Re: [PATCH net] net/mlx4_en: Don't reuse RX page when XDP is set

[David Miller <davem@davemloft.net>]

From: Tariq Toukan <tariqt@mellanox.com>
Date: Sun, 15 Jul 2018 13:54:39 +0300

> From: Saeed Mahameed <saeedm@mellanox.com>
> 
> When a new rx packet arrives, the rx path will decide whether to reuse
> the remainder of the page or not according to one of the below conditions:
> 1. frag_info->frag_stride == PAGE_SIZE / 2
> 2. frags->page_offset + frag_info->frag_size > PAGE_SIZE;
> 
> The first condition is no met for when XDP is set.
> For XDP, page_offset is always set to priv->rx_headroom which is
> XDP_PACKET_HEADROOM and frag_info->frag_size is around mtu size + some
> padding, still the 2nd release condition will hold since
> XDP_PACKET_HEADROOM + 1536 < PAGE_SIZE, as a result the page will not
> be released and will be _wrongly_ reused for next free rx descriptor.
> 
> In XDP there is an assumption to have a page per packet and reuse can
> break such assumption and might cause packet data corruptions.
> 
> Fix this by adding an extra condition (!priv->rx_headroom) to the 2nd
> case to avoid page reuse when XDP is set, since rx_headroom is set to 0
> for non XDP setup and set to XDP_PACKET_HEADROOM for XDP setup.
> 
> No additional cache line is required for the new condition.
> 
> Fixes: 34db548bfb95 ("mlx4: add page recycling in receive path")
> Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
> Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
> Suggested-by: Martin KaFai Lau <kafai@fb.com>

Applied and queued up for -stable.