arch/x86/xen/smp.c - maze/linux - Git at Google

 /*
  * Xen SMP support
  *
  * This file implements the Xen versions of smp_ops.  SMP under Xen is
  * very straightforward.  Bringing a CPU up is simply a matter of
  * loading its initial context and setting it running.
  *
  * IPIs are handled through the Xen event mechanism.
  *
  * Because virtual CPUs can be scheduled onto any real CPU, there's no
  * useful topology information for the kernel to make use of.  As a
  * result, all CPUs are treated as if they're single-core and
  * single-threaded.
  */
 #include <linux/sched.h>
 #include <linux/err.h>
 #include <linux/smp.h>

 #include <asm/paravirt.h>
 #include <asm/desc.h>
 #include <asm/pgtable.h>
 #include <asm/cpu.h>

 #include <xen/interface/xen.h>
 #include <xen/interface/vcpu.h>

 #include <asm/xen/interface.h>
 #include <asm/xen/hypercall.h>

 #include <xen/page.h>
 #include <xen/events.h>

 #include "xen-ops.h"
 #include "mmu.h"

 cpumask_var_t xen_cpu_initialized_map;

 static DEFINE_PER_CPU(int, resched_irq);
 static DEFINE_PER_CPU(int, callfunc_irq);
 static DEFINE_PER_CPU(int, callfuncsingle_irq);
 static DEFINE_PER_CPU(int, debug_irq) = -1;

 static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id);
 static irqreturn_t xen_call_function_single_interrupt(int irq, void *dev_id);

 /*
  * Reschedule call back. Nothing to do,
  * all the work is done automatically when
  * we return from the interrupt.
  */
 static irqreturn_t xen_reschedule_interrupt(int irq, void *dev_id)
 {
 	inc_irq_stat(irq_resched_count);

 	return IRQ_HANDLED;
 }

 static __cpuinit void cpu_bringup(void)
 {
 	int cpu = smp_processor_id();

 	cpu_init();
 	touch_softlockup_watchdog();
 	preempt_disable();

 	xen_enable_sysenter();
 	xen_enable_syscall();

 	cpu = smp_processor_id();
 	smp_store_cpu_info(cpu);
 	cpu_data(cpu).x86_max_cores = 1;
 	set_cpu_sibling_map(cpu);

 	xen_setup_cpu_clockevents();

 	cpu_set(cpu, cpu_online_map);
 	percpu_write(cpu_state, CPU_ONLINE);
 	wmb();

 	/* We can take interrupts now: we're officially "up". */
 	local_irq_enable();

 	wmb();			/* make sure everything is out */
 }

 static __cpuinit void cpu_bringup_and_idle(void)
 {
 	cpu_bringup();
 	cpu_idle();
 }

 static int xen_smp_intr_init(unsigned int cpu)
 {
 	int rc;
 	const char *resched_name, *callfunc_name, *debug_name;

 	resched_name = kasprintf(GFP_KERNEL, "resched%d", cpu);
 	rc = bind_ipi_to_irqhandler(XEN_RESCHEDULE_VECTOR,
 				    cpu,
 				    xen_reschedule_interrupt,
 				    IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
 				    resched_name,
 				    NULL);
 	if (rc < 0)
 		goto fail;
 	per_cpu(resched_irq, cpu) = rc;

 	callfunc_name = kasprintf(GFP_KERNEL, "callfunc%d", cpu);
 	rc = bind_ipi_to_irqhandler(XEN_CALL_FUNCTION_VECTOR,
 				    cpu,
 				    xen_call_function_interrupt,
 				    IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
 				    callfunc_name,
 				    NULL);
 	if (rc < 0)
 		goto fail;
 	per_cpu(callfunc_irq, cpu) = rc;

 	debug_name = kasprintf(GFP_KERNEL, "debug%d", cpu);
 	rc = bind_virq_to_irqhandler(VIRQ_DEBUG, cpu, xen_debug_interrupt,
 				     IRQF_DISABLED | IRQF_PERCPU | IRQF_NOBALANCING,
 				     debug_name, NULL);
 	if (rc < 0)
 		goto fail;
 	per_cpu(debug_irq, cpu) = rc;

 	callfunc_name = kasprintf(GFP_KERNEL, "callfuncsingle%d", cpu);
 	rc = bind_ipi_to_irqhandler(XEN_CALL_FUNCTION_SINGLE_VECTOR,
 				    cpu,
 				    xen_call_function_single_interrupt,
 				    IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
 				    callfunc_name,
 				    NULL);
 	if (rc < 0)
 		goto fail;
 	per_cpu(callfuncsingle_irq, cpu) = rc;

