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;
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);
return 1;
}
+ /*
+ * 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.
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;
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,
#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);
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;
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))
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);
}
/*
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;
}
git.openpandora.org / pandora-kernel.git / commitdiff