diff --git a/[refs] b/[refs]
index 06bda073b8d2..7453810f4326 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: ab9cf4996bb989983e73da894b8dd0239aa2c3c2
+refs/heads/master: d0a69d6321ca759bb8d47803d06ba8571ab42d07
diff --git a/trunk/arch/x86/include/asm/bitops.h b/trunk/arch/x86/include/asm/bitops.h
index a6983b277220..72f5009deb5a 100644
--- a/trunk/arch/x86/include/asm/bitops.h
+++ b/trunk/arch/x86/include/asm/bitops.h
@@ -264,6 +264,13 @@ static inline int test_and_clear_bit(int nr, volatile unsigned long *addr)
  * This operation is non-atomic and can be reordered.
  * If two examples of this operation race, one can appear to succeed
  * but actually fail.  You must protect multiple accesses with a lock.
+ *
+ * Note: the operation is performed atomically with respect to
+ * the local CPU, but not other CPUs. Portable code should not
+ * rely on this behaviour.
+ * KVM relies on this behaviour on x86 for modifying memory that is also
+ * accessed from a hypervisor on the same CPU if running in a VM: don't change
+ * this without also updating arch/x86/kernel/kvm.c
  */
 static inline int __test_and_clear_bit(int nr, volatile unsigned long *addr)
 {