Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 270 insertions, 0 deletions

diff --git a/pkg/sentry/kernel/timekeeper.go b/pkg/sentry/kernel/timekeeper.go
new file mode 100644
index 000000000..3f16c1676
--- /dev/null
+++ b/pkg/sentry/kernel/timekeeper.go
@@ -0,0 +1,270 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package kernel
+
+import (
+	"sync"
+	"time"
+
+	"gvisor.googlesource.com/gvisor/pkg/log"
+	ktime "gvisor.googlesource.com/gvisor/pkg/sentry/kernel/time"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+	sentrytime "gvisor.googlesource.com/gvisor/pkg/sentry/time"
+)
+
+// Timekeeper manages all of the kernel clocks.
+type Timekeeper struct {
+	// clocks are the clock sources.
+	//
+	// These are not saved directly, as the new machine's clock may behave
+	// differently.
+	//
+	// It is set only once, by SetClocks.
+	clocks sentrytime.Clocks `state:"nosave"`
+
+	// bootTime is the realtime when the system "booted". i.e., when
+	// SetClocks was called in the initial (not restored) run.
+	bootTime ktime.Time
+
+	// monotonicOffset is the offset to apply to the monotonic clock output
+	// from clocks.
+	//
+	// It is set only once, by SetClocks.
+	monotonicOffset int64 `state:"nosave"`
+
+	// restored indicates that this Timekeeper was restored from a state
+	// file.
+	restored bool `state:"nosave"`
+
+	// saveMonotonic is the (offset) value of the monotonic clock at the
+	// time of save.
+	//
+	// It is only valid if restored is true.
+	//
+	// It is only used in SetClocks after restore to compute the new
+	// monotonicOffset.
+	saveMonotonic int64
+
+	// saveRealtime is the value of the realtime clock at the time of save.
+	//
+	// It is only valid if restored is true.
+	//
+	// It is only used in SetClocks after restore to compute the new
+	// monotonicOffset.
+	saveRealtime int64
+
+	// params manages the parameter page.
+	params *VDSOParamPage
+
+	// mu protects destruction with stop and wg.
+	mu sync.Mutex `state:"nosave"`
+
+	// stop is used to tell the update goroutine to exit.
+	stop chan struct{} `state:"nosave"`
+
+	// wg is used to indicate that the update goroutine has exited.
+	wg sync.WaitGroup `state:"nosave"`
+}
+
+// NewTimekeeper returns a Timekeeper that is automatically kept up-to-date.
+// NewTimekeeper does not take ownership of paramPage.
+//
+// SetClocks must be called on the returned Timekeeper before it is usable.
+func NewTimekeeper(platform platform.Platform, paramPage platform.FileRange) (*Timekeeper, error) {
+	return &Timekeeper{
+		params: NewVDSOParamPage(platform, paramPage),
+	}, nil
+}
+
+// SetClocks the backing clock source.
+//
+// SetClocks must be called before the Timekeeper is used, and it may not be
+// called more than once, as changing the clock source without extra correction
+// could cause time discontinuities.
+//
+// It must also be called after Load.
+func (t *Timekeeper) SetClocks(c sentrytime.Clocks) {
+	// Update the params, marking them "not ready", as we may need to
+	// restart calibration on this new machine.
+	if t.restored {
+		if err := t.params.Write(func() vdsoParams {
+			return vdsoParams{}
+		}); err != nil {
+			panic("unable to reset VDSO params: " + err.Error())
+		}
+	}
+
+	if t.clocks != nil {
+		panic("SetClocks called on previously-initialized Timekeeper")
+	}
+
+	t.clocks = c
+
+	// Compute the offset of the monotonic clock from the base Clocks.
+	//
+	// In a fresh (not restored) sentry, monotonic time starts at zero.
+	//
+	// In a restored sentry, monotonic time jumps forward by approximately
+	// the same amount as real time. There are no guarantees here, we are
+	// just making a best-effort attempt to to make it appear that the app
+	// was simply not scheduled for a long period, rather than that the
+	// real time clock was changed.
+	//
+	// If real time went backwards, it remains the same.
