arch/x86/kernel/kvm.c

   1 /*
   2  * KVM paravirt_ops implementation
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  17  *
  18  * Copyright (C) 2007, Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  19  * Copyright IBM Corporation, 2007
  20  *   Authors: Anthony Liguori <aliguori@us.ibm.com>
  21  */
  22
  23 #include <linux/context_tracking.h>
  24 #include <linux/module.h>
  25 #include <linux/kernel.h>
  26 #include <linux/kvm_para.h>
  27 #include <linux/cpu.h>
  28 #include <linux/mm.h>
  29 #include <linux/highmem.h>
  30 #include <linux/hardirq.h>
  31 #include <linux/notifier.h>
  32 #include <linux/reboot.h>
  33 #include <linux/hash.h>
  34 #include <linux/sched.h>
  35 #include <linux/slab.h>
  36 #include <linux/kprobes.h>
  37 #include <linux/debugfs.h>
  38 #include <asm/timer.h>
  39 #include <asm/cpu.h>
  40 #include <asm/traps.h>
  41 #include <asm/desc.h>
  42 #include <asm/tlbflush.h>
  43 #include <asm/idle.h>
  44 #include <asm/apic.h>
  45 #include <asm/apicdef.h>
  46 #include <asm/hypervisor.h>
  47 #include <asm/kvm_guest.h>
  48
  49 static int kvmapf = 1;
  50
  51 static int parse_no_kvmapf(char *arg)
  52 {
  53         kvmapf = 0;
  54         return 0;
  55 }
  56
  57 early_param("no-kvmapf", parse_no_kvmapf);
  58
  59 static int steal_acc = 1;
  60 static int parse_no_stealacc(char *arg)
  61 {
  62         steal_acc = 0;
  63         return 0;
  64 }
  65
  66 early_param("no-steal-acc", parse_no_stealacc);
  67
  68 static int kvmclock_vsyscall = 1;
  69 static int parse_no_kvmclock_vsyscall(char *arg)
  70 {
  71         kvmclock_vsyscall = 0;
  72         return 0;
  73 }
  74
  75 early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
  76
  77 static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
  78 static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
  79 static int has_steal_clock = 0;
  80
  81 /*
  82  * No need for any "IO delay" on KVM
  83  */
  84 static void kvm_io_delay(void)
  85 {
  86 }
  87
  88 #define KVM_TASK_SLEEP_HASHBITS 8
  89 #define KVM_TASK_SLEEP_HASHSIZE (1<<KVM_TASK_SLEEP_HASHBITS)
  90
  91 struct kvm_task_sleep_node {
  92         struct hlist_node link;
  93         wait_queue_head_t wq;
  94         u32 token;
  95         int cpu;
  96         bool halted;
  97 };
  98
  99 static struct kvm_task_sleep_head {
 100         spinlock_t lock;
 101         struct hlist_head list;
 102 } async_pf_sleepers[KVM_TASK_SLEEP_HASHSIZE];
 103
 104 static struct kvm_task_sleep_node *_find_apf_task(struct kvm_task_sleep_head *b,
 105                                                   u32 token)
 106 {
 107         struct hlist_node *p;
 108
 109         hlist_for_each(p, &b->list) {
 110                 struct kvm_task_sleep_node *n =
 111                         hlist_entry(p, typeof(*n), link);
 112                 if (n->token == token)
 113                         return n;
 114         }
 115
 116         return NULL;
 117 }
 118
 119 void kvm_async_pf_task_wait(u32 token)
 120 {
 121         u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
 122         struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
 123         struct kvm_task_sleep_node n, *e;
 124         DEFINE_WAIT(wait);
 125
 126         rcu_irq_enter();
 127
 128         spin_lock(&b->lock);
 129         e = _find_apf_task(b, token);
 130         if (e) {
 131                 /* dummy entry exist -> wake up was delivered ahead of PF */
 132                 hlist_del(&e->link);
 133                 kfree(e);
 134                 spin_unlock(&b->lock);
 135
 136                 rcu_irq_exit();
 137                 return;
 138         }
 139
 140         n.token = token;
 141         n.cpu = smp_processor_id();
 142         n.halted = is_idle_task(current) || preempt_count() > 1;
 143         init_waitqueue_head(&n.wq);
 144         hlist_add_head(&n.link, &b->list);
 145         spin_unlock(&b->lock);
 146
 147         for (;;) {
 148                 if (!n.halted)
 149                         prepare_to_wait(&n.wq, &wait, TASK_UNINTERRUPTIBLE);
 150                 if (hlist_unhashed(&n.link))
 151                         break;
 152
 153                 if (!n.halted) {
 154                         local_irq_enable();
 155                         schedule();
 156                         local_irq_disable();
 157                 } else {
 158                         /*
 159                          * We cannot reschedule. So halt.
