linux-kernel - [PATCH -rcu/kcsan 01/23] kcsan: Refactor reading of instrumented memory

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Date:   Tue,  5 Oct 2021 12:58:43 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, "Paul E . McKenney" <paulmck@...nel.org>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>,
        Will Deacon <will@...nel.org>, kasan-dev@...glegroups.com,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org
Subject: [PATCH -rcu/kcsan 01/23] 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: Marco Elver <elver@...gle.com>
---
 kernel/kcsan/core.c | 51 +++++++++++++++------------------------------
 1 file changed, 17 insertions(+), 34 deletions(-)

diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 4b84c8e7884b..6bfd3040f46b 100644
--- a/kernel/kcsan/core.c
+++ b/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)
-- 
2.33.0.800.g4c38ced690-goog