---

yaml
---
r: 228938
b: refs/heads/master
c: ab846f1
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: c410b8307702c1e1f35be3fd868ad18e4ba0410f
+refs/heads/master: ab846f13f69fa64f8ed69ce0c3e239e075910d23

trunk/arch/x86/kernel/traps.c

@@ -84,6 +84,11 @@ EXPORT_SYMBOL_GPL(used_vectors);
 static int ignore_nmis;
 
 int unknown_nmi_panic;
+/*
+ * Prevent NMI reason port (0x61) being accessed simultaneously, can
+ * only be used in NMI handler.
+ */
+static DEFINE_RAW_SPINLOCK(nmi_reason_lock);
 
 static inline void conditional_sti(struct pt_regs *regs)
 {
@@ -392,7 +397,6 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
 static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
 {
 	unsigned char reason = 0;
-	int cpu;
 
 	/*
 	 * CPU-specific NMI must be processed before non-CPU-specific
@@ -402,13 +406,12 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
 	if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
 		return;
 
-	cpu = smp_processor_id();
-
-	/* Only the BSP gets external NMIs from the system. */
-	if (!cpu)
-		reason = get_nmi_reason();
+	/* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
+	raw_spin_lock(&nmi_reason_lock);
+	reason = get_nmi_reason();
 
 	if (!(reason & NMI_REASON_MASK)) {
+		raw_spin_unlock(&nmi_reason_lock);
 		unknown_nmi_error(reason, regs);
 
 		return;
@@ -426,6 +429,7 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
 	 */
 	reassert_nmi();
 #endif
+	raw_spin_unlock(&nmi_reason_lock);
 }
 
 dotraplinkage notrace __kprobes void