From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.tipi-net.de (mail.tipi-net.de [194.13.80.246]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0639E4F405D; Mon, 19 Oct 2026 12:30:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=194.13.80.246 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792413066; cv=none; b=HH+Vo9SHTDlXaLFGimDl5xIBnFC/LQgkgNqSWI50DJRg/9jNA7iW1AFDt/7NdvbB0zItJd+uNrROrxVmpk0kChZhz7JZ0yT6dEmNOVKk1u1oVzIunquS1sOwfAhCVhJsALrhU9jRswnNfHuYH6xYQ5Z9o5ZWRtMSsynlBP8g8OE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792413066; c=relaxed/simple; bh=YmBNLpGwEJ5g2wzB992hE03maLroJhYJZLMXy+jysJE=; h=MIME-Version:Date:From:To:Cc:Subject:In-Reply-To:References: Message-ID:Content-Type; b=MDkW5P5Im+dGemmaK4T3VmV5lgMKqJRgqw5SSY/J7sQXxbu2TtB0RpKj/RcC5chptHBGCqEOXwnVtVPTRlmf2eAI8GQsQnVYA6nAVLvpDzenxbRD6xV2M0hebENgcKA6C48QpYNK+p3brZde0WUOHPI/n/rZ6UqY3vYQ1Z273Y0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tipi-net.de; spf=pass smtp.mailfrom=tipi-net.de; dkim=pass (2048-bit key) header.d=tipi-net.de header.i=@tipi-net.de header.b=JT7G+fFQ; arc=none smtp.client-ip=194.13.80.246 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tipi-net.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=tipi-net.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=tipi-net.de header.i=@tipi-net.de header.b="JT7G+fFQ" Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id E2831A15A5; Mon, 19 Oct 2026 14:30:41 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tipi-net.de; s=dkim; t=1792413046; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=5YPK5QrD2Biz8WIt271WspbuAzVZVpswCa9MB98GM1c=; b=JT7G+fFQL8UZU1tGRwhUPlEeeGyOPklh3lTZgt6QBqhkNKQ39YJWB2imB+euV3PKNylpXg 8hmMFIebrSnkz0uxql1S/azwpbuV/4afb+FnCR4lSQBQEQc/WZij0O6tayPU0iz9Esa9G9 gUaVR2o/Va51J13fFMSpzfnZsmBm+/geEvAXAngzKopeKTh+Uo1I0VRX9w6dmHM5O3Wjte nMdWFTFoEId761r9qoxQhjLP/g2dv1t7EfmwBz3MkqgBD8Zanl888bkv9qBjXhxRxhd4MF 6RH30UV+a8QK98WkGlAVaOTxOZCGfvUWlnW+ulM3DM0NCwe4s0YyEGWfzcxSjQ== Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Mon, 19 Oct 2026 14:30:41 +0200 From: Nicolai Buchwitz To: Lorenzo Bianconi Cc: Maxime Chevallier , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Maxime Coquelin , Alexandre Torgue , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Jose Abreu , Ong Boon Leong , netdev@vger.kernel.org, linux-arm-kernel@lists.infradead.org, bpf@vger.kernel.org Subject: Re: [PATCH net-next v8 2/5] net: stmmac: drop split frames on AF_XDP zero-copy RX In-Reply-To: References: <20261018-stmmac-rx-mb-v8-0-5f58c0b25849@oss.qualcomm.com> <20261018-stmmac-rx-mb-v8-2-5f58c0b25849@oss.qualcomm.com> <8c9e47e535ecc8190fa1c93ad5b5e32a@tipi-net.de> Message-ID: X-Sender: nb@tipi-net.de Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit X-Last-TLS-Session-Version: TLSv1.3 On 19.10.2026 14:17, Lorenzo Bianconi wrote: >> Hi Lorenzo >> >> On 18.10.2026 19:07, Lorenzo Bianconi wrote: >> > stmmac_rx_zc() assumes a 1:1 mapping between a received frame and an >> > XSK pool buffer and drops any frame that spans more than one RX >> > descriptor: >> > >> > /* XSK pool expects RX frame 1:1 mapped to XSK buffer */ >> > if (likely(status & rx_not_ls)) { >> > xsk_buff_free(buf->xdp); >> > buf->xdp = NULL; >> > dirty++; >> > count++; >> > goto read_again; >> > } >> > >> > The non-last descriptors are freed and dropped, but the frame is not >> > marked as errored. When the poll reaches the last descriptor of the >> > same frame, error is still 0, so the fragment is handled as a complete >> > frame: it