APPLIED X: [SRU][Xenial][PATCH] i40e: Limit TX descriptor count in cases where frag size is greater than 16K

[Stefan Bader]

On 12.09.2017 01:01, Dan Streetman wrote:
> From: Alexander Duyck <alexander.h.duyck at intel.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1713553
> 
> The i40e driver was incorrectly assuming that we would always be pulling
> no more than 1 descriptor from each fragment.  It is in fact possible for
> us to end up with the case where 2 descriptors worth of data may be pulled
> when a frame is larger than one of the pieces generated when aligning the
> payload to either 4K or pieces smaller than 16K.
> 
> To adjust for this we just need to make certain to test all the way to the
> end of the fragments as it is possible for us to span 2 descriptors in the
> block before us so we need to guarantee that even the last 6 descriptors
> have enough data to fill a full frame.
> 
> Change-ID: Ic2ecb4d6b745f447d334e66c14002152f50e2f99
> Signed-off-by: Alexander Duyck <alexander.h.duyck at intel.com>
> Tested-by: Andrew Bowers <andrewx.bowers at intel.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher at intel.com>
> (cherry-picked from 841493a3f64395b60554afbcaa17f4350f90e764 upstream)
> Signed-off-by: Dan Streetman <dan.streetman at canonical.com>
> ---
> This patch is already in Zesty/Artful kernels, and is a required
> follow-on patch to what was applied for lp bug 1700834.
> 
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c   | 7 ++-----
>  drivers/net/ethernet/intel/i40evf/i40e_txrx.c | 7 ++-----
>  2 files changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> index c57476633913..8cfb5fe972ba 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -2617,9 +2617,7 @@ bool __i40e_chk_linearize(struct sk_buff *skb)
>  		return false;
>  
>  	/* We need to walk through the list and validate that each group
> -	 * of 6 fragments totals at least gso_size.  However we don't need
> -	 * to perform such validation on the last 6 since the last 6 cannot
> -	 * inherit any data from a descriptor after them.
> +	 * of 6 fragments totals at least gso_size.
>  	 */
>  	nr_frags -= I40E_MAX_BUFFER_TXD - 2;
>  	frag = &skb_shinfo(skb)->frags[0];
> @@ -2650,8 +2648,7 @@ bool __i40e_chk_linearize(struct sk_buff *skb)
>  		if (sum < 0)
>  			return true;
>  
> -		/* use pre-decrement to avoid processing last fragment */
> -		if (!--nr_frags)
> +		if (!nr_frags--)
>  			break;
>  
>  		sum -= skb_frag_size(stale++);
> diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
> index f0646bc26d04..50d1dd278860 100644
> --- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
> @@ -1820,9 +1820,7 @@ bool __i40evf_chk_linearize(struct sk_buff *skb)
>  		return false;
>  
>  	/* We need to walk through the list and validate that each group
> -	 * of 6 fragments totals at least gso_size.  However we don't need
> -	 * to perform such validation on the last 6 since the last 6 cannot
> -	 * inherit any data from a descriptor after them.
> +	 * of 6 fragments totals at least gso_size.
>  	 */
>  	nr_frags -= I40E_MAX_BUFFER_TXD - 2;
>  	frag = &skb_shinfo(skb)->frags[0];
> @@ -1853,8 +1851,7 @@ bool __i40evf_chk_linearize(struct sk_buff *skb)
>  		if (sum < 0)
>  			return true;
>  
> -		/* use pre-decrement to avoid processing last fragment */
> -		if (!--nr_frags)
> +		if (!nr_frags--)
>  			break;
>  
>  		sum -= skb_frag_size(stale++);
> 
Applied to Xenial master-next

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