arch/x86/xen/smp_pv.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * 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/sched/task_stack.h>
 #include <linux/err.h>
 #include <linux/slab.h>
 #include <linux/smp.h>
 #include <linux/irq_work.h>
 #include <linux/tick.h>
 #include <linux/nmi.h>
 #include <linux/cpuhotplug.h>
 #include <linux/stackprotector.h>
 #include <linux/pgtable.h>

 #include <asm/paravirt.h>
 #include <asm/idtentry.h>
 #include <asm/desc.h>
 #include <asm/cpu.h>
 #include <asm/apic.h>
 #include <asm/io_apic.h>

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

 #include <asm/spec-ctrl.h>
 #include <asm/xen/interface.h>
 #include <asm/xen/hypercall.h>

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

 #include <xen/hvc-console.h>
 #include "xen-ops.h"

 cpumask_var_t xen_cpu_initialized_map;

 static DEFINE_PER_CPU(struct xen_common_irq, xen_irq_work) = { .irq = -1 };
 static DEFINE_PER_CPU(struct xen_common_irq, xen_pmu_irq) = { .irq = -1 };

 static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id);

 static void cpu_bringup(void)
 {
 	int cpu;

 	cr4_init();
 	cpuhp_ap_sync_alive();
 	cpu_init();
 	fpu__init_cpu();
 	touch_softlockup_watchdog();

 	/* PVH runs in ring 0 and allows us to do native syscalls. Yay! */
 	if (!xen_feature(XENFEAT_supervisor_mode_kernel)) {
 		xen_enable_sysenter();
 		xen_enable_syscall();
 	}
 	cpu = smp_processor_id();
 	smp_store_cpu_info(cpu);
 	set_cpu_sibling_map(cpu);

 	speculative_store_bypass_ht_init();

 	xen_setup_cpu_clockevents();

 	notify_cpu_starting(cpu);

 	set_cpu_online(cpu, true);

 	smp_mb();

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

 asmlinkage __visible void cpu_bringup_and_idle(void)
 {
 	cpu_bringup();
 	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
 }

 void xen_smp_intr_free_pv(unsigned int cpu)
 {
 	kfree(per_cpu(xen_irq_work, cpu).name);
 	per_cpu(xen_irq_work, cpu).name = NULL;
 	if (per_cpu(xen_irq_work, cpu).irq >= 0) {
 		unbind_from_irqhandler(per_cpu(xen_irq_work, cpu).irq, NULL);
 		per_cpu(xen_irq_work, cpu).irq = -1;
 	}

 	kfree(per_cpu(xen_pmu_irq, cpu).name);
 	per_cpu(xen_pmu_irq, cpu).name = NULL;
 	if (per_cpu(xen_pmu_irq, cpu).irq >= 0) {
 		unbind_from_irqhandler(per_cpu(xen_pmu_irq, cpu).irq, NULL);
 		per_cpu(xen_pmu_irq, cpu).irq = -1;
 	}
 }

 int xen_smp_intr_init_pv(unsigned int cpu)
 {
 	int rc;
 	char *callfunc_name, *pmu_name;

 	callfunc_name = kasprintf(GFP_KERNEL, "irqwork%d", cpu);
 	per_cpu(xen_irq_work, cpu).name = callfunc_name;
 	rc = bind_ipi_to_irqhandler(XEN_IRQ_WORK_VECTOR,
 				    cpu,
 				    xen_irq_work_interrupt,
 				    IRQF_PERCPU|IRQF_NOBALANCING,
 				    callfunc_name,
 				    NULL);
 	if (rc < 0)
 		goto fail;
 	per_cpu(xen_irq_work, cpu).irq = rc;

 	if (is_xen_pmu) {
 		pmu_name = kasprintf(GFP_KERNEL, "pmu%d", cpu);
 		per_cpu(xen_pmu_irq, cpu).name = pmu_name;
 		rc = bind_virq_to_irqhandler(VIRQ_XENPMU, cpu,
 					     xen_pmu_irq_handler,
 					     IRQF_PERCPU|IRQF_NOBALANCING,
 					     pmu_name, NULL);
 		if (rc < 0)
 			goto fail;
 		per_cpu(xen_pmu_irq, cpu).irq = rc;
 	}

 	return 0;

  fail:
 	xen_smp_intr_free_pv(cpu);
 	return rc;
 }

 static void __init xen_pv_smp_config(void)
 {
 	u32 apicid = 0;
 	int i;

 	topology_register_boot_apic(apicid);

 	for (i = 0; i < nr_cpu_ids; i++)
 		topology_register_apic(apicid++, CPU_ACPIID_INVALID, true);

