net/mlx5e: xsk: Discard unaligned XSK frames on striding RQ

Striding RQ uses MTT page mapping, where each page corresponds to an XSK
frame. MTT pages have alignment requirements, and XSK frames don't have
any alignment guarantees in the unaligned mode. Frames with improper
alignment must be discarded, otherwise the packet data will be written
at a wrong address.

Fixes: 282c0c798f ("net/mlx5e: Allow XSK frames smaller than a page")
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Link: https://lore.kernel.org/r/20220729121356.3990867-1-maximmi@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.h

@@ -7,6 +7,8 @@
 #include "en.h"
 #include <net/xdp_sock_drv.h>
 
+#define MLX5E_MTT_PTAG_MASK 0xfffffffffffffff8ULL
+
 /* RX data path */
 
 struct sk_buff *mlx5e_xsk_skb_from_cqe_mpwrq_linear(struct mlx5e_rq *rq,
@@ -21,6 +23,7 @@ struct sk_buff *mlx5e_xsk_skb_from_cqe_linear(struct mlx5e_rq *rq,
 static inline int mlx5e_xsk_page_alloc_pool(struct mlx5e_rq *rq,
 					    struct mlx5e_dma_info *dma_info)
 {
+retry:
 	dma_info->xsk = xsk_buff_alloc(rq->xsk_pool);
 	if (!dma_info->xsk)
 		return -ENOMEM;
@@ -32,6 +35,17 @@ static inline int mlx5e_xsk_page_alloc_pool(struct mlx5e_rq *rq,
 	 */
 	dma_info->addr = xsk_buff_xdp_get_frame_dma(dma_info->xsk);
 
+	/* MTT page mapping has alignment requirements. If they are not
+	 * satisfied, leak the descriptor so that it won't come again, and try
+	 * to allocate a new one.
+	 */
+	if (rq->wq_type == MLX5_WQ_TYPE_LINKED_LIST_STRIDING_RQ) {
+		if (unlikely(dma_info->addr & ~MLX5E_MTT_PTAG_MASK)) {
+			xsk_buff_discard(dma_info->xsk);
+			goto retry;
+		}
+	}
+
 	return 0;
 }
 

include/net/xdp_sock_drv.h

@@ -95,6 +95,13 @@ static inline void xsk_buff_free(struct xdp_buff *xdp)
 	xp_free(xskb);
 }
 
+static inline void xsk_buff_discard(struct xdp_buff *xdp)
+{
+	struct xdp_buff_xsk *xskb = container_of(xdp, struct xdp_buff_xsk, xdp);
+
+	xp_release(xskb);
+}
+
 static inline void xsk_buff_set_size(struct xdp_buff *xdp, u32 size)
 {
 	xdp->data = xdp->data_hard_start + XDP_PACKET_HEADROOM;
@@ -238,6 +245,10 @@ static inline void xsk_buff_free(struct xdp_buff *xdp)
 {
 }
 
+static inline void xsk_buff_discard(struct xdp_buff *xdp)
+{
+}
+
 static inline void xsk_buff_set_size(struct xdp_buff *xdp, u32 size)
 {
 }