 	return 0;

  fail:
 	if (per_cpu(resched_irq, cpu) >= 0)
 		unbind_from_irqhandler(per_cpu(resched_irq, cpu), NULL);
 	if (per_cpu(callfunc_irq, cpu) >= 0)
 		unbind_from_irqhandler(per_cpu(callfunc_irq, cpu), NULL);
 	if (per_cpu(debug_irq, cpu) >= 0)
 		unbind_from_irqhandler(per_cpu(debug_irq, cpu), NULL);
 	if (per_cpu(callfuncsingle_irq, cpu) >= 0)
 		unbind_from_irqhandler(per_cpu(callfuncsingle_irq, cpu), NULL);

 	return rc;
 }

 static void __init xen_fill_possible_map(void)
 {
 	int i, rc;

 	for (i = 0; i < nr_cpu_ids; i++) {
 		rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL);
 		if (rc >= 0) {
 			num_processors++;
 			cpu_set(i, cpu_possible_map);
 		}
 	}
 }

 static void __init xen_smp_prepare_boot_cpu(void)
 {
 	BUG_ON(smp_processor_id() != 0);
 	native_smp_prepare_boot_cpu();

 	/* We've switched to the "real" per-cpu gdt, so make sure the
 	   old memory can be recycled */
 	make_lowmem_page_readwrite(xen_initial_gdt);

 	xen_setup_vcpu_info_placement();
 }

 static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
 {
 	unsigned cpu;

 	xen_init_lock_cpu(0);

 	smp_store_cpu_info(0);
 	cpu_data(0).x86_max_cores = 1;
 	set_cpu_sibling_map(0);

 	if (xen_smp_intr_init(0))
 		BUG();

 	if (!alloc_cpumask_var(&xen_cpu_initialized_map, GFP_KERNEL))
 		panic("could not allocate xen_cpu_initialized_map\n");

 	cpumask_copy(xen_cpu_initialized_map, cpumask_of(0));

 	/* Restrict the possible_map according to max_cpus. */
 	while ((num_possible_cpus() > 1) && (num_possible_cpus() > max_cpus)) {
 		for (cpu = nr_cpu_ids - 1; !cpu_possible(cpu); cpu--)
 			continue;
 		cpu_clear(cpu, cpu_possible_map);
 	}

 	for_each_possible_cpu (cpu) {
 		struct task_struct *idle;

 		if (cpu == 0)
 			continue;

 		idle = fork_idle(cpu);
 		if (IS_ERR(idle))
 			panic("failed fork for CPU %d", cpu);

 		cpu_set(cpu, cpu_present_map);
 	}
 }

 static __cpuinit int
 cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
 {
 	struct vcpu_guest_context *ctxt;
 	struct desc_struct *gdt;

 	if (cpumask_test_and_set_cpu(cpu, xen_cpu_initialized_map))
 		return 0;

 	ctxt = kzalloc(sizeof(*ctxt), GFP_KERNEL);
 	if (ctxt == NULL)
 		return -ENOMEM;

 	gdt = get_cpu_gdt_table(cpu);

 	ctxt->flags = VGCF_IN_KERNEL;
 	ctxt->user_regs.ds = __USER_DS;
 	ctxt->user_regs.es = __USER_DS;
 	ctxt->user_regs.ss = __KERNEL_DS;
 #ifdef CONFIG_X86_32
 	ctxt->user_regs.fs = __KERNEL_PERCPU;
 #else
 	ctxt->gs_base_kernel = per_cpu_offset(cpu);
 #endif
 	ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
 	ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */

 	memset(&ctxt->fpu_ctxt, 0, sizeof(ctxt->fpu_ctxt));

 	xen_copy_trap_info(ctxt->trap_ctxt);

 	ctxt->ldt_ents = 0;

 	BUG_ON((unsigned long)gdt & ~PAGE_MASK);
 	make_lowmem_page_readonly(gdt);

 	ctxt->gdt_frames[0] = virt_to_mfn(gdt);
 	ctxt->gdt_ents      = GDT_ENTRIES;

 	ctxt->user_regs.cs = __KERNEL_CS;
 	ctxt->user_regs.esp = idle->thread.sp0 - sizeof(struct pt_regs);

 	ctxt->kernel_ss = __KERNEL_DS;
 	ctxt->kernel_sp = idle->thread.sp0;

