text: #include <linux/init.h>
  
  #include <asm/x86_init.h>
  #include <asm/apic.h>
  #include <asm/xen/hypercall.h>
  
  #include <xen/xen.h>
  #include <xen/interface/physdev.h>
  #include "xen-ops.h"
  #include "pmu.h"
  #include "smp.h"
  
  static unsigned int xen_io_apic_read(unsigned apic, unsigned reg)
  {
  	struct physdev_apic apic_op;
  	int ret;
  
  	apic_op.apic_physbase = mpc_ioapic_addr(apic);
  	apic_op.reg = reg;
  	ret = HYPERVISOR_physdev_op(PHYSDEVOP_apic_read, &apic_op);
  	if (!ret)
  		return apic_op.value;
  
  	/* fallback to return an emulated IO_APIC values */
  	if (reg == 0x1)
  		return 0x00170020;
  	else if (reg == 0x0)
  		return apic << 24;
  
  	return 0xfd;
  }
  
  static unsigned long xen_set_apic_id(unsigned int x)
  {
  	WARN_ON(1);
  	return x;
  }
  
  static unsigned int xen_get_apic_id(unsigned long x)
  {
  	return ((x)>>24) & 0xFFu;
  }
  
  static u32 xen_apic_read(u32 reg)
  {
  	struct xen_platform_op op = {
  		.cmd = XENPF_get_cpuinfo,
  		.interface_version = XENPF_INTERFACE_VERSION,
  		.u.pcpu_info.xen_cpuid = 0,
  	};
  	int ret = 0;
  
  	/* Shouldn't need this as APIC is turned off for PV, and we only
  	 * get called on the bootup processor. But just in case. */
  	if (!xen_initial_domain() || smp_processor_id())
  		return 0;
  
  	if (reg == APIC_LVR)
  		return 0x10;
  #ifdef CONFIG_X86_32
  	if (reg == APIC_LDR)
  		return SET_APIC_LOGICAL_ID(1UL << smp_processor_id());
  #endif
  	if (reg != APIC_ID)
  		return 0;
  
  	ret = HYPERVISOR_platform_op(&op);
  	if (ret)
  		op.u.pcpu_info.apic_id = BAD_APICID;
  
  	return op.u.pcpu_info.apic_id << 24;
  }
  
  static void xen_apic_write(u32 reg, u32 val)
  {
  	if (reg == APIC_LVTPC) {
  		(void)pmu_apic_update(reg);
  		return;
  	}
  
  	/* Warn to see if there's any stray references */
  	WARN(1,"register: %x, value: %x\n", reg, val);
  }
  
  static u64 xen_apic_icr_read(void)
  {
  	return 0;
  }
  
  static void xen_apic_icr_write(u32 low, u32 id)
  {
  	/* Warn to see if there's any stray references */
  	WARN_ON(1);
  }
  
  static u32 xen_safe_apic_wait_icr_idle(void)
  {
          return 0;
  }
  
  static int xen_apic_probe_pv(void)
  {
  	if (xen_pv_domain())
  		return 1;
  
  	return 0;
  }
  
  static int xen_madt_oem_check(char *oem_id, char *oem_table_id)
  {
  	return xen_pv_domain();
  }
  
  static int xen_id_always_valid(int apicid)
  {
  	return 1;
  }
  
  static int xen_id_always_registered(void)
  {
  	return 1;
  }
  
  static int xen_phys_pkg_id(int initial_apic_id, int index_msb)
  {
  	return initial_apic_id >> index_msb;
  }
  
  #ifdef CONFIG_X86_32
  static int xen_x86_32_early_logical_apicid(int cpu)
  {
  	/* Match with APIC_LDR read. Otherwise setup_local_APIC complains. */
  	return 1 << cpu;
  }
  #endif
  
  static void xen_noop(void)
  {
  }
  
  static void xen_silent_inquire(int apicid)
  {
  }
  
  static int xen_cpu_present_to_apicid(int cpu)
  {
  	if (cpu_present(cpu))
  		return xen_get_apic_id(xen_apic_read(APIC_ID));
  	else
  		return BAD_APICID;
  }
  
  static struct apic xen_pv_apic = {
  	.name 				= "Xen PV",
  	.probe 				= xen_apic_probe_pv,
  	.acpi_madt_oem_check		= xen_madt_oem_check,
  	.apic_id_valid 			= xen_id_always_valid,
  	.apic_id_registered 		= xen_id_always_registered,
  
  	/* .irq_delivery_mode - used in native_compose_msi_msg only */
  	/* .irq_dest_mode     - used in native_compose_msi_msg only */
  
  	.target_cpus			= default_target_cpus,
  	.disable_esr			= 0,
  	/* .dest_logical      -  default_send_IPI_ use it but we use our own. */
  	.check_apicid_used		= default_check_apicid_used, /* Used on 32-bit */
  
  	.vector_allocation_domain	= flat_vector_allocation_domain,
  	.init_apic_ldr			= xen_noop, /* setup_local_APIC calls it */
  
  	.ioapic_phys_id_map		= default_ioapic_phys_id_map, /* Used on 32-bit */
  	.setup_apic_routing		= NULL,
  	.cpu_present_to_apicid		= xen_cpu_present_to_apicid,
  	.apicid_to_cpu_present		= physid_set_mask_of_physid, /* Used on 32-bit */
  	.check_phys_apicid_present	= default_check_phys_apicid_present, /* smp_sanity_check needs it */
  	.phys_pkg_id			= xen_phys_pkg_id, /* detect_ht */
  
  	.get_apic_id 			= xen_get_apic_id,
  	.set_apic_id 			= xen_set_apic_id, /* Can be NULL on 32-bit. */
  
  	.cpu_mask_to_apicid_and		= flat_cpu_mask_to_apicid_and,
  
  #ifdef CONFIG_SMP
  	.send_IPI_mask 			= xen_send_IPI_mask,
  	.send_IPI_mask_allbutself 	= xen_send_IPI_mask_allbutself,
  	.send_IPI_allbutself 		= xen_send_IPI_allbutself,
  	.send_IPI_all 			= xen_send_IPI_all,
  	.send_IPI_self 			= xen_send_IPI_self,
  #endif
  	/* .wait_for_init_deassert- used  by AP bootup - smp_callin which we don't use */
  	.inquire_remote_apic		= xen_silent_inquire,
  
  	.read				= xen_apic_read,
  	.write				= xen_apic_write,
  	.eoi_write			= xen_apic_write,
  
  	.icr_read 			= xen_apic_icr_read,
  	.icr_write 			= xen_apic_icr_write,
  	.wait_icr_idle 			= xen_noop,
  	.safe_wait_icr_idle 		= xen_safe_apic_wait_icr_idle,
  
  #ifdef CONFIG_X86_32
  	/* generic_processor_info and setup_local_APIC. */
  	.x86_32_early_logical_apicid	= xen_x86_32_early_logical_apicid,
  #endif
  };
  
  static void __init xen_apic_check(void)
  {
  	if (apic == &xen_pv_apic)
  		return;
  
  	pr_info("Switched APIC routing from %s to %s.\n", apic->name,
  		xen_pv_apic.name);
  	apic = &xen_pv_apic;
  }
  void __init xen_init_apic(void)
  {
  	x86_io_apic_ops.read = xen_io_apic_read;
  	/* On PV guests the APIC CPUID bit is disabled so none of the
  	 * routines end up executing. */
  	if (!xen_initial_domain())
  		apic = &xen_pv_apic;
  
  	x86_platform.apic_post_init = xen_apic_check;
  }
  apic_driver(xen_pv_apic);
  