[PATCH -v2 5/7] Make NMI reason io port (0x61) can be processed on any CPU

[Huang Ying <ying.huang@intel.com>]

In original NMI handler, NMI reason io port (0x61) is only processed
on BSP. This makes it impossible to hot-remove BSP. To solve the
issue, a raw spinlock is used to make the port can be processed on any
CPU.

Signed-off-by: Huang Ying <ying.huang@intel.com>
---
 arch/x86/kernel/traps.c |   38 +++++++++++++++++++++-----------------
 1 file changed, 21 insertions(+), 17 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -83,6 +83,12 @@ EXPORT_SYMBOL_GPL(used_vectors);
 
 static int ignore_nmis;
 
+/*
+ * 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)
 {
 	if (regs->flags & X86_EFLAGS_IF)
@@ -378,9 +384,6 @@ unknown_nmi_error(unsigned char reason,
 static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
 {
 	unsigned char reason = 0;
-	int cpu;
-
-	cpu = smp_processor_id();
 
 	/*
 	 * CPU-specific NMI must be processed before non-CPU-specific
@@ -400,23 +403,24 @@ static notrace __kprobes void default_do
 	if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
 		return;
 
-	if (!cpu) {
-		reason = get_nmi_reason();
-		if (reason & NMI_REASON_MASK) {
-			if (reason & NMI_REASON_SERR)
-				pci_serr_error(reason, regs);
-			else if (reason & NMI_REASON_IOCHK)
-				io_check_error(reason, regs);
+	raw_spin_lock(&nmi_reason_lock);
+	reason = get_nmi_reason();
+	if (reason & NMI_REASON_MASK) {
+		if (reason & NMI_REASON_SERR)
+			pci_serr_error(reason, regs);
+		else if (reason & NMI_REASON_IOCHK)
+			io_check_error(reason, regs);
 #ifdef CONFIG_X86_32
-			/*
-			 * Reassert NMI in case it became active
-			 * meanwhile as it's edge-triggered:
-			 */
-			reassert_nmi();
+		/*
+		 * Reassert NMI in case it became active
+		 * meanwhile as it's edge-triggered:
+		 */
+		reassert_nmi();
 #endif
-			return;
-		}
+		raw_spin_unlock(&nmi_reason_lock);
+		return;
 	}
+	raw_spin_unlock(&nmi_reason_lock);
 
 #if defined(CONFIG_X86_LOCAL_APIC) && !defined(CONFIG_LOCKUP_DETECTOR)
 	if (nmi_watchdog_tick(regs, reason))