 #ifdef CONFIG_X86_32
 	ctxt->event_callback_cs     = __KERNEL_CS;
 	ctxt->failsafe_callback_cs  = __KERNEL_CS;
 #endif
 	ctxt->event_callback_eip    = (unsigned long)xen_hypervisor_callback;
 	ctxt->failsafe_callback_eip = (unsigned long)xen_failsafe_callback;

 	per_cpu(xen_cr3, cpu) = __pa(swapper_pg_dir);
 	ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_mfn(swapper_pg_dir));

 	if (HYPERVISOR_vcpu_op(VCPUOP_initialise, cpu, ctxt))
 		BUG();

 	kfree(ctxt);
 	return 0;
 }

 static int __cpuinit xen_cpu_up(unsigned int cpu)
 {
 	struct task_struct *idle = idle_task(cpu);
 	int rc;

 	per_cpu(current_task, cpu) = idle;
 #ifdef CONFIG_X86_32
 	irq_ctx_init(cpu);
 #else
 	clear_tsk_thread_flag(idle, TIF_FORK);
 	per_cpu(kernel_stack, cpu) =
 		(unsigned long)task_stack_page(idle) -
 		KERNEL_STACK_OFFSET + THREAD_SIZE;
 #endif
 	xen_setup_timer(cpu);
 	xen_init_lock_cpu(cpu);

 	per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;

 	/* make sure interrupts start blocked */
 	per_cpu(xen_vcpu, cpu)->evtchn_upcall_mask = 1;

 	rc = cpu_initialize_context(cpu, idle);
 	if (rc)
 		return rc;

 	if (num_online_cpus() == 1)
 		alternatives_smp_switch(1);

 	rc = xen_smp_intr_init(cpu);
 	if (rc)
 		return rc;

 	rc = HYPERVISOR_vcpu_op(VCPUOP_up, cpu, NULL);
 	BUG_ON(rc);

 	while(per_cpu(cpu_state, cpu) != CPU_ONLINE) {
 		HYPERVISOR_sched_op(SCHEDOP_yield, 0);
 		barrier();
 	}

 	return 0;
 }

 static void xen_smp_cpus_done(unsigned int max_cpus)
 {
 }

 #ifdef CONFIG_HOTPLUG_CPU
 static int xen_cpu_disable(void)
 {
 	unsigned int cpu = smp_processor_id();
 	if (cpu == 0)
 		return -EBUSY;

 	cpu_disable_common();

 	load_cr3(swapper_pg_dir);
 	return 0;
 }

 static void xen_cpu_die(unsigned int cpu)
 {
 	while (HYPERVISOR_vcpu_op(VCPUOP_is_up, cpu, NULL)) {
 		current->state = TASK_UNINTERRUPTIBLE;
 		schedule_timeout(HZ/10);
 	}
 	unbind_from_irqhandler(per_cpu(resched_irq, cpu), NULL);
 	unbind_from_irqhandler(per_cpu(callfunc_irq, cpu), NULL);
 	unbind_from_irqhandler(per_cpu(debug_irq, cpu), NULL);
 	unbind_from_irqhandler(per_cpu(callfuncsingle_irq, cpu), NULL);
 	xen_uninit_lock_cpu(cpu);
 	xen_teardown_timer(cpu);

 	if (num_online_cpus() == 1)
 		alternatives_smp_switch(0);
 }

 static void __cpuinit xen_play_dead(void) /* used only with CPU_HOTPLUG */
 {
 	play_dead_common();
 	HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
 	cpu_bringup();
 }

 #else /* !CONFIG_HOTPLUG_CPU */
 static int xen_cpu_disable(void)
 {
 	return -ENOSYS;
 }

 static void xen_cpu_die(unsigned int cpu)
 {
 	BUG();
 }

 static void xen_play_dead(void)
 {
 	BUG();
 }

 #endif
 static void stop_self(void *v)
 {
 	int cpu = smp_processor_id();

 	/* make sure we're not pinning something down */
 	load_cr3(swapper_pg_dir);
 	/* should set up a minimal gdt */

