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Date: Wed, 23 Jul 2025 17:19:47 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Meghana Malladi <m-malladi@ti.com>
Cc: <namcao@linutronix.de>, <jacob.e.keller@intel.com>, <sdf@fomichev.me>,
 <john.fastabend@gmail.com>, <hawk@kernel.org>, <daniel@iogearbox.net>,
 <ast@kernel.org>, <pabeni@redhat.com>, <edumazet@google.com>,
 <davem@davemloft.net>, <andrew+netdev@lunn.ch>, <bpf@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>,
 <linux-arm-kernel@lists.infradead.org>, <srk@ti.com>, Vignesh Raghavendra
 <vigneshr@ti.com>, Roger Quadros <rogerq@kernel.org>, <danishanwar@ti.com>
Subject: Re: [PATCH net] net: ti: icssg-prueth: Fix skb handling for
 XDP_PASS
Message-ID: <20250723171947.76995990@kernel.org>
In-Reply-To: <20250721124918.3347679-1-m-malladi@ti.com>
References: <20250721124918.3347679-1-m-malladi@ti.com>
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On Mon, 21 Jul 2025 18:19:18 +0530 Meghana Malladi wrote:
> diff --git a/drivers/net/ethernet/ti/icssg/icssg_common.c b/drivers/net/ethernet/ti/icssg/icssg_common.c
> index 12f25cec6255..a0e7def33e8e 100644
> --- a/drivers/net/ethernet/ti/icssg/icssg_common.c
> +++ b/drivers/net/ethernet/ti/icssg/icssg_common.c
> @@ -757,15 +757,12 @@ static int emac_rx_packet(struct prueth_emac *emac, u32 flow_id, u32 *xdp_state)
>  		xdp_prepare_buff(&xdp, pa, PRUETH_HEADROOM, pkt_len, false);
>  
>  		*xdp_state = emac_run_xdp(emac, &xdp, page, &pkt_len);
> -		if (*xdp_state == ICSSG_XDP_PASS)
> -			skb = xdp_build_skb_from_buff(&xdp);
> -		else
> +		if (*xdp_state != ICSSG_XDP_PASS)
>  			goto requeue;
> -	} else {
> -		/* prepare skb and send to n/w stack */
> -		skb = napi_build_skb(pa, PAGE_SIZE);
>  	}
>  
> +	/* prepare skb and send to n/w stack */
> +	skb = napi_build_skb(pa, PAGE_SIZE);
>  	if (!skb) {
>  		ndev->stats.rx_dropped++;
>  		page_pool_recycle_direct(pool, page);

I'm not sure this is correct. We seem to hardcode headroom to
PRUETH_HEADROOM lower in this function. If XDP adds or removes
network headers and then returns XDP_PASS we'll look for the packet 
at the wrong offset.

We just merged some XDP tests, could you try running 
tools/testing/selftests/drivers/net/xdp.py ? 
Some general instructions can be found here:
https://github.com/linux-netdev/nipa/wiki/Running-driver-tests

Not sure how stable the test is for all NICs but I think the 
 xdp.test_xdp_native_adjst_head_grow_data
test case will exercise what I'm suspecting will fail.