 160                          */
 161                         rcu_irq_exit();
 162                         native_safe_halt();
 163                         rcu_irq_enter();
 164                         local_irq_disable();
 165                 }
 166         }
 167         if (!n.halted)
 168                 finish_wait(&n.wq, &wait);
 169
 170         rcu_irq_exit();
 171         return;
 172 }
 173 EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);
 174
 175 static void apf_task_wake_one(struct kvm_task_sleep_node *n)
 176 {
 177         hlist_del_init(&n->link);
 178         if (n->halted)
 179                 smp_send_reschedule(n->cpu);
 180         else if (waitqueue_active(&n->wq))
 181                 wake_up(&n->wq);
 182 }
 183
 184 static void apf_task_wake_all(void)
 185 {
 186         int i;
 187
 188         for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++) {
 189                 struct hlist_node *p, *next;
 190                 struct kvm_task_sleep_head *b = &async_pf_sleepers[i];
 191                 spin_lock(&b->lock);
 192                 hlist_for_each_safe(p, next, &b->list) {
 193                         struct kvm_task_sleep_node *n =
 194                                 hlist_entry(p, typeof(*n), link);
 195                         if (n->cpu == smp_processor_id())
 196                                 apf_task_wake_one(n);
 197                 }
 198                 spin_unlock(&b->lock);
 199         }
 200 }
 201
 202 void kvm_async_pf_task_wake(u32 token)
 203 {
 204         u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
 205         struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
 206         struct kvm_task_sleep_node *n;
 207
 208         if (token == ~0) {
 209                 apf_task_wake_all();
 210                 return;
 211         }
 212
 213 again:
 214         spin_lock(&b->lock);
 215         n = _find_apf_task(b, token);
 216         if (!n) {
 217                 /*
 218                  * async PF was not yet handled.
 219                  * Add dummy entry for the token.
 220                  */
 221                 n = kzalloc(sizeof(*n), GFP_ATOMIC);
 222                 if (!n) {
 223                         /*
 224                          * Allocation failed! Busy wait while other cpu
 225                          * handles async PF.
