Re: [PATCH net] ice: fix VF queue configuration with low MTU values

[Jacob Keller <jacob.e.keller@intel.com>]

On 4/6/2026 7:56 AM, Jose Ignacio Tornos Martinez wrote:
> The ice driver's VF queue configuration validation rejects
> databuffer_size values below 1024 bytes, which prevents VFs from
> using MTU values below 871 bytes.
> 
> The iavf driver calculates databuffer_size based on the MTU using:
>   databuffer_size = ALIGN(MTU + LIBETH_RX_LL_LEN, 128)
> 
> where LIBETH_RX_LL_LEN = 26 (ETH_HLEN + 2*VLAN_HLEN + ETH_FCS_LEN).
> 
> For MTU values below 871:
>   MTU 870: 870 + 26 = 896, aligned to 128 = 896 (< 1024, rejected)
>   MTU 871: 871 + 26 = 897, aligned to 128 = 1024 (>= 1024, accepted)
> 
> The 1024-byte minimum seems unnecessarily restrictive, because the hardware
> supports databuffer_size as low as 128 bytes (the alignment boundary),
> which should allow MTU values down to the standard minimum of 68 bytes.
> 
> I haven't found the reason why the limit was configured in the commit
> 9c7dd7566d18 ("ice: add validation in OP_CONFIG_VSI_QUEUES VF message"), so
> with no more information and since it is working, change the minimum
> databuffer_size validation from 1024 to 128 bytes to allow standard low
> MTU values while still preventing invalid configurations.
> 

I dug through some of our internal history and found that there was no
justification on why 1024 was chosen.

I agree with your assessment that the value of 128 makes the most sense
as it is the actual hardware minimum. I wonder if we used to always use
data buffer sizes of 1024 before the conversion to libeth. Either way, I
think it makes sense to allow smaller buffers since the modern iAVF will
request them.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

> Fixes: 9c7dd7566d18 ("ice: add validation in OP_CONFIG_VSI_QUEUES VF message")
> cc: stable@vger.kernel.org
> Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
> ---
>  drivers/net/ethernet/intel/ice/virt/queues.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/virt/queues.c b/drivers/net/ethernet/intel/ice/virt/queues.c
> index f73d5a3e83d4..31be2f76181c 100644
> --- a/drivers/net/ethernet/intel/ice/virt/queues.c
> +++ b/drivers/net/ethernet/intel/ice/virt/queues.c
> @@ -840,7 +840,7 @@ int ice_vc_cfg_qs_msg(struct ice_vf *vf, u8 *msg)
>  
>  			if (qpi->rxq.databuffer_size != 0 &&
>  			    (qpi->rxq.databuffer_size > ((16 * 1024) - 128) ||
> -			     qpi->rxq.databuffer_size < 1024))
> +			     qpi->rxq.databuffer_size < 128))
>  				goto error_param;
>  
>  			ring->rx_buf_len = qpi->rxq.databuffer_size;