Pileus Git - ~andy/linux/blob - arch/x86/xen/smp.c

   1 /*
   2  * Xen SMP support
   3  *
   4  * This file implements the Xen versions of smp_ops.  SMP under Xen is
   5  * very straightforward.  Bringing a CPU up is simply a matter of
   6  * loading its initial context and setting it running.
   7  *
   8  * IPIs are handled through the Xen event mechanism.
   9  *
  10  * Because virtual CPUs can be scheduled onto any real CPU, there's no
  11  * useful topology information for the kernel to make use of.  As a
  12  * result, all CPUs are treated as if they're single-core and
  13  * single-threaded.
  14  */
  15 #include <linux/sched.h>
  16 #include <linux/err.h>
  17 #include <linux/slab.h>
  18 #include <linux/smp.h>
  19
  20 #include <asm/paravirt.h>
  21 #include <asm/desc.h>
  22 #include <asm/pgtable.h>
  23 #include <asm/cpu.h>
  24
  25 #include <xen/interface/xen.h>
  26 #include <xen/interface/vcpu.h>
  27
  28 #include <asm/xen/interface.h>
  29 #include <asm/xen/hypercall.h>
  30
  31 #include <xen/xen.h>
  32 #include <xen/page.h>
  33 #include <xen/events.h>
  34
  35 #include <xen/hvc-console.h>
  36 #include "xen-ops.h"
  37 #include "mmu.h"
  38
  39 cpumask_var_t xen_cpu_initialized_map;
  40
  41 static DEFINE_PER_CPU(int, xen_resched_irq);
  42 static DEFINE_PER_CPU(int, xen_callfunc_irq);
  43 static DEFINE_PER_CPU(int, xen_callfuncsingle_irq);
  44 static DEFINE_PER_CPU(int, xen_debug_irq) = -1;
  45
  46 static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id);
  47 static irqreturn_t xen_call_function_single_interrupt(int irq, void *dev_id);
  48
  49 /*
  50  * Reschedule call back.
  51  */
  52 static irqreturn_t xen_reschedule_interrupt(int irq, void *dev_id)
  53 {
  54         inc_irq_stat(irq_resched_count);
  55         scheduler_ipi();
  56
  57         return IRQ_HANDLED;
  58 }
  59
  60 static void __cpuinit cpu_bringup(void)
  61 {
  62         int cpu;
  63
  64         cpu_init();
  65         touch_softlockup_watchdog();
  66         preempt_disable();
  67
  68         xen_enable_sysenter();
  69         xen_enable_syscall();
  70
  71         cpu = smp_processor_id();
  72         smp_store_cpu_info(cpu);
  73         cpu_data(cpu).x86_max_cores = 1;
  74         set_cpu_sibling_map(cpu);
  75
  76         xen_setup_cpu_clockevents();
  77
  78         notify_cpu_starting(cpu);
  79
  80         ipi_call_lock();
  81         set_cpu_online(cpu, true);
  82         ipi_call_unlock();
  83
  84         this_cpu_write(cpu_state, CPU_ONLINE);
  85
  86         wmb();
  87
  88         /* We can take interrupts now: we're officially "up". */
  89         local_irq_enable();
  90
  91         wmb();                  /* make sure everything is out */
  92 }
  93
  94 static void __cpuinit cpu_bringup_and_idle(void)
  95 {
  96         cpu_bringup();
  97         cpu_idle();
  98 }
  99
 100 static int xen_smp_intr_init(unsigned int cpu)
 101 {
 102         int rc;
 103         const char *resched_name, *callfunc_name, *debug_name;
 104
 105         resched_name = kasprintf(GFP_KERNEL, "resched%d", cpu);
 106         rc = bind_ipi_to_irqhandler(XEN_RESCHEDULE_VECTOR,
 107                                     cpu,
 108                                     xen_reschedule_interrupt,
 109                                     IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
 110                                     resched_name,
 111                                     NULL);
 112         if (rc < 0)
 113                 goto fail;
 114         per_cpu(xen_resched_irq, cpu) = rc;
 115
 116         callfunc_name = kasprintf(GFP_KERNEL, "callfunc%d", cpu);
 117         rc = bind_ipi_to_irqhandler(XEN_CALL_FUNCTION_VECTOR,
 118                                     cpu,
 119                                     xen_call_function_interrupt,
