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 <linux/nmi.h>
  39 #include <asm/timer.h>
  40 #include <asm/cpu.h>
  41 #include <asm/traps.h>
  42 #include <asm/desc.h>
  43 #include <asm/tlbflush.h>
  44 #include <asm/idle.h>
  45 #include <asm/apic.h>
  46 #include <asm/apicdef.h>
  47 #include <asm/hypervisor.h>
  48 #include <asm/kvm_guest.h>
  49
  50 static int kvmapf = 1;
  51
  52 static int parse_no_kvmapf(char *arg)
  53 {
  54         kvmapf = 0;
  55         return 0;
  56 }
  57
  58 early_param("no-kvmapf", parse_no_kvmapf);
  59
  60 static int steal_acc = 1;
  61 static int parse_no_stealacc(char *arg)
  62 {
  63         steal_acc = 0;
  64         return 0;
  65 }
  66
  67 early_param("no-steal-acc", parse_no_stealacc);
  68
  69 static int kvmclock_vsyscall = 1;
  70 static int parse_no_kvmclock_vsyscall(char *arg)
  71 {
  72         kvmclock_vsyscall = 0;
  73         return 0;
  74 }
  75
  76 early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
  77
  78 static DEFINE_PER_CPU(struct kvm_vcpu_pv_apf_data, apf_reason) __aligned(64);
  79 static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
  80 static int has_steal_clock = 0;
  81
  82 /*
  83  * No need for any "IO delay" on KVM
  84  */
  85 static void kvm_io_delay(void)
  86 {
  87 }
  88
  89 #define KVM_TASK_SLEEP_HASHBITS 8
  90 #define KVM_TASK_SLEEP_HASHSIZE (1<<KVM_TASK_SLEEP_HASHBITS)
  91
  92 struct kvm_task_sleep_node {
  93         struct hlist_node link;
  94         wait_queue_head_t wq;
  95         u32 token;
  96         int cpu;
  97         bool halted;
  98 };
  99
 100 static struct kvm_task_sleep_head {
 101         spinlock_t lock;
 102         struct hlist_head list;
 103 } async_pf_sleepers[KVM_TASK_SLEEP_HASHSIZE];
 104
 105 static struct kvm_task_sleep_node *_find_apf_task(struct kvm_task_sleep_head *b,
 106                                                   u32 token)
 107 {
 108         struct hlist_node *p;
 109
 110         hlist_for_each(p, &b->list) {
 111                 struct kvm_task_sleep_node *n =
 112                         hlist_entry(p, typeof(*n), link);
 113                 if (n->token == token)
 114                         return n;
 115         }
 116
 117         return NULL;
 118 }
 119
 120 void kvm_async_pf_task_wait(u32 token)
 121 {
 122         u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
 123         struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
 124         struct kvm_task_sleep_node n, *e;
 125         DEFINE_WAIT(wait);
 126
 127         rcu_irq_enter();
 128
 129         spin_lock(&b->lock);
 130         e = _find_apf_task(b, token);
 131         if (e) {
 132                 /* dummy entry exist -> wake up was delivered ahead of PF */
 133                 hlist_del(&e->link);
 134                 kfree(e);
 135                 spin_unlock(&b->lock);
 136
 137                 rcu_irq_exit();
 138                 return;
 139         }
 140
 141         n.token = token;
 142         n.cpu = smp_processor_id();
 143         n.halted = is_idle_task(current) || preempt_count() > 1;
 144         init_waitqueue_head(&n.wq);
 145         hlist_add_head(&n.link, &b->list);
 146         spin_unlock(&b->lock);
 147
 148         for (;;) {
 149                 if (!n.halted)
 150                         prepare_to_wait(&n.wq, &wait, TASK_UNINTERRUPTIBLE);
 151                 if (hlist_unhashed(&n.link))
 152                         break;
 153
 154                 if (!n.halted) {
 155                         local_irq_enable();
 156                         schedule();
 157                         local_irq_disable();
 158                 } else {
 159                         /*
 160                          * We cannot reschedule. So halt.
