hw/i386/kvm/clock.c

   1 /*
   2  * QEMU KVM support, paravirtual clock device
   3  *
   4  * Copyright (C) 2011 Siemens AG
   5  *
   6  * Authors:
   7  *  Jan Kiszka        <jan.kiszka@siemens.com>
   8  *
   9  * This work is licensed under the terms of the GNU GPL version 2.
  10  * See the COPYING file in the top-level directory.
  11  *
  12  * Contributions after 2012-01-13 are licensed under the terms of the
  13  * GNU GPL, version 2 or (at your option) any later version.
  14  */
  15
  16 #include "qemu/osdep.h"
  17 #include "cpu.h"
  18 #include "qemu/host-utils.h"
  19 #include "qemu/module.h"
  20 #include "sysemu/kvm.h"
  21 #include "sysemu/runstate.h"
  22 #include "sysemu/hw_accel.h"
  23 #include "kvm_i386.h"
  24 #include "migration/vmstate.h"
  25 #include "hw/sysbus.h"
  26 #include "hw/kvm/clock.h"
  27 #include "hw/qdev-properties.h"
  28 #include "qapi/error.h"
  29
  30 #include <linux/kvm.h>
  31 #include "standard-headers/asm-x86/kvm_para.h"
  32
  33 #define TYPE_KVM_CLOCK "kvmclock"
  34 #define KVM_CLOCK(obj) OBJECT_CHECK(KVMClockState, (obj), TYPE_KVM_CLOCK)
  35
  36 typedef struct KVMClockState {
  37     /*< private >*/
  38     SysBusDevice busdev;
  39     /*< public >*/
  40
  41     uint64_t clock;
  42     bool clock_valid;
  43
  44     /* whether the 'clock' value was obtained in the 'paused' state */
  45     bool runstate_paused;
  46
  47     /* whether machine type supports reliable KVM_GET_CLOCK */
  48     bool mach_use_reliable_get_clock;
  49
  50     /* whether the 'clock' value was obtained in a host with
  51      * reliable KVM_GET_CLOCK */
  52     bool clock_is_reliable;
  53 } KVMClockState;
  54
  55 struct pvclock_vcpu_time_info {
  56     uint32_t   version;
  57     uint32_t   pad0;
  58     uint64_t   tsc_timestamp;
  59     uint64_t   system_time;
  60     uint32_t   tsc_to_system_mul;
  61     int8_t     tsc_shift;
  62     uint8_t    flags;
  63     uint8_t    pad[2];
  64 } __attribute__((__packed__)); /* 32 bytes */
  65
  66 static uint64_t kvmclock_current_nsec(KVMClockState *s)
  67 {
  68     CPUState *cpu = first_cpu;
  69     CPUX86State *env = cpu->env_ptr;
  70     hwaddr kvmclock_struct_pa;
  71     uint64_t migration_tsc = env->tsc;
  72     struct pvclock_vcpu_time_info time;
  73     uint64_t delta;
  74     uint64_t nsec_lo;
  75     uint64_t nsec_hi;
  76     uint64_t nsec;
  77
  78     cpu_synchronize_state(cpu);
  79
  80     if (!(env->system_time_msr & 1ULL)) {
  81         /* KVM clock not active */
  82         return 0;
  83     }
  84
  85     kvmclock_struct_pa = env->system_time_msr & ~1ULL;
  86     cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time));
  87
  88     assert(time.tsc_timestamp <= migration_tsc);
  89     delta = migration_tsc - time.tsc_timestamp;
  90     if (time.tsc_shift < 0) {
  91         delta >>= -time.tsc_shift;
  92     } else {
  93         delta <<= time.tsc_shift;
  94     }
  95
  96     mulu64(&nsec_lo, &nsec_hi, delta, time.tsc_to_system_mul);
  97     nsec = (nsec_lo >> 32) | (nsec_hi << 32);
  98     return nsec + time.system_time;
  99 }
 100
 101 static void kvm_update_clock(KVMClockState *s)
 102 {
 103     struct kvm_clock_data data;
 104     int ret;
 105
 106     ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
 107     if (ret < 0) {
 108         fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));
 109                 abort();
 110     }
 111     s->clock = data.clock;
 112
 113     /* If kvm_has_adjust_clock_stable() is false, KVM_GET_CLOCK returns
 114      * essentially CLOCK_MONOTONIC plus a guest-specific adjustment.  This
 115      * can drift from the TSC-based value that is computed by the guest,
 116      * so we need to go through kvmclock_current_nsec().  If
 117      * kvm_has_adjust_clock_stable() is true, and the flags contain
 118      * KVM_CLOCK_TSC_STABLE, then KVM_GET_CLOCK returns a TSC-based value
 119      * and kvmclock_current_nsec() is not necessary.
 120      *
 121      * Here, however, we need not check KVM_CLOCK_TSC_STABLE.  This is because:
 122      *
 123      * - if the host has disabled the kvmclock master clock, the guest already
 124      *   has protection against time going backwards.  This "safety net" is only
 125      *   absent when kvmclock is stable;
 126      *
 127      * - therefore, we can replace a check like
 128      *
 129      *       if last KVM_GET_CLOCK was not reliable then
 130      *               read from memory
 131      *
 132      *   with
 133      *
 134      *       if last KVM_GET_CLOCK was not reliable && masterclock is enabled
 135      *               read from memory
 136      *
 137      * However:
 138      *
 139      * - if kvm_has_adjust_clock_stable() returns false, the left side is
 140      *   always true (KVM_GET_CLOCK is never reliable), and the right side is
 141      *   unknown (because we don't have data.flags).  We must assume it's true
 142      *   and read from memory.
 143      *
 144      * - if kvm_has_adjust_clock_stable() returns true, the result of the &&
 145      *   is always false (masterclock is enabled iff KVM_GET_CLOCK is reliable)
 146      *
 147      * So we can just use this instead:
 148      *
 149      *       if !kvm_has_adjust_clock_stable() then
 150      *               read from memory
 151      */
 152     s->clock_is_reliable = kvm_has_adjust_clock_stable();
 153 }
 154
 155 static void do_kvmclock_ctrl(CPUState *cpu, run_on_cpu_data data)
 156 {
 157     int ret = kvm_vcpu_ioctl(cpu, KVM_KVMCLOCK_CTRL, 0);
 158
 159     if (ret && ret != -EINVAL) {
 160         fprintf(stderr, "%s: %s\n", __func__, strerror(-ret));
 161     }
 162 }
 163
 164 static void kvmclock_vm_state_change(void *opaque, int running,
 165                                      RunState state)
 166 {
 167     KVMClockState *s = opaque;
 168     CPUState *cpu;
 169     int cap_clock_ctrl = kvm_check_extension(kvm_state, KVM_CAP_KVMCLOCK_CTRL);
 170     int ret;
 171
 172     if (running) {
 173         struct kvm_clock_data data = {};
 174
 175         /*
 176          * If the host where s->clock was read did not support reliable
 177          * KVM_GET_CLOCK, read kvmclock value from memory.
 178          */
 179         if (!s->clock_is_reliable) {
 180             uint64_t pvclock_via_mem = kvmclock_current_nsec(s);
 181             /* We can't rely on the saved clock value, just discard it */
 182             if (pvclock_via_mem) {
 183                 s->clock = pvclock_via_mem;
 184             }
 185         }
 186
 187         s->clock_valid = false;
 188
 189         data.clock = s->clock;
 190         ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
 191         if (ret < 0) {
 192             fprintf(stderr, "KVM_SET_CLOCK failed: %s\n", strerror(ret));
 193             abort();
 194         }
 195
 196         if (!cap_clock_ctrl) {
 197             return;
 198         }
 199         CPU_FOREACH(cpu) {
 200             run_on_cpu(cpu, do_kvmclock_ctrl, RUN_ON_CPU_NULL);
 201         }
 202     } else {
 203
 204         if (s->clock_valid) {
 205             return;
 206         }
 207
 208         s->runstate_paused = runstate_check(RUN_STATE_PAUSED);
 209
 210         kvm_synchronize_all_tsc();
 211
 212         kvm_update_clock(s);
 213         /*
 214          * If the VM is stopped, declare the clock state valid to
 215          * avoid re-reading it on next vmsave (which would return
 216          * a different value). Will be reset when the VM is continued.
 217          */
 218         s->clock_valid = true;
 219     }
 220 }
 221
 222 static void kvmclock_realize(DeviceState *dev, Error **errp)
 223 {
 224     KVMClockState *s = KVM_CLOCK(dev);
 225
 226     if (!kvm_enabled()) {
 227         error_setg(errp, "kvmclock device requires KVM");
 228         return;
 229     }
 230
 231     kvm_update_clock(s);
 232
 233     qemu_add_vm_change_state_handler(kvmclock_vm_state_change, s);
 234 }
 235
 236 static bool kvmclock_clock_is_reliable_needed(void *opaque)
 237 {
 238     KVMClockState *s = opaque;
 239
 240     return s->mach_use_reliable_get_clock;
 241 }
 242
 243 static const VMStateDescription kvmclock_reliable_get_clock = {
 244     .name = "kvmclock/clock_is_reliable",
 245     .version_id = 1,
 246     .minimum_version_id = 1,
 247     .needed = kvmclock_clock_is_reliable_needed,
 248     .fields = (VMStateField[]) {
 249         VMSTATE_BOOL(clock_is_reliable, KVMClockState),
 250         VMSTATE_END_OF_LIST()
 251     }
 252 };
 253
 254 /*
 255  * When migrating, assume the source has an unreliable
 256  * KVM_GET_CLOCK unless told otherwise.
 257  */
 258 static int kvmclock_pre_load(void *opaque)
 259 {
 260     KVMClockState *s = opaque;
 261
 262     s->clock_is_reliable = false;
 263
 264     return 0;
 265 }
 266
 267 /*
 268  * When migrating a running guest, read the clock just
 269  * before migration, so that the guest clock counts
 270  * during the events between:
 271  *
 272  *  * vm_stop()
 273  *  *
 274  *  * pre_save()
 275  *
 276  *  This reduces kvmclock difference on migration from 5s
 277  *  to 0.1s (when max_downtime == 5s), because sending the
 278  *  final pages of memory (which happens between vm_stop()
 279  *  and pre_save()) takes max_downtime.
 280  */
 281 static int kvmclock_pre_save(void *opaque)
 282 {
 283     KVMClockState *s = opaque;
 284
 285     if (!s->runstate_paused) {
 286         kvm_update_clock(s);
 287     }
 288
 289     return 0;
 290 }
 291
 292 static const VMStateDescription kvmclock_vmsd = {
 293     .name = "kvmclock",
 294     .version_id = 1,
 295     .minimum_version_id = 1,
 296     .pre_load = kvmclock_pre_load,
 297     .pre_save = kvmclock_pre_save,
 298     .fields = (VMStateField[]) {
 299         VMSTATE_UINT64(clock, KVMClockState),
 300         VMSTATE_END_OF_LIST()
 301     },
 302     .subsections = (const VMStateDescription * []) {
 303         &kvmclock_reliable_get_clock,
 304         NULL
 305     }
 306 };
 307
 308 static Property kvmclock_properties[] = {
 309     DEFINE_PROP_BOOL("x-mach-use-reliable-get-clock", KVMClockState,
 310                       mach_use_reliable_get_clock, true),
 311     DEFINE_PROP_END_OF_LIST(),
 312 };
 313
 314 static void kvmclock_class_init(ObjectClass *klass, void *data)
 315 {
 316     DeviceClass *dc = DEVICE_CLASS(klass);
 317
 318     dc->realize = kvmclock_realize;
 319     dc->vmsd = &kvmclock_vmsd;
 320     dc->props = kvmclock_properties;
 321 }
 322
 323 static const TypeInfo kvmclock_info = {
 324     .name          = TYPE_KVM_CLOCK,
 325     .parent        = TYPE_SYS_BUS_DEVICE,
 326     .instance_size = sizeof(KVMClockState),
 327     .class_init    = kvmclock_class_init,
 328 };
 329
 330 /* Note: Must be called after VCPU initialization. */
 331 void kvmclock_create(void)
 332 {
 333     X86CPU *cpu = X86_CPU(first_cpu);
 334
 335     if (kvm_enabled() &&
 336         cpu->env.features[FEAT_KVM] & ((1ULL << KVM_FEATURE_CLOCKSOURCE) |
 337                                        (1ULL << KVM_FEATURE_CLOCKSOURCE2))) {
 338         sysbus_create_simple(TYPE_KVM_CLOCK, -1, NULL);
 339     }
 340 }
 341
 342 static void kvmclock_register_types(void)
 343 {
 344     type_register_static(&kvmclock_info);
 345 }
 346
 347 type_init(kvmclock_register_types)