linux-kernel - [PATCH net] net: stmmac: fix the crash issue for zero copy XDP

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Message-Id: <20251204071332.1907111-1-wei.fang@nxp.com>
Date: Thu,  4 Dec 2025 15:13:32 +0800
From: Wei Fang <wei.fang@....com>
To: andrew+netdev@...n.ch,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	mcoquelin.stm32@...il.com,
	alexandre.torgue@...s.st.com,
	ast@...nel.org,
	daniel@...earbox.net,
	hawk@...nel.org,
	john.fastabend@...il.com,
	sdf@...ichev.me,
	rmk+kernel@...linux.org.uk,
	0x1207@...il.com,
	hayashi.kunihiko@...ionext.com,
	vladimir.oltean@....com,
	boon.leong.ong@...el.com
Cc: imx@...ts.linux.dev,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org,
	bpf@...r.kernel.org
Subject: [PATCH net] net: stmmac: fix the crash issue for zero copy XDP_TX action

There is a crash issue when running zero copy XDP_TX action, the crash
log is shown below.

[  216.122464] Unable to handle kernel paging request at virtual address fffeffff80000000
[  216.187524] Internal error: Oops: 0000000096000144 [#1]  SMP
[  216.301694] Call trace:
[  216.304130]  dcache_clean_poc+0x20/0x38 (P)
[  216.308308]  __dma_sync_single_for_device+0x1bc/0x1e0
[  216.313351]  stmmac_xdp_xmit_xdpf+0x354/0x400
[  216.317701]  __stmmac_xdp_run_prog+0x164/0x368
[  216.322139]  stmmac_napi_poll_rxtx+0xba8/0xf00
[  216.326576]  __napi_poll+0x40/0x218
[  216.408054] Kernel panic - not syncing: Oops: Fatal exception in interrupt

For XDP_TX action, the xdp_buff is converted to xdp_frame by
xdp_convert_buff_to_frame(). The memory type of the resulting xdp_frame
depends on the memory type of the xdp_buff. For page pool based xdp_buff
it produces xdp_frame with memory type MEM_TYPE_PAGE_POOL. For zero copy
XSK pool based xdp_buff it produces xdp_frame with memory type
MEM_TYPE_PAGE_ORDER0. However, stmmac_xdp_xmit_back() does not check the
memory type and always uses the page pool type, this leads to invalid
mappings and causes the crash. Therefore, check the xdp_buff memory type
in stmmac_xdp_xmit_back() to fix this issue.

Fixes: bba2556efad6 ("net: stmmac: Enable RX via AF_XDP zero-copy")
Signed-off-by: Wei Fang <wei.fang@....com>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c   | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 7b90ecd3a55e..a6664f300e4a 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -88,6 +88,7 @@ MODULE_PARM_DESC(phyaddr, "Physical device address");
 #define STMMAC_XDP_CONSUMED	BIT(0)
 #define STMMAC_XDP_TX		BIT(1)
 #define STMMAC_XDP_REDIRECT	BIT(2)
+#define STMMAC_XSK_CONSUMED	BIT(3)
 
 static int flow_ctrl = 0xdead;
 module_param(flow_ctrl, int, 0644);
@@ -4988,6 +4989,7 @@ static int stmmac_xdp_get_tx_queue(struct stmmac_priv *priv,
 static int stmmac_xdp_xmit_back(struct stmmac_priv *priv,
 				struct xdp_buff *xdp)
 {
+	bool zc = !!(xdp->rxq->mem.type == MEM_TYPE_XSK_BUFF_POOL);
 	struct xdp_frame *xdpf = xdp_convert_buff_to_frame(xdp);
 	int cpu = smp_processor_id();
 	struct netdev_queue *nq;
@@ -5004,9 +5006,18 @@ static int stmmac_xdp_xmit_back(struct stmmac_priv *priv,
 	/* Avoids TX time-out as we are sharing with slow path */
 	txq_trans_cond_update(nq);
 
-	res = stmmac_xdp_xmit_xdpf(priv, queue, xdpf, false);
-	if (res == STMMAC_XDP_TX)
+	/* For zero copy XDP_TX action, dma_map is true */
+	res = stmmac_xdp_xmit_xdpf(priv, queue, xdpf, zc);
+	if (res == STMMAC_XDP_TX) {
 		stmmac_flush_tx_descriptors(priv, queue);
+	} else if (res == STMMAC_XDP_CONSUMED && zc) {
+		/* xdp has been freed by xdp_convert_buff_to_frame(),
+		 * no need to call xsk_buff_free() again, so return
+		 * STMMAC_XSK_CONSUMED.
+		 */
+		res = STMMAC_XSK_CONSUMED;
+		xdp_return_frame(xdpf);
+	}
 
 	__netif_tx_unlock(nq);
 
@@ -5356,6 +5367,8 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue)
 			break;
 		case STMMAC_XDP_CONSUMED:
 			xsk_buff_free(buf->xdp);
+			fallthrough;
+		case STMMAC_XSK_CONSUMED:
 			rx_dropped++;
 			break;
 		case STMMAC_XDP_TX:
-- 
2.34.1