6 files changed, 88 insertions, 13 deletions
diff --git a/pkg/tcpip/link/sharedmem/queue/rx.go b/pkg/tcpip/link/sharedmem/queue/rx.go
index a78826ebc..89bdf5ef6 100644
--- a/pkg/tcpip/link/sharedmem/queue/rx.go
+++ b/pkg/tcpip/link/sharedmem/queue/rx.go
@@ -49,9 +49,16 @@ const (
 	sizeOfConsumedBuffer = 28
 
 	// The following are the allowed states of the shared data area.
-	eventFDUninitialized = 0
-	eventFDDisabled      = 1
-	eventFDEnabled       = 2
+	// EventFDUinitialized is the value stored at the start of the shared data
+	// region when it hasn't been initialized.
+	EventFDUninitialized = 0
+	// EventFDDisabled is the value stored at the start of the shared data region
+	// when notifications using eventFD has been disabled.
+	EventFDDisabled = 1
+	// EventFDEnabled is the value stored at the start of the shared data region
+	// when eventFD should be notified as the peer might be blocked waiting on
+	// notifications.
+	EventFDEnabled = 2
 )
 
 // RxBuffer is the descriptor of a receive buffer.
@@ -84,13 +91,13 @@ func (r *Rx) Init(tx, rx []byte, sharedEventFDState *uint32) {
 // EnableNotification updates the shared state such that the peer will notify
 // the eventfd when there are packets to be dequeued.
 func (r *Rx) EnableNotification() {
-	atomic.StoreUint32(r.sharedEventFDState, eventFDEnabled)
+	atomic.StoreUint32(r.sharedEventFDState, EventFDEnabled)
 }
 
 // DisableNotification updates the shared state such that the peer will not
 // notify the eventfd.
 func (r *Rx) DisableNotification() {
-	atomic.StoreUint32(r.sharedEventFDState, eventFDDisabled)
+	atomic.StoreUint32(r.sharedEventFDState, EventFDDisabled)
 }
 
 // PostedBuffersLimit returns the maximum number of buffers that can be posted
diff --git a/pkg/tcpip/link/sharedmem/queue/tx.go b/pkg/tcpip/link/sharedmem/queue/tx.go
index beffe807b..09907c761 100644
--- a/pkg/tcpip/link/sharedmem/queue/tx.go
+++ b/pkg/tcpip/link/sharedmem/queue/tx.go
@@ -16,6 +16,7 @@ package queue
 
 import (
 	"encoding/binary"
+	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/tcpip/link/sharedmem/pipe"
@@ -49,14 +50,23 @@ type TxBuffer struct {
 //
 // This struct is thread-compatible.
 type Tx struct {
-	tx pipe.Tx
-	rx pipe.Rx
+	tx                 pipe.Tx
+	rx                 pipe.Rx
+	sharedEventFDState *uint32
 }
 
 // Init initializes the transmit queue with the given pipes.
-func (t *Tx) Init(tx, rx []byte) {
+func (t *Tx) Init(tx, rx []byte, sharedEventFDState *uint32) {
 	t.tx.Init(tx)
 	t.rx.Init(rx)
+	t.sharedEventFDState = sharedEventFDState
+}
+
+// NotificationsEnabled returns true if eventFD should be used to notify the
+// peer of events (eg. packet transmit etc).
+func (t *Tx) NotificationsEnabled() bool {
+	// Notifications are considered enabled unless explicitly disabled.
+	return atomic.LoadUint32(t.sharedEventFDState) != EventFDDisabled
 }
 
 // Enqueue queues the given linked list of buffers for transmission as one
diff --git a/pkg/tcpip/link/sharedmem/server_rx.go b/pkg/tcpip/link/sharedmem/server_rx.go
index 6ea21ffd1..40068334b 100644
--- a/pkg/tcpip/link/sharedmem/server_rx.go
+++ b/pkg/tcpip/link/sharedmem/server_rx.go
@@ -18,6 +18,8 @@
 package sharedmem
 
 import (
+	"sync/atomic"
+
 	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/cleanup"
 	"gvisor.dev/gvisor/pkg/eventfd"
@@ -42,6 +44,10 @@ type serverRx struct {
 
 	// sharedData the memory region to use to enable/disable notifications.
 	sharedData []byte
+
+	// sharedEventFDState is the memory region in sharedData used to enable
+	// disable notifications on eventFD.
+	sharedEventFDState *uint32
 }
 
 // init initializes all state needed by the serverTx queue based on the
@@ -89,6 +95,7 @@ func (s *serverRx) init(c *QueueConfig) error {
 	s.data = data
 	s.eventFD = efd
 	s.sharedData = sharedData
+	s.sharedEventFDState = sharedDataPointer(sharedData)
 
 	cu.Release()
 	return nil
@@ -102,6 +109,18 @@ func (s *serverRx) cleanup() {
 	s.eventFD.Close()
 }
 
