[hyperv] Tear down NetVSC RX buffer GPADL after closing VMBus device

On Windows Server 2012 R2, the receive buffer teardown completion
message seems to occasionally be deferred until after the VMBus
channel has been closed.  This happens even if there are no packets
currently in the receive buffer.

Work around this problem by separating the revocation and teardown of
the receive buffer, and deferring the teardown until after the VMBus
channel has been closed.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/netvsc.c

 
 	/* Send message and wait for completion */
 	if ( ( rc = netvsc_control ( netvsc, buffer->revoke_xrid,
-				     &msg, sizeof ( msg ) ) ) != 0 )
+				     &msg, sizeof ( msg ) ) ) != 0 ) {
+		DBGC ( netvsc, "NETVSC %s could not revoke buffer: %s\n",
+		       netvsc->name, strerror ( rc ) );
 		return rc;
+	}
 
 	return 0;
 }
 		goto err_register_pages;
 	}
 
-	/* Establish data buffer */
-	if ( ( rc = netvsc_establish_buffer ( netvsc, buffer ) ) != 0 )
-		goto err_establish_buffer;
-
 	return 0;
 
-	netvsc_revoke_buffer ( netvsc, buffer );
- err_establish_buffer:
 	vmbus_unregister_pages ( vmdev, &buffer->pages );
  err_register_pages:
 	vmbus_gpadl_teardown ( vmdev, gpadl );
 	struct vmbus_device *vmdev = netvsc->vmdev;
 	int rc;
 
-	/* Revoke buffer */
-	if ( ( rc = netvsc_revoke_buffer ( netvsc, buffer ) ) != 0 ) {
-		DBGC ( netvsc, "NETVSC %s could not revoke buffer: %s\n",
-		       netvsc->name, strerror ( rc ) );
-		/* Continue to attempt to tear down the GPA descriptor
-		 * list, which should forcibly prevent the host from
-		 * subsequently accessing this memory.
-		 */
-	}
-
 	/* Unregister transfer pages */
 	vmbus_unregister_pages ( vmdev, &buffer->pages );
 
 	struct netvsc_device *netvsc = rndis->priv;
 	int rc;
 
+	/* Initialise receive buffer */
+	if ( ( rc = netvsc_create_buffer ( netvsc, &netvsc->rx ) ) != 0 )
+		goto err_create_rx;
+
 	/* Open channel */
 	if ( ( rc = vmbus_open ( netvsc->vmdev, &netvsc_channel_operations,
 				 PAGE_SIZE, PAGE_SIZE, NETVSC_MTU ) ) != 0 ) {
 	if ( ( rc = netvsc_create_ring ( netvsc, &netvsc->tx ) ) != 0 )
 		goto err_create_tx;
 
-	/* Initialise receive buffer */
-	if ( ( rc = netvsc_create_buffer ( netvsc, &netvsc->rx ) ) != 0 )
-		goto err_create_rx;
+	/* Establish receive buffer */
+	if ( ( rc = netvsc_establish_buffer ( netvsc, &netvsc->rx ) ) != 0 )
+		goto err_establish_rx;
 
 	return 0;
 
-	netvsc_destroy_buffer ( netvsc, &netvsc->rx );
- err_create_rx:
+	netvsc_revoke_buffer ( netvsc, &netvsc->rx );
+ err_establish_rx:
 	netvsc_destroy_ring ( netvsc, &netvsc->tx, NULL );
  err_create_tx:
  err_ndis_version:
  err_initialise:
 	vmbus_close ( netvsc->vmdev );
  err_vmbus_open:
+	netvsc_destroy_buffer ( netvsc, &netvsc->rx );
+ err_create_rx:
 	return rc;
 }
 
 static void netvsc_close ( struct rndis_device *rndis ) {
 	struct netvsc_device *netvsc = rndis->priv;
 
-	/* Destroy receive buffer */
-	netvsc_destroy_buffer ( netvsc, &netvsc->rx );
+	/* Revoke receive buffer */
+	netvsc_revoke_buffer ( netvsc, &netvsc->rx );
 
 	/* Destroy transmit ring */
 	netvsc_destroy_ring ( netvsc, &netvsc->tx, netvsc_cancel_transmit );
 
 	/* Close channel */
 	vmbus_close ( netvsc->vmdev );
+
+	/* Destroy receive buffer */
+	netvsc_destroy_buffer ( netvsc, &netvsc->rx );
 }
 
 /** RNDIS operations */