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