[PATCH v6 05/29] jump_label: Add annotations for validating noinstr usage
From: Valentin Schneider <vschneid@redhat.com>
Date: 2025-10-10 15:42:15
Also in:
linux-arch, linux-arm-kernel, linux-mm, linux-riscv, lkml, loongarch, rcu
Subsystem:
static branch/call, the rest · Maintainers:
Peter Zijlstra, Josh Poimboeuf, Jason Baron, Alice Ryhl, Linus Torvalds
From: Josh Poimboeuf <jpoimboe@kernel.org> Deferring a code patching IPI is unsafe if the patched code is in a noinstr region. In that case the text poke code must trigger an immediate IPI to all CPUs, which can rudely interrupt an isolated NO_HZ CPU running in userspace. Some noinstr static branches may really need to be patched at runtime, despite the resulting disruption. Add DEFINE_STATIC_KEY_*_NOINSTR() variants for those. They don't do anything special yet; that will come later. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> --- include/linux/jump_label.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index fdb79dd1ebd8c..c4f6240ff4d95 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h@@ -388,6 +388,23 @@ struct static_key_false { #define DEFINE_STATIC_KEY_FALSE_RO(name) \ struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT +/* + * The _NOINSTR variants are used to tell objtool the static key is allowed to + * be used in noinstr code. + * + * They should almost never be used, as they prevent code patching IPIs from + * being deferred, which can be problematic for isolated NOHZ_FULL CPUs running + * in pure userspace. + * + * If using one of these _NOINSTR variants, please add a comment above the + * definition with the rationale. + */ +#define DEFINE_STATIC_KEY_TRUE_NOINSTR(name) \ + DEFINE_STATIC_KEY_TRUE(name) + +#define DEFINE_STATIC_KEY_FALSE_NOINSTR(name) \ + DEFINE_STATIC_KEY_FALSE(name) + #define DECLARE_STATIC_KEY_FALSE(name) \ extern struct static_key_false name
--
2.51.0