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/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 #include "qom/object.h"
  33
  34 #define TYPE_KVM_CLOCK "kvmclock"
  35 OBJECT_DECLARE_SIMPLE_TYPE(KVMClockState, KVM_CLOCK)
  36
  37 struct KVMClockState {
  38     /*< private >*/
  39     SysBusDevice busdev;
  40     /*< public >*/
  41
  42     uint64_t clock;
  43     bool clock_valid;
  44
  45     /* whether the 'clock' value was obtained in the 'paused' state */
  46     bool runstate_paused;
  47
  48     /* whether machine type supports reliable KVM_GET_CLOCK */
  49     bool mach_use_reliable_get_clock;
  50
  51     /* whether the 'clock' value was obtained in a host with
  52      * reliable KVM_GET_CLOCK */
  53     bool clock_is_reliable;
  54 };
  55
  56 struct pvclock_vcpu_time_info {
  57     uint32_t   version;
  58     uint32_t   pad0;
  59     uint64_t   tsc_timestamp;
  60     uint64_t   system_time;
  61     uint32_t   tsc_to_system_mul;
  62     int8_t     tsc_shift;
  63     uint8_t    flags;
  64     uint8_t    pad[2];
  65 } __attribute__((__packed__)); /* 32 bytes */
  66
  67 static uint64_t kvmclock_current_nsec(KVMClockState *s)
  68 {
  69     CPUState *cpu = first_cpu;
  70     CPUX86State *env = cpu->env_ptr;
  71     hwaddr kvmclock_struct_pa;
  72     uint64_t migration_tsc = env->tsc;
  73     struct pvclock_vcpu_time_info time;
  74     uint64_t delta;
  75     uint64_t nsec_lo;
  76     uint64_t nsec_hi;
  77     uint64_t nsec;
  78
  79     cpu_synchronize_state(cpu);
  80
  81     if (!(env->system_time_msr & 1ULL)) {
  82         /* KVM clock not active */
  83         return 0;
  84     }
  85
  86     kvmclock_struct_pa = env->system_time_msr & ~1ULL;
  87     cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time));
  88
  89     assert(time.tsc_timestamp <= migration_tsc);
  90     delta = migration_tsc - time.tsc_timestamp;
  91     if (time.tsc_shift < 0) {
  92         delta >>= -time.tsc_shift;
  93     } else {
  94         delta <<= time.tsc_shift;
  95     }
  96
  97     mulu64(&nsec_lo, &nsec_hi, delta, time.tsc_to_system_mul);
  98     nsec = (nsec_lo >> 32) | (nsec_hi << 32);
  99     return nsec + time.system_time;
 100 }
 101
 102 static void kvm_update_clock(KVMClockState *s)
 103 {
 104     struct kvm_clock_data data;
 105     int ret;
 106
 107     ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
 108     if (ret < 0) {
 109         fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));
 110                 abort();
 111     }
 112     s->clock = data.clock;
 113
 114     /* If kvm_has_adjust_clock_stable() is false, KVM_GET_CLOCK returns
 115      * essentially CLOCK_MONOTONIC plus a guest-specific adjustment.  This
 116      * can drift from the TSC-based value that is computed by the guest,
 117      * so we need to go through kvmclock_current_nsec().  If
 118      * kvm_has_adjust_clock_stable() is true, and the flags contain
 119      * KVM_CLOCK_TSC_STABLE, then KVM_GET_CLOCK returns a TSC-based value
 120      * and kvmclock_current_nsec() is not necessary.
 121      *
 122      * Here, however, we need not check KVM_CLOCK_TSC_STABLE.  This is because:
 123      *
 124      * - if the host has disabled the kvmclock master clock, the guest already
 125      *   has protection against time going backwards.  This "safety net" is only
 126      *   absent when kvmclock is stable;
 127      *
 128      * - therefore, we can replace a check like
 129      *
 130      *       if last KVM_GET_CLOCK was not reliable then
 131      *               read from memory
 132      *
 133      *   with
 134      *
 135      *       if last KVM_GET_CLOCK was not reliable && masterclock is enabled
 136      *               read from memory
 137      *
 138      * However:
 139      *
 140      * - if kvm_has_adjust_clock_stable() returns false, the left side is
 141      *   always true (KVM_GET_CLOCK is never reliable), and the right side is
 142      *   unknown (because we don't have data.flags).  We must assume it's true
 143      *   and read from memory.
 144      *
 145      * - if kvm_has_adjust_clock_stable() returns true, the result of the &&
 146      *   is always false (masterclock is enabled iff KVM_GET_CLOCK is reliable)
 147      *
 148      * So we can just use this instead:
 149      *
 150      *       if !kvm_has_adjust_clock_stable() then
 151      *               read from memory
 152      */
 153     s->clock_is_reliable = kvm_has_adjust_clock_stable();
 154 }
 155
 156 static void do_kvmclock_ctrl(CPUState *cpu, run_on_cpu_data data)
 157 {
 158     int ret = kvm_vcpu_ioctl(cpu, KVM_KVMCLOCK_CTRL, 0);
 159
 160     if (ret && ret != -EINVAL) {
 161         fprintf(stderr, "%s: %s\n", __func__, strerror(-ret));
 162     }
 163 }
 164
 165 static void kvmclock_vm_state_change(void *opaque, int running,
 166                                      RunState state)
 167 {
 168     KVMClockState *s = opaque;
 169     CPUState *cpu;
 170     int cap_clock_ctrl = kvm_check_extension(kvm_state, KVM_CAP_KVMCLOCK_CTRL);
 171     int ret;
 172
 173     if (running) {
 174         struct kvm_clock_data data = {};
 175
 176         /*
 177          * If the host where s->clock was read did not support reliable
 178          * KVM_GET_CLOCK, read kvmclock value from memory.
 179          */
 180         if (!s->clock_is_reliable) {
 181             uint64_t pvclock_via_mem = kvmclock_current_nsec(s);
 182             /* We can't rely on the saved clock value, just discard it */
 183             if (pvclock_via_mem) {
 184                 s->clock = pvclock_via_mem;
 185             }
 186         }
 187
 188         s->clock_valid = false;
 189
 190         data.clock = s->clock;
 191         ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
 192         if (ret < 0) {
 193             fprintf(stderr, "KVM_SET_CLOCK failed: %s\n", strerror(ret));
 194             abort();
 195         }
 196
 197         if (!cap_clock_ctrl) {
 198             return;
 199         }
 200         CPU_FOREACH(cpu) {
 201             run_on_cpu(cpu, do_kvmclock_ctrl, RUN_ON_CPU_NULL);
 202         }
 203     } else {
 204
 205         if (s->clock_valid) {
 206             return;
 207         }
 208
 209         s->runstate_paused = runstate_check(RUN_STATE_PAUSED);
 210
 211         kvm_synchronize_all_tsc();
 212
 213         kvm_update_clock(s);
 214         /*
 215          * If the VM is stopped, declare the clock state valid to
 216          * avoid re-reading it on next vmsave (which would return
 217          * a different value). Will be reset when the VM is continued.
 218          */
 219         s->clock_valid = true;
 220     }
 221 }
 222
 223 static void kvmclock_realize(DeviceState *dev, Error **errp)
 224 {
 225     KVMClockState *s = KVM_CLOCK(dev);
 226
 227     if (!kvm_enabled()) {
 228         error_setg(errp, "kvmclock device requires KVM");
 229         return;
 230     }
 231
 232     kvm_update_clock(s);
 233
 234     qemu_add_vm_change_state_handler(kvmclock_vm_state_change, s);
 235 }
 236
 237 static bool kvmclock_clock_is_reliable_needed(void *opaque)
 238 {
 239     KVMClockState *s = opaque;
 240
 241     return s->mach_use_reliable_get_clock;
 242 }
 243
 244 static const VMStateDescription kvmclock_reliable_get_clock = {
 245     .name = "kvmclock/clock_is_reliable",
 246     .version_id = 1,
 247     .minimum_version_id = 1,
 248     .needed = kvmclock_clock_is_reliable_needed,
 249     .fields = (VMStateField[]) {
 250         VMSTATE_BOOL(clock_is_reliable, KVMClockState),
 251         VMSTATE_END_OF_LIST()
 252     }
 253 };
 254
 255 /*
 256  * When migrating, assume the source has an unreliable
 257  * KVM_GET_CLOCK unless told otherwise.
 258  */
 259 static int kvmclock_pre_load(void *opaque)
 260 {
 261     KVMClockState *s = opaque;
 262
 263     s->clock_is_reliable = false;
 264
 265     return 0;
 266 }
 267
 268 /*
 269  * When migrating a running guest, read the clock just
 270  * before migration, so that the guest clock counts
 271  * during the events between:
 272  *
 273  *  * vm_stop()
 274  *  *
 275  *  * pre_save()
 276  *
 277  *  This reduces kvmclock difference on migration from 5s
 278  *  to 0.1s (when max_downtime == 5s), because sending the
 279  *  final pages of memory (which happens between vm_stop()
 280  *  and pre_save()) takes max_downtime.
 281  */
 282 static int kvmclock_pre_save(void *opaque)
 283 {
 284     KVMClockState *s = opaque;
 285
 286     if (!s->runstate_paused) {
 287         kvm_update_clock(s);
 288     }
 289
 290     return 0;
 291 }
 292
 293 static const VMStateDescription kvmclock_vmsd = {
 294     .name = "kvmclock",
 295     .version_id = 1,
 296     .minimum_version_id = 1,
 297     .pre_load = kvmclock_pre_load,
 298     .pre_save = kvmclock_pre_save,
 299     .fields = (VMStateField[]) {
 300         VMSTATE_UINT64(clock, KVMClockState),
 301         VMSTATE_END_OF_LIST()
 302     },
 303     .subsections = (const VMStateDescription * []) {
 304         &kvmclock_reliable_get_clock,
 305         NULL
 306     }
 307 };
 308
 309 static Property kvmclock_properties[] = {
 310     DEFINE_PROP_BOOL("x-mach-use-reliable-get-clock", KVMClockState,
 311                       mach_use_reliable_get_clock, true),
 312     DEFINE_PROP_END_OF_LIST(),
 313 };
 314
 315 static void kvmclock_class_init(ObjectClass *klass, void *data)
 316 {
 317     DeviceClass *dc = DEVICE_CLASS(klass);
 318
 319     dc->realize = kvmclock_realize;
 320     dc->vmsd = &kvmclock_vmsd;
 321     device_class_set_props(dc, kvmclock_properties);
 322 }
 323
 324 static const TypeInfo kvmclock_info = {
 325     .name          = TYPE_KVM_CLOCK,
 326     .parent        = TYPE_SYS_BUS_DEVICE,
 327     .instance_size = sizeof(KVMClockState),
 328     .class_init    = kvmclock_class_init,
 329 };
 330
 331 /* Note: Must be called after VCPU initialization. */
 332 void kvmclock_create(bool create_always)
 333 {
 334     X86CPU *cpu = X86_CPU(first_cpu);
 335
 336     if (!kvm_enabled() || !kvm_has_adjust_clock())
 337         return;
 338
 339     if (create_always ||
 340         cpu->env.features[FEAT_KVM] & ((1ULL << KVM_FEATURE_CLOCKSOURCE) |
 341                                        (1ULL << KVM_FEATURE_CLOCKSOURCE2))) {
 342         sysbus_create_simple(TYPE_KVM_CLOCK, -1, NULL);
 343     }
 344 }
 345
 346 static void kvmclock_register_types(void)
 347 {
 348     type_register_static(&kvmclock_info);
 349 }
 350
 351 type_init(kvmclock_register_types)