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"; 286 287 /* 288 * KVM isn't paravirt in the sense of paravirt_enabled. A KVM 289 * guest kernel works like a bare metal kernel with additional 290 * features, and paravirt_enabled is about features that are 291 * missing. 292 */ 293 pv_info.paravirt_enabled = 0; 294 295 if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY)) 296 pv_cpu_ops.io_delay = kvm_io_delay; 297 298 #ifdef CONFIG_X86_IO_APIC 299 no_timer_check = 1; 300 #endif 301 } 302 303 static void kvm_register_steal_time(void) 304 { 305 int cpu = smp_processor_id(); 306 struct kvm_steal_time *st = &per_cpu(steal_time, cpu); 307 308 if (!has_steal_clock) 309 return; 310 311 memset(st, 0, sizeof(*st)); 312 313 wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED)); 314 pr_info("kvm-stealtime: cpu %d, msr %llx\n", 315 cpu, (unsigned long long) slow_virt_to_phys(st)); 316 } 317 318 static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED; 319 320 static void kvm_guest_apic_eoi_write(u32 reg, u32 val) 321 { 322 /** 323 * This relies on __test_and_clear_bit to modify the memory 324 * in a way that is atomic with respect to the local CPU. 325 * The hypervisor only accesses this memory from the local CPU so 326 * there's no need for lock or memory barriers. 327 * An optimization barrier is implied in apic write. 328 */ 329 if (__test_and_clear_bit(KVM_PV_EOI_BIT, this_cpu_ptr(&kvm_apic_eoi))) 330 return; 331 apic_write(APIC_EOI, APIC_EOI_ACK); 332 } 333 334 static void kvm_guest_cpu_init(void) 335 { 336 if (!kvm_para_available()) 337 return; 338 339 if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) { 340 u64 pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason)); 341 342 #ifdef CONFIG_PREEMPT 343 pa |= KVM_ASYNC_PF_SEND_ALWAYS; 344 #endif 345 wrmsrl(MSR_KVM_ASYNC_PF_EN, pa | KVM_ASYNC_PF_ENABLED); 346 __this_cpu_write(apf_reason.enabled, 1); 347 printk(KERN_INFO"KVM setup async PF for cpu %d\n", 348 smp_processor_id()); 349 } 350 351 if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) { 352 unsigned long pa; 353 /* Size alignment is implied but just to make it explicit. */ 354 BUILD_BUG_ON(__alignof__(kvm_apic_eoi) < 4); 355 __this_cpu_write(kvm_apic_eoi, 0); 356 pa = slow_virt_to_phys(this_cpu_ptr(&kvm_apic_eoi)) 357 | KVM_MSR_ENABLED; 358 wrmsrl(MSR_KVM_PV_EOI_EN, pa); 359 } 360 361 if (has_steal_clock) 362 kvm_register_steal_time(); 363 } 364 365 static void kvm_pv_disable_apf(void) 366 { 367 if (!__this_cpu_read(apf_reason.enabled)) 368 return; 369 370 wrmsrl(MSR_KVM_ASYNC_PF_EN, 0); 371 __this_cpu_write(apf_reason.enabled, 0); 372 373 printk(KERN_INFO"Unregister pv shared memory for cpu %d\n", 374 smp_processor_id()); 375 } 376 377 static void kvm_pv_guest_cpu_reboot(void *unused) 378 { 379 /* 380 * We disable PV EOI before we load a new kernel by kexec, 381 * since MSR_KVM_PV_EOI_EN stores a pointer into old kernel's memory. 382 * New kernel can re-enable when it boots. 383 */ 384 if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) 385 wrmsrl(MSR_KVM_PV_EOI_EN, 0); 386 kvm_pv_disable_apf(); 387 kvm_disable_steal_time(); 388 } 389 390 static int kvm_pv_reboot_notify(struct notifier_block *nb, 391 unsigned long code, void *unused) 392 { 393 if (code == SYS_RESTART) 394 on_each_cpu(kvm_pv_guest_cpu_reboot, NULL, 1); 395 return NOTIFY_DONE; 396 } 397 398 static struct notifier_block kvm_pv_reboot_nb = { 399 .notifier_call = kvm_pv_reboot_notify, 400 }; 401 402 static u64 kvm_steal_clock(int cpu) 403 { 404 u64 steal; 405 struct kvm_steal_time *src; 406 int version; 407 408 src = &per_cpu(steal_time, cpu); 409 do { 410 version = src->version; 411 rmb(); 412 steal = src->steal; 413 rmb(); 414 } while ((version & 1) || (version != src->version)); 415 416 return steal; 417 } 418 419 void kvm_disable_steal_time(void) 420 { 421 if (!has_steal_clock) 422 return; 423 424 wrmsr(MSR_KVM_STEAL_TIME, 0, 0); 425 } 426 427 #ifdef