 226                          */
 227                         spin_unlock(&b->lock);
 228                         cpu_relax();
 229                         goto again;
 230                 }
 231                 n->token = token;
 232                 n->cpu = smp_processor_id();
 233                 init_waitqueue_head(&n->wq);
 234                 hlist_add_head(&n->link, &b->list);
 235         } else
 236                 apf_task_wake_one(n);
 237         spin_unlock(&b->lock);
 238         return;
 239 }
 240 EXPORT_SYMBOL_GPL(kvm_async_pf_task_wake);
 241
 242 u32 kvm_read_and_reset_pf_reason(void)
 243 {
 244         u32 reason = 0;
 245
 246         if (__get_cpu_var(apf_reason).enabled) {
 247                 reason = __get_cpu_var(apf_reason).reason;
 248                 __get_cpu_var(apf_reason).reason = 0;
 249         }
 250
 251         return reason;
 252 }
 253 EXPORT_SYMBOL_GPL(kvm_read_and_reset_pf_reason);
 254 NOKPROBE_SYMBOL(kvm_read_and_reset_pf_reason);
 255
 256 dotraplinkage void
 257 do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
 258 {
 259         enum ctx_state prev_state;
 260
 261         switch (kvm_read_and_reset_pf_reason()) {
 262         default:
 263                 trace_do_page_fault(regs, error_code);
 264                 break;
 265         case KVM_PV_REASON_PAGE_NOT_PRESENT:
 266                 /* page is swapped out by the host. */
 267                 prev_state = exception_enter();
 268                 exit_idle();
 269                 kvm_async_pf_task_wait((u32)read_cr2());
 270                 exception_exit(prev_state);
 271                 break;
 272         case KVM_PV_REASON_PAGE_READY:
 273                 rcu_irq_enter();
 274                 exit_idle();
 275                 kvm_async_pf_task_wake((u32)read_cr2());
 276                 rcu_irq_exit();
 277                 break;
 278         }
 279 }
 280 NOKPROBE_SYMBOL(do_async_page_fault);
 281
 282 static void __init paravirt_ops_setup(void)
 283 {
 284         pv_info.name = "KVM";
 285         pv_info.paravirt_enabled = 1;
 286
 287         if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))
 288                 pv_cpu_ops.io_delay = kvm_io_delay;
 289
 290 #ifdef CONFIG_X86_IO_APIC
 291         no_timer_check = 1;
 292 #endif
 293 }
 294
 295 static void kvm_register_steal_time(void)
 296 {
 297         int cpu = smp_processor_id();
 298         struct kvm_steal_time *st = &per_cpu(steal_time, cpu);
 299
 300         if (!has_steal_clock)
 301                 return;
 302
 303         memset(st, 0, sizeof(*st));
 304
 305         wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
 306         pr_info("kvm-stealtime: cpu %d, msr %llx\n",
 307                 cpu, (unsigned long long) slow_virt_to_phys(st));
 308 }
 309
 310 static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
 311
 312 static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
 313 {
 314         /**
 315          * This relies on __test_and_clear_bit to modify the memory
 316          * in a way that is atomic with respect to the local CPU.
 317          * The hypervisor only accesses this memory from the local CPU so
 318          * there's no need for lock or memory barriers.
 319          * An optimization barrier is implied in apic write.
 320          */
 321         if (__test_and_clear_bit(KVM_PV_EOI_BIT, &__get_cpu_var(kvm_apic_eoi)))
 322                 return;
 323         apic_write(APIC_EOI, APIC_EOI_ACK);
 324 }
 325
 326 void kvm_guest_cpu_init(void)
 327 {
 328         if (!kvm_para_available())
 329                 return;
 330
 331         if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) {
 332                 u64 pa = slow_virt_to_phys(&__get_cpu_var(apf_reason));
 333
 334 #ifdef CONFIG_PREEMPT
 335                 pa |= KVM_ASYNC_PF_SEND_ALWAYS;
 336 #endif
 337                 wrmsrl(MSR_KVM_ASYNC_PF_EN, pa | KVM_ASYNC_PF_ENABLED);
 338                 __get_cpu_var(apf_reason).enabled = 1;
 339                 printk(KERN_INFO"KVM setup async PF for cpu %d\n",
 340                        smp_processor_id());
 341         }
 342
 343         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
 344                 unsigned long pa;
 345                 /* Size alignment is implied but just to make it explicit. */
 346                 BUILD_BUG_ON(__alignof__(kvm_apic_eoi) < 4);
 347                 __get_cpu_var(kvm_apic_eoi) = 0;
 348                 pa = slow_virt_to_phys(&__get_cpu_var(kvm_apic_eoi))
 349                         | KVM_MSR_ENABLED;
 350                 wrmsrl(MSR_KVM_PV_EOI_EN, pa);
 351         }
 352
 353         if (has_steal_clock)
 354                 kvm_register_steal_time();
 355 }
 356
 357 static void kvm_pv_disable_apf(void)
 358 {
 359         if (!__get_cpu_var(apf_reason).enabled)
 360                 return;
 361
 362         wrmsrl(MSR_KVM_ASYNC_PF_EN, 0);
 363         __get_cpu_var(apf_reason).enabled = 0;
 364
 365         printk(KERN_INFO"Unregister pv shared memory for cpu %d\n",
 366                smp_processor_id());
 367 }
 368
 369 static void kvm_pv_guest_cpu_reboot(void *unused)
 370 {
 371         /*
 372          * We disable PV EOI before we load a new kernel by kexec,
 373          * since MSR_KVM_PV_EOI_EN stores a pointer into old kernel's memory.