 120                                     IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
 121                                     callfunc_name,
 122                                     NULL);
 123         if (rc < 0)
 124                 goto fail;
 125         per_cpu(xen_callfunc_irq, cpu) = rc;
 126
 127         debug_name = kasprintf(GFP_KERNEL, "debug%d", cpu);
 128         rc = bind_virq_to_irqhandler(VIRQ_DEBUG, cpu, xen_debug_interrupt,
 129                                      IRQF_DISABLED | IRQF_PERCPU | IRQF_NOBALANCING,
 130                                      debug_name, NULL);
 131         if (rc < 0)
 132                 goto fail;
 133         per_cpu(xen_debug_irq, cpu) = rc;
 134
 135         callfunc_name = kasprintf(GFP_KERNEL, "callfuncsingle%d", cpu);
 136         rc = bind_ipi_to_irqhandler(XEN_CALL_FUNCTION_SINGLE_VECTOR,
 137                                     cpu,
 138                                     xen_call_function_single_interrupt,
 139                                     IRQF_DISABLED|IRQF_PERCPU|IRQF_NOBALANCING,
 140                                     callfunc_name,
 141                                     NULL);
 142         if (rc < 0)
 143                 goto fail;
 144         per_cpu(xen_callfuncsingle_irq, cpu) = rc;
 145
 146         return 0;
 147
 148  fail:
 149         if (per_cpu(xen_resched_irq, cpu) >= 0)
 150                 unbind_from_irqhandler(per_cpu(xen_resched_irq, cpu), NULL);
 151         if (per_cpu(xen_callfunc_irq, cpu) >= 0)
 152                 unbind_from_irqhandler(per_cpu(xen_callfunc_irq, cpu), NULL);
 153         if (per_cpu(xen_debug_irq, cpu) >= 0)
 154                 unbind_from_irqhandler(per_cpu(xen_debug_irq, cpu), NULL);
 155         if (per_cpu(xen_callfuncsingle_irq, cpu) >= 0)
 156                 unbind_from_irqhandler(per_cpu(xen_callfuncsingle_irq, cpu),
 157                                        NULL);
 158
 159         return rc;
 160 }
 161
 162 static void __init xen_fill_possible_map(void)
 163 {
 164         int i, rc;
 165
 166         if (xen_initial_domain())
 167                 return;
 168
 169         for (i = 0; i < nr_cpu_ids; i++) {
 170                 rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL);
 171                 if (rc >= 0) {
 172                         num_processors++;
 173                         set_cpu_possible(i, true);
 174                 }
 175         }
 176 }
 177
 178 static void __init xen_filter_cpu_maps(void)
 179 {
 180         int i, rc;
 181
 182         if (!xen_initial_domain())
 183                 return;
 184
 185         num_processors = 0;
 186         disabled_cpus = 0;
 187         for (i = 0; i < nr_cpu_ids; i++) {
 188                 rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL);
 189                 if (rc >= 0) {
 190                         num_processors++;
 191                         set_cpu_possible(i, true);
 192                 } else {
 193                         set_cpu_possible(i, false);
 194                         set_cpu_present(i, false);
 195                 }
 196         }
 197 }
 198
 199 static void __init xen_smp_prepare_boot_cpu(void)
 200 {
 201         BUG_ON(smp_processor_id() != 0);
 202         native_smp_prepare_boot_cpu();
 203
 204         /* We've switched to the "real" per-cpu gdt, so make sure the
 205            old memory can be recycled */
 206         make_lowmem_page_readwrite(xen_initial_gdt);
 207
 208         xen_filter_cpu_maps();
 209         xen_setup_vcpu_info_placement();
 210 }
 211
 212 static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
 213 {
 214         unsigned cpu;
 215         unsigned int i;
 216
 217         if (skip_ioapic_setup) {
 218                 char *m = (max_cpus == 0) ?
