On Fri, 10 Oct 2025 17:38:16 +0200 Valentin Schneider <[email protected]> wrote:
> From: Josh Poimboeuf <[email protected]> > > 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 <[email protected]> > --- > 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) > + I think it would be a good idea to add a comment describing when these macros are supposed to be used, similar to the explanation you wrote for the _NOINSTR variants. Just to provide a clue for people adding a new static key in the future, because the commit message may become a bit hard to find if there are a few cleanup patches on top. Just my two cents, Petr T