is passed to the XDP program, copied into an skb on XDP_PASS, >> > or converted for XDP_TX. The tail starts in the middle of the original >> > payload at a predictable offset and, parsed as a fresh frame (len == 0), >> > stmmac_rx_buf1_len() reports the full dma_buf_sz length for it even >> > though the DMA engine only wrote the tail remainder into that buffer, so >> > the reads extend past the received bytes and can reach beyond the end of >> > the XSK pool buffer. GMAC4 always enables jumbo frames (GMAC_CONFIG_JE >> > in GMAC_CORE_INIT), so an on-link peer can trigger such a split even >> > when the interface MTU is left at 1500. >> > >> > Set error when the 1:1 mapping check drops a descriptor, so the >> > remaining descriptors of the frame - including the last one - are >> > drained and released with xsk_buff_free() instead of being processed as >> > a new frame. Account every freed buffer with dirty and count the >> > dropped frame once in the poll budget / rx_pkt_n. The direct 1:1 >> > mapping drop also increments rx_dropped. >> > >> > Normalize the legacy normal and enhanced descriptor callbacks to report >> > rx_not_ls together with discard_frame for non-last descriptors. This >> > allows both stmmac_rx_zc() and stmmac_rx() to drain split frames on >> > dwmac100 and dwmac1000 instead of reparsing the final fragment as a new >> > packet. >> > >> > Fixes: bba2556efad6 ("net: stmmac: Enable RX via AF_XDP zero-copy") >> > Reviewed-by: Nicolai Buchwitz >> >> This grew quite a bit since v6 (legacy desc changes, stmmac_rx() etc), >> so my R-b should have been dropped. I had another look and two small >> notes below. > > Hi Nicolai, > > ack, right. > >> >> > Signed-off-by: Lorenzo Bianconi >> > --- >> >> > [...] >> >> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c >> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c >> > @@ -5695,18 +5695,21 @@ static int stmmac_rx_zc(struct stmmac_priv >> > *priv, int limit, u32 queue) >> > if (priv->extend_desc) >> > stmmac_rx_extended_status(priv, &priv->xstats, >> > rx_q->dma_erx + entry); >> > - if (unlikely(status == discard_frame)) { >> > - xsk_buff_free(buf->xdp); >> > - buf->xdp = NULL; >> > - dirty++; >> > + >> > + if (unlikely(status & discard_frame)) { >> > error = 1; >> > if (!priv->hwts_rx_en) >> > rx_errors++; >> > } >> >> There's no !error check here, so on the legacy descriptors a split >> frame now counts once per descriptor in rx_errors. stmmac_rx() in 3/5 >> counts it once. Could you add the !error check here too? > > ack, I agree we should align stmmac_rx() and stmmac_rx_zc(). In order > to avoid > reposting the full series for this change, do you agree to address it > as a > follow-up patch? Would be ok for me if nothing else is flagged in this version. In the end it will be Maxime's / the net dev maintainers decision :) > > Regards, > Lorenzo > >> >> > [...] >> >> > @@ -5883,7 +5887,8 @@ static int stmmac_rx(struct stmmac_priv *priv, int >> > limit, u32 queue) >> > >> > if (priv->extend_desc) >> > stmmac_rx_extended_status(priv, &priv->xstats, rx_q->dma_erx + >> > entry); >> > - if (unlikely(status == discard_frame)) { >> > + >> > + if (unlikely(status & discard_frame)) { >> >> AFAIU this also changes GMAC4: a frame with an error plus an IP header >> error returns discard_frame | csum_none, which the old "==" let >> through. Dropping it is right, but maybe worth a line in the commit >> message? >> >> > [...] >> >> With the !error check added: >> >> Reviewed-by: Nicolai Buchwitz >> >> Thanks, >> Nicolai