 	/* Pretend to be a proper enumerated system */
 	smp_found_config = 1;
 }

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

 	if (!xen_feature(XENFEAT_writable_page_tables))
 		/* 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();

 	/*
 	 * The alternative logic (which patches the unlock/lock) runs before
 	 * the smp bootup up code is activated. Hence we need to set this up
 	 * the core kernel is being patched. Otherwise we will have only
 	 * modules patched but not core code.
 	 */
 	xen_init_spinlocks();
 }

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

 	if (ioapic_is_disabled) {
 		char *m = (max_cpus == 0) ?
 			"The nosmp parameter is incompatible with Xen; " \
 			"use Xen dom0_max_vcpus=1 parameter" :
 			"The noapic parameter is incompatible with Xen";

 		xen_raw_printk(m);
 		panic(m);
 	}
 	xen_init_lock_cpu(0);

 	smp_prepare_cpus_common();

 	speculative_store_bypass_ht_init();

 	xen_pmu_init(0);

 	if (xen_smp_intr_init(0) || xen_smp_intr_init_pv(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;
 		set_cpu_possible(cpu, false);
 	}

 	for_each_possible_cpu(cpu)
 		set_cpu_present(cpu, true);
 }

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

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

 	ctxt = kzalloc(sizeof(*ctxt), GFP_KERNEL);
 	if (ctxt == NULL) {
 		cpumask_clear_cpu(cpu, xen_cpu_initialized_map);
 		return -ENOMEM;
 	}

 	gdt = get_cpu_gdt_rw(cpu);

 	/*
 	 * Bring up the CPU in cpu_bringup_and_idle() with the stack
 	 * pointing just below where pt_regs would be if it were a normal
 	 * kernel entry.
 	 */
 	ctxt->user_regs.eip = (unsigned long)asm_cpu_bringup_and_idle;
 	ctxt->flags = VGCF_IN_KERNEL;
 	ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
 	ctxt->user_regs.ds = __USER_DS;
 	ctxt->user_regs.es = __USER_DS;
 	ctxt->user_regs.ss = __KERNEL_DS;
 	ctxt->user_regs.cs = __KERNEL_CS;
 	ctxt->user_regs.esp = (unsigned long)task_pt_regs(idle);

 	xen_copy_trap_info(ctxt->trap_ctxt);

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

 	gdt_mfn = arbitrary_virt_to_mfn(gdt);
 	make_lowmem_page_readonly(gdt);
 	make_lowmem_page_readonly(mfn_to_virt(gdt_mfn));

 	ctxt->gdt_frames[0] = gdt_mfn;
 	ctxt->gdt_ents      = GDT_ENTRIES;

 	/*
 	 * Set SS:SP that Xen will use when entering guest kernel mode
 	 * from guest user mode.  Subsequent calls to load_sp0() can
 	 * change this value.
 	 */
 	ctxt->kernel_ss = __KERNEL_DS;
 	ctxt->kernel_sp = task_top_of_stack(idle);

 	ctxt->gs_base_kernel = per_cpu_offset(cpu);
 	ctxt->event_callback_eip    =
 		(unsigned long)xen_asm_exc_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_gfn(swapper_pg_dir));
 	if (HYPERVISOR_vcpu_op(VCPUOP_initialise, xen_vcpu_nr(cpu), ctxt))
 		BUG();

 	kfree(ctxt);
 	return 0;
 }

 static int xen_pv_kick_ap(unsigned int cpu, struct task_struct *idle)
 {
 	int rc;

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

 	xen_setup_runstate_info(cpu);

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

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

 	xen_pmu_init(cpu);
 	mc_percpu_init(cpu);

 	/*
 	 * Why is this a BUG? If the hypercall fails then everything can be
 	 * rolled back, no?
 	 */
 	BUG_ON(HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL));

 	return 0;
 }

 static void xen_pv_poll_sync_state(void)
 {
 	HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
 }

 #ifdef CONFIG_HOTPLUG_CPU
 static int xen_pv_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_pv_cpu_die(unsigned int cpu)
 {
 	while (HYPERVISOR_vcpu_op(VCPUOP_is_up, xen_vcpu_nr(cpu), NULL)) {
 		__set_current_state(TASK_UNINTERRUPTIBLE);
 		schedule_timeout(HZ/10);
 	}
 }

 static void xen_pv_cleanup_dead_cpu(unsigned int cpu)
 {
 	xen_smp_intr_free(cpu);
 	xen_uninit_lock_cpu(cpu);
 	xen_teardown_timer(cpu);
 	xen_pmu_finish(cpu);
 }

 static void __noreturn xen_pv_play_dead(void) /* used only with HOTPLUG_CPU */
 {
 	play_dead_common();
 	HYPERVISOR_vcpu_op(VCPUOP_down, xen_vcpu_nr(smp_processor_id()), NULL);
 	xen_cpu_bringup_again((unsigned long)task_pt_regs(current));
 	BUG();
 }