 161                          */
 162                         rcu_irq_exit();
 163                         native_safe_halt();
 164                         rcu_irq_enter();
 165                         local_irq_disable();
 166                 }
 167         }
 168         if (!n.halted)
 169                 finish_wait(&n.wq, &wait);
 170
 171         rcu_irq_exit();
 172         return;
 173 }
 174 EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);
 175
 176 static void apf_task_wake_one(struct kvm_task_sleep_node *n)
 177 {
 178         hlist_del_init(&n->link);
 179         if (n->halted)
 180                 smp_send_reschedule(n->cpu);
 181         else if (waitqueue_active(&n->wq))
 182                 wake_up(&n->wq);
 183 }
 184
 185 static void apf_task_wake_all(void)
 186 {
 187         int i;
 188
 189         for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++) {
 190                 struct hlist_node *p, *next;
 191                 struct kvm_task_sleep_head *b = &async_pf_sleepers[i];
 192                 spin_lock(&b->lock);
 193                 hlist_for_each_safe(p, next, &b->list) {
 194                         struct kvm_task_sleep_node *n =
 195                                 hlist_entry(p, typeof(*n), link);
 196                         if (n->cpu == smp_processor_id())
 197                                 apf_task_wake_one(n);
 198                 }
 199                 spin_unlock(&b->lock);
 200         }
 201 }
 202
 203 void kvm_async_pf_task_wake(u32 token)
 204 {
 205         u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
 206         struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
 207         struct kvm_task_sleep_node *n;
 208
 209         if (token == ~0) {
 210                 apf_task_wake_all();
 211                 return;
 212         }
 213
 214 again:
 215         spin_lock(&b->lock);
 216         n = _find_apf_task(b, token);
 217         if (!n) {
 218                 /*
 219                  * async PF was not yet handled.
 220                  * Add dummy entry for the token.
 221                  */
 222                 n = kzalloc(sizeof(*n), GFP_ATOMIC);
 223                 if (!n) {
 224                         /*
 225                          * Allocation failed! Busy wait while other cpu
 226                          * handles async PF.
 227                          */
 228                         spin_unlock(&b->lock);
 229                         cpu_relax();
 230                         goto again;
 231                 }
 232                 n->token = token;
 233                 n->cpu = smp_processor_id();
 234                 init_waitqueue_head(&n->wq);
 235                 hlist_add_head(&n->link, &b->list);
 236         } else
 237                 apf_task_wake_one(n);
 238         spin_unlock(&b->lock);
 239         return;
 240 }
 241 EXPORT_SYMBOL_GPL(kvm_async_pf_task_wake);
 242
 243 u32 kvm_read_and_reset_pf_reason(void)
 244 {
 245         u32 reason = 0;
 246
 247         if (__this_cpu_read(apf_reason.enabled)) {
 248                 reason = __this_cpu_read(apf_reason.reason);
 249                 __this_cpu_write(apf_reason.reason, 0);
 250         }
 251
 252         return reason;
 253 }
 254 EXPORT_SYMBOL_GPL(kvm_read_and_reset_pf_reason);
 255 NOKPROBE_SYMBOL(kvm_read_and_reset_pf_reason);
 256
 257 dotraplinkage void
 258 do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
 259 {
 260         enum ctx_state prev_state;
 261
 262         switch (kvm_read_and_reset_pf_reason()) {
 263         default:
 264                 trace_do_page_fault(regs, error_code);
 265                 break;
 266         case KVM_PV_REASON_PAGE_NOT_PRESENT:
 267                 /* page is swapped out by the host. */
 268                 prev_state = exception_enter();
 269                 exit_idle();
 270                 kvm_async_pf_task_wait((u32)read_cr2());
 271                 exception_exit(prev_state);
 272                 break;
 273         case KVM_PV_REASON_PAGE_READY:
 274                 rcu_irq_enter();
 275                 exit_idle();
 276                 kvm_async_pf_task_wake((u32)read_cr2());
 277                 rcu_irq_exit();
 278                 break;
 279         }
 280 }
 281 NOKPROBE_SYMBOL(do_async_page_fault);
 282
 283 static void __init paravirt_ops_setup(void)
 284 {
 285         pv_info.name = "KVM";
 286         pv_info.paravirt_enabled = 1;
 287
 288         if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))
 289                 pv_cpu_ops.io_delay = kvm_io_delay;
 290
 291 #ifdef CONFIG_X86_IO_APIC
 292         no_timer_check = 1;
 293 #endif
 294 }
 295
 296 static void kvm_register_steal_time(void)
 297 {
 298         int cpu = smp_processor_id();
 299         struct kvm_steal_time *st = &per_cpu(steal_time, cpu);
 300
 301         if (!has_steal_clock)
 302                 return;
 303
 304         memset(st, 0, sizeof(*st));
 305
 306         wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
 307         pr_info("kvm-stealtime: cpu %d, msr %llx\n",
 308                 cpu, (unsigned long long) slow_virt_to_phys(st));
 309 }
 310
 311 static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
 312
 313 static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
 314 {
 315         /**
 316          * This relies on __test_and_clear_bit to modify the memory
 317          * in a way that is atomic with respect to the local CPU.
