x86/uaccess, ftrace: Fix ftrace_likely_update() vs. SMAP

For CONFIG_TRACE_BRANCH_PROFILING=y the likely/unlikely things get
overloaded and generate callouts to this code, and thus also when
AC=1.

Make it safe.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/trace/trace_branch.c

@@ -205,6 +205,8 @@ void trace_likely_condition(struct ftrace_likely_data *f, int val, int expect)
 void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 			  int expect, int is_constant)
 {
+	unsigned long flags = user_access_save();
+
 	/* A constant is always correct */
 	if (is_constant) {
 		f->constant++;
@@ -223,6 +225,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 		f->data.correct++;
 	else
 		f->data.incorrect++;
+
+	user_access_restore(flags);
 }
 EXPORT_SYMBOL(ftrace_likely_update);