net/mlx5e: resize configured default RSS context table on channel change

mlx5e_ethtool_set_channels() rejected channel count changes that
required a different RQT size when the default context indirection
table was user-configured. This restriction was introduced by
commit ee3572409f ("net/mlx5e: RSS, Block changing channels number
when RXFH is configured").

Lift the restriction. Validate the resize upfront with
ethtool_rxfh_indir_can_resize(), then fold or unfold the table
in-place via ethtool_rxfh_indir_resize() inside state_lock, before
mlx5e_safe_switch_params(), so the preactivate callback sees the
correct table content when it programs the HW.

Signed-off-by: Yael Chemla <ychemla@nvidia.com>
Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260511172719.330490-5-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlx5/core/en/rss.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
 // Copyright (c) 2021, NVIDIA CORPORATION & AFFILIATES.
 
+#include <linux/ethtool.h>
 #include "rss.h"
 
 #define mlx5e_rss_warn(__dev, format, ...)			\
@@ -85,6 +86,11 @@ bool mlx5e_rss_get_inner_ft_support(struct mlx5e_rss *rss)
 	return rss->params.inner_ft_support;
 }
 
+u32 *mlx5e_rss_get_indir_table(struct mlx5e_rss *rss)
+{
+	return rss->indir.table;
+}
+
 void mlx5e_rss_set_indir_actual_size(struct mlx5e_rss *rss, u32 size)
 {
 	rss->indir.actual_table_size = size;
@@ -102,6 +108,13 @@ void mlx5e_rss_ctx_resize(struct mlx5e_rss *rss, u32 new_size)
 		rss->indir.table[i] = rss->indir.table[i % old_size];
 }
 
+void mlx5e_rss_indir_resize(struct mlx5e_rss *rss, struct net_device *netdev,
+			    u32 new_size)
+{
+	ethtool_rxfh_indir_resize(netdev, rss->indir.table,
+				  rss->indir.actual_table_size, new_size);
+}
+
 int mlx5e_rss_params_indir_init(struct mlx5e_rss_params_indir *indir,
 				u32 actual_table_size, u32 max_table_size)
 {

drivers/net/ethernet/mellanox/mlx5/core/en/rss.h

@@ -35,6 +35,8 @@ int mlx5e_rss_params_indir_init(struct mlx5e_rss_params_indir *indir,
 				u32 actual_table_size, u32 max_table_size);
 void mlx5e_rss_params_indir_cleanup(struct mlx5e_rss_params_indir *indir);
 void mlx5e_rss_ctx_resize(struct mlx5e_rss *rss, u32 new_size);
+void mlx5e_rss_indir_resize(struct mlx5e_rss *rss, struct net_device *netdev,
+			    u32 new_size);
 struct mlx5e_rss *
 mlx5e_rss_init(struct mlx5_core_dev *mdev,
 	       const struct mlx5e_rss_params *params,
@@ -46,6 +48,7 @@ void mlx5e_rss_refcnt_dec(struct mlx5e_rss *rss);
 unsigned int mlx5e_rss_refcnt_read(struct mlx5e_rss *rss);
 
 bool mlx5e_rss_get_inner_ft_support(struct mlx5e_rss *rss);
+u32 *mlx5e_rss_get_indir_table(struct mlx5e_rss *rss);
 void mlx5e_rss_set_indir_actual_size(struct mlx5e_rss *rss, u32 size);
 u32 mlx5e_rss_get_tirn(struct mlx5e_rss *rss, enum mlx5_traffic_types tt,
 		       bool inner);

drivers/net/ethernet/mellanox/mlx5/core/en/rx_res.c

@@ -40,15 +40,31 @@ static u32 *get_vhca_ids(struct mlx5e_rx_res *res, int offset)
 	return multi_vhca ? res->rss_vhca_ids + offset : NULL;
 }
 
-void mlx5e_rx_res_rss_update_num_channels(struct mlx5e_rx_res *res, u32 nch)
+/* Updates the indirection table SW shadow, does not update the HW resources yet
+ */
+void mlx5e_rx_res_rss_update_num_channels(struct mlx5e_rx_res *res, u32 nch,
+					  struct net_device *netdev)
 {
 	u32 new_size = mlx5e_rqt_size(res->mdev, nch);
 	int i;
 
 	WARN_ON_ONCE(res->rss_active);
 
-	/* Default context */
+	/* Default context: fold/unfold user-configured table, then update size
+	 * and reset to uniform when unconfigured.
+	 */
+	mlx5e_rss_indir_resize(res->rss[0], netdev, new_size);
+
+	/* mlx5e_rss_indir_resize() is a no-op when the table is not
+	 * user-configured. actual_table_size is updated after the resize
+	 * because ethtool_rxfh_indir_resize() uses it as the old size to
+	 * replicate the pattern; updating it first would make the grow a no-op.
+	 * It must be updated before mlx5e_rss_set_indir_uniform() so that
+	 * the uniform fill covers all new entries, not just the old ones.
+	 */
 	mlx5e_rss_set_indir_actual_size(res->rss[0], new_size);
+	if (!netif_is_rxfh_configured(netdev))
+		mlx5e_rss_set_indir_uniform(res->rss[0], nch);
 
