[PATCH v4 06/30] static_call: Add read-only-after-init static calls

[Valentin Schneider <vschneid@xxxxxxxxxx>]

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 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 78a77a4ae0ea8..ea6ca57e2a829 100644
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -192,6 +192,14 @@ 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) = {                \
@@ -200,6 +208,14 @@ 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) = {                \
-- 
2.43.0