hv_netvsc: Fix the receive buffer size limit

The max should be 31 MB on host with NVSP version > 2.

On legacy hosts (NVSP version <=2) only 15 MB receive buffer is allowed,
otherwise the buffer request will be rejected by the host, resulting
vNIC not coming up.

The NVSP version is only available after negotiation. So, we add the
limit checking for legacy hosts in netvsc_init_buf().

Fixes: 5023a6db ("netvsc: increase default receive buffer size")
Signed-off-by: NHaiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: NStephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/hyperv/hyperv_net.h

@@ -637,9 +637,11 @@ struct nvsp_message {
 #define NETVSC_MTU 65535
 #define NETVSC_MTU_MIN ETH_MIN_MTU
 
-#define NETVSC_RECEIVE_BUFFER_SIZE		(1024*1024*16)	/* 16MB */
-#define NETVSC_RECEIVE_BUFFER_SIZE_LEGACY	(1024*1024*15)  /* 15MB */
+/* Max buffer sizes allowed by a host */
+#define NETVSC_RECEIVE_BUFFER_SIZE		(1024 * 1024 * 31) /* 31MB */
+#define NETVSC_RECEIVE_BUFFER_SIZE_LEGACY	(1024 * 1024 * 15) /* 15MB */
 #define NETVSC_SEND_BUFFER_SIZE			(1024 * 1024 * 15)   /* 15MB */
+
 #define NETVSC_INVALID_INDEX			-1
 
 #define NETVSC_SEND_SECTION_SIZE		6144

drivers/net/hyperv/netvsc.c

@@ -268,6 +268,11 @@ static int netvsc_init_buf(struct hv_device *device,
 	buf_size = device_info->recv_sections * device_info->recv_section_size;
 	buf_size = roundup(buf_size, PAGE_SIZE);
 
+	/* Legacy hosts only allow smaller receive buffer */
+	if (net_device->nvsp_version <= NVSP_PROTOCOL_VERSION_2)
+		buf_size = min_t(unsigned int, buf_size,
+				 NETVSC_RECEIVE_BUFFER_SIZE_LEGACY);
+
 	net_device->recv_buf = vzalloc(buf_size);
 	if (!net_device->recv_buf) {
 		netdev_err(ndev,