 318          * The hypervisor only accesses this memory from the local CPU so
 319          * there's no need for lock or memory barriers.
 320          * An optimization barrier is implied in apic write.
 321          */
 322         if (__test_and_clear_bit(KVM_PV_EOI_BIT, this_cpu_ptr(&kvm_apic_eoi)))
 323                 return;
 324         apic_write(APIC_EOI, APIC_EOI_ACK);
 325 }
 326
 327 void kvm_guest_cpu_init(void)
 328 {
 329         if (!kvm_para_available())
 330                 return;
 331
 332         if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) {
 333                 u64 pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason));
 334
 335 #ifdef CONFIG_PREEMPT
 336                 pa |= KVM_ASYNC_PF_SEND_ALWAYS;
 337 #endif
 338                 wrmsrl(MSR_KVM_ASYNC_PF_EN, pa | KVM_ASYNC_PF_ENABLED);
 339                 __this_cpu_write(apf_reason.enabled, 1);
 340                 printk(KERN_INFO"KVM setup async PF for cpu %d\n",
 341                        smp_processor_id());
 342         }
 343
 344         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
 345                 unsigned long pa;
 346                 /* Size alignment is implied but just to make it explicit. */
 347                 BUILD_BUG_ON(__alignof__(kvm_apic_eoi) < 4);
 348                 __this_cpu_write(kvm_apic_eoi, 0);
 349                 pa = slow_virt_to_phys(this_cpu_ptr(&kvm_apic_eoi))
 350                         | KVM_MSR_ENABLED;
 351                 wrmsrl(MSR_KVM_PV_EOI_EN, pa);
 352         }
 353
 354         if (has_steal_clock)
 355                 kvm_register_steal_time();
 356 }
 357
 358 static void kvm_pv_disable_apf(void)
 359 {
 360         if (!__this_cpu_read(apf_reason.enabled))
 361                 return;
 362
 363         wrmsrl(MSR_KVM_ASYNC_PF_EN, 0);
 364         __this_cpu_write(apf_reason.enabled, 0);
 365
 366         printk(KERN_INFO"Unregister pv shared memory for cpu %d\n",
 367                smp_processor_id());
 368 }
 369
 370 static void kvm_pv_guest_cpu_reboot(void *unused)
 371 {
 372         /*
 373          * We disable PV EOI before we load a new kernel by kexec,
 374          * since MSR_KVM_PV_EOI_EN stores a pointer into old kernel's memory.
 375          * New kernel can re-enable when it boots.
 376          */
 377         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
 378                 wrmsrl(MSR_KVM_PV_EOI_EN, 0);
 379         kvm_pv_disable_apf();
 380         kvm_disable_steal_time();
 381 }
 382
 383 static int kvm_pv_reboot_notify(struct notifier_block *nb,
 384                                 unsigned long code, void *unused)
 385 {
 386         if (code == SYS_RESTART)
 387                 on_each_cpu(kvm_pv_guest_cpu_reboot, NULL, 1);
 388         return NOTIFY_DONE;
 389 }
 390
 391 static struct notifier_block kvm_pv_reboot_nb = {
 392         .notifier_call = kvm_pv_reboot_notify,
 393 };
 394
 395 static u64 kvm_steal_clock(int cpu)
 396 {
 397         u64 steal;
 398         struct kvm_steal_time *src;
 399         int version;
 400
 401         src = &per_cpu(steal_time, cpu);
 402         do {
 403                 version = src->version;
 404                 rmb();
 405                 steal = src->steal;
 406                 rmb();
 407         } while ((version & 1) || (version != src->version));
 408
 409         return steal;
 410 }
 411
 412 void kvm_disable_steal_time(void)
 413 {
 414         if (!has_steal_clock)
 415                 return;
 416
 417         wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
 418 }
 419
 420 #ifdef CONFIG_SMP
 421 static void __init kvm_smp_prepare_boot_cpu(void)
 422 {
 423         kvm_guest_cpu_init();
 424         native_smp_prepare_boot_cpu();
 425         kvm_spinlock_init();
 426 }
 427
 428 static void kvm_guest_cpu_online(void *dummy)
 429 {
 430         kvm_guest_cpu_init();
 431 }
 432
 433 static void kvm_guest_cpu_offline(void *dummy)
 434 {
 435         kvm_disable_steal_time();
 436         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
 437                 wrmsrl(MSR_KVM_PV_EOI_EN, 0);
 438         kvm_pv_disable_apf();
 439         apf_task_wake_all();
 440 }
 441
 442 static int kvm_cpu_notify(struct notifier_block *self, unsigned long action,
 443                           void *hcpu)
 444 {
 445         int cpu = (unsigned long)hcpu;
 446         switch (action) {
 447         case CPU_ONLINE:
 448         case CPU_DOWN_FAILED:
 449         case CPU_ONLINE_FROZEN:
 450                 smp_call_function_single(cpu, kvm_guest_cpu_online, NULL, 0);
 451                 break;
 452         case CPU_DOWN_PREPARE:
 453         case CPU_DOWN_PREPARE_FROZEN:
 454                 smp_call_function_single(cpu, kvm_guest_cpu_offline, NULL, 1);
 455                 break;
 456         default:
 457                 break;
 458         }
 459         return NOTIFY_OK;
 460 }
 461
 462 static struct notifier_block kvm_cpu_notifier = {
 463         .notifier_call  = kvm_cpu_notify,
 464 };
 465 #endif
 466
 467 static void __init kvm_apf_trap_init(void)
 468 {
 469         set_intr_gate(14, async_page_fault);
 470 }
 471
 472 void __init kvm_guest_init(void)
 473 {
 474         int i;
 475
 476         if (!kvm_para_available())
 477                 return;
 478
 479         paravirt_ops_setup();
 480         register_reboot_notifier(&kvm_pv_reboot_nb);
 481         for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++)
 482                 spin_lock_init(&async_pf_sleepers[i].lock);
 483         if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF))
 484                 x86_init.irqs.trap_init = kvm_apf_trap_init;
 485
 486         if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
 487                 has_steal_clock = 1;
 488                 pv_time_ops.steal_clock = kvm_steal_clock;
 489         }
 490
 491         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
 492                 apic_set_eoi_write(kvm_guest_apic_eoi_write);
 493
 494         if (kvmclock_vsyscall)
 495                 kvm_setup_vsyscall_timeinfo();
 496
 497 #ifdef CONFIG_SMP
 498         smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
 499         register_cpu_notifier(&kvm_cpu_notifier);
 500 #else
 501         kvm_guest_cpu_init();
 502 #endif
 503
 504         /*
 505          * Hard lockup detection is enabled by default. Disable it, as guests
 506          * can get false positives too easily, for example if the host is
 507          * overcommitted.
 508          */
 509         watchdog_enable_hardlockup_detector(false);
 510 }
 511
 512 static noinline uint32_t __kvm_cpuid_base(void)
 513 {
 514         if (boot_cpu_data.cpuid_level < 0)
 515                 return 0;       /* So we don't blow up on old processors */
 516
 517         if (cpu_has_hypervisor)
 518                 return hypervisor_cpuid_base("KVMKVMKVM\0\0\0", 0);
 519
 520         return 0;
 521 }
 522
 523 static inline uint32_t kvm_cpuid_base(void)
 524 {
 525         static int kvm_cpuid_base = -1;
 526
 527         if (kvm_cpuid_base == -1)
 528                 kvm_cpuid_base = __kvm_cpuid_base();
 529
 530         return kvm_cpuid_base;
 531 }
 532
 533 bool kvm_para_available(void)
 534 {
 535         return kvm_cpuid_base() != 0;
 536 }
 537 EXPORT_SYMBOL_GPL(kvm_para_available);
 538
 539 unsigned int kvm_arch_para_features(void)
 540 {
 541         return cpuid_eax(kvm_cpuid_base() | KVM_CPUID_FEATURES);
 542 }
 543
 544 static uint32_t __init kvm_detect(void)
 545 {
 546         return kvm_cpuid_base();
 547 }
 548
 549 const struct hypervisor_x86 x86_hyper_kvm __refconst = {
 550         .name                   = "KVM",
 551         .detect                 = kvm_detect,
 552         .x2apic_available       = kvm_para_available,
 553 };
 554 EXPORT_SYMBOL_GPL(x86_hyper_kvm);
 555
 556 static __init int activate_jump_labels(void)
 557 {
 558         if (has_steal_clock) {
 559                 static_key_slow_inc(&paravirt_steal_enabled);
 560                 if (steal_acc)
 561                         static_key_slow_inc(&paravirt_steal_rq_enabled);
 562         }
 563
 564         return 0;
 565 }
 566 arch_initcall(activate_jump_labels);
 567
 568 #ifdef CONFIG_PARAVIRT_SPINLOCKS
 569
 570 /* Kick a cpu by its apicid. Used to wake up a halted vcpu */
 571 static void kvm_kick_cpu(int cpu)
 572 {
 573         int apicid;
 574         unsigned long flags = 0;
 575
 576         apicid = per_cpu(x86_cpu_to_apicid, cpu);
 577         kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
 578 }
 579
 580 enum kvm_contention_stat {
 581         TAKEN_SLOW,
 582         TAKEN_SLOW_PICKUP,
 583         RELEASED_SLOW,
 584         RELEASED_SLOW_KICKED,
 585         NR_CONTENTION_STATS
 586 };
 587
 588 #ifdef CONFIG_KVM_DEBUG_FS
 589 #define HISTO_BUCKETS   30
 590