 374          * New kernel can re-enable when it boots.
 375          */
 376         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
 377                 wrmsrl(MSR_KVM_PV_EOI_EN, 0);
 378         kvm_pv_disable_apf();
 379         kvm_disable_steal_time();
 380 }
 381
 382 static int kvm_pv_reboot_notify(struct notifier_block *nb,
 383                                 unsigned long code, void *unused)
 384 {
 385         if (code == SYS_RESTART)
 386                 on_each_cpu(kvm_pv_guest_cpu_reboot, NULL, 1);
 387         return NOTIFY_DONE;
 388 }
 389
 390 static struct notifier_block kvm_pv_reboot_nb = {
 391         .notifier_call = kvm_pv_reboot_notify,
 392 };
 393
 394 static u64 kvm_steal_clock(int cpu)
 395 {
 396         u64 steal;
 397         struct kvm_steal_time *src;
 398         int version;
 399
 400         src = &per_cpu(steal_time, cpu);
 401         do {
 402                 version = src->version;
 403                 rmb();
 404                 steal = src->steal;
 405                 rmb();
 406         } while ((version & 1) || (version != src->version));
 407
 408         return steal;
 409 }
 410
 411 void kvm_disable_steal_time(void)
 412 {
 413         if (!has_steal_clock)
 414                 return;
 415
 416         wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
 417 }
 418
 419 #ifdef CONFIG_SMP
 420 static void __init kvm_smp_prepare_boot_cpu(void)
 421 {
 422         kvm_guest_cpu_init();
 423         native_smp_prepare_boot_cpu();
 424         kvm_spinlock_init();
 425 }
 426
 427 static void kvm_guest_cpu_online(void *dummy)
 428 {
 429         kvm_guest_cpu_init();
 430 }
 431
 432 static void kvm_guest_cpu_offline(void *dummy)
 433 {
 434         kvm_disable_steal_time();
 435         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
 436                 wrmsrl(MSR_KVM_PV_EOI_EN, 0);
 437         kvm_pv_disable_apf();
 438         apf_task_wake_all();
 439 }
 440
 441 static int kvm_cpu_notify(struct notifier_block *self, unsigned long action,
 442                           void *hcpu)
 443 {
 444         int cpu = (unsigned long)hcpu;
 445         switch (action) {
 446         case CPU_ONLINE:
 447         case CPU_DOWN_FAILED:
 448         case CPU_ONLINE_FROZEN:
 449                 smp_call_function_single(cpu, kvm_guest_cpu_online, NULL, 0);
 450                 break;
 451         case CPU_DOWN_PREPARE:
 452         case CPU_DOWN_PREPARE_FROZEN:
 453                 smp_call_function_single(cpu, kvm_guest_cpu_offline, NULL, 1);
 454                 break;
 455         default:
 456                 break;
 457         }
 458         return NOTIFY_OK;
 459 }
 460
 461 static struct notifier_block kvm_cpu_notifier = {
 462         .notifier_call  = kvm_cpu_notify,
 463 };
 464 #endif
 465
 466 static void __init kvm_apf_trap_init(void)
 467 {
 468         set_intr_gate(14, async_page_fault);
 469 }
 470
 471 void __init kvm_guest_init(void)
 472 {
 473         int i;
 474
 475         if (!kvm_para_available())
 476                 return;
 477
 478         paravirt_ops_setup();
 479         register_reboot_notifier(&kvm_pv_reboot_nb);
 480         for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++)
 481                 spin_lock_init(&async_pf_sleepers[i].lock);
 482         if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF))
 483                 x86_init.irqs.trap_init = kvm_apf_trap_init;
 484
 485         if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
 486                 has_steal_clock = 1;
 487                 pv_time_ops.steal_clock = kvm_steal_clock;