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

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

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

 static void __noreturn xen_pv_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 */

 	set_cpu_online(cpu, false);

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

 static void xen_pv_stop_other_cpus(int wait)
 {
 	smp_call_function(stop_self, NULL, wait);
 }

 static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id)
 {
 	irq_work_run();
 	inc_irq_stat(apic_irq_work_irqs);

 	return IRQ_HANDLED;
 }

 void __init xen_smp_count_cpus(void)
 {
 	unsigned int cpus;

 	for (cpus = 0; cpus < nr_cpu_ids; cpus++) {
 		if (HYPERVISOR_vcpu_op(VCPUOP_is_up, cpus, NULL) < 0)
 			break;
 	}

 	pr_info("Xen PV: Detected %u vCPUS\n", cpus);
 	if (cpus < nr_cpu_ids)
 		set_nr_cpu_ids(cpus);
 }

 static const struct smp_ops xen_smp_ops __initconst = {
 	.smp_prepare_boot_cpu = xen_pv_smp_prepare_boot_cpu,
 	.smp_prepare_cpus = xen_pv_smp_prepare_cpus,
 	.smp_cpus_done = xen_smp_cpus_done,

 	.kick_ap_alive = xen_pv_kick_ap,
 	.cpu_die = xen_pv_cpu_die,
 	.cleanup_dead_cpu = xen_pv_cleanup_dead_cpu,
 	.poll_sync_state = xen_pv_poll_sync_state,
 	.cpu_disable = xen_pv_cpu_disable,
 	.play_dead = xen_pv_play_dead,

 	.stop_other_cpus = xen_pv_stop_other_cpus,
 	.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;

 	/* Avoid searching for BIOS MP tables */
 	x86_init.mpparse.find_mptable		= x86_init_noop;
 	x86_init.mpparse.early_parse_smp_cfg	= x86_init_noop;

 	/* XEN/PV Dom0 has halfways sane topology information via CPUID/MADT */
 	if (xen_initial_domain())
 		x86_init.mpparse.parse_smp_cfg	= x86_init_noop;
 	else
 		x86_init.mpparse.parse_smp_cfg	= xen_pv_smp_config;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* 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/sched/task_stack.h>
	#include <linux/err.h>
	#include <linux/slab.h>
	#include <linux/smp.h>
	#include <linux/irq_work.h>
	#include <linux/tick.h>
	#include <linux/nmi.h>
	#include <linux/cpuhotplug.h>
	#include <linux/stackprotector.h>
	#include <linux/pgtable.h>

	#include <asm/paravirt.h>
	#include <asm/idtentry.h>
	#include <asm/desc.h>
	#include <asm/cpu.h>
	#include <asm/apic.h>
	#include <asm/io_apic.h>

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

	#include <asm/spec-ctrl.h>
	#include <asm/xen/interface.h>
	#include <asm/xen/hypercall.h>

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

	#include <xen/hvc-console.h>
	#include "xen-ops.h"

	cpumask_var_t xen_cpu_initialized_map;

	static DEFINE_PER_CPU(struct xen_common_irq, xen_irq_work) = { .irq = -1 };
	static DEFINE_PER_CPU(struct xen_common_irq, xen_pmu_irq) = { .irq = -1 };

	static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id);

	static void cpu_bringup(void)
	{
	int cpu;

	cr4_init();
	cpuhp_ap_sync_alive();
	cpu_init();
	fpu__init_cpu();
	touch_softlockup_watchdog();

	/* PVH runs in ring 0 and allows us to do native syscalls. Yay! */
	if (!xen_feature(XENFEAT_supervisor_mode_kernel)) {
	xen_enable_sysenter();
	xen_enable_syscall();
	}
	cpu = smp_processor_id();
	smp_store_cpu_info(cpu);
	set_cpu_sibling_map(cpu);

	speculative_store_bypass_ht_init();

	xen_setup_cpu_clockevents();

	notify_cpu_starting(cpu);

	set_cpu_online(cpu, true);

	smp_mb();

