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

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

[Tariq Toukan]

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>
CC: Eric Dumazet <edumazet@google.com>
---
 drivers/net/ethernet/mellanox/mlx4/en_rx.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
index 9f54ccbddea7..3360f7b9ee73 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
@@ -474,10 +474,10 @@ static int mlx4_en_complete_rx_desc(struct mlx4_en_priv *priv,
 {
 	const struct mlx4_en_frag_info *frag_info = priv->frag_info;
 	unsigned int truesize = 0;
+	bool release = true;
 	int nr, frag_size;
 	struct page *page;
 	dma_addr_t dma;
-	bool release;
 
 	/* Collect used fragments while replacing them in the HW descriptors */
 	for (nr = 0;; frags++) {
@@ -500,7 +500,11 @@ static int mlx4_en_complete_rx_desc(struct mlx4_en_priv *priv,
 			release = page_count(page) != 1 ||
 				  page_is_pfmemalloc(page) ||
 				  page_to_nid(page) != numa_mem_id();
-		} else {
+		} else if (!priv->rx_headroom) {
+			/* rx_headroom for non XDP setup is always 0.
+			 * When XDP is set, the above condition will
+			 * guarantee page is always released.
+			 */
 			u32 sz_align = ALIGN(frag_size, SMP_CACHE_BYTES);
 
 			frags->page_offset += sz_align;
-- 
1.8.3.1

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

[David Miller]

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.