[net,v1] i40e: fix xdp_redirect logs error message when testing with MTU=1500

From: Bartosz Staszewski <bartoszx.staszewski@intel.com>

The driver is currently logging an error message "MTU too large to enable XDP"
when trying to enable XDP on totally normal MTU.

This was caused by whenever the  interface was down, function
i40e_xdp was passing vsi->rx_buf_len field to i40e_xdp_setup()
which was equal 0. i40e_open() then  calls i40e_vsi_configure_rx()
which configures that field, but that only happens when interface is up.
When it is down, i40e_open() is not being called, thusvsi->rx_buf_len
which causes the bug is not set.

Solution for this is calculate buffer length in newly created
function - i40e_calculate_vsi_rx_buf_len() that return actual buffer
length. Buffer length is being calculated based on the same rules applied
previously in i40e_vsi_configure_rx() function.

Fixes: 613142b0bb88 ("i40e: Log error for oversized MTU on device")
Signed-off-by: Bartosz Staszewski <bartoszx.staszewski@intel.com>
Signed-off-by: Mateusz Palczewski <mateusz.palczewski@intel.com>
---
 drivers/net/ethernet/intel/i40e/i40e_main.c | 42 +++++++++++++++------
 1 file changed, 30 insertions(+), 12 deletions(-)

On 10/14/2022 3:02 AM, Mateusz Palczewski wrote:
> From: Bartosz Staszewski <bartoszx.staszewski@intel.com>
> 
> The driver is currently logging an error message "MTU too large to enable XDP"
> when trying to enable XDP on totally normal MTU.
> 
> This was caused by whenever the  interface was down, function
> i40e_xdp was passing vsi->rx_buf_len field to i40e_xdp_setup()
> which was equal 0. i40e_open() then  calls i40e_vsi_configure_rx()
> which configures that field, but that only happens when interface is up.
> When it is down, i40e_open() is not being called, thusvsi->rx_buf_len
> which causes the bug is not set.
> 
> Solution for this is calculate buffer length in newly created
> function - i40e_calculate_vsi_rx_buf_len() that return actual buffer
> length. Buffer length is being calculated based on the same rules applied
> previously in i40e_vsi_configure_rx() function.
> 
> Fixes: 613142b0bb88 ("i40e: Log error for oversized MTU on device")
> Signed-off-by: Bartosz Staszewski <bartoszx.staszewski@intel.com>
> Signed-off-by: Mateusz Palczewski <mateusz.palczewski@intel.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c | 42 +++++++++++++++------
>  1 file changed, 30 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index b5dcd15ced36..2fec0cff282c 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -3693,6 +3693,30 @@ static int i40e_vsi_configure_tx(struct i40e_vsi *vsi)
>  	return err;
>  }
>  
> +/**
> + * i40e_calculate_vsi_rx_buf_len - Calculates buffer length
> + *
> + * @vsi: VSI to calculate rx_buf_len from
> + */
> +static u16 i40e_calculate_vsi_rx_buf_len(struct i40e_vsi *vsi)
> +{
> +	u16 ret;
> +
> +	if (!vsi->netdev || (vsi->back->flags & I40E_FLAG_LEGACY_RX)) {
> +		ret = I40E_RXBUFFER_2048;
> +#if (PAGE_SIZE < 8192)
> +	} else if (!I40E_2K_TOO_SMALL_WITH_PADDING &&
> +		   (vsi->netdev->mtu <= ETH_DATA_LEN)) {

This has a checkpatch error here because of the unnecessary parenthesis.

I can fix this up locally when applying the patch to net-queue.

