Later commits will cause objtool to warn about non __ro_after_init static
keys being used in .noinstr sections in order to safely defer instruction
patching IPIs targeted at NOHZ_FULL CPUs.
Two such keys currently exist: mds_idle_clear and __sched_clock_stable,
which can both be modified at runtime.
As discussed at LPC 2024 during the realtime micro-conference, modifying
these specific keys incurs additional interference (SMT hotplug) or can
even be downright incompatible with NOHZ_FULL (unstable TSC).
Suppressing the IPI associated with modifying such keys is thus a minor
concern wrt NOHZ_FULL interference, so add a jump type that will be
leveraged by both the kernel (to know not to defer the IPI) and objtool (to
know not to generate the aforementioned warning).
Signed-off-by: Valentin Schneider <vschn...@redhat.com>
---
include/linux/jump_label.h | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index f5a2727ca4a9a..93e729545b941 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -200,7 +200,8 @@ struct module;
#define JUMP_TYPE_FALSE 0UL
#define JUMP_TYPE_TRUE 1UL
#define JUMP_TYPE_LINKED 2UL
-#define JUMP_TYPE_MASK 3UL
+#define JUMP_TYPE_FORCEFUL 4UL
+#define JUMP_TYPE_MASK 7UL
static __always_inline bool static_key_false(struct static_key *key)
{
@@ -244,12 +245,15 @@ extern enum jump_label_type jump_label_init_type(struct
jump_entry *entry);
* raw value, but have added a BUILD_BUG_ON() to catch any issues in
* jump_label_init() see: kernel/jump_label.c.
*/
-#define STATIC_KEY_INIT_TRUE \
- { .enabled = { 1 }, \
- { .type = JUMP_TYPE_TRUE } }
-#define STATIC_KEY_INIT_FALSE \
- { .enabled = { 0 }, \
- { .type = JUMP_TYPE_FALSE } }
+#define __STATIC_KEY_INIT(_true, force)
\
+ { .enabled = { _true }, \
+ { .type = (_true ? JUMP_TYPE_TRUE : JUMP_TYPE_FALSE) | \
+ (force ? JUMP_TYPE_FORCEFUL : 0UL)} }
+
+#define STATIC_KEY_INIT_TRUE __STATIC_KEY_INIT(true, false)
+#define STATIC_KEY_INIT_FALSE __STATIC_KEY_INIT(false, false)
+#define STATIC_KEY_INIT_TRUE_FORCE __STATIC_KEY_INIT(true, true)
+#define STATIC_KEY_INIT_FALSE_FORCE __STATIC_KEY_INIT(false, true)
#else /* !CONFIG_JUMP_LABEL */
@@ -369,6 +373,8 @@ struct static_key_false {
#define STATIC_KEY_TRUE_INIT (struct static_key_true) { .key =
STATIC_KEY_INIT_TRUE, }
#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key =
STATIC_KEY_INIT_FALSE, }
+#define STATIC_KEY_TRUE_FORCE_INIT (struct static_key_true) { .key =
STATIC_KEY_INIT_TRUE_FORCE, }
+#define STATIC_KEY_FALSE_FORCE_INIT (struct static_key_false){ .key =
STATIC_KEY_INIT_FALSE_FORCE, }
#define DEFINE_STATIC_KEY_TRUE(name) \
struct static_key_true name = STATIC_KEY_TRUE_INIT
@@ -376,6 +382,9 @@ struct static_key_false {
#define DEFINE_STATIC_KEY_TRUE_RO(name) \
struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
+#define DEFINE_STATIC_KEY_TRUE_FORCE(name) \
+ struct static_key_true name = STATIC_KEY_TRUE_FORCE_INIT
+
#define DECLARE_STATIC_KEY_TRUE(name) \
extern struct static_key_true name
@@ -385,6 +394,9 @@ struct static_key_false {
#define DEFINE_STATIC_KEY_FALSE_RO(name) \
struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
+#define DEFINE_STATIC_KEY_FALSE_FORCE(name) \
+ struct static_key_false name = STATIC_KEY_FALSE_FORCE_INIT
+
#define DECLARE_STATIC_KEY_FALSE(name) \
extern struct static_key_false name
--
2.43.0
