net: ethtool: Don't check if RSS context exists in case of context 0

JIRA: https://issues.redhat.com/browse/RHEL-89014

commit d78ebc7
Author: Gal Pressman <gal@nvidia.com>
Date:   Thu Jun 12 10:19:57 2025 +0300

    net: ethtool: Don't check if RSS context exists in case of context 0

    Context 0 (default context) always exists, there is no need to check
    whether it exists or not when adding a flow steering rule.

    The existing check fails when creating a flow steering rule for context
    0 as it is not stored in the rss_ctx xarray.

    For example:
    $ ethtool --config-ntuple eth2 flow-type tcp4 dst-ip 194.237.147.23 dst-port 19983 context 0 loc 618
    rmgr: Cannot insert RX class rule: Invalid argument
    Cannot insert classification rule

    An example usecase for this could be:
    - A high-priority rule (loc 0) directing specific port traffic to
      context 0.
    - A low-priority rule (loc 1) directing all other TCP traffic to context
      1.

    This is a user-visible regression that was caught in our testing
    environment, it was not reported by a user yet.

    Fixes: de7f758 ("net: ethtool: prevent flow steering to RSS contexts which don't exist")
    Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
    Reviewed-by: Nimrod Oren <noren@nvidia.com>
    Signed-off-by: Gal Pressman <gal@nvidia.com>
    Reviewed-by: Joe Damato <jdamato@fastly.com>
    Reviewed-by: Edward Cree <ecree.xilinx@gmail.com>
    Link: https://patch.msgid.link/20250612071958.1696361-2-gal@nvidia.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Mohammad Heib <mheib@redhat.com>

Author: mohammadheib

net/ethtool/ioctl.c

@@ -1000,7 +1000,8 @@ static noinline_for_stack int ethtool_set_rxnfc(struct net_device *dev,
 		    ethtool_get_flow_spec_ring(info.fs.ring_cookie))
 			return -EINVAL;
 
-		if (!xa_load(&dev->ethtool->rss_ctx, info.rss_context))
+		if (info.rss_context &&
+		    !xa_load(&dev->ethtool->rss_ctx, info.rss_context))
 			return -EINVAL;
 	}