gve: Allow ethtool to configure rx_buf_len

Add support for getting and setting the RX buffer length via the
ethtool ring parameters (`ethtool -g`/`-G`). The driver restricts the
allowed buffer length to 2048 (SZ_2K) by default and allows 4096 (SZ_4K)
based on device options.

As XDP is only supported when the `rx_buf_len` is 2048, the driver now
enforces this in two places:
1.  In `gve_xdp_set`, rejecting XDP programs if the current buffer
    length is not 2048.
2.  In `gve_set_rx_buf_len_config`, rejecting buffer length changes if XDP
    is loaded and the new length is not 2048.

Signed-off-by: Ankit Garg <nktgrg@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Reviewed-by: Jordan Rhee <jordanrhee@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Joshua Washington <joshwash@google.com>
Link: https://patch.msgid.link/20251106192746.243525-4-joshwash@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/google/gve/gve.h

@@ -1167,6 +1167,12 @@ static inline bool gve_is_gqi(struct gve_priv *priv)
 		priv->queue_format == GVE_GQI_QPL_FORMAT;
 }
 
+static inline bool gve_is_dqo(struct gve_priv *priv)
+{
+	return priv->queue_format == GVE_DQO_RDA_FORMAT ||
+	       priv->queue_format == GVE_DQO_QPL_FORMAT;
+}
+
 static inline u32 gve_num_tx_queues(struct gve_priv *priv)
 {
 	return priv->tx_cfg.num_queues + priv->tx_cfg.num_xdp_queues;
@@ -1248,6 +1254,9 @@ void gve_rx_free_rings_gqi(struct gve_priv *priv,
 void gve_rx_start_ring_gqi(struct gve_priv *priv, int idx);
 void gve_rx_stop_ring_gqi(struct gve_priv *priv, int idx);
 bool gve_header_split_supported(const struct gve_priv *priv);
+int gve_set_rx_buf_len_config(struct gve_priv *priv, u32 rx_buf_len,
+			      struct netlink_ext_ack *extack,
+			      struct gve_rx_alloc_rings_cfg *rx_alloc_cfg);
 int gve_set_hsplit_config(struct gve_priv *priv, u8 tcp_data_split,
 			  struct gve_rx_alloc_rings_cfg *rx_alloc_cfg);
 /* rx buffer handling */

drivers/net/ethernet/google/gve/gve_ethtool.c

@@ -529,6 +529,8 @@ static void gve_get_ringparam(struct net_device *netdev,
 	cmd->rx_pending = priv->rx_desc_cnt;
 	cmd->tx_pending = priv->tx_desc_cnt;
 
+	kernel_cmd->rx_buf_len = priv->rx_cfg.packet_buffer_size;
+
 	if (!gve_header_split_supported(priv))
 		kernel_cmd->tcp_data_split = ETHTOOL_TCP_DATA_SPLIT_UNKNOWN;
 	else if (priv->header_split_enabled)
@@ -589,6 +591,12 @@ static int gve_set_ringparam(struct net_device *netdev,
 	int err;
 
 	gve_get_curr_alloc_cfgs(priv, &tx_alloc_cfg, &rx_alloc_cfg);
+
+	err = gve_set_rx_buf_len_config(priv, kernel_cmd->rx_buf_len, extack,
+					&rx_alloc_cfg);
+	if (err)
+		return err;
+
 	err = gve_set_hsplit_config(priv, kernel_cmd->tcp_data_split,
 				    &rx_alloc_cfg);
 	if (err)
@@ -605,6 +613,8 @@ static int gve_set_ringparam(struct net_device *netdev,
 			return err;
 	} else {
 		/* Set ring params for the next up */
+		priv->rx_cfg.packet_buffer_size =
+			rx_alloc_cfg.packet_buffer_size;
 		priv->header_split_enabled = rx_alloc_cfg.enable_header_split;
 		priv->tx_desc_cnt = tx_alloc_cfg.ring_size;
 		priv->rx_desc_cnt = rx_alloc_cfg.ring_size;
@@ -944,7 +954,8 @@ static int gve_get_ts_info(struct net_device *netdev,
 
 const struct ethtool_ops gve_ethtool_ops = {
 	.supported_coalesce_params = ETHTOOL_COALESCE_USECS,
-	.supported_ring_params = ETHTOOL_RING_USE_TCP_DATA_SPLIT,
+	.supported_ring_params = ETHTOOL_RING_USE_TCP_DATA_SPLIT |
+				 ETHTOOL_RING_USE_RX_BUF_LEN,
 	.get_drvinfo = gve_get_drvinfo,
 	.get_strings = gve_get_strings,
 	.get_sset_count = gve_get_sset_count,

drivers/net/ethernet/google/gve/gve_main.c

@@ -1725,6 +1725,13 @@ static int gve_verify_xdp_configuration(struct net_device *dev,
 		return -EOPNOTSUPP;
 	}
 
+	if (priv->rx_cfg.packet_buffer_size != SZ_2K) {
+		NL_SET_ERR_MSG_FMT_MOD(extack,
+				       "XDP is not supported for Rx buf len %d, only %d supported.",
+				       priv->rx_cfg.packet_buffer_size, SZ_2K);
+		return -EOPNOTSUPP;
+	}
+
 	max_xdp_mtu = priv->rx_cfg.packet_buffer_size - sizeof(struct ethhdr);
 	if (priv->queue_format == GVE_GQI_QPL_FORMAT)
 		max_xdp_mtu -= GVE_RX_PAD;
@@ -2056,6 +2063,38 @@ bool gve_header_split_supported(const struct gve_priv *priv)
 		priv->queue_format == GVE_DQO_RDA_FORMAT && !priv->xdp_prog;
 }
 
+int gve_set_rx_buf_len_config(struct gve_priv *priv, u32 rx_buf_len,
+			      struct netlink_ext_ack *extack,
+			      struct gve_rx_alloc_rings_cfg *rx_alloc_cfg)
+{
+	u32 old_rx_buf_len = rx_alloc_cfg->packet_buffer_size;
+
+	if (rx_buf_len == old_rx_buf_len)
+		return 0;
+
+	/* device options may not always contain support for 4K buffers */
+	if (!gve_is_dqo(priv) || priv->max_rx_buffer_size < SZ_4K) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "Modifying Rx buf len is not supported");
+		return -EOPNOTSUPP;
+	}
+
+	if (priv->xdp_prog && rx_buf_len != SZ_2K) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "Rx buf len can only be 2048 when XDP is on");
+		return -EINVAL;
+	}
+
+	if (rx_buf_len != SZ_2K && rx_buf_len != SZ_4K) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "Rx buf len can only be 2048 or 4096");
+		return -EINVAL;
+	}
+	rx_alloc_cfg->packet_buffer_size = rx_buf_len;
+
+	return 0;
+}
+
 int gve_set_hsplit_config(struct gve_priv *priv, u8 tcp_data_split,
 			  struct gve_rx_alloc_rings_cfg *rx_alloc_cfg)
 {