 219                         "The nosmp parameter is incompatible with Xen; " \
 220                         "use Xen dom0_max_vcpus=1 parameter" :
 221                         "The noapic parameter is incompatible with Xen";
 222
 223                 xen_raw_printk(m);
 224                 panic(m);
 225         }
 226         xen_init_lock_cpu(0);
 227
 228         smp_store_cpu_info(0);
 229         cpu_data(0).x86_max_cores = 1;
 230
 231         for_each_possible_cpu(i) {
 232                 zalloc_cpumask_var(&per_cpu(cpu_sibling_map, i), GFP_KERNEL);
 233                 zalloc_cpumask_var(&per_cpu(cpu_core_map, i), GFP_KERNEL);
 234                 zalloc_cpumask_var(&per_cpu(cpu_llc_shared_map, i), GFP_KERNEL);
 235         }
 236         set_cpu_sibling_map(0);
 237
 238         if (xen_smp_intr_init(0))
 239                 BUG();
 240
 241         if (!alloc_cpumask_var(&xen_cpu_initialized_map, GFP_KERNEL))
 242                 panic("could not allocate xen_cpu_initialized_map\n");
 243
 244         cpumask_copy(xen_cpu_initialized_map, cpumask_of(0));
 245
 246         /* Restrict the possible_map according to max_cpus. */
 247         while ((num_possible_cpus() > 1) && (num_possible_cpus() > max_cpus)) {
 248                 for (cpu = nr_cpu_ids - 1; !cpu_possible(cpu); cpu--)
 249                         continue;
 250                 set_cpu_possible(cpu, false);
 251         }
 252
 253         for_each_possible_cpu (cpu) {
 254                 struct task_struct *idle;
 255
 256                 if (cpu == 0)
 257                         continue;
 258
 259                 idle = fork_idle(cpu);
 260                 if (IS_ERR(idle))
 261                         panic("failed fork for CPU %d", cpu);
 262
 263                 set_cpu_present(cpu, true);
 264         }
 265 }
 266
 267 static int __cpuinit
 268 cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
 269 {
 270         struct vcpu_guest_context *ctxt;
 271         struct desc_struct *gdt;
 272         unsigned long gdt_mfn;
 273
 274         if (cpumask_test_and_set_cpu(cpu, xen_cpu_initialized_map))
 275                 return 0;
 276
 277         ctxt = kzalloc(sizeof(*ctxt), GFP_KERNEL);
 278         if (ctxt == NULL)
 279                 return -ENOMEM;
 280
 281         gdt = get_cpu_gdt_table(cpu);
 282
 283         ctxt->flags = VGCF_IN_KERNEL;
 284         ctxt->user_regs.ds = __USER_DS;
 285         ctxt->user_regs.es = __USER_DS;
 286         ctxt->user_regs.ss = __KERNEL_DS;
 287 #ifdef CONFIG_X86_32
 288         ctxt->user_regs.fs = __KERNEL_PERCPU;
 289         ctxt->user_regs.gs = __KERNEL_STACK_CANARY;
 290 #else
 291         ctxt->gs_base_kernel = per_cpu_offset(cpu);
 292 #endif
 293         ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
 294         ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
 295
 296         memset(&ctxt->fpu_ctxt, 0, sizeof(ctxt->fpu_ctxt));
 297
 298         xen_copy_trap_info(ctxt->trap_ctxt);
 299
 300         ctxt->ldt_ents = 0;
 301
 302         BUG_ON((unsigned long)gdt & ~PAGE_MASK);
 303
 304         gdt_mfn = arbitrary_virt_to_mfn(gdt);
 305         make_lowmem_page_readonly(gdt);
 306         make_lowmem_page_readonly(mfn_to_virt(gdt_mfn));
 307
 308         ctxt->gdt_frames[0] = gdt_mfn;
 309         ctxt->gdt_ents      = GDT_ENTRIES;
 310
 311         ctxt->user_regs.cs = __KERNEL_CS;
 312         ctxt->user_regs.esp = idle->thread.sp0 - sizeof(struct pt_regs);
 313
 314         ctxt->kernel_ss = __KERNEL_DS;
 315         ctxt->kernel_sp = idle->thread.sp0;