 488         }
 489
 490         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
 491                 apic_set_eoi_write(kvm_guest_apic_eoi_write);
 492
 493         if (kvmclock_vsyscall)
 494                 kvm_setup_vsyscall_timeinfo();
 495
 496 #ifdef CONFIG_SMP
 497         smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
 498         register_cpu_notifier(&kvm_cpu_notifier);
 499 #else
 500         kvm_guest_cpu_init();
 501 #endif
 502 }
 503
 504 static noinline uint32_t __kvm_cpuid_base(void)
 505 {
 506         if (boot_cpu_data.cpuid_level < 0)
 507                 return 0;       /* So we don't blow up on old processors */
 508
 509         if (cpu_has_hypervisor)
 510                 return hypervisor_cpuid_base("KVMKVMKVM\0\0\0", 0);
 511
 512         return 0;
 513 }
 514
 515 static inline uint32_t kvm_cpuid_base(void)
 516 {
 517         static int kvm_cpuid_base = -1;
 518
 519         if (kvm_cpuid_base == -1)
 520                 kvm_cpuid_base = __kvm_cpuid_base();
 521
 522         return kvm_cpuid_base;
 523 }
 524
 525 bool kvm_para_available(void)
 526 {
 527         return kvm_cpuid_base() != 0;
 528 }
 529 EXPORT_SYMBOL_GPL(kvm_para_available);
 530
 531 unsigned int kvm_arch_para_features(void)
 532 {
 533         return cpuid_eax(kvm_cpuid_base() | KVM_CPUID_FEATURES);
 534 }
 535
 536 static uint32_t __init kvm_detect(void)
 537 {
 538         return kvm_cpuid_base();
 539 }
 540
 541 const struct hypervisor_x86 x86_hyper_kvm __refconst = {
 542         .name                   = "KVM",
 543         .detect                 = kvm_detect,
 544         .x2apic_available       = kvm_para_available,
 545 };
 546 EXPORT_SYMBOL_GPL(x86_hyper_kvm);
 547
 548 static __init int activate_jump_labels(void)
 549 {
 550         if (has_steal_clock) {
 551                 static_key_slow_inc(&paravirt_steal_enabled);
 552                 if (steal_acc)
 553                         static_key_slow_inc(&paravirt_steal_rq_enabled);
 554         }
 555
 556         return 0;
 557 }
 558 arch_initcall(activate_jump_labels);
 559
 560 #ifdef CONFIG_PARAVIRT_SPINLOCKS
 561
 562 /* Kick a cpu by its apicid. Used to wake up a halted vcpu */
 563 static void kvm_kick_cpu(int cpu)
 564 {
 565         int apicid;
 566         unsigned long flags = 0;
 567
 568         apicid = per_cpu(x86_cpu_to_apicid, cpu);
 569         kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
 570 }
 571
 572 enum kvm_contention_stat {
 573         TAKEN_SLOW,
 574         TAKEN_SLOW_PICKUP,
 575         RELEASED_SLOW,
 576         RELEASED_SLOW_KICKED,
 577         NR_CONTENTION_STATS
 578 };
 579
 580 #ifdef CONFIG_KVM_DEBUG_FS
 581 #define HISTO_BUCKETS   30
 582
 583 static struct kvm_spinlock_stats
 584 {
 585         u32 contention_stats[NR_CONTENTION_STATS];
 586         u32 histo_spin_blocked[HISTO_BUCKETS+1];
 587         u64 time_blocked;
 588 } spinlock_stats;
 589
 590 static u8 zero_stats;
 591
 592 static inline void check_zero(void)
 593 {
 594         u8 ret;
 595         u8 old;
 596
 597         old = ACCESS_ONCE(zero_stats);
 598         if (unlikely(old)) {
 599                 ret = cmpxchg(&zero_stats, old, 0);
 600                 /* This ensures only one fellow resets the stat */
 601                 if (ret == old)
 602                         memset(&spinlock_stats, 0, sizeof(spinlock_stats));
 603         }
 604 }
 605
 606 static inline void add_stats(enum kvm_contention_stat var, u32 val)
 607 {
 608         check_zero();
 609         spinlock_stats.contention_stats[var] += val;
