diff options
Diffstat (limited to 'arch/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 235 |
1 files changed, 227 insertions, 8 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c077b817d1c..a7b97a49d8a 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1048,7 +1048,9 @@ static inline u64 get_kernel_ns(void) return timespec_to_ns(&ts); } +#ifdef CONFIG_X86_64 static atomic_t kvm_guest_has_master_clock = ATOMIC_INIT(0); +#endif static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz); unsigned long max_tsc_khz; @@ -1190,21 +1192,170 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data) EXPORT_SYMBOL_GPL(kvm_write_tsc); +#ifdef CONFIG_X86_64 + +static cycle_t read_tsc(void) +{ + cycle_t ret; + u64 last; + + /* + * Empirically, a fence (of type that depends on the CPU) + * before rdtsc is enough to ensure that rdtsc is ordered + * with respect to loads. The various CPU manuals are unclear + * as to whether rdtsc can be reordered with later loads, + * but no one has ever seen it happen. + */ + rdtsc_barrier(); + ret = (cycle_t)vget_cycles(); + + last = pvclock_gtod_data.clock.cycle_last; + + if (likely(ret >= last)) + return ret; + + /* + * GCC likes to generate cmov here, but this branch is extremely + * predictable (it's just a funciton of time and the likely is + * very likely) and there's a data dependence, so force GCC + * to generate a branch instead. I don't barrier() because + * we don't actually need a barrier, and if this function + * ever gets inlined it will generate worse code. + */ + asm volatile (""); + return last; +} + +static inline u64 vgettsc(cycle_t *cycle_now) +{ + long v; + struct pvclock_gtod_data *gtod = &pvclock_gtod_data; + + *cycle_now = read_tsc(); + + v = (*cycle_now - gtod->clock.cycle_last) & gtod->clock.mask; + return v * gtod->clock.mult; +} + +static int do_monotonic(struct timespec *ts, cycle_t *cycle_now) +{ + unsigned long seq; + u64 ns; + int mode; + struct pvclock_gtod_data *gtod = &pvclock_gtod_data; + + ts->tv_nsec = 0; + do { + seq = read_seqcount_begin(>od->seq); + mode = gtod->clock.vclock_mode; + ts->tv_sec = gtod->monotonic_time_sec; + ns = gtod->monotonic_time_snsec; + ns += vgettsc(cycle_now); + ns >>= gtod->clock.shift; + } while (unlikely(read_seqcount_retry(>od->seq, seq))); + timespec_add_ns(ts, ns); + + return mode; +} + +/* returns true if host is using tsc clocksource */ +static bool kvm_get_time_and_clockread(s64 *kernel_ns, cycle_t *cycle_now) +{ + struct timespec ts; + + /* checked again under seqlock below */ + if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC) + return false; + + if (do_monotonic(&ts, cycle_now) != VCLOCK_TSC) + return false; + + monotonic_to_bootbased(&ts); + *kernel_ns = timespec_to_ns(&ts); + + return true; +} +#endif + +/* + * + * Assuming a stable TSC across physical CPUS, the following condition + * is possible. Each numbered line represents an event visible to both + * CPUs at the next numbered event. + * + * "timespecX" represents host monotonic time. "tscX" represents + * RDTSC value. + * + * VCPU0 on CPU0 | VCPU1 on CPU1 + * + * 1. read timespec0,tsc0 + * 2. | timespec1 = timespec0 + N + * | tsc1 = tsc0 + M + * 3. transition to guest | transition to guest + * 4. ret0 = timespec0 + (rdtsc - tsc0) | + * 5. | ret1 = timespec1 + (rdtsc - tsc1) + * | ret1 = timespec0 + N + (rdtsc - (tsc0 + M)) + * + * Since ret0 update is visible to VCPU1 at time 5, to obey monotonicity: + * + * - ret0 < ret1 + * - timespec0 + (rdtsc - tsc0) < timespec0 + N + (rdtsc - (tsc0 + M)) + * ... + * - 0 < N - M => M < N + * + * That is, when timespec0 != timespec1, M < N. Unfortunately that is not + * always the case (the difference between two distinct xtime instances + * might be smaller then the difference between corresponding TSC reads, + * when updating guest vcpus pvclock areas). + * + * To avoid that problem, do not allow visibility of distinct + * system_timestamp/tsc_timestamp values simultaneously: use a master + * copy of host monotonic time values. Update that master copy + * in lockstep. + * + * Rely on synchronization of host TSCs for monotonicity. + * + */ + +static void pvclock_update_vm_gtod_copy(struct kvm *kvm) +{ +#ifdef CONFIG_X86_64 + struct kvm_arch *ka = &kvm->arch; + int vclock_mode; + + /* + * If the host uses TSC clock, then passthrough TSC as stable + * to the guest. + */ + ka->use_master_clock = kvm_get_time_and_clockread( + &ka->master_kernel_ns, + &ka->master_cycle_now); + + if (ka->use_master_clock) + atomic_set(&kvm_guest_has_master_clock, 1); + + vclock_mode = pvclock_gtod_data.clock.vclock_mode; + trace_kvm_update_master_clock(ka->use_master_clock, vclock_mode); +#endif +} + static int kvm_guest_time_update(struct kvm_vcpu *v) { - unsigned long flags; + unsigned long flags, this_tsc_khz; struct kvm_vcpu_arch *vcpu = &v->arch; + struct kvm_arch *ka = &v->kvm->arch; void *shared_kaddr; - unsigned long this_tsc_khz; s64 kernel_ns, max_kernel_ns; - u64 tsc_timestamp; + u64 tsc_timestamp, host_tsc; struct pvclock_vcpu_time_info *guest_hv_clock; u8 pvclock_flags; + bool use_master_clock; + + kernel_ns = 0; + host_tsc = 0; /* Keep irq disabled to prevent changes to the clock */ local_irq_save(flags); - tsc_timestamp = kvm_x86_ops->read_l1_tsc(v, native_read_tsc()); - kernel_ns = get_kernel_ns(); this_tsc_khz = __get_cpu_var(cpu_tsc_khz); if (unlikely(this_tsc_khz == 0)) { local_irq_restore(flags); @@ -1213,6 +1364,24 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) } /* + * If the host uses TSC clock, then passthrough TSC as stable + * to the guest. + */ + spin_lock(&ka->pvclock_gtod_sync_lock); + use_master_clock = ka->use_master_clock; + if (use_master_clock) { + host_tsc = ka->master_cycle_now; + kernel_ns = ka->master_kernel_ns; + } + spin_unlock(&ka->pvclock_gtod_sync_lock); + if (!use_master_clock) { + host_tsc = native_read_tsc(); + kernel_ns = get_kernel_ns(); + } + + tsc_timestamp = kvm_x86_ops->read_l1_tsc(v, host_tsc); + + /* * We may have to catch up the TSC to match elapsed wall clock * time for two reasons, even if kvmclock is used. * 1) CPU could have been running below the maximum TSC rate @@ -1273,9 +1442,14 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) vcpu->hw_tsc_khz = this_tsc_khz; } - if (max_kernel_ns > kernel_ns) - kernel_ns = max_kernel_ns; - + /* with a master <monotonic time, tsc value> tuple, + * pvclock clock reads always increase at the (scaled) rate + * of guest TSC - no need to deal with sampling errors. + */ + if (!use_master_clock) { + if (max_kernel_ns > kernel_ns) + kernel_ns = max_kernel_ns; + } /* With all the info we got, fill in the values */ vcpu->hv_clock.tsc_timestamp = tsc_timestamp; vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset; @@ -1301,6 +1475,10 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) vcpu->pvclock_set_guest_stopped_request = false; } + /* If the host uses TSC clocksource, then it is stable */ + if (use_master_clock) + pvclock_flags |= PVCLOCK_TSC_STABLE_BIT; + vcpu->hv_clock.flags = pvclock_flags; memcpy(shared_kaddr + vcpu->time_offset, &vcpu->hv_clock, @@ -4912,6 +5090,17 @@ static void kvm_set_mmio_spte_mask(void) #ifdef CONFIG_X86_64 static void pvclock_gtod_update_fn(struct work_struct *work) { + struct kvm *kvm; + + struct kvm_vcpu *vcpu; + int i; + + raw_spin_lock(&kvm_lock); + list_for_each_entry(kvm, &vm_list, vm_list) + kvm_for_each_vcpu(i, vcpu, kvm) + set_bit(KVM_REQ_MASTERCLOCK_UPDATE, &vcpu->requests); + atomic_set(&kvm_guest_has_master_clock, 0); + raw_spin_unlock(&kvm_lock); } static DECLARE_WORK(pvclock_gtod_work, pvclock_gtod_update_fn); @@ -5303,6 +5492,29 @@ static void process_nmi(struct kvm_vcpu *vcpu) kvm_make_request(KVM_REQ_EVENT, vcpu); } +static void kvm_gen_update_masterclock(struct kvm *kvm) +{ +#ifdef CONFIG_X86_64 + int i; + struct kvm_vcpu *vcpu; + struct kvm_arch *ka = &kvm->arch; + + spin_lock(&ka->pvclock_gtod_sync_lock); + kvm_make_mclock_inprogress_request(kvm); + /* no guest entries from this point */ + pvclock_update_vm_gtod_copy(kvm); + + kvm_for_each_vcpu(i, vcpu, kvm) + set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests); + + /* guest entries allowed */ + kvm_for_each_vcpu(i, vcpu, kvm) + clear_bit(KVM_REQ_MCLOCK_INPROGRESS, &vcpu->requests); + + spin_unlock(&ka->pvclock_gtod_sync_lock); +#endif +} + static int vcpu_enter_guest(struct kvm_vcpu *vcpu) { int r; @@ -5315,6 +5527,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) kvm_mmu_unload(vcpu); if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu)) __kvm_migrate_timers(vcpu); + if (kvm_check_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu)) + kvm_gen_update_masterclock(vcpu->kvm); if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu)) { r = kvm_guest_time_update(vcpu); if (unlikely(r)) @@ -6219,6 +6433,8 @@ int kvm_arch_hardware_enable(void *garbage) kvm_for_each_vcpu(i, vcpu, kvm) { vcpu->arch.tsc_offset_adjustment += delta_cyc; vcpu->arch.last_host_tsc = local_tsc; + set_bit(KVM_REQ_MASTERCLOCK_UPDATE, + &vcpu->requests); } /* @@ -6356,6 +6572,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) raw_spin_lock_init(&kvm->arch.tsc_write_lock); mutex_init(&kvm->arch.apic_map_lock); + spin_lock_init(&kvm->arch.pvclock_gtod_sync_lock); + + pvclock_update_vm_gtod_copy(kvm); return 0; } |