 316
 317 #ifdef CONFIG_X86_32
 318         ctxt->event_callback_cs     = __KERNEL_CS;
 319         ctxt->failsafe_callback_cs  = __KERNEL_CS;
 320 #endif
 321         ctxt->event_callback_eip    = (unsigned long)xen_hypervisor_callback;
 322         ctxt->failsafe_callback_eip = (unsigned long)xen_failsafe_callback;
 323
 324         per_cpu(xen_cr3, cpu) = __pa(swapper_pg_dir);
 325         ctxt->ctrlreg[3] = xen_pfn_to_cr3(virt_to_mfn(swapper_pg_dir));
 326
 327         if (HYPERVISOR_vcpu_op(VCPUOP_initialise, cpu, ctxt))
 328                 BUG();
 329
 330         kfree(ctxt);
 331         return 0;
 332 }
 333
 334 static int __cpuinit xen_cpu_up(unsigned int cpu)
 335 {
 336         struct task_struct *idle = idle_task(cpu);
 337         int rc;
 338
 339         per_cpu(current_task, cpu) = idle;
 340 #ifdef CONFIG_X86_32
 341         irq_ctx_init(cpu);
 342 #else
 343         clear_tsk_thread_flag(idle, TIF_FORK);
 344         per_cpu(kernel_stack, cpu) =
 345                 (unsigned long)task_stack_page(idle) -
 346                 KERNEL_STACK_OFFSET + THREAD_SIZE;
 347 #endif
 348         xen_setup_runstate_info(cpu);
 349         xen_setup_timer(cpu);
 350         xen_init_lock_cpu(cpu);
 351
 352         per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
 353
 354         /* make sure interrupts start blocked */
 355         per_cpu(xen_vcpu, cpu)->evtchn_upcall_mask = 1;
 356
 357         rc = cpu_initialize_context(cpu, idle);
 358         if (rc)
 359                 return rc;
 360
 361         if (num_online_cpus() == 1)
 362                 alternatives_smp_switch(1);
 363
 364         rc = xen_smp_intr_init(cpu);
 365         if (rc)
 366                 return rc;
 367
 368         rc = HYPERVISOR_vcpu_op(VCPUOP_up, cpu, NULL);
 369         BUG_ON(rc);
 370
 371         while(per_cpu(cpu_state, cpu) != CPU_ONLINE) {
 372                 HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
 373                 barrier();
 374         }
 375
 376         return 0;
 377 }
 378
 379 static void xen_smp_cpus_done(unsigned int max_cpus)
 380 {
 381 }
 382
 383 #ifdef CONFIG_HOTPLUG_CPU
 384 static int xen_cpu_disable(void)
 385 {
 386         unsigned int cpu = smp_processor_id();
 387         if (cpu == 0)
 388                 return -EBUSY;
 389
 390         cpu_disable_common();
 391
 392         load_cr3(swapper_pg_dir);
 393         return 0;
 394 }
 395
 396 static void xen_cpu_die(unsigned int cpu)
 397 {
 398         while (HYPERVISOR_vcpu_op(VCPUOP_is_up, cpu, NULL)) {
 399                 current->state = TASK_UNINTERRUPTIBLE;
 400                 schedule_timeout(HZ/10);
 401         }
 402         unbind_from_irqhandler(per_cpu(xen_resched_irq, cpu), NULL);
 403         unbind_from_irqhandler(per_cpu(xen_callfunc_irq, cpu), NULL);
 404         unbind_from_irqhandler(per_cpu(xen_debug_irq, cpu), NULL);
 405         unbind_from_irqhandler(per_cpu(xen_callfuncsingle_irq, cpu), NULL);
 406         xen_uninit_lock_cpu(cpu);
 407         xen_teardown_timer(cpu);
 408
 409         if (num_online_cpus() == 1)
 410                 alternatives_smp_switch(0);
 411 }
 412
 413 static void __cpuinit xen_play_dead(void) /* used only with HOTPLUG_CPU */
 414 {
 415         play_dead_common();
 416         HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
 417         cpu_bringup();
 418         /*
 419          * Balance out the preempt calls - as we are running in cpu_idle
 420          * loop which has been called at bootup from cpu_bringup_and_idle.
