diff --git a/arch/x86/kernel/apic_32.c b/arch/x86/kernel/apic_32.c
index d6c898358371..fad94b0decc1 100644
--- a/arch/x86/kernel/apic_32.c
+++ b/arch/x86/kernel/apic_32.c
@@ -646,6 +646,9 @@ int setup_profiling_timer(unsigned int multiplier)
  *
  * Vector mappings are hard coded. On K8 only offset 0 (APIC500) and
  * MCE interrupts are supported. Thus MCE offset must be set to 0.
+ *
+ * If mask=1, the LVT entry does not generate interrupts while mask=0
+ * enables the vector. See also the BKDGs.
  */
 
 #define APIC_EILVT_LVTOFF_MCE 0
diff --git a/arch/x86/kernel/apic_64.c b/arch/x86/kernel/apic_64.c
index 7f1f030da7ee..42bf69f8bc8e 100644
--- a/arch/x86/kernel/apic_64.c
+++ b/arch/x86/kernel/apic_64.c
@@ -205,6 +205,9 @@ static void __setup_APIC_LVTT(unsigned int clocks, int oneshot, int irqen)
  *
  * Vector mappings are hard coded. On K8 only offset 0 (APIC500) and
  * MCE interrupts are supported. Thus MCE offset must be set to 0.
+ *
+ * If mask=1, the LVT entry does not generate interrupts while mask=0
+ * enables the vector. See also the BKDGs.
  */
 
 #define APIC_EILVT_LVTOFF_MCE 0