 	HYPERVISOR_vcpu_op(VCPUOP_down, cpu, NULL);
 	BUG();
 }

 static void xen_smp_send_stop(void)
 {
 	smp_call_function(stop_self, NULL, 0);
 }

 static void xen_smp_send_reschedule(int cpu)
 {
 	xen_send_IPI_one(cpu, XEN_RESCHEDULE_VECTOR);
 }

 static void xen_send_IPI_mask(const struct cpumask *mask,
 			      enum ipi_vector vector)
 {
 	unsigned cpu;

 	for_each_cpu_and(cpu, mask, cpu_online_mask)
 		xen_send_IPI_one(cpu, vector);
 }

 static void xen_smp_send_call_function_ipi(const struct cpumask *mask)
 {
 	int cpu;

 	xen_send_IPI_mask(mask, XEN_CALL_FUNCTION_VECTOR);

 	/* Make sure other vcpus get a chance to run if they need to. */
 	for_each_cpu(cpu, mask) {
 		if (xen_vcpu_stolen(cpu)) {
 			HYPERVISOR_sched_op(SCHEDOP_yield, 0);
 			break;
 		}
 	}
 }

 static void xen_smp_send_call_function_single_ipi(int cpu)
 {
 	xen_send_IPI_mask(cpumask_of(cpu),
 			  XEN_CALL_FUNCTION_SINGLE_VECTOR);
 }

 static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id)
 {
 	irq_enter();
 	generic_smp_call_function_interrupt();
 	inc_irq_stat(irq_call_count);
 	irq_exit();

 	return IRQ_HANDLED;
 }

 static irqreturn_t xen_call_function_single_interrupt(int irq, void *dev_id)
 {
 	irq_enter();
 	generic_smp_call_function_single_interrupt();
 	inc_irq_stat(irq_call_count);
 	irq_exit();

 	return IRQ_HANDLED;
 }

 static const struct smp_ops xen_smp_ops __initdata = {
 	.smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu,
 	.smp_prepare_cpus = xen_smp_prepare_cpus,
 	.smp_cpus_done = xen_smp_cpus_done,

 	.cpu_up = xen_cpu_up,
 	.cpu_die = xen_cpu_die,
 	.cpu_disable = xen_cpu_disable,
 	.play_dead = xen_play_dead,

 	.smp_send_stop = xen_smp_send_stop,
 	.smp_send_reschedule = xen_smp_send_reschedule,

 	.send_call_func_ipi = xen_smp_send_call_function_ipi,
 	.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi,
 };

 void __init xen_smp_init(void)
 {
 	smp_ops = xen_smp_ops;
 	xen_fill_possible_map();
 	xen_init_spinlocks();
 }
	/*
	* Xen SMP support
	*
	* This file implements the Xen versions of smp_ops. SMP under Xen is
	* very straightforward. Bringing a CPU up is simply a matter of
	* loading its initial context and setting it running.
	*
	* IPIs are handled through the Xen event mechanism.
	*
	* Because virtual CPUs can be scheduled onto any real CPU, there's no
	* useful topology information for the kernel to make use of. As a
	* result, all CPUs are treated as if they're single-core and
	* single-threaded.
	*/
	#include <linux/sched.h>
	#include <linux/err.h>
	#include <linux/smp.h>

	#include <asm/paravirt.h>
	#include <asm/desc.h>
	#include <asm/pgtable.h>
	#include <asm/cpu.h>

	#include <xen/interface/xen.h>
	#include <xen/interface/vcpu.h>

	#include <asm/xen/interface.h>
	#include <asm/xen/hypercall.h>

	#include <xen/page.h>
	#include <xen/events.h>

	#include "xen-ops.h"
	#include "mmu.h"

	cpumask_var_t xen_cpu_initialized_map;

	static DEFINE_PER_CPU(int, resched_irq);
	static DEFINE_PER_CPU(int, callfunc_irq);
	static DEFINE_PER_CPU(int, callfuncsingle_irq);
	static DEFINE_PER_CPU(int, debug_irq) = -1;

	static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id);
	static irqreturn_t xen_call_function_single_interrupt(int irq, void *dev_id);

	/*
	* Reschedule call back. Nothing to do,
	* all the work is done automatically when
	* we return from the interrupt.
	*/
	static irqreturn_t xen_reschedule_interrupt(int irq, void *dev_id)
	{
	inc_irq_stat(irq_resched_count);

	return IRQ_HANDLED;
	}

	static __cpuinit void cpu_bringup(void)
	{
	int cpu = smp_processor_id();

	cpu_init();
	touch_softlockup_watchdog();
	preempt_disable();

	xen_enable_sysenter();
	xen_enable_syscall();

	cpu = smp_processor_id();
	smp_store_cpu_info(cpu);
	cpu_data(cpu).x86_max_cores = 1;
	set_cpu_sibling_map(cpu);

	xen_setup_cpu_clockevents();

	cpu_set(cpu, cpu_online_map);
	percpu_write(cpu_state, CPU_ONLINE);
	wmb();

