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

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files 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;