[shimV2] bind GCS/host hvsock listeners before starting the UVM

internal/controller/vm/vm.go

@@ -188,12 +188,30 @@ func (c *Controller) StartVM(ctx context.Context, opts *StartOptions) (err error
 	}()
 	defer cancel()
 
-	// we should set up the necessary listeners for guest-host communication.
-	// The guest needs to connect to predefined vsock ports.
-	// The host must already be listening on these ports before the guest attempts to connect,
-	// otherwise the connection would fail.
-	c.setupEntropyListener(gctx, g)
-	c.setupLoggingListener(gctx, g)
+	// Set up the host-side hvsock listeners for entropy and logs before
+	// starting the VM. The guest dials predefined vsock ports early in boot,
+	// so the listeners must be bound up front to avoid a race.
+	// Each setup call creates the listener synchronously and dispatches an
+	// accept goroutine onto the errgroup:
+	//   - entropy: writes seed bytes to the guest, then returns.
+	//   - logging: accepts the connection and spawns a long-running relay
+	//     for guest logs; the accept goroutine itself returns immediately.
+	//
+	// We intentionally wait on the error group after VM start but before
+	// establishing the GCS connection, to ensure entropy is seeded and the
+	// log channel is wired up first.
+	if err = c.setupEntropyListener(gctx, g); err != nil {
+		return fmt.Errorf("failed to set up entropy listener: %w", err)
+	}
+	if err = c.setupLoggingListener(gctx, g); err != nil {
+		return fmt.Errorf("failed to set up logging listener: %w", err)
+	}
+	// Open the host-side GCS hvsock listener before VM start so the host
+	// is listening when the in-VM GCS dials. Otherwise, GCS falls back to
+	// the internal HCS bridge and our accept hangs until timeout.
+	if err = c.guest.PrepareConnection(opts.GCSServiceID); err != nil {
+		return fmt.Errorf("failed to prepare guest connection: %w", err)
+	}
 
 	err = c.uvm.Start(ctx)
 	if err != nil {
@@ -210,7 +228,9 @@ func (c *Controller) StartVM(ctx context.Context, opts *StartOptions) (err error
 		return err
 	}
 
-	err = c.guest.CreateConnection(ctx, opts.GCSServiceID, opts.ConfigOptions...)
+	// VM is started, entropy is seeded and log channel is up. Accept the
+	// GCS dial on the prepared listener and run the GCS protocol handshake.
+	err = c.guest.CreateConnection(ctx, opts.ConfigOptions...)
 	if err != nil {
 		return fmt.Errorf("failed to create guest connection: %w", err)
 	}

internal/controller/vm/vm_lcow.go

@@ -111,16 +111,18 @@ func (c *Controller) Plan9Controller() *plan9.Controller {
 // Linux VMs require entropy to initialize their random number generators during boot.
 // This method listens on a predefined vsock port and provides cryptographically secure
 // random data to the Linux init process when it connects.
-func (c *Controller) setupEntropyListener(ctx context.Context, group *errgroup.Group) {
+func (c *Controller) setupEntropyListener(ctx context.Context, group *errgroup.Group) error {
+	// The Linux guest will connect to this port during init to receive entropy.
+	entropyConn, err := winio.ListenHvsock(&winio.HvsockAddr{
+		VMID:      c.uvm.RuntimeID(),
+		ServiceID: winio.VsockServiceID(vmutils.LinuxEntropyVsockPort),
+	})
+	if err != nil {
+		return fmt.Errorf("failed to listen on hvSocket for entropy: %w", err)
+	}
+
 	group.Go(func() error {
-		// The Linux guest will connect to this port during init to receive entropy.
-		entropyConn, err := winio.ListenHvsock(&winio.HvsockAddr{
-			VMID:      c.uvm.RuntimeID(),
-			ServiceID: winio.VsockServiceID(vmutils.LinuxEntropyVsockPort),
-		})
-		if err != nil {
-			return fmt.Errorf("failed to listen on hvSocket for entropy: %w", err)
-		}
+		defer entropyConn.Close()
 
 		// Prepare to provide entropy to the init process in the background. This
 		// must be done in a goroutine since, when using the internal bridge, the
@@ -135,31 +137,34 @@ func (c *Controller) setupEntropyListener(ctx context.Context, group *errgroup.G
 		// Write the required amount of entropy to the connection.
 		// The init process will read this data and use it to seed the kernel's
 		// random number generator (CRNG).
-		_, err = io.CopyN(conn, rand.Reader, vmutils.LinuxEntropyBytes)
-		if err != nil {
+		if _, err = io.CopyN(conn, rand.Reader, vmutils.LinuxEntropyBytes); err != nil {
 			return fmt.Errorf("failed to write entropy to connection: %w", err)
 		}
 
