ethtool: use the rss context XArray in ring deactivation safety-check

ethtool_get_max_rxfh_channel() gets called when user requests
deactivating Rx channels. Check the additional RSS contexts, too.

While we do track whether RSS context has an indirection
table explicitly set by the user, no driver looks at that bit.
Assume drivers won't auto-regenerate the additional tables,
to be safe.
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20240710174043.754664-3-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ethtool/common.c

@@ -587,21 +587,47 @@ int ethtool_get_max_rxnfc_channel(struct net_device *dev, u64 *max)
 	return err;
 }
 
+static u32 ethtool_get_max_rss_ctx_channel(struct net_device *dev)
+{
+	struct ethtool_rxfh_context *ctx;
+	unsigned long context;
+	u32 max_ring = 0;
+
+	mutex_lock(&dev->ethtool->rss_lock);
+	xa_for_each(&dev->ethtool->rss_ctx, context, ctx) {
+		u32 i, *tbl;
+
+		tbl = ethtool_rxfh_context_indir(ctx);
+		for (i = 0; i < ctx->indir_size; i++)
+			max_ring = max(max_ring, tbl[i]);
+	}
+	mutex_unlock(&dev->ethtool->rss_lock);
+
+	return max_ring;
+}
+
 u32 ethtool_get_max_rxfh_channel(struct net_device *dev)
 {
 	struct ethtool_rxfh_param rxfh = {};
 	u32 dev_size, current_max;
 	int ret;
 
+	/* While we do track whether RSS context has an indirection
+	 * table explicitly set by the user, no driver looks at that bit.
+	 * Assume drivers won't auto-regenerate the additional tables,
+	 * to be safe.
+	 */
+	current_max = ethtool_get_max_rss_ctx_channel(dev);
+
 	if (!netif_is_rxfh_configured(dev))
-		return 0;
+		return current_max;
 
 	if (!dev->ethtool_ops->get_rxfh_indir_size ||
 	    !dev->ethtool_ops->get_rxfh)
-		return 0;
+		return current_max;
 	dev_size = dev->ethtool_ops->get_rxfh_indir_size(dev);
 	if (dev_size == 0)
-		return 0;
+		return current_max;
 
 	rxfh.indir = kcalloc(dev_size, sizeof(rxfh.indir[0]), GFP_USER);
 	if (!rxfh.indir)
@@ -613,7 +639,6 @@ u32 ethtool_get_max_rxfh_channel(struct net_device *dev)
 		goto out_free;
 	}
 
-	current_max = 0;
 	while (dev_size--)
 		current_max = max(current_max, rxfh.indir[dev_size]);