xen: Fix possible user space selector corruption

[linux/fpc-iii.git] / arch / x86 / xen / smp.c

/*
 * 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/slab.h>
#include <linux/smp.h>
#include <linux/irq_work.h>
#include <linux/tick.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/xen.h>
#include <xen/page.h>
#include <xen/events.h>

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

cpumask_var_t xen_cpu_initialized_map;

struct xen_common_irq {
        int irq;
        char *name;
};
static DEFINE_PER_CPU(struct xen_common_irq, xen_resched_irq) = { .irq = -1 };
static DEFINE_PER_CPU(struct xen_common_irq, xen_callfunc_irq) = { .irq = -1 };
static DEFINE_PER_CPU(struct xen_common_irq, xen_callfuncsingle_irq) = { .irq = -1 };
static DEFINE_PER_CPU(struct xen_common_irq, xen_irq_work) = { .irq = -1 };
static DEFINE_PER_CPU(struct xen_common_irq, xen_debug_irq) = { .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);
static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id);

/*
 * Reschedule call back.
 */
static irqreturn_t xen_reschedule_interrupt(int irq, void *dev_id)
{
        inc_irq_stat(irq_resched_count);
        scheduler_ipi();

        return IRQ_HANDLED;
}

static void cpu_bringup(void)
{
        int cpu;

        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();

        notify_cpu_starting(cpu);

        set_cpu_online(cpu, true);

        this_cpu_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 void cpu_bringup_and_idle(void)
{
        cpu_bringup();
        cpu_startup_entry(CPUHP_ONLINE);
}

static void xen_smp_intr_free(unsigned int cpu)
{
        if (per_cpu(xen_resched_irq, cpu).irq >= 0) {
                unbind_from_irqhandler(per_cpu(xen_resched_irq, cpu).irq, NULL);
                per_cpu(xen_resched_irq, cpu).irq = -1;
                kfree(per_cpu(xen_resched_irq, cpu).name);
                per_cpu(xen_resched_irq, cpu).name = NULL;
        }
        if (per_cpu(xen_callfunc_irq, cpu).irq >= 0) {
                unbind_from_irqhandler(per_cpu(xen_callfunc_irq, cpu).irq, NULL);
                per_cpu(xen_callfunc_irq, cpu).irq = -1;
                kfree(per_cpu(xen_callfunc_irq, cpu).name);
                per_cpu(xen_callfunc_irq, cpu).name = NULL;
        }
        if (per_cpu(xen_debug_irq, cpu).irq >= 0) {
                unbind_from_irqhandler(per_cpu(xen_debug_irq, cpu).irq, NULL);
                per_cpu(xen_debug_irq, cpu).irq = -1;
                kfree(per_cpu(xen_debug_irq, cpu).name);
                per_cpu(xen_debug_irq, cpu).name = NULL;
        }
        if (per_cpu(xen_callfuncsingle_irq, cpu).irq >= 0) {
                unbind_from_irqhandler(per_cpu(xen_callfuncsingle_irq, cpu).irq,
                                       NULL);
                per_cpu(xen_callfuncsingle_irq, cpu).irq = -1;
                kfree(per_cpu(xen_callfuncsingle_irq, cpu).name);
                per_cpu(xen_callfuncsingle_irq, cpu).name = NULL;
        }
        if (xen_hvm_domain())
                return;

        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_irq_work, cpu).name);
                per_cpu(xen_irq_work, cpu).name = NULL;
        }
};
static int xen_smp_intr_init(unsigned int cpu)
{
        int rc;
        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(xen_resched_irq, cpu).irq = rc;
        per_cpu(xen_resched_irq, cpu).name = resched_name;

        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(xen_callfunc_irq, cpu).irq = rc;
        per_cpu(xen_callfunc_irq, cpu).name = callfunc_name;

        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(xen_debug_irq, cpu).irq = rc;
        per_cpu(xen_debug_irq, cpu).name = debug_name;

        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(xen_callfuncsingle_irq, cpu).irq = rc;
        per_cpu(xen_callfuncsingle_irq, cpu).name = callfunc_name;

        /*
         * The IRQ worker on PVHVM goes through the native path and uses the
         * IPI mechanism.
         */
        if (xen_hvm_domain())
                return 0;