CONFIG_SMP 428 static void __init kvm_smp_prepare_boot_cpu(void) 429 { 430 kvm_guest_cpu_init(); 431 native_smp_prepare_boot_cpu(); 432 kvm_spinlock_init(); 433 } 434 435 static void kvm_guest_cpu_online(void *dummy) 436 { 437 kvm_guest_cpu_init(); 438 } 439 440 static void kvm_guest_cpu_offline(void *dummy) 441 { 442 kvm_disable_steal_time(); 443 if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) 444 wrmsrl(MSR_KVM_PV_EOI_EN, 0); 445 kvm_pv_disable_apf(); 446 apf_task_wake_all(); 447 } 448 449 static int kvm_cpu_notify(struct notifier_block *self, unsigned long action, 450 void *hcpu) 451 { 452 int cpu = (unsigned long)hcpu; 453 switch (action) { 454 case CPU_ONLINE: 455 case CPU_DOWN_FAILED: 456 case CPU_ONLINE_FROZEN: 457 smp_call_function_single(cpu, kvm_guest_cpu_online, NULL, 0); 458 break; 459 case CPU_DOWN_PREPARE: 460 case CPU_DOWN_PREPARE_FROZEN: 461 smp_call_function_single(cpu, kvm_guest_cpu_offline, NULL, 1); 462 break; 463 default: 464 break; 465 } 466 return NOTIFY_OK; 467 } 468 469 static struct notifier_block kvm_cpu_notifier = { 470 .notifier_call = kvm_cpu_notify, 471 }; 472 #endif 473 474 static void __init kvm_apf_trap_init(void) 475 { 476 set_intr_gate(14, async_page_fault); 477 } 478 479 void __init kvm_guest_init(void) 480 { 481 int i; 482 483 if (!kvm_para_available()) 484 return; 485 486 paravirt_ops_setup(); 487 register_reboot_notifier(&kvm_pv_reboot_nb); 488 for (i = 0; i < KVM_TASK_SLEEP_HASHSIZE; i++) 489 spin_lock_init(&async_pf_sleepers[i].lock); 490 if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF)) 491 x86_init.irqs.trap_init = kvm_apf_trap_init; 492 493 if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { 494 has_steal_clock = 1; 495 pv_time_ops.steal_clock = kvm_steal_clock; 496 } 497 498 if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) 499 apic_set_eoi_write(kvm_guest_apic_eoi_write); 500 501 if (kvmclock_vsyscall) 502 kvm_setup_vsyscall_timeinfo(); 503 504 #ifdef CONFIG_SMP 505 smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu; 506 register_cpu_notifier(&kvm_cpu_notifier); 507 #else 508 kvm_guest_cpu_init(); 509 #endif 510 511 /* 512 * Hard lockup detection is enabled by default. Disable it, as guests 513 * can get false positives too easily, for example if the host is 514 * overcommitted. 515 */ 516 hardlockup_detector_disable(); 517 } 518 519 static noinline uint32_t __kvm_cpuid_base(void) 520 { 521 if (boot_cpu_data.cpuid_level < 0) 522 return 0; /* So we don't blow up on old processors */ 523 524 if (cpu_has_hypervisor) 525 return hypervisor_cpuid_base("KVMKVMKVM\0\0\0", 0); 526 527 return 0; 528 } 529 530 static inline uint32_t kvm_cpuid_base(void) 531 { 532 static int kvm_cpuid_base = -1; 533 534 if (kvm_cpuid_base == -1) 535 kvm_cpuid_base = __kvm_cpuid_base(); 536 537 return kvm_cpuid_base; 538 } 539 540 bool kvm_para_available(void) 541 { 542 return kvm_cpuid_base() != 0; 543 } 544 EXPORT_SYMBOL_GPL(kvm_para_available); 545 546 unsigned int kvm_arch_para_features(void) 547 { 548 return cpuid_eax(kvm_cpuid_base() | KVM_CPUID_FEATURES); 549 } 550 551 static uint32_t __init kvm_detect(void) 552 { 553 return kvm_cpuid_base(); 554 } 555 556 const struct hypervisor_x86 x86_hyper_kvm __refconst = { 557 .name = "KVM", 558 .detect = kvm_detect, 559 .x2apic_available = kvm_para_available, 560 }; 561 EXPORT_SYMBOL_GPL(x86_hyper_kvm); 562 563 static __init int activate_jump_labels(void) 564 { 565 if (has_steal_clock) { 566 static_key_slow_inc(¶virt_steal_enabled); 567 if (steal_acc) 568 static_key_slow_inc(¶virt_steal_rq_enabled); 569 } 570 571 return 0; 572 } 573 arch_initcall(activate_jump_labels); 574 575 #ifdef CONFIG_PARAVIRT_SPINLOCKS 576 577 /* Kick a cpu by its apicid. Used to wake up a halted vcpu */ 578 static void kvm_kick_cpu(int cpu) 579 { 580 int apicid; 581 unsigned long flags = 0; 582 583 apicid = per_cpu(x86_cpu_to_apicid, cpu); 584 kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid); 