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