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

        return 0;

 fail:
        xen_smp_intr_free(cpu);
        return rc;
}

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

        if (xen_initial_domain())
                return;

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

static void __init xen_filter_cpu_maps(void)
{
        int i, rc;
        unsigned int subtract = 0;

        if (!xen_initial_domain())
                return;

        num_processors = 0;
        disabled_cpus = 0;
        for (i = 0; i < nr_cpu_ids; i++) {
                rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL);
                if (rc >= 0) {
                        num_processors++;
                        set_cpu_possible(i, true);
                } else {
                        set_cpu_possible(i, false);
                        set_cpu_present(i, false);
                        subtract++;
                }
        }
#ifdef CONFIG_HOTPLUG_CPU
        /* This is akin to using 'nr_cpus' on the Linux command line.
         * Which is OK as when we use 'dom0_max_vcpus=X' we can only
         * have up to X, while nr_cpu_ids is greater than X. This
         * normally is not a problem, except when CPU hotplugging
         * is involved and then there might be more than X CPUs
         * in the guest - which will not work as there is no
         * hypercall to expand the max number of VCPUs an already
         * running guest has. So cap it up to X. */
        if (subtract)
                nr_cpu_ids = nr_cpu_ids - subtract;
#endif

}

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

        if (xen_pv_domain()) {
                /* 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);

#ifdef CONFIG_X86_32
                /*
                 * Xen starts us with XEN_FLAT_RING1_DS, but linux code
                 * expects __USER_DS
                 */
                loadsegment(ds, __USER_DS);
                loadsegment(es, __USER_DS);
#endif

                xen_filter_cpu_maps();
                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_smp_prepare_cpus(unsigned int max_cpus)
{
        unsigned cpu;
        unsigned int i;

        if (skip_ioapic_setup) {
                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_store_boot_cpu_info();
        cpu_data(0).x86_max_cores = 1;

        for_each_possible_cpu(i) {
                zalloc_cpumask_var(&per_cpu(cpu_sibling_map, i), GFP_KERNEL);
                zalloc_cpumask_var(&per_cpu(cpu_core_map, i), GFP_KERNEL);
                zalloc_cpumask_var(&per_cpu(cpu_llc_shared_map, i), GFP_KERNEL);
        }
        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;
                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)
                return -ENOMEM;

        gdt = get_cpu_gdt_table(cpu);

        ctxt->flags = VGCF_IN_KERNEL;
        ctxt->user_regs.ss = __KERNEL_DS;
#ifdef CONFIG_X86_32
        ctxt->user_regs.fs = __KERNEL_PERCPU;
        ctxt->user_regs.gs = __KERNEL_STACK_CANARY;
#else
        ctxt->gs_base_kernel = per_cpu_offset(cpu);
#endif
        ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;

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

        {
                ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
                ctxt->user_regs.ds = __USER_DS;
                ctxt->user_regs.es = __USER_DS;

                xen_copy_trap_info(ctxt->trap_ctxt);

                ctxt->ldt_ents = 0;

                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;

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

        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 xen_cpu_up(unsigned int cpu, struct task_struct *idle)
{
        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_runstate_info(cpu);
        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)
                /* Just in case we booted with a single CPU. */
                alternatives_enable_smp();

        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, NULL);
                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 (xen_pv_domain() && HYPERVISOR_vcpu_op(VCPUOP_is_up, cpu, NULL)) {
                current->state = TASK_UNINTERRUPTIBLE;
                schedule_timeout(HZ/10);
        }
        xen_smp_intr_free(cpu);
        xen_uninit_lock_cpu(cpu);
        xen_teardown_timer(cpu);
}

static void xen_play_dead(void) /* used only with HOTPLUG_CPU */
{
        play_dead_common();
        HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
        cpu_bringup();
        /*
         * commit 4b0c0f294 (tick: Cleanup NOHZ per cpu data on cpu down)
         * clears certain data that the cpu_idle loop (which called us
         * and that we return from) expects. The only way to get that
         * data back is to call:
         */
        tick_nohz_idle_enter();
}

#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 */

        set_cpu_online(cpu, false);

