kcsan: Refactor reading of instrumented memory

Factor out the switch statement reading instrumented memory into a
helper read_instrumented_memory().

No functional change.
Signed-off-by: NMarco Elver <elver@google.com>
Acked-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NPaul E. McKenney <paulmck@kernel.org>

kernel/kcsan/core.c

@@ -325,6 +325,21 @@ static void delay_access(int type)
 	udelay(delay);
 }
 
+/*
+ * Reads the instrumented memory for value change detection; value change
+ * detection is currently done for accesses up to a size of 8 bytes.
+ */
+static __always_inline u64 read_instrumented_memory(const volatile void *ptr, size_t size)
+{
+	switch (size) {
+	case 1:  return READ_ONCE(*(const u8 *)ptr);
+	case 2:  return READ_ONCE(*(const u16 *)ptr);
+	case 4:  return READ_ONCE(*(const u32 *)ptr);
+	case 8:  return READ_ONCE(*(const u64 *)ptr);
+	default: return 0; /* Ignore; we do not diff the values. */
+	}
+}
+
 void kcsan_save_irqtrace(struct task_struct *task)
 {
 #ifdef CONFIG_TRACE_IRQFLAGS
@@ -482,23 +497,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned
 	 * Read the current value, to later check and infer a race if the data
 	 * was modified via a non-instrumented access, e.g. from a device.
 	 */
-	old = 0;
-	switch (size) {
-	case 1:
-		old = READ_ONCE(*(const u8 *)ptr);
-		break;
-	case 2:
-		old = READ_ONCE(*(const u16 *)ptr);
-		break;
-	case 4:
-		old = READ_ONCE(*(const u32 *)ptr);
-		break;
-	case 8:
-		old = READ_ONCE(*(const u64 *)ptr);
-		break;
-	default:
-		break; /* ignore; we do not diff the values */
-	}
+	old = read_instrumented_memory(ptr, size);
 
 	/*
 	 * Delay this thread, to increase probability of observing a racy
@@ -511,23 +510,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned
 	 * racy access.
 	 */
 	access_mask = ctx->access_mask;
-	new = 0;
-	switch (size) {
-	case 1:
-		new = READ_ONCE(*(const u8 *)ptr);
-		break;
-	case 2:
-		new = READ_ONCE(*(const u16 *)ptr);
-		break;
-	case 4:
-		new = READ_ONCE(*(const u32 *)ptr);
-		break;
-	case 8:
-		new = READ_ONCE(*(const u64 *)ptr);
-		break;
-	default:
-		break; /* ignore; we do not diff the values */
-	}
+	new = read_instrumented_memory(ptr, size);
 
 	diff = old ^ new;
 	if (access_mask)