[PATCH net] net: rss: fix reporting RXH_XFRM_NO_CHANGE as input_xfrm for contexts

[PATCH net] net: rss: fix reporting RXH_XFRM_NO_CHANGE as input_xfrm for contexts

[Jakub Kicinski]

Initializing input_xfrm to RXH_XFRM_NO_CHANGE in RSS contexts is
problematic. I think I did this to make it clear that the context
does not have its own settings applied. But unlike ETH_RSS_HASH_NO_CHANGE
which is zero, RXH_XFRM_NO_CHANGE is 0xff. We need to be careful
when reading the value back, and remember to treat 0xff as 0.

Remove the initialization and switch to storing 0. This lets us
also remove the workaround in ethnl_rss_set(). Get side does not
need any adjustments and context get no longer reports:

  RSS input transformation:
    symmetric-xor: on
    symmetric-or-xor: on
    Unknown bits in RSS input transformation: 0xfc

for NICs which don't support input_xfrm.

Remove the init of hfunc to ETH_RSS_HASH_NO_CHANGE while at it.
As already mentioned this is a noop since ETH_RSS_HASH_NO_CHANGE
is 0 and struct is zalloc'd. But as this fix exemplifies storing
NO_CHANGE as state is fragile.

This issue is implicitly caught by running our selftests because
YNL in selftests errors out on unknown bits.

Fixes: d3e2c7bab124 ("ethtool: rss: support setting input-xfrm via Netlink")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: andrew@lunn.ch
CC: maxime.chevallier@bootlin.com
CC: gal@nvidia.com
---
 net/ethtool/common.c | 3 ---
 net/ethtool/rss.c    | 9 ++-------
 2 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/net/ethtool/common.c b/net/ethtool/common.c
index c5ed88bccbb4..5fae329795c8 100644
--- a/net/ethtool/common.c
+++ b/net/ethtool/common.c
@@ -901,9 +901,6 @@ ethtool_rxfh_ctx_alloc(const struct ethtool_ops *ops,
 	ctx->key_off = key_off;
 	ctx->priv_size = ops->rxfh_priv_size;
 
-	ctx->hfunc = ETH_RSS_HASH_NO_CHANGE;
-	ctx->input_xfrm = RXH_XFRM_NO_CHANGE;
-
 	return ctx;
 }
 
diff --git a/net/ethtool/rss.c b/net/ethtool/rss.c
index 4dced53be4b3..da5934cceb07 100644
--- a/net/ethtool/rss.c
+++ b/net/ethtool/rss.c
@@ -824,8 +824,8 @@ rss_set_ctx_update(struct ethtool_rxfh_context *ctx, struct nlattr **tb,
 static int
 ethnl_rss_set(struct ethnl_req_info *req_info, struct genl_info *info)
 {
-	bool indir_reset = false, indir_mod, xfrm_sym = false;
 	struct rss_req_info *request = RSS_REQINFO(req_info);
+	bool indir_reset = false, indir_mod, xfrm_sym;
 	struct ethtool_rxfh_context *ctx = NULL;
 	struct net_device *dev = req_info->dev;
 	bool mod = false, fields_mod = false;
@@ -860,12 +860,7 @@ ethnl_rss_set(struct ethnl_req_info *req_info, struct genl_info *info)
 
 	rxfh.input_xfrm = data.input_xfrm;
 	ethnl_update_u8(&rxfh.input_xfrm, tb[ETHTOOL_A_RSS_INPUT_XFRM], &mod);
-	/* For drivers which don't support input_xfrm it will be set to 0xff
-	 * in the RSS context info. In all other case input_xfrm != 0 means
-	 * symmetric hashing is requested.
-	 */
-	if (!request->rss_context || ops->rxfh_per_ctx_key)
-		xfrm_sym = rxfh.input_xfrm || data.input_xfrm;
+	xfrm_sym = rxfh.input_xfrm || data.input_xfrm;
 	if (rxfh.input_xfrm == data.input_xfrm)
 		rxfh.input_xfrm = RXH_XFRM_NO_CHANGE;
 
-- 
2.52.0

Re: [PATCH net] net: rss: fix reporting RXH_XFRM_NO_CHANGE as input_xfrm for contexts

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Fri, 30 Jan 2026 11:03:11 -0800 you wrote:
> Initializing input_xfrm to RXH_XFRM_NO_CHANGE in RSS contexts is
> problematic. I think I did this to make it clear that the context
> does not have its own settings applied. But unlike ETH_RSS_HASH_NO_CHANGE
> which is zero, RXH_XFRM_NO_CHANGE is 0xff. We need to be careful
> when reading the value back, and remember to treat 0xff as 0.
> 
> Remove the initialization and switch to storing 0. This lets us
> also remove the workaround in ethnl_rss_set(). Get side does not
> need any adjustments and context get no longer reports:
> 
> [...]

Here is the summary with links:
  - [net] net: rss: fix reporting RXH_XFRM_NO_CHANGE as input_xfrm for contexts
    https://git.kernel.org/netdev/net/c/1c172febdf06

You are awesome, thank you!
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