 		return nil
 	})
+
+	return nil
 }
 
 // setupLoggingListener sets up logging for LCOW UVMs.
 //
 // This method establishes a vsock connection to receive log output from GCS
 // running inside the Linux VM. The logs are parsed and
 // forwarded to the host's logging system for monitoring and debugging.
-func (c *Controller) setupLoggingListener(ctx context.Context, group *errgroup.Group) {
+func (c *Controller) setupLoggingListener(ctx context.Context, group *errgroup.Group) error {
+	// The GCS will connect to this port to stream log output.
+	logConn, err := winio.ListenHvsock(&winio.HvsockAddr{
+		VMID:      c.uvm.RuntimeID(),
+		ServiceID: winio.VsockServiceID(vmutils.LinuxLogVsockPort),
+	})
+	if err != nil {
+		close(c.logOutputDone)
+		return fmt.Errorf("failed to listen on hvSocket for logs: %w", err)
+	}
+
 	group.Go(func() error {
-		// The GCS will connect to this port to stream log output.
-		logConn, err := winio.ListenHvsock(&winio.HvsockAddr{
-			VMID:      c.uvm.RuntimeID(),
-			ServiceID: winio.VsockServiceID(vmutils.LinuxLogVsockPort),
-		})
-		if err != nil {
-			close(c.logOutputDone)
-			return fmt.Errorf("failed to listen on hvSocket for logs: %w", err)
-		}
+		defer logConn.Close()
 
 		// Accept the connection from the GCS.
 		conn, err := vmmanager.AcceptConnection(ctx, c.uvm, logConn, true)
@@ -170,6 +175,8 @@ func (c *Controller) setupLoggingListener(ctx context.Context, group *errgroup.G
 
 		// Launch a separate goroutine to process logs for the lifetime of the VM.
 		go func() {
+			defer conn.Close()
+
 			// Parse GCS log output and forward it to the host logging system.
 			vmutils.ParseGCSLogrus(c.uvm.ID())(conn)
 
@@ -180,6 +187,8 @@ func (c *Controller) setupLoggingListener(ctx context.Context, group *errgroup.G
 
 		return nil
 	})
+
+	return nil
 }
 
 // finalizeGCSConnection finalizes the GCS connection for LCOW VMs.

internal/controller/vm/vm_wcow.go

@@ -40,7 +40,7 @@ func (c *Controller) buildConfidentialOptions(_ context.Context) (*guestresource
 // This is a no-op implementation to satisfy the platform-specific interface.
 //
 // For comparison, LCOW VMs require entropy to be provided during boot.
-func (c *Controller) setupEntropyListener(_ context.Context, _ *errgroup.Group) {}
+func (c *Controller) setupEntropyListener(_ context.Context, _ *errgroup.Group) error { return nil }
 
 // setupLoggingListener sets up logging for WCOW UVMs.
 //
@@ -52,25 +52,22 @@ func (c *Controller) setupEntropyListener(_ context.Context, _ *errgroup.Group)
 // The listener is configured to accept only one concurrent connection at a time
 // to prevent resource exhaustion, but will accept new connections if the current one is closed.
 // This supports scenarios where the logging service inside the VM needs to restart.
-func (c *Controller) setupLoggingListener(ctx context.Context, _ *errgroup.Group) {
+func (c *Controller) setupLoggingListener(ctx context.Context, _ *errgroup.Group) error {
+	baseListener, err := winio.ListenHvsock(&winio.HvsockAddr{
+		VMID:      c.uvm.RuntimeID(),
+		ServiceID: prot.WindowsLoggingHvsockServiceID,
+	})
+	if err != nil {
+		close(c.logOutputDone)
+		return fmt.Errorf("failed to listen for windows logging connections: %w", err)
+	}
+
 	// For Windows, the listener can receive a connection later (after VM starts),
 	// so we start the output handler in a goroutine with a non-timeout context.
 	// This allows the output handler to run independently of the VM creation lifecycle.
 	// This is useful for the case when the logging service is restarted.
 	go func() {
-		baseListener, err := winio.ListenHvsock(&winio.HvsockAddr{
-			VMID:      c.uvm.RuntimeID(),
-			ServiceID: prot.WindowsLoggingHvsockServiceID,
-		})
-		if err != nil {
-			// Close the output done channel to signal that logging setup
-			// has failed and no logs will be processed.
-			close(c.logOutputDone)
-			logrus.WithError(err).Error("failed to listen for windows logging connections")
-
-			// Return early due to error.
-			return
-		}
+		defer baseListener.Close()
 
 		// Use a WaitGroup to track active log processing goroutines.
 		// This ensures we wait for all log processing to complete before closing logOutputDone.
@@ -91,6 +88,8 @@ func (c *Controller) setupLoggingListener(ctx context.Context, _ *errgroup.Group
 			wg.Add(1)
 			go func() {
 				defer wg.Done()
+				defer conn.Close()
+
 				logrus.Info("uvm output handler starting")
 
 				// Parse GCS log output and forward it to the host logging system.
@@ -107,6 +106,8 @@ func (c *Controller) setupLoggingListener(ctx context.Context, _ *errgroup.Group
 		// Signal that log output processing has completed.
 		close(c.logOutputDone)
 	}()
+
+	return nil
 }
 
