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Date: Wed, 17 Apr 2024 13:42:13 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
To: Larysa Zaremba <larysa.zaremba@intel.com>
CC: Tony Nguyen <anthony.l.nguyen@intel.com>,
	<intel-wired-lan@lists.osuosl.org>, <linux-kernel@vger.kernel.org>,
	<alan.brady@intel.com>, <jesse.brandeburg@intel.com>, Emil Tantilov
	<emil.s.tantilov@intel.com>, "David S. Miller" <davem@davemloft.net>, "Eric
 Dumazet" <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>, Paolo Abeni
	<pabeni@redhat.com>, Lukasz Czapnik <lukasz.czapnik@intel.com>, "Michal
 Swiatkowski" <michal.swiatkowski@linux.intel.com>
Subject: Re: [PATCH iwl-net] ice: Interpret .set_channels() input differently
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References: <20240416125856.1263314-1-larysa.zaremba@intel.com>
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On Tue, Apr 16, 2024 at 02:58:54PM +0200, Larysa Zaremba wrote:
> A bug occurs because a safety check guarding AF_XDP-related queues in
> ethnl_set_channels(), does not trigger. This happens, because kernel and
> ice driver interpret the ethtool command differently.
> 
> How the bug occurs:
> 1. ethtool -l <IFNAME> -> combined: 40
> 2. Attach AF_XDP to queue 30
> 3. ethtool -L <IFNAME> rx 15 tx 15
>    combined number is not specified, so command becomes {rx_count = 15,
>    tx_count = 15, combined_count = 40}.
> 4. ethnl_set_channels checks, if there are any AF_XDP of queues from the
>    new (combined_count + rx_count) to the old one, so from 55 to 40, check
>    does not trigger.
> 5. ice interprets `rx 15 tx 15` as 15 combined channels and deletes the
>    queue that AF_XDP is attached to.
> 
> Interpret the command in a way that is more consistent with ethtool
> manual [0] (--show-channels and --set-channels).
> 
> Considering that in the ice driver only the difference between RX and TX
> queues forms dedicated channels, change the correct way to set number of
> channels to:
> 
> ethtool -L <IFNAME> combined 10 /* For symmetric queues */
> ethtool -L <IFNAME> combined 8 tx 2 rx 0 /* For asymmetric queues */

Makes sense for usage above:
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>

Nonetheless I still think core should not allow user to shoot himself to
foot, but let's keep it as a separate thing.

Thanks!

> 
> [0] https://man7.org/linux/man-pages/man8/ethtool.8.html
> 
> Fixes: 87324e747fde ("ice: Implement ethtool ops for channels")
> Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
> Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_ethtool.c | 22 ++++++--------------
>  1 file changed, 6 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_ethtool.c b/drivers/net/ethernet/intel/ice/ice_ethtool.c
> index 78b833b3e1d7..d91f41f61bce 100644
> --- a/drivers/net/ethernet/intel/ice/ice_ethtool.c
> +++ b/drivers/net/ethernet/intel/ice/ice_ethtool.c
> @@ -3593,7 +3593,6 @@ static int ice_set_channels(struct net_device *dev, struct ethtool_channels *ch)
>  	struct ice_pf *pf = vsi->back;
>  	int new_rx = 0, new_tx = 0;
>  	bool locked = false;
> -	u32 curr_combined;
>  	int ret = 0;
>  
>  	/* do not support changing channels in Safe Mode */
> @@ -3615,22 +3614,13 @@ static int ice_set_channels(struct net_device *dev, struct ethtool_channels *ch)
>  		return -EOPNOTSUPP;
>  	}
>  
> -	curr_combined = ice_get_combined_cnt(vsi);
> +	if (!ch->combined_count) {
> +		netdev_err(dev, "Please specify at least 1 combined channel\n");
> +		return -EINVAL;
> +	}
>  
> -	/* these checks are for cases where user didn't specify a particular
> -	 * value on cmd line but we get non-zero value anyway via
> -	 * get_channels(); look at ethtool.c in ethtool repository (the user
> -	 * space part), particularly, do_schannels() routine
> -	 */
> -	if (ch->rx_count == vsi->num_rxq - curr_combined)
> -		ch->rx_count = 0;
> -	if (ch->tx_count == vsi->num_txq - curr_combined)
> -		ch->tx_count = 0;
> -	if (ch->combined_count == curr_combined)
> -		ch->combined_count = 0;
> -
> -	if (!(ch->combined_count || (ch->rx_count && ch->tx_count))) {
> -		netdev_err(dev, "Please specify at least 1 Rx and 1 Tx channel\n");
> +	if (ch->rx_count && ch->tx_count) {
> +		netdev_err(dev, "Dedicated RX or TX channels cannot be used simultaneously\n");
>  		return -EINVAL;
>  	}
>  
> -- 
> 2.43.0
>