	/* We can take interrupts now: we're officially "up". */
	local_irq_enable();

	wmb(); /* make sure everything is out */
	}

	static __cpuinit void cpu_bringup_and_idle(void)
	{
	cpu_bringup();
	cpu_idle();
	}

	static int xen_smp_intr_init(unsigned int cpu)
	{
	int rc;
	const char resched_name, callfunc_name, *debug_name;

	resched_name = kasprintf(GFP_KERNEL, "resched%d", cpu);
	rc = bind_ipi_to_irqhandler(XEN_RESCHEDULE_VECTOR,
	cpu,
	xen_reschedule_interrupt,
	IRQF_DISABLED\|IRQF_PERCPU\|IRQF_NOBALANCING,
	resched_name,
	NULL);
	if (rc < 0)
	goto fail;
	per_cpu(resched_irq, cpu) = rc;

	callfunc_name = kasprintf(GFP_KERNEL, "callfunc%d", cpu);
	rc = bind_ipi_to_irqhandler(XEN_CALL_FUNCTION_VECTOR,
	cpu,
	xen_call_function_interrupt,
	IRQF_DISABLED\|IRQF_PERCPU\|IRQF_NOBALANCING,
	callfunc_name,
	NULL);
	if (rc < 0)
	goto fail;
	per_cpu(callfunc_irq, cpu) = rc;

	debug_name = kasprintf(GFP_KERNEL, "debug%d", cpu);
	rc = bind_virq_to_irqhandler(VIRQ_DEBUG, cpu, xen_debug_interrupt,
	IRQF_DISABLED \| IRQF_PERCPU \| IRQF_NOBALANCING,
	debug_name, NULL);
	if (rc < 0)
	goto fail;
	per_cpu(debug_irq, cpu) = rc;

	callfunc_name = kasprintf(GFP_KERNEL, "callfuncsingle%d", cpu);
	rc = bind_ipi_to_irqhandler(XEN_CALL_FUNCTION_SINGLE_VECTOR,
	cpu,
	xen_call_function_single_interrupt,
	IRQF_DISABLED\|IRQF_PERCPU\|IRQF_NOBALANCING,
	callfunc_name,
	NULL);
	if (rc < 0)
	goto fail;
	per_cpu(callfuncsingle_irq, cpu) = rc;

	return 0;

	fail:
	if (per_cpu(resched_irq, cpu) >= 0)
	unbind_from_irqhandler(per_cpu(resched_irq, cpu), NULL);
	if (per_cpu(callfunc_irq, cpu) >= 0)
	unbind_from_irqhandler(per_cpu(callfunc_irq, cpu), NULL);
	if (per_cpu(debug_irq, cpu) >= 0)
	unbind_from_irqhandler(per_cpu(debug_irq, cpu), NULL);
	if (per_cpu(callfuncsingle_irq, cpu) >= 0)
	unbind_from_irqhandler(per_cpu(callfuncsingle_irq, cpu), NULL);

	return rc;
	}

	static void __init xen_fill_possible_map(void)
	{
	int i, rc;

	for (i = 0; i < nr_cpu_ids; i++) {
	rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL);
	if (rc >= 0) {
	num_processors++;
	cpu_set(i, cpu_possible_map);
	}
	}
	}

	static void __init xen_smp_prepare_boot_cpu(void)
	{
	BUG_ON(smp_processor_id() != 0);
	native_smp_prepare_boot_cpu();

	/* We've switched to the "real" per-cpu gdt, so make sure the
	old memory can be recycled */
	make_lowmem_page_readwrite(xen_initial_gdt);

	xen_setup_vcpu_info_placement();
	}

	static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
	{
	unsigned cpu;

	xen_init_lock_cpu(0);

	smp_store_cpu_info(0);
	cpu_data(0).x86_max_cores = 1;
	set_cpu_sibling_map(0);

	if (xen_smp_intr_init(0))
	BUG();

	if (!alloc_cpumask_var(&xen_cpu_initialized_map, GFP_KERNEL))
	panic("could not allocate xen_cpu_initialized_map\n");

	cpumask_copy(xen_cpu_initialized_map, cpumask_of(0));

