x86/entry: Fix noinstr fail

  vmlinux.o: warning: objtool: __do_fast_syscall_32()+0x47: call to syscall_enter_from_user_mode_work() leaves .noinstr.text section

Fixes: 4facb95b ("x86/entry: Unbreak 32bit fast syscall")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210106144017.472696632@infradead.org

arch/x86/entry/common.c

@@ -73,10 +73,8 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs,
 						  unsigned int nr)
 {
 	if (likely(nr < IA32_NR_syscalls)) {
-		instrumentation_begin();
 		nr = array_index_nospec(nr, IA32_NR_syscalls);
 		regs->ax = ia32_sys_call_table[nr](regs);
-		instrumentation_end();
 	}
 }
 
@@ -91,8 +89,11 @@ __visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
 	 * or may not be necessary, but it matches the old asm behavior.
 	 */
 	nr = (unsigned int)syscall_enter_from_user_mode(regs, nr);
+	instrumentation_begin();
 
 	do_syscall_32_irqs_on(regs, nr);
+
+	instrumentation_end();
 	syscall_exit_to_user_mode(regs);
 }
 
@@ -121,11 +122,12 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
 		res = get_user(*(u32 *)&regs->bp,
 		       (u32 __user __force *)(unsigned long)(u32)regs->sp);
 	}
-	instrumentation_end();
 
 	if (res) {
 		/* User code screwed up. */
 		regs->ax = -EFAULT;
+
+		instrumentation_end();
 		syscall_exit_to_user_mode(regs);
 		return false;
 	}
@@ -135,6 +137,8 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
 
 	/* Now this is just like a normal syscall. */
 	do_syscall_32_irqs_on(regs, nr);
+
+	instrumentation_end();
 	syscall_exit_to_user_mode(regs);
 	return true;
 }