 	/* Non-default contexts */
 	for (i = 1; i < MLX5E_MAX_NUM_RSS; i++) {
@@ -218,13 +234,6 @@ static void mlx5e_rx_res_rss_disable(struct mlx5e_rx_res *res)
 	}
 }
 
-/* Updates the indirection table SW shadow, does not update the HW resources yet */
-void mlx5e_rx_res_rss_set_indir_uniform(struct mlx5e_rx_res *res, unsigned int nch)
-{
-	WARN_ON_ONCE(res->rss_active);
-	mlx5e_rss_set_indir_uniform(res->rss[0], nch);
-}
-
 void mlx5e_rx_res_rss_get_rxfh(struct mlx5e_rx_res *res, u32 rss_idx,
 			       u32 *indir, u8 *key, u8 *hfunc, bool *symmetric)
 {

drivers/net/ethernet/mellanox/mlx5/core/en/rx_res.h

@@ -48,7 +48,6 @@ void mlx5e_rx_res_xsk_update(struct mlx5e_rx_res *res, struct mlx5e_channels *ch
 			     unsigned int ix, bool xsk);
 
 /* Configuration API */
-void mlx5e_rx_res_rss_set_indir_uniform(struct mlx5e_rx_res *res, unsigned int nch);
 void mlx5e_rx_res_rss_get_rxfh(struct mlx5e_rx_res *res, u32 rss_idx,
 			       u32 *indir, u8 *key, u8 *hfunc,
 			       bool *symmetric);
@@ -68,7 +67,8 @@ int mlx5e_rx_res_rss_destroy(struct mlx5e_rx_res *res, u32 rss_idx);
 int mlx5e_rx_res_rss_cnt(struct mlx5e_rx_res *res);
 int mlx5e_rx_res_rss_index(struct mlx5e_rx_res *res, struct mlx5e_rss *rss);
 struct mlx5e_rss *mlx5e_rx_res_rss_get(struct mlx5e_rx_res *res, u32 rss_idx);
-void mlx5e_rx_res_rss_update_num_channels(struct mlx5e_rx_res *res, u32 nch);
+void mlx5e_rx_res_rss_update_num_channels(struct mlx5e_rx_res *res, u32 nch,
+					  struct net_device *netdev);
 
 /* Workaround for hairpin */
 struct mlx5e_rss_params_hash mlx5e_rx_res_get_current_hash(struct mlx5e_rx_res *res);

drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c

@@ -501,6 +501,7 @@ int mlx5e_ethtool_set_channels(struct mlx5e_priv *priv,
 	unsigned int count = ch->combined_count;
 	int new_rqt_size, cur_rqt_size;
 	struct mlx5e_params new_params;
+	struct mlx5e_rss *rss0;
 	bool arfs_enabled;
 	bool has_rss_ctxs;
 	bool opened;
@@ -538,19 +539,16 @@ int mlx5e_ethtool_set_channels(struct mlx5e_priv *priv,
 	}
 
 	cur_rqt_size = mlx5e_rqt_size(priv->mdev, cur_params->num_channels);
+	rss0 = mlx5e_rx_res_rss_get(priv->rx_res, 0);
 
-	/* If RXFH is configured, changing the channels number is allowed only if
-	 * it does not require resizing the RSS table. This is because the previous
-	 * configuration may no longer be compatible with the new RSS table.
-	 */
-	if (netif_is_rxfh_configured(priv->netdev)) {
-		if (new_rqt_size != cur_rqt_size) {
-			err = -EINVAL;
-			netdev_err(priv->netdev,
-				   "%s: RXFH is configured, block changing channels number that affects RSS table size (new: %d, current: %d)\n",
-				   __func__, new_rqt_size, cur_rqt_size);
-			goto out;
-		}
+	if (!ethtool_rxfh_indir_can_resize(priv->netdev,
+					   mlx5e_rss_get_indir_table(rss0),
+					   cur_rqt_size, new_rqt_size)) {
+		netdev_err(priv->netdev,
+			   "%s: cannot resize RSS table (%u -> %u); reset indirection table to allow this change\n",
+			   __func__, cur_rqt_size, new_rqt_size);
+		err = -EINVAL;
+		goto out;
 	}
 
 	/* Don't allow changing the number of channels if HTB offload is active,

drivers/net/ethernet/mellanox/mlx5/core/en_main.c

@@ -3296,12 +3296,9 @@ static int mlx5e_num_channels_changed(struct mlx5e_priv *priv)
 	}
 
 	/* This function may be called on attach, before priv->rx_res is created. */
-	if (priv->rx_res) {
-		mlx5e_rx_res_rss_update_num_channels(priv->rx_res, count);
-
-		if (!netif_is_rxfh_configured(priv->netdev))
-			mlx5e_rx_res_rss_set_indir_uniform(priv->rx_res, count);
-	}
+	if (priv->rx_res)
+		mlx5e_rx_res_rss_update_num_channels(priv->rx_res, count,
+						     netdev);
 
 	return 0;
 }