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

	asmlinkage __visible void cpu_bringup_and_idle(void)
	{
	cpu_bringup();
	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
	}

	void xen_smp_intr_free_pv(unsigned int cpu)
	{
	kfree(per_cpu(xen_irq_work, cpu).name);
	per_cpu(xen_irq_work, cpu).name = NULL;
	if (per_cpu(xen_irq_work, cpu).irq >= 0) {
	unbind_from_irqhandler(per_cpu(xen_irq_work, cpu).irq, NULL);
	per_cpu(xen_irq_work, cpu).irq = -1;
	}

	kfree(per_cpu(xen_pmu_irq, cpu).name);
	per_cpu(xen_pmu_irq, cpu).name = NULL;
	if (per_cpu(xen_pmu_irq, cpu).irq >= 0) {
	unbind_from_irqhandler(per_cpu(xen_pmu_irq, cpu).irq, NULL);
	per_cpu(xen_pmu_irq, cpu).irq = -1;
	}
	}

	int xen_smp_intr_init_pv(unsigned int cpu)
	{
	int rc;
	char callfunc_name, pmu_name;

	callfunc_name = kasprintf(GFP_KERNEL, "irqwork%d", cpu);
	per_cpu(xen_irq_work, cpu).name = callfunc_name;
	rc = bind_ipi_to_irqhandler(XEN_IRQ_WORK_VECTOR,
	cpu,
	xen_irq_work_interrupt,
	IRQF_PERCPU\|IRQF_NOBALANCING,
	callfunc_name,
	NULL);
	if (rc < 0)
	goto fail;
	per_cpu(xen_irq_work, cpu).irq = rc;

	if (is_xen_pmu) {
	pmu_name = kasprintf(GFP_KERNEL, "pmu%d", cpu);
	per_cpu(xen_pmu_irq, cpu).name = pmu_name;
	rc = bind_virq_to_irqhandler(VIRQ_XENPMU, cpu,
	xen_pmu_irq_handler,
	IRQF_PERCPU\|IRQF_NOBALANCING,
	pmu_name, NULL);
	if (rc < 0)
	goto fail;
	per_cpu(xen_pmu_irq, cpu).irq = rc;
	}

	return 0;

	fail:
	xen_smp_intr_free_pv(cpu);
	return rc;
	}

	static void __init xen_pv_smp_config(void)
	{
	u32 apicid = 0;
	int i;

	topology_register_boot_apic(apicid);

	for (i = 0; i < nr_cpu_ids; i++)
	topology_register_apic(apicid++, CPU_ACPIID_INVALID, true);

	/* Pretend to be a proper enumerated system */
	smp_found_config = 1;
	}

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

	if (!xen_feature(XENFEAT_writable_page_tables))
	/* 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();

	/*
	* The alternative logic (which patches the unlock/lock) runs before
	* the smp bootup up code is activated. Hence we need to set this up
	* the core kernel is being patched. Otherwise we will have only
	* modules patched but not core code.
	*/
	xen_init_spinlocks();
	}

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

	if (ioapic_is_disabled) {
	char *m = (max_cpus == 0) ?
	"The nosmp parameter is incompatible with Xen; " \
	"use Xen dom0_max_vcpus=1 parameter" :
	"The noapic parameter is incompatible with Xen";

	xen_raw_printk(m);
	panic(m);
	}
	xen_init_lock_cpu(0);

	smp_prepare_cpus_common();

	speculative_store_bypass_ht_init();

	xen_pmu_init(0);

	if (xen_smp_intr_init(0) \|\| xen_smp_intr_init_pv(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;
	set_cpu_possible(cpu, false);
	}

	for_each_possible_cpu(cpu)
	set_cpu_present(cpu, true);
	}

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

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

	ctxt = kzalloc(sizeof(*ctxt), GFP_KERNEL);
	if (ctxt == NULL) {
	cpumask_clear_cpu(cpu, xen_cpu_initialized_map);
	return -ENOMEM;
	}

	gdt = get_cpu_gdt_rw(cpu);

	/*
	* Bring up the CPU in cpu_bringup_and_idle() with the stack
	* pointing just below where pt_regs would be if it were a normal
	* kernel entry.
	*/
	ctxt->user_regs.eip = (unsigned long)asm_cpu_bringup_and_idle;
	ctxt->flags = VGCF_IN_KERNEL;
	ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
	ctxt->user_regs.ds = __USER_DS;
	ctxt->user_regs.es = __USER_DS;
	ctxt->user_regs.ss = __KERNEL_DS;
	ctxt->user_regs.cs = __KERNEL_CS;
	ctxt->user_regs.esp = (unsigned long)task_pt_regs(idle);

	xen_copy_trap_info(ctxt->trap_ctxt);