 591 static struct kvm_spinlock_stats
 592 {
 593         u32 contention_stats[NR_CONTENTION_STATS];
 594         u32 histo_spin_blocked[HISTO_BUCKETS+1];
 595         u64 time_blocked;
 596 } spinlock_stats;
 597
 598 static u8 zero_stats;
 599
 600 static inline void check_zero(void)
 601 {
 602         u8 ret;
 603         u8 old;
 604
 605         old = ACCESS_ONCE(zero_stats);
 606         if (unlikely(old)) {
 607                 ret = cmpxchg(&zero_stats, old, 0);
 608                 /* This ensures only one fellow resets the stat */
 609                 if (ret == old)
 610                         memset(&spinlock_stats, 0, sizeof(spinlock_stats));
 611         }
 612 }
 613
 614 static inline void add_stats(enum kvm_contention_stat var, u32 val)
 615 {
 616         check_zero();
 617         spinlock_stats.contention_stats[var] += val;
 618 }
 619
 620
 621 static inline u64 spin_time_start(void)
 622 {
 623         return sched_clock();
 624 }
 625
 626 static void __spin_time_accum(u64 delta, u32 *array)
 627 {
 628         unsigned index;
 629
 630         index = ilog2(delta);
 631         check_zero();
 632
 633         if (index < HISTO_BUCKETS)
 634                 array[index]++;
 635         else
 636                 array[HISTO_BUCKETS]++;
 637 }
 638
 639 static inline void spin_time_accum_blocked(u64 start)
 640 {
 641         u32 delta;
 642
 643         delta = sched_clock() - start;
 644         __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
 645         spinlock_stats.time_blocked += delta;
 646 }
 647
 648 static struct dentry *d_spin_debug;
 649 static struct dentry *d_kvm_debug;
 650
 651 struct dentry *kvm_init_debugfs(void)
 652 {
 653         d_kvm_debug = debugfs_create_dir("kvm-guest", NULL);
 654         if (!d_kvm_debug)
 655                 printk(KERN_WARNING "Could not create 'kvm' debugfs directory\n");
 656
 657         return d_kvm_debug;
 658 }
 659
 660 static int __init kvm_spinlock_debugfs(void)
 661 {
 662         struct dentry *d_kvm;
 663
 664         d_kvm = kvm_init_debugfs();
 665         if (d_kvm == NULL)
 666                 return -ENOMEM;
 667
 668         d_spin_debug = debugfs_create_dir("spinlocks", d_kvm);
 669
 670         debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
 671
 672         debugfs_create_u32("taken_slow", 0444, d_spin_debug,
 673                    &spinlock_stats.contention_stats[TAKEN_SLOW]);
 674         debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
 675                    &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
 676
 677         debugfs_create_u32("released_slow", 0444, d_spin_debug,
 678                    &spinlock_stats.contention_stats[RELEASED_SLOW]);
 679         debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
 680                    &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
 681
 682         debugfs_create_u64("time_blocked", 0444, d_spin_debug,
 683                            &spinlock_stats.time_blocked);
 684
 685         debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
 686                      spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
 687
 688         return 0;
 689 }
 690 fs_initcall(kvm_spinlock_debugfs);
 691 #else  /* !CONFIG_KVM_DEBUG_FS */
 692 static inline void add_stats(enum kvm_contention_stat var, u32 val)
 693 {
 694 }
 695
 696 static inline u64 spin_time_start(void)
 697 {
 698         return 0;
 699 }
 700
 701 static inline void spin_time_accum_blocked(u64 start)
 702 {
 703 }
 704 #endif  /* CONFIG_KVM_DEBUG_FS */
 705
 706 struct kvm_lock_waiting {
 707         struct arch_spinlock *lock;
 708         __ticket_t want;
 709 };
 710
 711 /* cpus 'waiting' on a spinlock to become available */
 712 static cpumask_t waiting_cpus;
 713
 714 /* Track spinlock on which a cpu is waiting */
 715 static DEFINE_PER_CPU(struct kvm_lock_waiting, klock_waiting);
 716
 717 __visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
 718 {
 719         struct kvm_lock_waiting *w;
 720         int cpu;
 721         u64 start;
 722         unsigned long flags;
 723
 724         if (in_nmi())
 725                 return;
 726
 727         w = this_cpu_ptr(&klock_waiting);
 728         cpu = smp_processor_id();
 729         start = spin_time_start();
 730
 731         /*
 732          * Make sure an interrupt handler can't upset things in a
 733          * partially setup state.
