linux-kernel - [PATCH -v3 4/6] Make NMI reason io port (0x61) can be processed on any CPU

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Date:	Sat,  9 Oct 2010 14:49:45 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	Robert Richter <robert.richter@....com>,
	Huang Ying <ying.huang@...el.com>
Subject: [PATCH -v3 4/6] Make NMI reason io port (0x61) can be processed on any CPU

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@...el.com>
---
 arch/x86/kernel/traps.c |   45 +++++++++++++++++++++++++--------------------
 1 file changed, 25 insertions(+), 20 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)
@@ -383,7 +389,6 @@ unknown_nmi_error(unsigned char reason,
 static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
 {
 	unsigned char reason = 0;
-	int cpu;
 
 	/*
 	 * CPU-specific NMI must be processed before non-CPU-specific
@@ -400,28 +405,28 @@ static notrace __kprobes void default_do
 		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 (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
-			    == NOTIFY_STOP)
-				return;
-			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 (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
+		    == NOTIFY_STOP)
+			goto unlock_return;
+		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;
-		}
+unlock_return:
+		raw_spin_unlock(&nmi_reason_lock);
+		return;
 	}
+	raw_spin_unlock(&nmi_reason_lock);
 
 	if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
 		return;
--
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