x86/mrst: Avoid reporting wrong nmi status

Moorestown/Medfield platform does not have port 0x61 to report
NMI status, nor does it have external NMI sources. The only NMI
sources are from lapic, as results of perf counter overflow or
IPI, e.g. NMI watchdog or spin lock debug.

Reading port 0x61 on Moorestown will return 0xff which misled
NMI handlers to false critical errors such memory parity error.
The subsequent ioport access for NMI handling can also cause
undefined behavior on Moorestown.

This patch allows kernel process NMI due to watchdog or backrace
dump without unnecessary hangs.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
[hand applied]
Signed-off-by: Alan Cox <alan@linux.intel.com>

arch/x86/include/asm/mach_traps.h

@@ -17,7 +17,7 @@
 #define NMI_REASON_CLEAR_IOCHK	0x08
 #define NMI_REASON_CLEAR_MASK	0x0f
 
-static inline unsigned char get_nmi_reason(void)
+static inline unsigned char default_get_nmi_reason(void)
 {
 	return inb(NMI_REASON_PORT);
 }

arch/x86/include/asm/x86_init.h

@@ -167,6 +167,7 @@ struct x86_platform_ops {
 	void (*iommu_shutdown)(void);
 	bool (*is_untracked_pat_range)(u64 start, u64 end);
 	void (*nmi_init)(void);
+	unsigned char (*get_nmi_reason)(void);
 	int (*i8042_detect)(void);
 };
 

arch/x86/kernel/nmi.c

@@ -348,7 +348,7 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
 
 	/* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
 	raw_spin_lock(&nmi_reason_lock);
-	reason = get_nmi_reason();
+	reason = x86_platform.get_nmi_reason();
 
 	if (reason & NMI_REASON_MASK) {
 		if (reason & NMI_REASON_SERR)

arch/x86/kernel/x86_init.c

@@ -21,6 +21,7 @@
 #include <asm/pat.h>
 #include <asm/tsc.h>
 #include <asm/iommu.h>
+#include <asm/mach_traps.h>
 
 void __cpuinit x86_init_noop(void) { }
 void __init x86_init_uint_noop(unsigned int unused) { }
@@ -104,6 +105,7 @@ struct x86_platform_ops x86_platform = {
 	.iommu_shutdown			= iommu_shutdown_noop,
 	.is_untracked_pat_range		= is_ISA_range,
 	.nmi_init			= default_nmi_init,
+	.get_nmi_reason			= default_get_nmi_reason,
 	.i8042_detect			= default_i8042_detect
 };
 

arch/x86/platform/mrst/mrst.c

@@ -276,6 +276,17 @@ static void mrst_reboot(void)
 	intel_scu_ipc_simple_command(0xf1, 0);
 }
 
+/*
+ * Moorestown does not have external NMI source nor port 0x61 to report
+ * NMI status. The possible NMI sources are from pmu as a result of NMI
+ * watchdog or lock debug. Reading io port 0x61 results in 0xff which
+ * misled NMI handler.
+ */
+static unsigned char mrst_get_nmi_reason(void)
+{
+	return 0;
+}
+
 /*
  * Moorestown specific x86_init function overrides and early setup
  * calls.
@@ -297,6 +308,8 @@ void __init x86_mrst_early_setup(void)
 	x86_platform.calibrate_tsc = mrst_calibrate_tsc;
 	x86_platform.i8042_detect = mrst_i8042_detect;
 	x86_init.timers.wallclock_init = mrst_rtc_init;
+	x86_platform.get_nmi_reason = mrst_get_nmi_reason;
+
 	x86_init.pci.init = pci_mrst_init;
 	x86_init.pci.fixup_irqs = x86_init_noop;