 610 }
 611
 612
 613 static inline u64 spin_time_start(void)
 614 {
 615         return sched_clock();
 616 }
 617
 618 static void __spin_time_accum(u64 delta, u32 *array)
 619 {
 620         unsigned index;
 621
 622         index = ilog2(delta);
 623         check_zero();
 624
 625         if (index < HISTO_BUCKETS)
 626                 array[index]++;
 627         else
 628                 array[HISTO_BUCKETS]++;
 629 }
 630
 631 static inline void spin_time_accum_blocked(u64 start)
 632 {
 633         u32 delta;
 634
 635         delta = sched_clock() - start;
 636         __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
 637         spinlock_stats.time_blocked += delta;
 638 }
 639
 640 static struct dentry *d_spin_debug;
 641 static struct dentry *d_kvm_debug;
 642
 643 struct dentry *kvm_init_debugfs(void)
 644 {
 645         d_kvm_debug = debugfs_create_dir("kvm-guest", NULL);
 646         if (!d_kvm_debug)
 647                 printk(KERN_WARNING "Could not create 'kvm' debugfs directory\n");
 648
 649         return d_kvm_debug;
 650 }
 651
 652 static int __init kvm_spinlock_debugfs(void)
 653 {
 654         struct dentry *d_kvm;
 655
 656         d_kvm = kvm_init_debugfs();
 657         if (d_kvm == NULL)
 658                 return -ENOMEM;
 659
 660         d_spin_debug = debugfs_create_dir("spinlocks", d_kvm);
 661
 662         debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
 663
 664         debugfs_create_u32("taken_slow", 0444, d_spin_debug,
 665                    &spinlock_stats.contention_stats[TAKEN_SLOW]);
 666         debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
 667                    &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
 668
 669         debugfs_create_u32("released_slow", 0444, d_spin_debug,
 670                    &spinlock_stats.contention_stats[RELEASED_SLOW]);
 671         debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
 672                    &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
 673
 674         debugfs_create_u64("time_blocked", 0444, d_spin_debug,
 675                            &spinlock_stats.time_blocked);
 676
 677         debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
 678                      spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
 679
 680         return 0;
 681 }
 682 fs_initcall(kvm_spinlock_debugfs);
 683 #else  /* !CONFIG_KVM_DEBUG_FS */
 684 static inline void add_stats(enum kvm_contention_stat var, u32 val)
 685 {
 686 }
 687
 688 static inline u64 spin_time_start(void)
 689 {
 690         return 0;
 691 }
 692
 693 static inline void spin_time_accum_blocked(u64 start)
 694 {
 695 }
 696 #endif  /* CONFIG_KVM_DEBUG_FS */
 697
 698 struct kvm_lock_waiting {
 699         struct arch_spinlock *lock;
 700         __ticket_t want;
 701 };
 702
 703 /* cpus 'waiting' on a spinlock to become available */
 704 static cpumask_t waiting_cpus;
 705
 706 /* Track spinlock on which a cpu is waiting */
 707 static DEFINE_PER_CPU(struct kvm_lock_waiting, klock_waiting);
 708
 709 __visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
 710 {
 711         struct kvm_lock_waiting *w;
 712         int cpu;
 713         u64 start;
 714         unsigned long flags;
 715
 716         if (in_nmi())
 717                 return;
 718
 719         w = &__get_cpu_var(klock_waiting);
 720         cpu = smp_processor_id();
 721         start = spin_time_start();
 722
 723         /*
 724          * Make sure an interrupt handler can't upset things in a
 725          * partially setup state.