585 } 586 587 588 #ifdef CONFIG_QUEUED_SPINLOCKS 589 590 #include <asm/qspinlock.h> 591 592 static void kvm_wait(u8 *ptr, u8 val) 593 { 594 unsigned long flags; 595 596 if (in_nmi()) 597 return; 598 599 local_irq_save(flags); 600 601 if (READ_ONCE(*ptr) != val) 602 goto out; 603 604 /* 605 * halt until it's our turn and kicked. Note that we do safe halt 606 * for irq enabled case to avoid hang when lock info is overwritten 607 * in irq spinlock slowpath and no spurious interrupt occur to save us. 608 */ 609 if (arch_irqs_disabled_flags(flags)) 610 halt(); 611 else 612 safe_halt(); 613 614 out: 615 local_irq_restore(flags); 616 } 617 618 #else /* !CONFIG_QUEUED_SPINLOCKS */ 619 620 enum kvm_contention_stat { 621 TAKEN_SLOW, 622 TAKEN_SLOW_PICKUP, 623 RELEASED_SLOW, 624 RELEASED_SLOW_KICKED, 625 NR_CONTENTION_STATS 626 }; 627 628 #ifdef CONFIG_KVM_DEBUG_FS 629 #define HISTO_BUCKETS 30 630 631 static struct kvm_spinlock_stats 632 { 633 u32 contention_stats[NR_CONTENTION_STATS]; 634 u32 histo_spin_blocked[HISTO_BUCKETS+1]; 635 u64 time_blocked; 636 } spinlock_stats; 637 638 static u8 zero_stats; 639 640 static inline void check_zero(void) 641 { 642 u8 ret; 643 u8 old; 644 645 old = READ_ONCE(zero_stats); 646 if (unlikely(old)) { 647 ret = cmpxchg(&zero_stats, old, 0); 648 /* This ensures only one fellow resets the stat */ 649 if (ret == old) 650 memset(&spinlock_stats, 0, sizeof(spinlock_stats)); 651 } 652 } 653 654 static inline void add_stats(enum kvm_contention_stat var, u32 val) 655 { 656 check_zero(); 657 spinlock_stats.contention_stats[var] += val; 658 } 659 660 661 static inline u64 spin_time_start(void) 662 { 663 return sched_clock(); 664 } 665 666 static void __spin_time_accum(u64 delta, u32 *array) 667 { 668 unsigned index; 669 670 index = ilog2(delta); 671 check_zero(); 672 673 if (index < HISTO_BUCKETS) 674 array[index]++; 675 else 676 array[HISTO_BUCKETS]++; 677 } 678 679 static inline void spin_time_accum_blocked(u64 start) 680 { 681 u32 delta; 682 683 delta = sched_clock() - start; 684 __spin_time_accum(delta, spinlock_stats.histo_spin_blocked); 685 spinlock_stats.time_blocked += delta; 686 } 687 688 static struct dentry *d_spin_debug; 689 static struct dentry *d_kvm_debug; 690 691 static struct dentry *kvm_init_debugfs(void) 692 { 693 d_kvm_debug = debugfs_create_dir("kvm-guest", NULL); 694 if (!d_kvm_debug) 695 printk(KERN_WARNING "Could not create 'kvm' debugfs directory\n"); 696 697 return d_kvm_debug; 698 } 699 700 static int __init kvm_spinlock_debugfs(void) 701 { 702 struct dentry *d_kvm; 703 704 d_kvm = kvm_init_debugfs(); 705 if (d_kvm == NULL) 706 return -ENOMEM; 707 708 d_spin_debug = debugfs_create_dir("spinlocks", d_kvm); 709 710 debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats); 711 712 debugfs_create_u32("taken_slow", 0444, d_spin_debug, 713 &spinlock_stats.contention_stats[TAKEN_SLOW]); 714 debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug, 715 &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]); 716 717 debugfs_create_u32("released_slow", 0444, d_spin_debug, 718 &spinlock_stats.contention_stats[RELEASED_SLOW]); 719 debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug, 720 &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]); 721 722 debugfs_create_u64("time_blocked", 0444, d_spin_debug, 723 &spinlock_stats.time_blocked); 724 725 debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug, 726 spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1); 727 728 return 0; 729 } 730 fs_initcall(kvm_spinlock_debugfs); 731 #else /* !CONFIG_KVM_DEBUG_FS */ 732 static inline void add_stats(enum kvm_contention_stat var, u32 val) 733 { 734 } 735 736 static inline u64 spin_time_start(void) 737 { 738 return 0; 739 } 740 741 static inline void spin_time_accum_blocked(u64 start) 742 { 743 } 744 #endif /* CONFIG_KVM_DEBUG_FS */ 745 746 struct kvm_lock_waiting { 747 struct arch_spinlock *lock; 748 __ticket_t