qemu

clock.c (9741B)

---

 /*
  * QEMU KVM support, paravirtual clock device
  *
  * Copyright (C) 2011 Siemens AG
  *
  * Authors:
  *  Jan Kiszka        <jan.kiszka@siemens.com>
  *
  * This work is licensed under the terms of the GNU GPL version 2.
  * See the COPYING file in the top-level directory.
  *
  * Contributions after 2012-01-13 are licensed under the terms of the
  * GNU GPL, version 2 or (at your option) any later version.
  */
 
 #include "qemu/osdep.h"
 #include "qemu/host-utils.h"
 #include "qemu/module.h"
 #include "sysemu/kvm.h"
 #include "sysemu/runstate.h"
 #include "sysemu/hw_accel.h"
 #include "kvm/kvm_i386.h"
 #include "migration/vmstate.h"
 #include "hw/sysbus.h"
 #include "hw/kvm/clock.h"
 #include "hw/qdev-properties.h"
 #include "qapi/error.h"
 
 #include <linux/kvm.h>
 #include "standard-headers/asm-x86/kvm_para.h"
 #include "qom/object.h"
 
 #define TYPE_KVM_CLOCK "kvmclock"
 OBJECT_DECLARE_SIMPLE_TYPE(KVMClockState, KVM_CLOCK)
 
 struct KVMClockState {
     /*< private >*/
     SysBusDevice busdev;
     /*< public >*/
 
     uint64_t clock;
     bool clock_valid;
 
     /* whether the 'clock' value was obtained in the 'paused' state */
     bool runstate_paused;
 
     /* whether machine type supports reliable KVM_GET_CLOCK */
     bool mach_use_reliable_get_clock;
 
     /* whether the 'clock' value was obtained in a host with
      * reliable KVM_GET_CLOCK */
     bool clock_is_reliable;
 };
 
 struct pvclock_vcpu_time_info {
     uint32_t   version;
     uint32_t   pad0;
     uint64_t   tsc_timestamp;
     uint64_t   system_time;
     uint32_t   tsc_to_system_mul;
     int8_t     tsc_shift;
     uint8_t    flags;
     uint8_t    pad[2];
 } __attribute__((__packed__)); /* 32 bytes */
 
 static uint64_t kvmclock_current_nsec(KVMClockState *s)
 {
     CPUState *cpu = first_cpu;
     CPUX86State *env = cpu->env_ptr;
     hwaddr kvmclock_struct_pa;
     uint64_t migration_tsc = env->tsc;
     struct pvclock_vcpu_time_info time;
     uint64_t delta;
     uint64_t nsec_lo;
     uint64_t nsec_hi;
     uint64_t nsec;
 
     cpu_synchronize_state(cpu);
 
     if (!(env->system_time_msr & 1ULL)) {
         /* KVM clock not active */
         return 0;
     }
 
     kvmclock_struct_pa = env->system_time_msr & ~1ULL;
     cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time));
 
     assert(time.tsc_timestamp <= migration_tsc);
     delta = migration_tsc - time.tsc_timestamp;
     if (time.tsc_shift < 0) {
         delta >>= -time.tsc_shift;
     } else {
         delta <<= time.tsc_shift;
     }
 
     mulu64(&nsec_lo, &nsec_hi, delta, time.tsc_to_system_mul);
     nsec = (nsec_lo >> 32) | (nsec_hi << 32);
     return nsec + time.system_time;
 }
 
 static void kvm_update_clock(KVMClockState *s)
 {
     struct kvm_clock_data data;
     int ret;
 
     ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
     if (ret < 0) {
         fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(-ret));
                 abort();
     }
     s->clock = data.clock;
 
     /* If kvm_has_adjust_clock_stable() is false, KVM_GET_CLOCK returns
      * essentially CLOCK_MONOTONIC plus a guest-specific adjustment.  This
      * can drift from the TSC-based value that is computed by the guest,
      * so we need to go through kvmclock_current_nsec().  If
      * kvm_has_adjust_clock_stable() is true, and the flags contain
      * KVM_CLOCK_TSC_STABLE, then KVM_GET_CLOCK returns a TSC-based value
      * and kvmclock_current_nsec() is not necessary.
      *
      * Here, however, we need not check KVM_CLOCK_TSC_STABLE.  This is because:
      *
      * - if the host has disabled the kvmclock master clock, the guest already
      *   has protection against time going backwards.  This "safety net" is only
      *   absent when kvmclock is stable;
      *
      * - therefore, we can replace a check like
      *
      *       if last KVM_GET_CLOCK was not reliable then
      *               read from memory
      *
      *   with
      *
      *       if last KVM_GET_CLOCK was not reliable && masterclock is enabled
      *               read from memory
      *
      * However:
      *
      * - if kvm_has_adjust_clock_stable() returns false, the left side is
      *   always true (KVM_GET_CLOCK is never reliable), and the right side is
      *   unknown (because we don't have data.flags).  We must assume it's true
      *   and read from memory.
      *
      * - if kvm_has_adjust_clock_stable() returns true, the result of the &&
      *   is always false (masterclock is enabled iff KVM_GET_CLOCK is reliable)
      *
      * So we can just use this instead:
      *
      *       if !kvm_has_adjust_clock_stable() then
      *               read from memory
      */
     s->clock_is_reliable = kvm_has_adjust_clock_stable();
 }
 
 static void do_kvmclock_ctrl(CPUState *cpu, run_on_cpu_data data)
 {
     int ret = kvm_vcpu_ioctl(cpu, KVM_KVMCLOCK_CTRL, 0);
 
     if (ret && ret != -EINVAL) {
         fprintf(stderr, "%s: %s\n", __func__, strerror(-ret));
     }
 }
 
 static void kvmclock_vm_state_change(void *opaque, bool running,
                                      RunState state)
 {
     KVMClockState *s = opaque;
     CPUState *cpu;
     int cap_clock_ctrl = kvm_check_extension(kvm_state, KVM_CAP_KVMCLOCK_CTRL);
     int ret;
 
     if (running) {
         struct kvm_clock_data data = {};
 
