hyperv: Increase the buffer length for netvsc_channel_cb()

When the buffer is too small for a packet from VMBus, a bigger buffer will be
allocated in netvsc_channel_cb() and retry reading the packet from VMBus.
Increasing this buffer size will reduce the retry overhead.
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/hyperv_net.h

@@ -591,7 +591,7 @@ struct nvsp_message {
 
 #define NETVSC_RECEIVE_BUFFER_ID		0xcafe
 
-#define NETVSC_PACKET_SIZE                      2048
+#define NETVSC_PACKET_SIZE                      4096
 
 #define VRSS_SEND_TAB_SIZE 16
 
@@ -642,7 +642,7 @@ struct netvsc_device {
 	int ring_size;
 
 	/* The primary channel callback buffer */
-	unsigned char cb_buffer[NETVSC_PACKET_SIZE];
+	unsigned char *cb_buffer;
 	/* The sub channel callback buffer */
 	unsigned char *sub_cb_buf;
 };

drivers/net/hyperv/netvsc.c

@@ -42,6 +42,12 @@ static struct netvsc_device *alloc_net_device(struct hv_device *device)
 	if (!net_device)
 		return NULL;
 
+	net_device->cb_buffer = kzalloc(NETVSC_PACKET_SIZE, GFP_KERNEL);
+	if (!net_device->cb_buffer) {
+		kfree(net_device);
+		return NULL;
+	}
+
 	init_waitqueue_head(&net_device->wait_drain);
 	net_device->start_remove = false;
 	net_device->destroy = false;
@@ -52,6 +58,12 @@ static struct netvsc_device *alloc_net_device(struct hv_device *device)
 	return net_device;
 }
 
+static void free_netvsc_device(struct netvsc_device *nvdev)
+{
+	kfree(nvdev->cb_buffer);
+	kfree(nvdev);
+}
+
 static struct netvsc_device *get_outbound_net_device(struct hv_device *device)
 {
 	struct netvsc_device *net_device;
@@ -551,7 +563,7 @@ int netvsc_device_remove(struct hv_device *device)
 	if (net_device->sub_cb_buf)
 		vfree(net_device->sub_cb_buf);
 
-	kfree(net_device);
+	free_netvsc_device(net_device);
 	return 0;
 }
 
@@ -1093,7 +1105,7 @@ int netvsc_device_add(struct hv_device *device, void *additional_info)
 	vmbus_close(device->channel);
 
 cleanup:
-	kfree(net_device);
+	free_netvsc_device(net_device);
 
 	return ret;
 }