Re: [PATCH v2 3/3] jump_label,noinstr: Avoid instrumentation for JUMP_LABEL=n builds

[Marco Elver <elver@google.com>]

On Mon, May 02, 2022 at 03:09PM +0200, Peter Zijlstra wrote:
> 
> Subject: jump_label,noinstr: Avoid instrumentation for JUMP_LABEL=n builds
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Mon May  2 12:30:20 CEST 2022
> 
> When building x86_64 with JUMP_LABEL=n it's possible for
> instrumentation to sneak into noinstr:
> 
> vmlinux.o: warning: objtool: exit_to_user_mode+0x14: call to static_key_count.constprop.0() leaves .noinstr.text section
> vmlinux.o: warning: objtool: syscall_exit_to_user_mode+0x2d: call to static_key_count.constprop.0() leaves .noinstr.text section
> vmlinux.o: warning: objtool: irqentry_exit_to_user_mode+0x1b: call to static_key_count.constprop.0() leaves .noinstr.text section
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  include/linux/jump_label.h |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- a/include/linux/jump_label.h
> +++ b/include/linux/jump_label.h
> @@ -256,9 +256,9 @@ extern void static_key_disable_cpuslocke
>  #include <linux/atomic.h>
>  #include <linux/bug.h>
>  
> -static inline int static_key_count(struct static_key *key)
> +static __always_inline int static_key_count(struct static_key *key)
>  {
> -	return atomic_read(&key->enabled);
> +	return arch_atomic_read(&key->enabled.count);

Curious if this compiles - s/.count// ?

>  }
>  
>  static __always_inline void jump_label_init(void)