Re: [PATCH iwl-net] ice: keep the RSS hash function on indirection-only updates

[Jakub Kicinski <kuba@kernel.org>]

On Wed,  7 Oct 2026 22:03:11 +0200 Maciej Fijalkowski wrote:
> The ethtool core passes RXH_XFRM_NO_CHANGE (0xff) in input_xfrm when a
> request does not touch the input transformation, e.g. when it only
> rewrites the RSS indirection table. ice_set_rxfh() tests input_xfrm only
> for RXH_XFRM_SYM_XOR, which 0xff has set, so such an update switches the
> VSI to symmetric Toeplitz hashing behind the user's back.
> 
> Once symmetric-xor is reported, the core requires all hashed flow types
> to be symmetric for any following RSS set. The GTP flow types hash on
> the TEID, so every later netlink RSS update fails with "hash field config
> is not symmetric", including the one that would put the indirection
> table back.
> 
> Keep the current hash function when input_xfrm is RXH_XFRM_NO_CHANGE.
> ice_set_rss_hfunc() then returns early and leaves the VSI as it is.
> 
> This has been encountered while trying to run xskxceiver within drv-net
> tests where one of the setup steps was queue pull out of RSS indirection
> table.
> 
> Fixes: 352e9bf23813 ("ice: enable symmetric-xor RSS for Toeplitz hash function")
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>

Hm, not seeing it on the list now but I thought I submitted this 
a while back:

--- a/drivers/net/ethernet/intel/ice/ice_ethtool.c
+++ b/drivers/net/ethernet/intel/ice/ice_ethtool.c
@@ -3681,10 +3681,10 @@ ice_set_rxfh(struct net_device *netdev, struct ethtool_rxfh_param *rxfh,
             struct netlink_ext_ack *extack)
 {
        struct ice_netdev_priv *np = netdev_priv(netdev);
-       u8 hfunc = ICE_AQ_VSI_Q_OPT_RSS_HASH_TPLZ;
        struct ice_vsi *vsi = np->vsi;
        struct ice_pf *pf = vsi->back;
        struct device *dev;
+       u8 hfunc;
        int err;
 
        dev = ice_pf_to_dev(pf);
@@ -3703,9 +3703,12 @@ ice_set_rxfh(struct net_device *netdev, struct ethtool_rxfh_param *rxfh,
                return -EOPNOTSUPP;
        }
 
-       /* Update the VSI's hash function */
-       if (rxfh->input_xfrm & RXH_XFRM_SYM_XOR)
+       if (rxfh->input_xfrm == RXH_XFRM_NO_CHANGE)
+               hfunc = vsi->rss_hfunc;
+       else if (rxfh->input_xfrm & RXH_XFRM_SYM_XOR)
                hfunc = ICE_AQ_VSI_Q_OPT_RSS_HASH_SYM_TPLZ;
+       else /* input_xfrm == 0; core rejects any other value */
+               hfunc = ICE_AQ_VSI_Q_OPT_RSS_HASH_TPLZ;
 
        err = ice_set_rss_hfunc(vsi, hfunc);
        if (err)

Could you double check if we need the trailing else as well? 
Not 100% sure now if I added it just in case or it mattered :S