x2apic: fix reserved APIC register accesses in print_local_APIC()

APIC_ARBPRI is a reserved register for XAPIC and beyond.
APIC_RRR is a reserved register except for 82489DX, APIC for Pentium processors.
APIC_EOI is a write only register.
APIC_DFR is reserved in x2apic mode.

Access to these registers in x2apic will result in #GP fault. Fix these
apic register accesses.

Signed-off-by: Yinghai Lu <[e-mail]>
Signed-off-by: Suresh Siddha <[e-mail]>
Cc: Maciej W. Rozycki <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/io_apic.c

···
 	printk(KERN_DEBUG "... APIC TASKPRI: %08x (%02x)\n", v, v & APIC_TPRI_MASK);
 
 	if (APIC_INTEGRATED(ver)) {                     /* !82489DX */
-		v = apic_read(APIC_ARBPRI);
-		printk(KERN_DEBUG "... APIC ARBPRI: %08x (%02x)\n", v,
-			v & APIC_ARBPRI_MASK);
+		if (!APIC_XAPIC(ver)) {
+			v = apic_read(APIC_ARBPRI);
+			printk(KERN_DEBUG "... APIC ARBPRI: %08x (%02x)\n", v,
+			       v & APIC_ARBPRI_MASK);
+		}
 		v = apic_read(APIC_PROCPRI);
 		printk(KERN_DEBUG "... APIC PROCPRI: %08x\n", v);
 	}
 
-	v = apic_read(APIC_EOI);
-	printk(KERN_DEBUG "... APIC EOI: %08x\n", v);
-	v = apic_read(APIC_RRR);
-	printk(KERN_DEBUG "... APIC RRR: %08x\n", v);
+	/*
+	 * Remote read supported only in the 82489DX and local APIC for
+	 * Pentium processors.
+	 */
+	if (!APIC_INTEGRATED(ver) || maxlvt == 3) {
+		v = apic_read(APIC_RRR);
+		printk(KERN_DEBUG "... APIC RRR: %08x\n", v);
+	}
+
 	v = apic_read(APIC_LDR);
 	printk(KERN_DEBUG "... APIC LDR: %08x\n", v);
-	v = apic_read(APIC_DFR);
-	printk(KERN_DEBUG "... APIC DFR: %08x\n", v);
+	if (!x2apic_enabled()) {
+		v = apic_read(APIC_DFR);
+		printk(KERN_DEBUG "... APIC DFR: %08x\n", v);
+	}
 	v = apic_read(APIC_SPIV);
 	printk(KERN_DEBUG "... APIC SPIV: %08x\n", v);
 

include/asm-x86/apic.h

···
 extern void enable_x2apic(void);
 extern void enable_IR_x2apic(void);
 extern void x2apic_icr_write(u32 low, u32 id);
+static inline int x2apic_enabled(void)
+{
+	int msr, msr2;
+
+	if (!cpu_has_x2apic)
+		return 0;
+
+	rdmsr(MSR_IA32_APICBASE, msr, msr2);
+	if (msr & X2APIC_ENABLE)
+		return 1;
+	return 0;
+}
+#else
+#define x2apic_enabled()	0
 #endif
 
 struct apic_ops {