+	wantMonotonic := int64(0)
+
+	nowMonotonic, err := t.clocks.GetTime(sentrytime.Monotonic)
+	if err != nil {
+		panic("Unable to get current monotonic time: " + err.Error())
+	}
+
+	nowRealtime, err := t.clocks.GetTime(sentrytime.Realtime)
+	if err != nil {
+		panic("Unable to get current realtime: " + err.Error())
+	}
+
+	if t.restored {
+		wantMonotonic = t.saveMonotonic
+		elapsed := nowRealtime - t.saveRealtime
+		if elapsed > 0 {
+			wantMonotonic += elapsed
+		}
+	}
+
+	t.monotonicOffset = wantMonotonic - nowMonotonic
+
+	if !t.restored {
+		// Hold on to the initial "boot" time.
+		t.bootTime = ktime.FromNanoseconds(nowRealtime)
+	}
+
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	t.startUpdater()
+}
+
+// startUpdater starts an update goroutine that keeps the clocks updated.
+//
+// mu must be held.
+func (t *Timekeeper) startUpdater() {
+	if t.stop != nil {
+		// Timekeeper already started
+		return
+	}
+	t.stop = make(chan struct{})
+
+	// Keep the clocks up to date.
+	//
+	// Note that the Go runtime uses host CLOCK_MONOTONIC to service the
+	// timer, so it may run at a *slightly* different rate from the
+	// application CLOCK_MONOTONIC. That is fine, as we only need to update
+	// at approximately this rate.
+	timer := time.NewTicker(sentrytime.ApproxUpdateInterval)
+	t.wg.Add(1)
+	go func() { // S/R-SAFE: stopped during save.
+		for {
+			// Start with an update immediately, so the clocks are
+			// ready ASAP.
+
+			// Call Update within a Write block to prevent the VDSO
+			// from using the old params between Update and
+			// Write.
+			if err := t.params.Write(func() vdsoParams {
+				monotonicParams, monotonicOk, realtimeParams, realtimeOk := t.clocks.Update()
+
+				var p vdsoParams
+				if monotonicOk {
+					p.monotonicReady = 1
+					p.monotonicBaseCycles = int64(monotonicParams.BaseCycles)
+					p.monotonicBaseRef = int64(monotonicParams.BaseRef) + t.monotonicOffset
+					p.monotonicFrequency = monotonicParams.Frequency
+				}
+				if realtimeOk {
+					p.realtimeReady = 1
+					p.realtimeBaseCycles = int64(realtimeParams.BaseCycles)
+					p.realtimeBaseRef = int64(realtimeParams.BaseRef)
+					p.realtimeFrequency = realtimeParams.Frequency
+				}
+
+				log.Debugf("Updating VDSO parameters: %+v", p)
+
+				return p
+			}); err != nil {
+				log.Warningf("Unable to update VDSO parameter page: %v", err)
+			}
+
+			select {
+			case <-timer.C:
+			case <-t.stop:
+				t.wg.Done()
+				return
+			}
+		}
+	}()
+}
+
+// stopUpdater stops the update goroutine, blocking until it exits.
+//
+// mu must be held.
+func (t *Timekeeper) stopUpdater() {
+	if t.stop == nil {
+		// Updater not running.
+		return
+	}
+
+	close(t.stop)
+	t.wg.Wait()
+	t.stop = nil
+}
+
+// Destroy destroys the Timekeeper, freeing all associated resources.
+func (t *Timekeeper) Destroy() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	t.stopUpdater()
+}
+
+// PauseUpdates stops clock parameter updates. This should only be used when
+// Tasks are not running and thus cannot access the clock.
+func (t *Timekeeper) PauseUpdates() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	t.stopUpdater()
+}
+
+// ResumeUpdates restarts clock parameter updates stopped by PauseUpdates.
+func (t *Timekeeper) ResumeUpdates() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	t.startUpdater()
+}
+
+// GetTime returns the current time in nanoseconds.
+func (t *Timekeeper) GetTime(c sentrytime.ClockID) (int64, error) {
+	if t.clocks == nil {
+		panic("Timekeeper used before initialized with SetClocks")
+	}
+	now, err := t.clocks.GetTime(c)
+	if err == nil && c == sentrytime.Monotonic {
+		now += t.monotonicOffset
+	}
+	return now, err
+}
+
+// BootTime returns the system boot real time.
+func (t *Timekeeper) BootTime() ktime.Time {
+	return t.bootTime
+}