	/* Restrict the possible_map according to max_cpus. */
	while ((num_possible_cpus() > 1) && (num_possible_cpus() > max_cpus)) {
	for (cpu = nr_cpu_ids - 1; !cpu_possible(cpu); cpu--)
	continue;
	cpu_clear(cpu, cpu_possible_map);
	}

	for_each_possible_cpu (cpu) {
	struct task_struct *idle;

	if (cpu == 0)
	continue;

	idle = fork_idle(cpu);
	if (IS_ERR(idle))
	panic("failed fork for CPU %d", cpu);

	cpu_set(cpu, cpu_present_map);
	}
	}

	static __cpuinit int
	cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
	{
	struct vcpu_guest_context *ctxt;
	struct desc_struct *gdt;

	if (cpumask_test_and_set_cpu(cpu, xen_cpu_initialized_map))
	return 0;

	ctxt = kzalloc(sizeof(*ctxt), GFP_KERNEL);
	if (ctxt == NULL)
	return -ENOMEM;

	gdt = get_cpu_gdt_table(cpu);

	ctxt->flags = VGCF_IN_KERNEL;
	ctxt->user_regs.ds = __USER_DS;
	ctxt->user_regs.es = __USER_DS;
	ctxt->user_regs.ss = __KERNEL_DS;
	#ifdef CONFIG_X86_32
	ctxt->user_regs.fs = __KERNEL_PERCPU;
	#else
	ctxt->gs_base_kernel = per_cpu_offset(cpu);
	#endif
	ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
	ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */

	memset(&ctxt->fpu_ctxt, 0, sizeof(ctxt->fpu_ctxt));

	xen_copy_trap_info(ctxt->trap_ctxt);

	ctxt->ldt_ents = 0;

	BUG_ON((unsigned long)gdt & ~PAGE_MASK);
	make_lowmem_page_readonly(gdt);

	ctxt->gdt_frames[0] = virt_to_mfn(gdt);
	ctxt->gdt_ents = GDT_ENTRIES;

	ctxt->user_regs.cs = __KERNEL_CS;
	ctxt->user_regs.esp = idle->thread.sp0 - sizeof(struct pt_regs);

	ctxt->kernel_ss = __KERNEL_DS;
	ctxt->kernel_sp = idle->thread.sp0;

	#ifdef CONFIG_X86_32
	ctxt->event_callback_cs = __KERNEL_CS;
	ctxt->failsafe_callback_cs = __KERNEL_CS;
	#endif
	ctxt->event_callback_eip = (unsigned long)xen_hypervisor_callback;
	ctxt->failsafe_callback_eip = (unsigned long)xen_failsafe_callback;

	per_cpu(xen_cr3, cpu) = __pa(swapper_pg_dir);
	ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_mfn(swapper_pg_dir));

	if (HYPERVISOR_vcpu_op(VCPUOP_initialise, cpu, ctxt))
	BUG();

	kfree(ctxt);
	return 0;
	}

	static int __cpuinit xen_cpu_up(unsigned int cpu)
	{
	struct task_struct *idle = idle_task(cpu);
	int rc;

	per_cpu(current_task, cpu) = idle;
	#ifdef CONFIG_X86_32
	irq_ctx_init(cpu);
	#else
	clear_tsk_thread_flag(idle, TIF_FORK);
	per_cpu(kernel_stack, cpu) =
	(unsigned long)task_stack_page(idle) -
	KERNEL_STACK_OFFSET + THREAD_SIZE;
	#endif
	xen_setup_timer(cpu);
	xen_init_lock_cpu(cpu);

	per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;

	/* make sure interrupts start blocked */
	per_cpu(xen_vcpu, cpu)->evtchn_upcall_mask = 1;

	rc = cpu_initialize_context(cpu, idle);
	if (rc)
	return rc;

	if (num_online_cpus() == 1)
	alternatives_smp_switch(1);

	rc = xen_smp_intr_init(cpu);
	if (rc)
	return rc;

	rc = HYPERVISOR_vcpu_op(VCPUOP_up, cpu, NULL);
	BUG_ON(rc);

	while(per_cpu(cpu_state, cpu) != CPU_ONLINE) {
	HYPERVISOR_sched_op(SCHEDOP_yield, 0);
	barrier();
	}

