[PATCH 5/9] x86, NMI: Allow NMI reason io port (0x61) to be processed on any CPU

[Don Zickus <dzickus@redhat.com>]

From: 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.

[ added a unlock and return to NMI_REASON_MASK path -dcz]

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>

---
 arch/x86/kernel/traps.c |   38 +++++++++++++++++++++-----------------
 1 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 0668b51..1c21271 100644
--- a/arch/x86/kernel/traps.c
+++ b/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
@@ -408,25 +412,25 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
 		return;
 
 	/* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
-	cpu = smp_processor_id();
-	/* Only the BSP gets external NMIs from the system. */
-	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);
+
 	unknown_nmi_error(reason, regs);
 }
 
-- 
1.7.3.2