diff options
Diffstat (limited to 'hw/i386/kvm')
| -rw-r--r-- | hw/i386/kvm/clock.c | 142 |
1 files changed, 127 insertions, 15 deletions
diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c index 0f75dd3..ef9d560 100644 --- a/hw/i386/kvm/clock.c +++ b/hw/i386/kvm/clock.c @@ -36,6 +36,13 @@ typedef struct KVMClockState { uint64_t clock; bool clock_valid; + + /* 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; } KVMClockState; struct pvclock_vcpu_time_info { @@ -81,6 +88,60 @@ static uint64_t kvmclock_current_nsec(KVMClockState *s) 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 kvmclock_vm_state_change(void *opaque, int running, RunState state) { @@ -91,15 +152,21 @@ static void kvmclock_vm_state_change(void *opaque, int running, if (running) { struct kvm_clock_data data = {}; - uint64_t time_at_migration = kvmclock_current_nsec(s); - - s->clock_valid = false; - /* We can't rely on the migrated clock value, just discard it */ - if (time_at_migration) { - s->clock = time_at_migration; + /* + * 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) { @@ -120,8 +187,6 @@ static void kvmclock_vm_state_change(void *opaque, int running, } } } else { - struct kvm_clock_data data; - int ret; if (s->clock_valid) { return; @@ -129,13 +194,7 @@ static void kvmclock_vm_state_change(void *opaque, int running, kvm_synchronize_all_tsc(); - 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; - + 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 @@ -149,25 +208,78 @@ static void kvmclock_realize(DeviceState *dev, Error **errp) { KVMClockState *s = KVM_CLOCK(dev); + 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, 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 void kvmclock_pre_save(void *opaque) +{ + KVMClockState *s = opaque; + + kvm_update_clock(s); +} + static const VMStateDescription kvmclock_vmsd = { .name = "kvmclock", .version_id = 1, .minimum_version_id = 1, + .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; + dc->props = kvmclock_properties; } static const TypeInfo kvmclock_info = { |