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.
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 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) = { \