+// EnableNotification updates the shared state such that the peer will notify
+// the eventfd when there are packets to be dequeued.
+func (s *serverRx) EnableNotification() {
+	atomic.StoreUint32(s.sharedEventFDState, queue.EventFDEnabled)
+}
+
+// DisableNotification updates the shared state such that the peer will not
+// notify the eventfd.
+func (s *serverRx) DisableNotification() {
+	atomic.StoreUint32(s.sharedEventFDState, queue.EventFDDisabled)
+}
+
 // completionNotificationSize is size in bytes of a completion notification sent
 // on the completion queue after a transmitted packet has been handled.
 const completionNotificationSize = 8
diff --git a/pkg/tcpip/link/sharedmem/server_tx.go b/pkg/tcpip/link/sharedmem/server_tx.go
index 13a82903f..79a9e382b 100644
--- a/pkg/tcpip/link/sharedmem/server_tx.go
+++ b/pkg/tcpip/link/sharedmem/server_tx.go
@@ -18,6 +18,8 @@
 package sharedmem
 
 import (
+	"sync/atomic"
+
 	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/cleanup"
 	"gvisor.dev/gvisor/pkg/eventfd"
@@ -45,6 +47,10 @@ type serverTx struct {
 
 	// sharedData the memory region to use to enable/disable notifications.
 	sharedData []byte
+
+	// sharedEventFDState is the memory region in sharedData used to enable/disable
+	// notifications on eventFD.
+	sharedEventFDState *uint32
 }
 
 // init initializes all tstate needed by the serverTx queue based on the
@@ -94,6 +100,7 @@ func (s *serverTx) init(c *QueueConfig) error {
 	s.data = data
 	s.eventFD = efd
 	s.sharedData = sharedData
+	s.sharedEventFDState = sharedDataPointer(sharedData)
 
 	return nil
 }
@@ -170,6 +177,13 @@ func (s *serverTx) transmit(views []buffer.View) bool {
 	return true
 }
 
+func (s *serverTx) notificationsEnabled() bool {
+	// notifications are considered to be enabled unless explicitly disabled.
+	return atomic.LoadUint32(s.sharedEventFDState) != queue.EventFDDisabled
+}
+
 func (s *serverTx) notify() {
-	s.eventFD.Notify()
+	if s.notificationsEnabled() {
+		s.eventFD.Notify()
+	}
 }
diff --git a/pkg/tcpip/link/sharedmem/sharedmem_server.go b/pkg/tcpip/link/sharedmem/sharedmem_server.go
index 43c5b8c63..c39eca33f 100644
--- a/pkg/tcpip/link/sharedmem/sharedmem_server.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem_server.go
@@ -287,8 +287,21 @@ func (e *serverEndpoint) dispatchLoop(d stack.NetworkDispatcher) {
 	for atomic.LoadUint32(&e.stopRequested) == 0 {
 		b := e.rx.receive()
 		if b == nil {
-			e.rx.waitForPackets()
-			continue
+			e.rx.EnableNotification()
+			// Now pull again to make sure we didn't receive any packets
+			// while notifications were not enabled.
+			for {
+				b = e.rx.receive()
+				if b != nil {
+					// Disable notifications as we only need to be notified when we are going
+					// to block on eventFD. This should prevent the peer from needlessly
+					// writing to eventFD when this end is already awake and processing
+					// packets.
+					e.rx.DisableNotification()
+					break
+				}
+				e.rx.waitForPackets()
+			}
 		}
 		pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 			Data: buffer.View(b).ToVectorisedView(),
diff --git a/pkg/tcpip/link/sharedmem/tx.go b/pkg/tcpip/link/sharedmem/tx.go
index d6c61afee..a74fc012b 100644
--- a/pkg/tcpip/link/sharedmem/tx.go
+++ b/pkg/tcpip/link/sharedmem/tx.go
@@ -34,6 +34,7 @@ type tx struct {
 	ids          idManager
 	bufs         bufferManager
 	eventFD      eventfd.Eventfd
+	sharedData   []byte
 	sharedDataFD int
 }
 
@@ -62,13 +63,22 @@ func (t *tx) init(mtu uint32, c *QueueConfig) error {
 		return err
 	}
 
+	sharedData, err := getBuffer(c.SharedDataFD)
+	if err != nil {
+		unix.Munmap(txPipe)
+		unix.Munmap(rxPipe)
+		unix.Munmap(data)
+	}
+
 	// Initialize state based on buffers.
-	t.q.Init(txPipe, rxPipe)
+	t.q.Init(txPipe, rxPipe, sharedDataPointer(sharedData))
 	t.ids.init()
 	t.bufs.init(0, len(data), int(mtu))
 	t.data = data
 	t.eventFD = c.EventFD
 	t.sharedDataFD = c.SharedDataFD
+	t.sharedData = sharedData
+
 	return nil
 }
 
@@ -149,7 +159,9 @@ func (t *tx) transmit(bufs ...buffer.View) bool {
 // notify writes to the tx.eventFD to indicate to the peer that there is data to
 // be read.
 func (t *tx) notify() {
-	t.eventFD.Notify()
+	if t.q.NotificationsEnabled() {
+		t.eventFD.Notify()
+	}
 }
 
 // idDescriptor is used by idManager to either point to a tx buffer (in case