 734          */
 735         local_irq_save(flags);
 736
 737         /*
 738          * The ordering protocol on this is that the "lock" pointer
 739          * may only be set non-NULL if the "want" ticket is correct.
 740          * If we're updating "want", we must first clear "lock".
 741          */
 742         w->lock = NULL;
 743         smp_wmb();
 744         w->want = want;
 745         smp_wmb();
 746         w->lock = lock;
 747
 748         add_stats(TAKEN_SLOW, 1);
 749
 750         /*
 751          * This uses set_bit, which is atomic but we should not rely on its
 752          * reordering gurantees. So barrier is needed after this call.
 753          */
 754         cpumask_set_cpu(cpu, &waiting_cpus);
 755
 756         barrier();
 757
 758         /*
 759          * Mark entry to slowpath before doing the pickup test to make
 760          * sure we don't deadlock with an unlocker.
 761          */
 762         __ticket_enter_slowpath(lock);
 763
 764         /*
 765          * check again make sure it didn't become free while
 766          * we weren't looking.
 767          */
 768         if (ACCESS_ONCE(lock->tickets.head) == want) {
 769                 add_stats(TAKEN_SLOW_PICKUP, 1);
 770                 goto out;
 771         }
 772
 773         /*
 774          * halt until it's our turn and kicked. Note that we do safe halt
 775          * for irq enabled case to avoid hang when lock info is overwritten
 776          * in irq spinlock slowpath and no spurious interrupt occur to save us.
 777          */
 778         if (arch_irqs_disabled_flags(flags))
 779                 halt();
 780         else
 781                 safe_halt();
 782
 783 out:
 784         cpumask_clear_cpu(cpu, &waiting_cpus);
 785         w->lock = NULL;
 786         local_irq_restore(flags);
 787         spin_time_accum_blocked(start);
 788 }
 789 PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);
 790
 791 /* Kick vcpu waiting on @lock->head to reach value @ticket */
 792 static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
 793 {
 794         int cpu;
 795
 796         add_stats(RELEASED_SLOW, 1);
 797         for_each_cpu(cpu, &waiting_cpus) {
 798                 const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu);
 799                 if (ACCESS_ONCE(w->lock) == lock &&
 800                     ACCESS_ONCE(w->want) == ticket) {
 801                         add_stats(RELEASED_SLOW_KICKED, 1);
 802                         kvm_kick_cpu(cpu);
 803                         break;
 804                 }
 805         }
 806 }
 807
 808 /*
 809  * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
 810  */
 811 void __init kvm_spinlock_init(void)
 812 {
 813         if (!kvm_para_available())
 814                 return;
 815         /* Does host kernel support KVM_FEATURE_PV_UNHALT? */
 816         if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
 817                 return;
 818
 819         pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
 820         pv_lock_ops.unlock_kick = kvm_unlock_kick;
 821 }
 822
 823 static __init int kvm_spinlock_init_jump(void)
 824 {
 825         if (!kvm_para_available())
 826                 return 0;
 827         if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
 828                 return 0;
 829
 830         static_key_slow_inc(&paravirt_ticketlocks_enabled);
 831         printk(KERN_INFO "KVM setup paravirtual spinlock\n");
 832
 833         return 0;
 834 }
 835 early_initcall(kvm_spinlock_init_jump);
 836
 837 #endif  /* CONFIG_PARAVIRT_SPINLOCKS */