 726          */
 727         local_irq_save(flags);
 728
 729         /*
 730          * The ordering protocol on this is that the "lock" pointer
 731          * may only be set non-NULL if the "want" ticket is correct.
 732          * If we're updating "want", we must first clear "lock".
 733          */
 734         w->lock = NULL;
 735         smp_wmb();
 736         w->want = want;
 737         smp_wmb();
 738         w->lock = lock;
 739
 740         add_stats(TAKEN_SLOW, 1);
 741
 742         /*
 743          * This uses set_bit, which is atomic but we should not rely on its
 744          * reordering gurantees. So barrier is needed after this call.
 745          */
 746         cpumask_set_cpu(cpu, &waiting_cpus);
 747
 748         barrier();
 749
 750         /*
 751          * Mark entry to slowpath before doing the pickup test to make
 752          * sure we don't deadlock with an unlocker.
 753          */
 754         __ticket_enter_slowpath(lock);
 755
 756         /*
 757          * check again make sure it didn't become free while
 758          * we weren't looking.
 759          */
 760         if (ACCESS_ONCE(lock->tickets.head) == want) {
 761                 add_stats(TAKEN_SLOW_PICKUP, 1);
 762                 goto out;
 763         }
 764
 765         /*
 766          * halt until it's our turn and kicked. Note that we do safe halt
 767          * for irq enabled case to avoid hang when lock info is overwritten
 768          * in irq spinlock slowpath and no spurious interrupt occur to save us.
 769          */
 770         if (arch_irqs_disabled_flags(flags))
 771                 halt();
 772         else
 773                 safe_halt();
 774
 775 out:
 776         cpumask_clear_cpu(cpu, &waiting_cpus);
 777         w->lock = NULL;
 778         local_irq_restore(flags);
 779         spin_time_accum_blocked(start);
 780 }
 781 PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);
 782
 783 /* Kick vcpu waiting on @lock->head to reach value @ticket */
 784 static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
 785 {
 786         int cpu;
 787
 788         add_stats(RELEASED_SLOW, 1);
 789         for_each_cpu(cpu, &waiting_cpus) {
 790                 const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu);
 791                 if (ACCESS_ONCE(w->lock) == lock &&
 792                     ACCESS_ONCE(w->want) == ticket) {
 793                         add_stats(RELEASED_SLOW_KICKED, 1);
 794                         kvm_kick_cpu(cpu);
 795                         break;
 796                 }
 797         }
 798 }
 799
 800 /*
 801  * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
 802  */
 803 void __init kvm_spinlock_init(void)
 804 {
 805         if (!kvm_para_available())
 806                 return;
 807         /* Does host kernel support KVM_FEATURE_PV_UNHALT? */
 808         if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
 809                 return;
 810
 811         pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
 812         pv_lock_ops.unlock_kick = kvm_unlock_kick;
 813 }
 814
 815 static __init int kvm_spinlock_init_jump(void)
 816 {
 817         if (!kvm_para_available())
 818                 return 0;
 819         if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
 820                 return 0;
 821
 822         static_key_slow_inc(&paravirt_ticketlocks_enabled);
 823         printk(KERN_INFO "KVM setup paravirtual spinlock\n");
 824
 825         return 0;
 826 }
 827 early_initcall(kvm_spinlock_init_jump);
 828
 829 #endif  /* CONFIG_PARAVIRT_SPINLOCKS */