X86: hyperv: Enable MSR based APIC access

index 939155f..76833c6 100644
@@ -110,6 +110,57 @@ static struct clocksource hyperv_cs = {
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 };
 
+static u64 ms_hv_apic_icr_read(void)
+{
+	u64 reg_val;
+
+	rdmsrl(HV_X64_MSR_ICR, reg_val);
+	return reg_val;
+}
+
+static void ms_hv_apic_icr_write(u32 low, u32 id)
+{
+	u64 reg_val;
+
+	reg_val = SET_APIC_DEST_FIELD(id);
+	reg_val = reg_val << 32;
+	reg_val |= low;
+
+	wrmsrl(HV_X64_MSR_ICR, reg_val);
+}
+
+static u32 ms_hv_apic_read(u32 reg)
+{
+	u32 reg_val, hi;
+
+	switch (reg) {
+	case APIC_EOI:
+		rdmsr(HV_X64_MSR_EOI, reg_val, hi);
+		return reg_val;
+	case APIC_TASKPRI:
+		rdmsr(HV_X64_MSR_TPR, reg_val, hi);
+		return reg_val;
+
+	default:
+		return native_apic_mem_read(reg);
+	}
+}
+
+static void ms_hv_apic_write(u32 reg, u32 val)
+{
+	switch (reg) {
+	case APIC_EOI:
+		wrmsr(HV_X64_MSR_EOI, val, 0);
+		break;
+	case APIC_TASKPRI:
+		wrmsr(HV_X64_MSR_TPR, val, 0);
+		break;
+	default:
+		native_apic_mem_write(reg, val);
+	}
+}
+
+
 static void __init ms_hyperv_init_platform(void)
 {
 	/*

@@ -143,6 +194,17 @@ static void __init ms_hyperv_init_platform(void)
 	no_timer_check = 1;
 #endif
 
+	if (ms_hyperv.features & HV_X64_MSR_APIC_ACCESS_AVAILABLE) {
+		/*
+		 * Setup the hooks for optimized APIC read/write.
+		 */
+		apic->read	= ms_hv_apic_read;
+		apic->write	= ms_hv_apic_write;
+		apic->icr_write	= ms_hv_apic_icr_write;
+		apic->icr_read	= ms_hv_apic_icr_read;
+		apic->eoi_write	= ms_hv_apic_write;
+	}
+
 }
 
 const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {