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