 // finalizeGCSConnection finalizes the GCS connection for WCOW UVMs.

internal/vm/guestmanager/doc.go

@@ -16,6 +16,8 @@ GCS connection:
 
 	g, err := guestmanager.New(ctx, uvm)
 	if err != nil { // handle error }
+	if err := g.PrepareConnection(gcsServiceID); err != nil { // handle error }
+	// (start the UVM here)
 	if err := g.CreateConnection(ctx); err != nil { // handle error }
 
 After the connection is established, use the manager interfaces for guest-side changes:

internal/vm/guestmanager/guest.go

@@ -5,6 +5,7 @@ package guestmanager
 import (
 	"context"
 	"fmt"
+	"net"
 	"sync"
 
 	"github.com/Microsoft/hcsshim/internal/gcs"
@@ -46,6 +47,8 @@ type Guest struct {
 	// gc is the active GCS connection to the guest.
 	// It will be nil if no connection is active.
 	gc *gcs.GuestConnection
+	// gcListener is bound by PrepareConnection and consumed by CreateConnection.
+	gcListener net.Listener
 }
 
 // New creates a new Guest Manager.
@@ -67,35 +70,53 @@ func WithInitializationState(state *gcs.InitialGuestState) ConfigOption {
 	}
 }
 
-// CreateConnection accepts the GCS connection and performs initial setup.
-func (gm *Guest) CreateConnection(ctx context.Context, GCSServiceID guid.GUID, opts ...ConfigOption) error {
+// PrepareConnection opens the host-side hvsock listener for the given GCS
+// service ID. Must be called before VM start so the host is listening when
+// the in-VM GCS dials. Idempotent for the same service ID.
+func (gm *Guest) PrepareConnection(GCSServiceID guid.GUID) error {
 	gm.mu.Lock()
 	defer gm.mu.Unlock()
 
-	// Return early if a connection is already active.
-	if gm.gc != nil {
-		// If the caller tried to connect to a different GCS service then error out.
+	// Idempotent if already prepared/connected with the same service ID.
+	if gm.gcListener != nil || gm.gc != nil {
 		if gm.gcsServiceID != GCSServiceID {
 			return fmt.Errorf("gcs service id mismatch: expected %s, got %s", gm.gcsServiceID, GCSServiceID)
 		}
 		return nil
 	}
 
-	gm.gcsServiceID = GCSServiceID
-
-	// The guest needs to connect to predefined GCS port.
-	// The host must already be listening on these port before the guest attempts to connect,
-	// otherwise the connection would fail.
-	vmConn, err := winio.ListenHvsock(&winio.HvsockAddr{
+	l, err := winio.ListenHvsock(&winio.HvsockAddr{
 		VMID:      gm.uvm.RuntimeID(),
 		ServiceID: GCSServiceID,
 	})
 	if err != nil {
 		return fmt.Errorf("failed to listen for guest connection: %w", err)
 	}
 
-	// Accept the connection
-	conn, err := vmmanager.AcceptConnection(ctx, gm.uvm, vmConn, true)
+	gm.gcsServiceID = GCSServiceID
+	gm.gcListener = l
+	return nil
+}
+
+// CreateConnection accepts the GCS dial on the prepared listener and runs
+// the GCS protocol handshake. Must be called after VM start. Idempotent if
+// a connection already exists.
+func (gm *Guest) CreateConnection(ctx context.Context, opts ...ConfigOption) error {
+	gm.mu.Lock()
+	defer gm.mu.Unlock()
+
+	if gm.gc != nil {
+		return nil
+	}
+	if gm.gcListener == nil {
+		return fmt.Errorf("CreateConnection called before PrepareConnection")
+	}
+
+	// AcceptConnection takes ownership of the listener and closes it.
+	l := gm.gcListener
+	gm.gcListener = nil
+
+	conn, err := vmmanager.AcceptConnection(ctx, gm.uvm, l, true)
 	if err != nil {
 		return fmt.Errorf("failed to connect to GCS: %w", err)
 	}
@@ -134,6 +155,9 @@ func (gm *Guest) CloseConnection() error {
 		err = gm.gc.Close()
 		gm.gc = nil
 	}
-
+	if gm.gcListener != nil {
+		_ = gm.gcListener.Close()
+		gm.gcListener = nil
+	}
 	return err
 }

internal/vm/vmmanager/utils.go

@@ -24,7 +24,7 @@ func AcceptConnection(ctx context.Context, uvm vmWaiter, l net.Listener, closeCo
 		conn net.Conn
 		err  error
 	}
-	resultCh := make(chan acceptResult)
+	resultCh := make(chan acceptResult, 1)
 
 	go func() {
 		c, err := l.Accept()
@@ -45,6 +45,7 @@ func AcceptConnection(ctx context.Context, uvm vmWaiter, l net.Listener, closeCo
 		}
 		return res.conn, res.err
 	case <-ctx.Done():
+		_ = l.Close()
 		return nil, ctx.Err()
 	case <-vmExitCh:
 	}