Thanks,
Jake

> +		ret = I40E_RXBUFFER_1536 - NET_IP_ALIGN;
> +#endif
> +	} else {
> +		ret = (PAGE_SIZE < 8192) ? I40E_RXBUFFER_3072 :
> +					   I40E_RXBUFFER_2048;
> +	}
> +
> +	return ret;
> +}
> +
>  /**
>   * i40e_vsi_configure_rx - Configure the VSI for Rx
>   * @vsi: the VSI being configured
> @@ -3704,20 +3728,14 @@ static int i40e_vsi_configure_rx(struct i40e_vsi *vsi)
>  	int err = 0;
>  	u16 i;
>  
> -	if (!vsi->netdev || (vsi->back->flags & I40E_FLAG_LEGACY_RX)) {
> -		vsi->max_frame = I40E_MAX_RXBUFFER;
> -		vsi->rx_buf_len = I40E_RXBUFFER_2048;
> +	vsi->max_frame = I40E_MAX_RXBUFFER;
> +	vsi->rx_buf_len = i40e_calculate_vsi_rx_buf_len(vsi);
> +
>  #if (PAGE_SIZE < 8192)
> -	} else if (!I40E_2K_TOO_SMALL_WITH_PADDING &&
> -		   (vsi->netdev->mtu <= ETH_DATA_LEN)) {
> +	if (vsi->netdev && !I40E_2K_TOO_SMALL_WITH_PADDING &&
> +	    (vsi->netdev->mtu <= ETH_DATA_LEN))
>  		vsi->max_frame = I40E_RXBUFFER_1536 - NET_IP_ALIGN;
> -		vsi->rx_buf_len = I40E_RXBUFFER_1536 - NET_IP_ALIGN;
>  #endif
> -	} else {
> -		vsi->max_frame = I40E_MAX_RXBUFFER;
> -		vsi->rx_buf_len = (PAGE_SIZE < 8192) ? I40E_RXBUFFER_3072 :
> -						       I40E_RXBUFFER_2048;
> -	}
>  
>  	/* set up individual rings */
>  	for (i = 0; i < vsi->num_queue_pairs && !err; i++)
> @@ -13265,7 +13283,7 @@ static int i40e_xdp_setup(struct i40e_vsi *vsi, struct bpf_prog *prog,
>  	int i;
>  
>  	/* Don't allow frames that span over multiple buffers */
> -	if (frame_size > vsi->rx_buf_len) {
> +	if (frame_size > i40e_calculate_vsi_rx_buf_len(vsi)) {
>  		NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP");
>  		return -EINVAL;
>  	}

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf Of
> Mateusz Palczewski
> Sent: Friday, October 14, 2022 3:33 PM
> To: intel-wired-lan@lists.osuosl.org
> Cc: Staszewski, BartoszX <bartoszx.staszewski@intel.com>
> Subject: [Intel-wired-lan] [PATCH net v1] i40e: fix xdp_redirect logs error
> message when testing with MTU=1500
> 
> From: Bartosz Staszewski <bartoszx.staszewski@intel.com>
> 
> The driver is currently logging an error message "MTU too large to enable
> XDP"
> when trying to enable XDP on totally normal MTU.
> 
> This was caused by whenever the  interface was down, function i40e_xdp
> was passing vsi->rx_buf_len field to i40e_xdp_setup() which was equal 0.
> i40e_open() then  calls i40e_vsi_configure_rx() which configures that field,
> but that only happens when interface is up.
> When it is down, i40e_open() is not being called, thusvsi->rx_buf_len which
> causes the bug is not set.
> 
> Solution for this is calculate buffer length in newly created function -
> i40e_calculate_vsi_rx_buf_len() that return actual buffer length. Buffer
> length is being calculated based on the same rules applied previously in
> i40e_vsi_configure_rx() function.
> 
> Fixes: 613142b0bb88 ("i40e: Log error for oversized MTU on device")
> Signed-off-by: Bartosz Staszewski <bartoszx.staszewski@intel.com>
> Signed-off-by: Mateusz Palczewski <mateusz.palczewski@intel.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c | 42 +++++++++++++++------
>  1 file changed, 30 insertions(+), 12 deletions(-)
> 
Tested-by: Shwetha Nagaraju <Shwetha.nagaraju@intel.com>