	return 0;
	}

	static void xen_smp_cpus_done(unsigned int max_cpus)
	{
	}

	#ifdef CONFIG_HOTPLUG_CPU
	static int xen_cpu_disable(void)
	{
	unsigned int cpu = smp_processor_id();
	if (cpu == 0)
	return -EBUSY;

	cpu_disable_common();

	load_cr3(swapper_pg_dir);
	return 0;
	}

	static void xen_cpu_die(unsigned int cpu)
	{
	while (HYPERVISOR_vcpu_op(VCPUOP_is_up, cpu, NULL)) {
	current->state = TASK_UNINTERRUPTIBLE;
	schedule_timeout(HZ/10);
	}
	unbind_from_irqhandler(per_cpu(resched_irq, cpu), NULL);
	unbind_from_irqhandler(per_cpu(callfunc_irq, cpu), NULL);
	unbind_from_irqhandler(per_cpu(debug_irq, cpu), NULL);
	unbind_from_irqhandler(per_cpu(callfuncsingle_irq, cpu), NULL);
	xen_uninit_lock_cpu(cpu);
	xen_teardown_timer(cpu);

	if (num_online_cpus() == 1)
	alternatives_smp_switch(0);
	}

	static void __cpuinit xen_play_dead(void) /* used only with CPU_HOTPLUG */
	{
	play_dead_common();
	HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
	cpu_bringup();
	}

	#else /* !CONFIG_HOTPLUG_CPU */
	static int xen_cpu_disable(void)
	{
	return -ENOSYS;
	}

	static void xen_cpu_die(unsigned int cpu)
	{
	BUG();
	}

	static void xen_play_dead(void)
	{
	BUG();
	}

	#endif
	static void stop_self(void *v)
	{
	int cpu = smp_processor_id();

	/* make sure we're not pinning something down */
	load_cr3(swapper_pg_dir);
	/* should set up a minimal gdt */

	HYPERVISOR_vcpu_op(VCPUOP_down, cpu, NULL);
	BUG();
	}

	static void xen_smp_send_stop(void)
	{
	smp_call_function(stop_self, NULL, 0);
	}

	static void xen_smp_send_reschedule(int cpu)
	{
	xen_send_IPI_one(cpu, XEN_RESCHEDULE_VECTOR);
	}

	static void xen_send_IPI_mask(const struct cpumask *mask,
	enum ipi_vector vector)
	{
	unsigned cpu;

	for_each_cpu_and(cpu, mask, cpu_online_mask)
	xen_send_IPI_one(cpu, vector);
	}

	static void xen_smp_send_call_function_ipi(const struct cpumask *mask)
	{
	int cpu;

	xen_send_IPI_mask(mask, XEN_CALL_FUNCTION_VECTOR);

	/* Make sure other vcpus get a chance to run if they need to. */
	for_each_cpu(cpu, mask) {
	if (xen_vcpu_stolen(cpu)) {
	HYPERVISOR_sched_op(SCHEDOP_yield, 0);
	break;
	}
	}
	}

	static void xen_smp_send_call_function_single_ipi(int cpu)
	{
	xen_send_IPI_mask(cpumask_of(cpu),
	XEN_CALL_FUNCTION_SINGLE_VECTOR);
	}

	static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id)
	{
	irq_enter();
	generic_smp_call_function_interrupt();
	inc_irq_stat(irq_call_count);
	irq_exit();

	return IRQ_HANDLED;
	}

	static irqreturn_t xen_call_function_single_interrupt(int irq, void *dev_id)
	{
	irq_enter();
	generic_smp_call_function_single_interrupt();
	inc_irq_stat(irq_call_count);
	irq_exit();

	return IRQ_HANDLED;
	}

	static const struct smp_ops xen_smp_ops __initdata = {
	.smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu,
	.smp_prepare_cpus = xen_smp_prepare_cpus,
	.smp_cpus_done = xen_smp_cpus_done,

	.cpu_up = xen_cpu_up,
	.cpu_die = xen_cpu_die,
	.cpu_disable = xen_cpu_disable,
	.play_dead = xen_play_dead,

	.smp_send_stop = xen_smp_send_stop,
	.smp_send_reschedule = xen_smp_send_reschedule,

	.send_call_func_ipi = xen_smp_send_call_function_ipi,
	.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi,
	};

	void __init xen_smp_init(void)
	{
	smp_ops = xen_smp_ops;
	xen_fill_possible_map();
	xen_init_spinlocks();
	}