[PATCH v2 2/3] static_call: Add read-only-after-init static calls

[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.

If a noinstr static call only needs to be patched during boot, its key
can be made ro-after-init to ensure it will never be patched at runtime.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 include/linux/static_call.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/static_call.h b/include/linux/static_call.h
index 141e6b176a1b..34970e178fdf 100644
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -190,6 +190,14 @@ extern long __static_call_return0(void);
 	};								\
 	ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func)
 
+#define DEFINE_STATIC_CALL_RO(name, _func)				\
+	DECLARE_STATIC_CALL(name, _func);				\
+	struct static_call_key __ro_after_init STATIC_CALL_KEY(name) = {\
+		.func = _func,						\
+		.type = 1,						\
+	};								\
+	ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func)
+
 #define DEFINE_STATIC_CALL_NULL(name, _func)				\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\
@@ -198,6 +206,14 @@ extern long __static_call_return0(void);
 	};								\
 	ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)
 
+#define DEFINE_STATIC_CALL_NULL_RO(name, _func)				\
+	DECLARE_STATIC_CALL(name, _func);				\
+	struct static_call_key __ro_after_init STATIC_CALL_KEY(name) = {\
+		.func = NULL,						\
+		.type = 1,						\
+	};								\
+	ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)
+
 #define DEFINE_STATIC_CALL_RET0(name, _func)				\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\
-- 
2.47.0