diff mbox series

[v6,2/6] init_on_alloc: Optimize static branches

Message ID 20210315180229.1224655-3-keescook@chromium.org (mailing list archive)
State New, archived
Headers show
Series Optionally randomize kernel stack offset each syscall | expand

Commit Message

Kees Cook March 15, 2021, 6:02 p.m. UTC 
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@google.com>
Link: https://lore.kernel.org/lkml/CAG_fn=X0DVwqLaHJTO6Jw7TGcMSm77GKHinrd0m_6y0SzWOrFA@mail.gmail.com/
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/mm.h | 10 ++++++----
 mm/page_alloc.c    |  4 ++--
 mm/slab.h          |  6 ++++--
 3 files changed, 12 insertions(+), 8 deletions(-)

Comments

Kees Cook March 15, 2021, 10:15 p.m. UTC | #1 
On Mon, Mar 15, 2021 at 11:02:25AM -0700, Kees Cook wrote:
> diff --git a/mm/slab.h b/mm/slab.h
> index 076582f58f68..b0977d525c06 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_FREE_DEFAULT_ON,

Gah, this should be CONFIG_INIT_ON_ALLOC_DEFAULT_ON.

I'll see if there are any more comments before sending a v7...

-Kees

> +				&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
>
Vlastimil Babka March 18, 2021, 12:46 p.m. UTC | #2 
On 3/15/21 7:02 PM, Kees Cook wrote:
> 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@google.com>
> Link: https://lore.kernel.org/lkml/CAG_fn=X0DVwqLaHJTO6Jw7TGcMSm77GKHinrd0m_6y0SzWOrFA@mail.gmail.com/
> Signed-off-by: Kees Cook <keescook@chromium.org>

For the fixed version

Acked-by: Vlastimil Babka <vbabka@suse.cz>
diff mbox series

Patch

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..b0977d525c06 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_FREE_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;