openwrt/target/linux/layerscape/patches-5.4/701-net-0080-sdk_dpaa-store-the-skb-backpointer-in-the-skb-headro.patch

From 1f00fa355829b510beb900ce1136f40802e6076e Mon Sep 17 00:00:00 2001
From: Camelia Groza <camelia.groza@nxp.com>
Date: Mon, 10 Sep 2018 14:31:05 +0300
Subject: [PATCH] sdk_dpaa: store the skb backpointer in the skb headroom

The skb backpointer is stored right before the FMan buffer, in order to
avoid overwriting. The memory area storing the backpointer was outside of
the skb. This made it hard to guarantee its size.

This patch changes the layout of the skb at buffer seed time: the area
reserved for storing the skb backpointer is part of the skb's headroom.
This makes it easier to track if the backpointer can be safely stored
when recycling the buffer.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
---
 .../net/ethernet/freescale/sdk_dpaa/dpaa_eth_sg.c  | 33 ++++++++++++++++------
 1 file changed, 24 insertions(+), 9 deletions(-)

--- a/drivers/net/ethernet/freescale/sdk_dpaa/dpaa_eth_sg.c
+++ b/drivers/net/ethernet/freescale/sdk_dpaa/dpaa_eth_sg.c
@@ -82,8 +82,8 @@ static void dpa_bp_recycle_frag(struct d
 
 static int _dpa_bp_add_8_bufs(const struct dpa_bp *dpa_bp)
 {
+	void *new_buf, *fman_buf;
 	struct bm_buffer bmb[8];
-	void *new_buf;
 	dma_addr_t addr;
 	uint8_t i;
 	struct device *dev = dpa_bp->dev;
@@ -113,21 +113,37 @@ static int _dpa_bp_add_8_bufs(const stru
 
 		if (unlikely(!new_buf))
 			goto netdev_alloc_failed;
-		new_buf = PTR_ALIGN(new_buf + SMP_CACHE_BYTES, SMP_CACHE_BYTES);
+		new_buf = PTR_ALIGN(new_buf, SMP_CACHE_BYTES);
 
-		skb = build_skb(new_buf, DPA_SKB_SIZE(dpa_bp->size) +
-			SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
+		/* Apart from the buffer that will be used by the FMan, the
+		 * skb also guarantees enough space to hold the backpointer
+		 * in the headroom and the shared info at the end.
+		 */
+		skb = build_skb(new_buf,
+				SMP_CACHE_BYTES + DPA_SKB_SIZE(dpa_bp->size) +
+				SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
 		if (unlikely(!skb)) {
 			put_page(virt_to_head_page(new_buf));
 			goto build_skb_failed;
 		}
 
-		/* Store the skb back-pointer before the start of the buffer.
-		 * Otherwise it will be overwritten by the FMan.
+		/* Reserve SMP_CACHE_BYTES in the skb's headroom to store the
+		 * backpointer. This area will not be synced to, or
+		 * overwritten by, the FMan.
+		 */
+		skb_reserve(skb, SMP_CACHE_BYTES);
+
+		/* We don't sync the first SMP_CACHE_BYTES of the buffer to
+		 * the FMan. The skb backpointer is stored at the end of the
+		 * reserved headroom. Otherwise it will be overwritten by the
+		 * FMan.
+		 * The buffer synced with the FMan starts right after the
+		 * reserved headroom.
 		 */
-		DPA_WRITE_SKB_PTR(skb, skbh, new_buf, -1);
+		fman_buf = new_buf + SMP_CACHE_BYTES;
+		DPA_WRITE_SKB_PTR(skb, skbh, fman_buf, -1);
 
-		addr = dma_map_single(dev, new_buf,
+		addr = dma_map_single(dev, fman_buf,
 				dpa_bp->size, DMA_BIDIRECTIONAL);
 		if (unlikely(dma_mapping_error(dev, addr)))
 			goto dma_map_failed;
@@ -477,7 +493,6 @@ static struct sk_buff *__hot sg_fd_to_sk
 				 DMA_BIDIRECTIONAL);
 		if (i == 0) {
 			DPA_READ_SKB_PTR(skb, skbh, sg_vaddr, -1);
-			DPA_BUG_ON(skb->head != sg_vaddr);
 #ifdef CONFIG_FSL_DPAA_1588
 			if (priv->tsu && priv->tsu->valid &&
 			    priv->tsu->hwts_rx_en_ioctl)