Re: [PATCH net 1/2] ice: Interpret .set_channels() input differently

[Simon Horman <horms@kernel.org>]

On Tue, May 14, 2024 at 11:51:12AM -0700, Jacob Keller wrote:
> From: Larysa Zaremba <larysa.zaremba@intel.com>
> 
> 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 */
> 
> [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>
> Tested-by: Chandan Kumar Rout <chandanx.rout@intel.com>
> Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com>
> Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>

Reviewed-by: Simon Horman <horms@kernel.org>