 421          * The cpucpu_bringup_and_idle called cpu_bringup which made a
 422          * preempt_disable() So this preempt_enable will balance it out.
 423          */
 424         preempt_enable();
 425 }
 426
 427 #else /* !CONFIG_HOTPLUG_CPU */
 428 static int xen_cpu_disable(void)
 429 {
 430         return -ENOSYS;
 431 }
 432
 433 static void xen_cpu_die(unsigned int cpu)
 434 {
 435         BUG();
 436 }
 437
 438 static void xen_play_dead(void)
 439 {
 440         BUG();
 441 }
 442
 443 #endif
 444 static void stop_self(void *v)
 445 {
 446         int cpu = smp_processor_id();
 447
 448         /* make sure we're not pinning something down */
 449         load_cr3(swapper_pg_dir);
 450         /* should set up a minimal gdt */
 451
 452         set_cpu_online(cpu, false);
 453
 454         HYPERVISOR_vcpu_op(VCPUOP_down, cpu, NULL);
 455         BUG();
 456 }
 457
 458 static void xen_stop_other_cpus(int wait)
 459 {
 460         smp_call_function(stop_self, NULL, wait);
 461 }
 462
 463 static void xen_smp_send_reschedule(int cpu)
 464 {
 465         xen_send_IPI_one(cpu, XEN_RESCHEDULE_VECTOR);
 466 }
 467
 468 static void __xen_send_IPI_mask(const struct cpumask *mask,
 469                               int vector)
 470 {
 471         unsigned cpu;
 472
 473         for_each_cpu_and(cpu, mask, cpu_online_mask)
 474                 xen_send_IPI_one(cpu, vector);
 475 }
 476
 477 static void xen_smp_send_call_function_ipi(const struct cpumask *mask)
 478 {
 479         int cpu;
 480
 481         __xen_send_IPI_mask(mask, XEN_CALL_FUNCTION_VECTOR);
 482
 483         /* Make sure other vcpus get a chance to run if they need to. */
 484         for_each_cpu(cpu, mask) {
 485                 if (xen_vcpu_stolen(cpu)) {
 486                         HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
 487                         break;
 488                 }
 489         }
 490 }
 491
 492 static void xen_smp_send_call_function_single_ipi(int cpu)
 493 {
 494         __xen_send_IPI_mask(cpumask_of(cpu),
 495                           XEN_CALL_FUNCTION_SINGLE_VECTOR);
 496 }
 497
 498 static inline int xen_map_vector(int vector)
 499 {
 500         int xen_vector;
 501
 502         switch (vector) {
 503         case RESCHEDULE_VECTOR:
 504                 xen_vector = XEN_RESCHEDULE_VECTOR;
 505                 break;
 506         case CALL_FUNCTION_VECTOR:
 507                 xen_vector = XEN_CALL_FUNCTION_VECTOR;
 508                 break;
 509         case CALL_FUNCTION_SINGLE_VECTOR:
 510                 xen_vector = XEN_CALL_FUNCTION_SINGLE_VECTOR;
 511                 break;
 512         default:
 513                 xen_vector = -1;
 514                 printk(KERN_ERR "xen: vector 0x%x is not implemented\n",
 515                         vector);
 516         }
 517
 518         return xen_vector;
 519 }
 520
 521 void xen_send_IPI_mask(const struct cpumask *mask,
 522                               int vector)
 523 {
 524         int xen_vector = xen_map_vector(vector);
 525
 526         if (xen_vector >= 0)
 527                 __xen_send_IPI_mask(mask, xen_vector);
 528 }
 529
 530 void xen_send_IPI_all(int vector)
 531 {
 532         int xen_vector = xen_map_vector(vector);
 533
 534         if (xen_vector >= 0)
 535                 __xen_send_IPI_mask(cpu_online_mask, xen_vector);
 536 }
 537
 538 void xen_send_IPI_self(int vector)
 539 {
 540         int xen_vector = xen_map_vector(vector);
 541
 542         if (xen_vector >= 0)
 543                 xen_send_IPI_one(smp_processor_id(), xen_vector);