want; 749 }; 750 751 /* cpus 'waiting' on a spinlock to become available */ 752 static cpumask_t waiting_cpus; 753 754 /* Track spinlock on which a cpu is waiting */ 755 static DEFINE_PER_CPU(struct kvm_lock_waiting, klock_waiting); 756 757 __visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want) 758 { 759 struct kvm_lock_waiting *w; 760 int cpu; 761 u64 start; 762 unsigned long flags; 763 __ticket_t head; 764 765 if (in_nmi()) 766 return; 767 768 w = this_cpu_ptr(&klock_waiting); 769 cpu = smp_processor_id(); 770 start = spin_time_start(); 771 772 /* 773 * Make sure an interrupt handler can't upset things in a 774 * partially setup state. 775 */ 776 local_irq_save(flags); 777 778 /* 779 * The ordering protocol on this is that the "lock" pointer 780 * may only be set non-NULL if the "want" ticket is correct. 781 * If we're updating "want", we must first clear "lock". 782 */ 783 w->lock = NULL; 784 smp_wmb(); 785 w->want = want; 786 smp_wmb(); 787 w->lock = lock; 788 789 add_stats(TAKEN_SLOW, 1); 790 791 /* 792 * This uses set_bit, which is atomic but we should not rely on its 793 * reordering gurantees. So barrier is needed after this call. 794 */ 795 cpumask_set_cpu(cpu, &waiting_cpus); 796 797 barrier(); 798 799 /* 800 * Mark entry to slowpath before doing the pickup test to make 801 * sure we don't deadlock with an unlocker. 802 */ 803 __ticket_enter_slowpath(lock); 804 805 /* make sure enter_slowpath, which is atomic does not cross the read */ 806 smp_mb__after_atomic(); 807 808 /* 809 * check again make sure it didn't become free while 810 * we weren't looking. 811 */ 812 head = READ_ONCE(lock->tickets.head); 813 if (__tickets_equal(head, want)) { 814 add_stats(TAKEN_SLOW_PICKUP, 1); 815 goto out; 816 } 817 818 /* 819 * halt until it's our turn and kicked. Note that we do safe halt 820 * for irq enabled case to avoid hang when lock info is overwritten 821 * in irq spinlock slowpath and no spurious interrupt occur to save us. 822 */ 823 if (arch_irqs_disabled_flags(flags)) 824 halt(); 825 else 826 safe_halt(); 827 828 out: 829 cpumask_clear_cpu(cpu, &waiting_cpus); 830 w->lock = NULL; 831 local_irq_restore(flags); 832 spin_time_accum_blocked(start); 833 } 834 PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning); 835 836 /* Kick vcpu waiting on @lock->head to reach value @ticket */ 837 static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket) 838 { 839 int cpu; 840 841 add_stats(RELEASED_SLOW, 1); 842 for_each_cpu(cpu, &waiting_cpus) { 843 const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu); 844 if (READ_ONCE(w->lock) == lock && 845 READ_ONCE(w->want) == ticket) { 846 add_stats(RELEASED_SLOW_KICKED, 1); 847 kvm_kick_cpu(cpu); 848 break; 849 } 850 } 851 } 852 853 #endif /* !CONFIG_QUEUED_SPINLOCKS */ 854 855 /* 856 * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present. 857 */ 858 void __init kvm_spinlock_init(void) 859 { 860 if (!kvm_para_available()) 861 return; 862 /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ 863 if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) 864 return; 865 866 #ifdef CONFIG_QUEUED_SPINLOCKS 867 __pv_init_lock_hash(); 868 pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; 869 pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock); 870 pv_lock_ops.wait = kvm_wait; 871 pv_lock_ops.kick = kvm_kick_cpu; 872 #else /* !CONFIG_QUEUED_SPINLOCKS */ 873 pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning); 874 pv_lock_ops.unlock_kick = kvm_unlock_kick; 875 #endif 876 } 877 878 static __init int kvm_spinlock_init_jump(void) 879 { 880 if (!kvm_para_available()) 881 return 0; 882 if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) 883 return 0; 884 885 static_key_slow_inc(¶virt_ticketlocks_enabled); 886 printk(KERN_INFO "KVM setup paravirtual spinlock\n"); 887 888 return 0; 889 } 890 early_initcall(kvm_spinlock_init_jump); 891 892 #endif /* CONFIG_PARAVIRT_SPINLOCKS */ 893