         /*
          * If the host where s->clock was read did not support reliable
          * KVM_GET_CLOCK, read kvmclock value from memory.
          */
         if (!s->clock_is_reliable) {
             uint64_t pvclock_via_mem = kvmclock_current_nsec(s);
             /* We can't rely on the saved clock value, just discard it */
             if (pvclock_via_mem) {
                 s->clock = pvclock_via_mem;
             }
         }
 
         s->clock_valid = false;
 
         data.clock = s->clock;
         ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
         if (ret < 0) {
             fprintf(stderr, "KVM_SET_CLOCK failed: %s\n", strerror(-ret));
             abort();
         }
 
         if (!cap_clock_ctrl) {
             return;
         }
         CPU_FOREACH(cpu) {
             run_on_cpu(cpu, do_kvmclock_ctrl, RUN_ON_CPU_NULL);
         }
     } else {
 
         if (s->clock_valid) {
             return;
         }
 
         s->runstate_paused = runstate_check(RUN_STATE_PAUSED);
 
         kvm_synchronize_all_tsc();
 
         kvm_update_clock(s);
         /*
          * If the VM is stopped, declare the clock state valid to
          * avoid re-reading it on next vmsave (which would return
          * a different value). Will be reset when the VM is continued.
          */
         s->clock_valid = true;
     }
 }
 
 static void kvmclock_realize(DeviceState *dev, Error **errp)
 {
     KVMClockState *s = KVM_CLOCK(dev);
 
     if (!kvm_enabled()) {
         error_setg(errp, "kvmclock device requires KVM");
         return;
     }
 
     kvm_update_clock(s);
 
     qemu_add_vm_change_state_handler(kvmclock_vm_state_change, s);
 }
 
 static bool kvmclock_clock_is_reliable_needed(void *opaque)
 {
     KVMClockState *s = opaque;
 
     return s->mach_use_reliable_get_clock;
 }
 
 static const VMStateDescription kvmclock_reliable_get_clock = {
     .name = "kvmclock/clock_is_reliable",
     .version_id = 1,
     .minimum_version_id = 1,
     .needed = kvmclock_clock_is_reliable_needed,
     .fields = (VMStateField[]) {
         VMSTATE_BOOL(clock_is_reliable, KVMClockState),
         VMSTATE_END_OF_LIST()
     }
 };
 
 /*
  * When migrating, assume the source has an unreliable
  * KVM_GET_CLOCK unless told otherwise.
  */
 static int kvmclock_pre_load(void *opaque)
 {
     KVMClockState *s = opaque;
 
     s->clock_is_reliable = false;
 
     return 0;
 }
 
 /*
  * When migrating a running guest, read the clock just
  * before migration, so that the guest clock counts
  * during the events between:
  *
  *  * vm_stop()
  *  *
  *  * pre_save()
  *
  *  This reduces kvmclock difference on migration from 5s
  *  to 0.1s (when max_downtime == 5s), because sending the
  *  final pages of memory (which happens between vm_stop()
  *  and pre_save()) takes max_downtime.
  */
 static int kvmclock_pre_save(void *opaque)
 {
     KVMClockState *s = opaque;
 
     if (!s->runstate_paused) {
         kvm_update_clock(s);
     }
 
     return 0;
 }
 
 static const VMStateDescription kvmclock_vmsd = {
     .name = "kvmclock",
     .version_id = 1,
     .minimum_version_id = 1,
     .pre_load = kvmclock_pre_load,
     .pre_save = kvmclock_pre_save,
     .fields = (VMStateField[]) {
         VMSTATE_UINT64(clock, KVMClockState),
         VMSTATE_END_OF_LIST()
     },
     .subsections = (const VMStateDescription * []) {
         &kvmclock_reliable_get_clock,
         NULL
     }
 };
 
 static Property kvmclock_properties[] = {
     DEFINE_PROP_BOOL("x-mach-use-reliable-get-clock", KVMClockState,
                       mach_use_reliable_get_clock, true),
     DEFINE_PROP_END_OF_LIST(),
 };
 
 static void kvmclock_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
 
     dc->realize = kvmclock_realize;
     dc->vmsd = &kvmclock_vmsd;
     device_class_set_props(dc, kvmclock_properties);
 }
 
 static const TypeInfo kvmclock_info = {
     .name          = TYPE_KVM_CLOCK,
     .parent        = TYPE_SYS_BUS_DEVICE,
     .instance_size = sizeof(KVMClockState),
     .class_init    = kvmclock_class_init,
 };
 
 /* Note: Must be called after VCPU initialization. */
 void kvmclock_create(bool create_always)
 {
     X86CPU *cpu = X86_CPU(first_cpu);
 
     if (!kvm_enabled() || !kvm_has_adjust_clock())
         return;
 
     if (create_always ||
         cpu->env.features[FEAT_KVM] & ((1ULL << KVM_FEATURE_CLOCKSOURCE) |
                                        (1ULL << KVM_FEATURE_CLOCKSOURCE2))) {
         sysbus_create_simple(TYPE_KVM_CLOCK, -1, NULL);
     }
 }
 
 static void kvmclock_register_types(void)
 {
     type_register_static(&kvmclock_info);
 }
 
 type_init(kvmclock_register_types)