numpages) { }
 static inline void kernel_unpoison_pages(struct page *page, int numpages) { }
 #endif
 
-DECLARE_STATIC_KEY_FALSE(init_on_alloc);
+DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc);
 static inline bool want_init_on_alloc(gfp_t flags)
 {
-	if (static_branch_unlikely(&init_on_alloc))
+	if (static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
+				&init_on_alloc))
 		return true;
 	return flags & __GFP_ZERO;
 }
 
-DECLARE_STATIC_KEY_FALSE(init_on_free);
+DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
 static inline bool want_init_on_free(void)
 {
-	return static_branch_unlikely(&init_on_free);
+	return static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON,
+				   &init_on_free);
 }
 
 extern bool _debug_pagealloc_enabled_early;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3e4b29ee2b1e..267c04b8911d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -167,10 +167,10 @@ unsigned long totalcma_pages __read_mostly;
 
 int percpu_pagelist_fraction;
 gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
-DEFINE_STATIC_KEY_FALSE(init_on_alloc);
+DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc);
 EXPORT_SYMBOL(init_on_alloc);
 
-DEFINE_STATIC_KEY_FALSE(init_on_free);
+DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
 EXPORT_SYMBOL(init_on_free);
 
 static bool _init_on_alloc_enabled_early __read_mostly
diff --git a/mm/slab.h b/mm/slab.h
index 076582f58f68..774c7221efdc 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -601,7 +601,8 @@ static inline void cache_random_seq_destroy(struct kmem_cache *cachep) { }
 
 static inline bool slab_want_init_on_alloc(gfp_t flags, struct kmem_cache *c)
 {
-	if (static_branch_unlikely(&init_on_alloc)) {
+	if (static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
+				&init_on_alloc)) {
 		if (c->ctor)
 			return false;
 		if (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON))
@@ -613,7 +614,8 @@ static inline bool slab_want_init_on_alloc(gfp_t flags, struct kmem_cache *c)
 
 static inline bool slab_want_init_on_free(struct kmem_cache *c)
 {
-	if (static_branch_unlikely(&init_on_free))
+	if (static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON,
+				&init_on_free))
 		return !(c->ctor ||
 			 (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)));
 	return false;
-- 
2.25.1