 544 }
 545
 546 void xen_send_IPI_mask_allbutself(const struct cpumask *mask,
 547                                 int vector)
 548 {
 549         unsigned cpu;
 550         unsigned int this_cpu = smp_processor_id();
 551
 552         if (!(num_online_cpus() > 1))
 553                 return;
 554
 555         for_each_cpu_and(cpu, mask, cpu_online_mask) {
 556                 if (this_cpu == cpu)
 557                         continue;
 558
 559                 xen_smp_send_call_function_single_ipi(cpu);
 560         }
 561 }
 562
 563 void xen_send_IPI_allbutself(int vector)
 564 {
 565         int xen_vector = xen_map_vector(vector);
 566
 567         if (xen_vector >= 0)
 568                 xen_send_IPI_mask_allbutself(cpu_online_mask, xen_vector);
 569 }
 570
 571 static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id)
 572 {
 573         irq_enter();
 574         generic_smp_call_function_interrupt();
 575         inc_irq_stat(irq_call_count);
 576         irq_exit();
 577
 578         return IRQ_HANDLED;
 579 }
 580
 581 static irqreturn_t xen_call_function_single_interrupt(int irq, void *dev_id)
 582 {
 583         irq_enter();
 584         generic_smp_call_function_single_interrupt();
 585         inc_irq_stat(irq_call_count);
 586         irq_exit();
 587
 588         return IRQ_HANDLED;
 589 }
 590
 591 static const struct smp_ops xen_smp_ops __initconst = {
 592         .smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu,
 593         .smp_prepare_cpus = xen_smp_prepare_cpus,
 594         .smp_cpus_done = xen_smp_cpus_done,
 595
 596         .cpu_up = xen_cpu_up,
 597         .cpu_die = xen_cpu_die,
 598         .cpu_disable = xen_cpu_disable,
 599         .play_dead = xen_play_dead,
 600
 601         .stop_other_cpus = xen_stop_other_cpus,
 602         .smp_send_reschedule = xen_smp_send_reschedule,
 603
 604         .send_call_func_ipi = xen_smp_send_call_function_ipi,
 605         .send_call_func_single_ipi = xen_smp_send_call_function_single_ipi,
 606 };
 607
 608 void __init xen_smp_init(void)
 609 {
 610         smp_ops = xen_smp_ops;
 611         xen_fill_possible_map();
 612         xen_init_spinlocks();
 613 }
 614
 615 static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus)
 616 {
 617         native_smp_prepare_cpus(max_cpus);
 618         WARN_ON(xen_smp_intr_init(0));
 619
 620         xen_init_lock_cpu(0);
 621 }
 622
 623 static int __cpuinit xen_hvm_cpu_up(unsigned int cpu)
 624 {
 625         int rc;
 626         rc = native_cpu_up(cpu);
 627         WARN_ON (xen_smp_intr_init(cpu));
 628         return rc;
 629 }
 630
 631 static void xen_hvm_cpu_die(unsigned int cpu)
 632 {
 633         unbind_from_irqhandler(per_cpu(xen_resched_irq, cpu), NULL);
 634         unbind_from_irqhandler(per_cpu(xen_callfunc_irq, cpu), NULL);
 635         unbind_from_irqhandler(per_cpu(xen_debug_irq, cpu), NULL);
 636         unbind_from_irqhandler(per_cpu(xen_callfuncsingle_irq, cpu), NULL);
 637         native_cpu_die(cpu);
 638 }
 639
 640 void __init xen_hvm_smp_init(void)
 641 {
 642         if (!xen_have_vector_callback)
 643                 return;
 644         smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
 645         smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
 646         smp_ops.cpu_up = xen_hvm_cpu_up;
 647         smp_ops.cpu_die = xen_hvm_cpu_die;
 648         smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
 649         smp_ops.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi;
 650 }