From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id F3263CCF2D6 for ; Mon, 19 Oct 2026 12:31:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:Message-ID:References:In-Reply-To:Subject:Cc:To:From:Date: MIME-Version:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=5YPK5QrD2Biz8WIt271WspbuAzVZVpswCa9MB98GM1c=; b=kKmWCG7iCELJCB6RtlFFj1jv+4 LTCFjVjzZJohF+H68v3vlFgJMTMrICquUHnQ934Z7Hmzw+rwpGgAkou80yLWpxsQHUTwdvGCpRvNw utGNoDZisM94XkaKSCV7/m8gtr2ltN4Vbwk8uJaUAu1mKA1mDHYRwao58TI/G/LmH5Q6RRwysUwL6 eLbrLBrNRXlr5gCUrULm+JPumw70NsUq9skfJA0FJ7BDyNQ6Szz9Xmg7vud0GLYrwIQTGHj1Ffyhk zyTY84E/S0Cq0bi6s9h/nNit5/NXax/3VKAW87vN4Vp7TzZX2gwiONYumwgjRQ3gSp6z3deJROXsG mZC4sz/w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xImW0-00000007OQq-08dJ; Mon, 19 Oct 2026 12:30:56 +0000 Received: from mail.tipi-net.de ([194.13.80.246]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xImVv-00000007OPF-0JWS for linux-arm-kernel@lists.infradead.org; Mon, 19 Oct 2026 12:30:54 +0000 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== 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261019_053052_052396_5A9EBE80 X-CRM114-Status: GOOD ( 30.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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