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

	gdt_mfn = arbitrary_virt_to_mfn(gdt);
	make_lowmem_page_readonly(gdt);
	make_lowmem_page_readonly(mfn_to_virt(gdt_mfn));

	ctxt->gdt_frames[0] = gdt_mfn;
	ctxt->gdt_ents = GDT_ENTRIES;

	/*
	* Set SS:SP that Xen will use when entering guest kernel mode
	* from guest user mode. Subsequent calls to load_sp0() can
	* change this value.
	*/
	ctxt->kernel_ss = __KERNEL_DS;
	ctxt->kernel_sp = task_top_of_stack(idle);

	ctxt->gs_base_kernel = per_cpu_offset(cpu);
	ctxt->event_callback_eip =
	(unsigned long)xen_asm_exc_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_gfn(swapper_pg_dir));
	if (HYPERVISOR_vcpu_op(VCPUOP_initialise, xen_vcpu_nr(cpu), ctxt))
	BUG();

	kfree(ctxt);
	return 0;
	}

	static int xen_pv_kick_ap(unsigned int cpu, struct task_struct *idle)
	{
	int rc;

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

	xen_setup_runstate_info(cpu);

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

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

	xen_pmu_init(cpu);
	mc_percpu_init(cpu);

	/*
	* Why is this a BUG? If the hypercall fails then everything can be
	* rolled back, no?
	*/
	BUG_ON(HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL));

	return 0;
	}

	static void xen_pv_poll_sync_state(void)
	{
	HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
	}

	#ifdef CONFIG_HOTPLUG_CPU
	static int xen_pv_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_pv_cpu_die(unsigned int cpu)
	{
	while (HYPERVISOR_vcpu_op(VCPUOP_is_up, xen_vcpu_nr(cpu), NULL)) {
	__set_current_state(TASK_UNINTERRUPTIBLE);
	schedule_timeout(HZ/10);
	}
	}

	static void xen_pv_cleanup_dead_cpu(unsigned int cpu)
	{
	xen_smp_intr_free(cpu);
	xen_uninit_lock_cpu(cpu);
	xen_teardown_timer(cpu);
	xen_pmu_finish(cpu);
	}

	static void __noreturn xen_pv_play_dead(void) /* used only with HOTPLUG_CPU */
	{
	play_dead_common();
	HYPERVISOR_vcpu_op(VCPUOP_down, xen_vcpu_nr(smp_processor_id()), NULL);
	xen_cpu_bringup_again((unsigned long)task_pt_regs(current));
	BUG();
	}

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

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

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

	static void __noreturn xen_pv_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 */

	set_cpu_online(cpu, false);

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

	static void xen_pv_stop_other_cpus(int wait)
	{
	smp_call_function(stop_self, NULL, wait);
	}

	static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id)
	{
	irq_work_run();
	inc_irq_stat(apic_irq_work_irqs);

	return IRQ_HANDLED;
	}

	void __init xen_smp_count_cpus(void)
	{
	unsigned int cpus;

	for (cpus = 0; cpus < nr_cpu_ids; cpus++) {
	if (HYPERVISOR_vcpu_op(VCPUOP_is_up, cpus, NULL) < 0)
	break;
	}

	pr_info("Xen PV: Detected %u vCPUS\n", cpus);
	if (cpus < nr_cpu_ids)
	set_nr_cpu_ids(cpus);
	}

	static const struct smp_ops xen_smp_ops __initconst = {
	.smp_prepare_boot_cpu = xen_pv_smp_prepare_boot_cpu,
	.smp_prepare_cpus = xen_pv_smp_prepare_cpus,
	.smp_cpus_done = xen_smp_cpus_done,

	.kick_ap_alive = xen_pv_kick_ap,
	.cpu_die = xen_pv_cpu_die,
	.cleanup_dead_cpu = xen_pv_cleanup_dead_cpu,
	.poll_sync_state = xen_pv_poll_sync_state,
	.cpu_disable = xen_pv_cpu_disable,
	.play_dead = xen_pv_play_dead,

	.stop_other_cpus = xen_pv_stop_other_cpus,
	.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;

	/* Avoid searching for BIOS MP tables */
	x86_init.mpparse.find_mptable = x86_init_noop;
	x86_init.mpparse.early_parse_smp_cfg = x86_init_noop;

	/* XEN/PV Dom0 has halfways sane topology information via CPUID/MADT */
	if (xen_initial_domain())
	x86_init.mpparse.parse_smp_cfg = x86_init_noop;
	else
	x86_init.mpparse.parse_smp_cfg = xen_pv_smp_config;
	}