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

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

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,
                              int 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, NULL);
                        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 inline int xen_map_vector(int vector)
{
        int xen_vector;

        switch (vector) {
        case RESCHEDULE_VECTOR:
                xen_vector = XEN_RESCHEDULE_VECTOR;
                break;
        case CALL_FUNCTION_VECTOR:
                xen_vector = XEN_CALL_FUNCTION_VECTOR;
                break;
        case CALL_FUNCTION_SINGLE_VECTOR:
                xen_vector = XEN_CALL_FUNCTION_SINGLE_VECTOR;
                break;
        case IRQ_WORK_VECTOR:
                xen_vector = XEN_IRQ_WORK_VECTOR;
                break;
#ifdef CONFIG_X86_64
        case NMI_VECTOR:
        case APIC_DM_NMI: /* Some use that instead of NMI_VECTOR */
                xen_vector = XEN_NMI_VECTOR;
                break;
#endif
        default:
                xen_vector = -1;
                printk(KERN_ERR "xen: vector 0x%x is not implemented\n",
                        vector);
        }

        return xen_vector;
}

void xen_send_IPI_mask(const struct cpumask *mask,
                              int vector)
{
        int xen_vector = xen_map_vector(vector);

        if (xen_vector >= 0)
                __xen_send_IPI_mask(mask, xen_vector);
}

void xen_send_IPI_all(int vector)
{
        int xen_vector = xen_map_vector(vector);

        if (xen_vector >= 0)
                __xen_send_IPI_mask(cpu_online_mask, xen_vector);
}

void xen_send_IPI_self(int vector)
{
        int xen_vector = xen_map_vector(vector);

        if (xen_vector >= 0)
                xen_send_IPI_one(smp_processor_id(), xen_vector);
}

void xen_send_IPI_mask_allbutself(const struct cpumask *mask,
                                int vector)
{
        unsigned cpu;
        unsigned int this_cpu = smp_processor_id();
        int xen_vector = xen_map_vector(vector);

        if (!(num_online_cpus() > 1) || (xen_vector < 0))
                return;

        for_each_cpu_and(cpu, mask, cpu_online_mask) {
                if (this_cpu == cpu)
                        continue;

                xen_send_IPI_one(cpu, xen_vector);
        }
}

void xen_send_IPI_allbutself(int vector)
{
        xen_send_IPI_mask_allbutself(cpu_online_mask, 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 irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id)
{
        irq_enter();
        irq_work_run();
        inc_irq_stat(apic_irq_work_irqs);
        irq_exit();

        return IRQ_HANDLED;
}

static const struct smp_ops xen_smp_ops __initconst = {
        .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,

        .stop_other_cpus = xen_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;
        xen_fill_possible_map();
}

static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus)
{
        native_smp_prepare_cpus(max_cpus);
        WARN_ON(xen_smp_intr_init(0));

        xen_init_lock_cpu(0);
}

static int xen_hvm_cpu_up(unsigned int cpu, struct task_struct *tidle)
{
        int rc;
        /*
         * xen_smp_intr_init() needs to run before native_cpu_up()
         * so that IPI vectors are set up on the booting CPU before
         * it is marked online in native_cpu_up().
        */
        rc = xen_smp_intr_init(cpu);
        WARN_ON(rc);
        if (!rc)
                rc =  native_cpu_up(cpu, tidle);

        /*
         * We must initialize the slowpath CPU kicker _after_ the native
         * path has executed. If we initialized it before none of the
         * unlocker IPI kicks would reach the booting CPU as the booting
         * CPU had not set itself 'online' in cpu_online_mask. That mask
         * is checked when IPIs are sent (on HVM at least).
         */
        xen_init_lock_cpu(cpu);
        return rc;
}

static void xen_hvm_cpu_die(unsigned int cpu)
{
        xen_cpu_die(cpu);
        native_cpu_die(cpu);
}

void __init xen_hvm_smp_init(void)
{
        if (!xen_have_vector_callback)
                return;
        smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
        smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
        smp_ops.cpu_up = xen_hvm_cpu_up;
        smp_ops.cpu_die = xen_hvm_cpu_die;
        smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
        smp_ops.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi;
        smp_ops.smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu;
}