linux-kernel - [PATCH 3/3] jump_label,noinstr: Avoid instrumentation for JUMP

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Message-ID: <20220502111216.350926848@infradead.org>
Date:   Mon, 02 May 2022 13:07:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, jpoimboe@...hat.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        elver@...gle.com, jbaron@...mai.com, rostedt@...dmis.org,
        ardb@...nel.org, kernel test robot <lkp@...el.com>
Subject: [PATCH 3/3] jump_label,noinstr: Avoid instrumentation for JUMP_LABEL=n builds

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@...el.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.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 READ_ONCE_NOCHECK(&key->enabled.count);
 }
 
 static __always_inline void jump_label_init(void)