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 3E9B138E5DF; Tue, 13 Oct 2026 08:25:06 +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=1791879912; cv=none; b=tX56V6sTdcLvWuUW5hDoifyPXm308RlCf3l/hfmaXtVRRFQDbCkOwFBBIR8GLFETzvXEntu/8L6UbVL50MBTM94dE8nhzvTArAlXpnLIpTV4OEURfHNCYOQYUH7PbLdJwSf14vCOaPIkpV5jBVMGterbmXoSDa6mq7fHDlmT4ZA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791879912; c=relaxed/simple; bh=RbWbzjpqMkedbk8YK4D47wKdcaiIV95H7NKUfCthpPY=; h=MIME-Version:Date:From:To:Cc:Subject:In-Reply-To:References: Message-ID:Content-Type; b=PvPXoQY5VGV5dXr4WGojNzqcnhImtVwow21QrgRCPCFDdI80SehSInbjKgcYYuAkk8EPsbVHzmJQ4yn0l5iRajD80UJ/oy0s+Y5Ujr8OrlfNpCvKmQqbdMvvVCoiz/KovyG4H42PoPlOXKqDBxXjqO94udnY3zklrgRdZU8/dsE= 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=F1DSAf6Q; 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="F1DSAf6Q" Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 02888A157F; Tue, 13 Oct 2026 10:24:57 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tipi-net.de; s=dkim; t=1791879903; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=un+RWDxQ0LzJC8cAfHiPgnBCvaRRs7NxkrufLYrfb0U=; b=F1DSAf6QlLFcxhiZ+os9THDj3f+sbAiNkAbcOvc7wgcb7nYRfw+b5BKQUQQfM3NFfoYab6 sqz09NJu3BR+RYkULLhb8xHoBadK/hkQcL5LbLK7ibudtEBUAs/qRtzlf73RbndFGPl4hO bBdSgNVYPyd2NSgw44bR86LH8IZhN1DYOcgYbi9Chw4QkGJA1uK63hPHUMJHcApfzsyzr8 iNEc9RcKdjtSr7OXx8DR8JQROrkQvGA74G054NltmY8InbjHHiO6v6IyzmOA+bUrPF0fzO Yf3h6dDDtF4EGjrztPxoxBNISOEvhaziefwpdtkOTOu/krw3ZtnoZKuhz4OSSg== Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Tue, 13 Oct 2026 10:24:57 +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 v6 3/4] net: stmmac: drop multi-buffer frames in XDP mode In-Reply-To: References: <20261012-stmmac-rx-mb-v6-0-2225050915c1@oss.qualcomm.com> <20261012-stmmac-rx-mb-v6-3-2225050915c1@oss.qualcomm.com> Message-ID: <3a483a6fbd86f50a02435932fe4a7ea3@tipi-net.de> 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 Hi Lorenzo On 13.10.2026 10:17, Lorenzo Bianconi wrote: > On Oct 12, Nicolai Buchwitz wrote: > [...] >> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c >> > b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c >> > index 426bb68c9bbc..8c08d44fdbd3 100644 >> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c >> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c >> > @@ -5893,18 +5893,24 @@ 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)) { >> > - page_pool_put_page(rx_q->page_pool, buf->page, 0, true); >> > - buf->page = NULL; >> > + >> > + if (unlikely(!error && status == discard_frame)) { >> > error = 1; >> > if (!priv->hwts_rx_en) >> > rx_errors++; >> > } >> > >> > - if (unlikely(error && (status & rx_not_ls))) >> > - goto read_again; >> > + /* We do not support SG in XDP mode */ >> > + if (unlikely(!error && (status & rx_not_ls) && >> > + stmmac_xdp_is_enabled(priv))) { >> > + rx_dropped++; >> > + error = 1; >> > + } >> >> AFAIU GMAC4 and XGMAC always use the second buffer of a descriptor. If >> so, at MTU 1500 a frame of up to 3072 bytes can fit in one descriptor, >> and this check would not catch it? >> >> The XDP program would then only see the first buffer. With XDP_TX the >> frame is cut and sent too short. With XDP_PASS the second buffer is >> added >> after the program already decided. >> >> Patch 4 fixes this. But if this patch should work on its own, should >> it >> also drop the frame when buf2_len is not zero? Or am I missing >> something? > > Hi Nicolai, > > IIUC your comment we are missing the case where we have a single > descriptor > (rx_not_ls is not set in status) but the packet is splitted over buf1 > and buf2, > right? Something like: > > ... > buf2_len = stmmac_rx_buf2_len(priv, p, status, len); > len += buf2_len; > > if (unlikely(stmmac_xdp_is_enabled(priv) && buf2_len)) { > rx_dropped++; > dev_kfree_skb(skb); > goto next; > } > ... > > Is my understanding correct? Yes, exactly. I think skb is always NULL there in XDP mode, so the dev_kfree_skb() can go. Both pages stay in the slot and stmmac_rx_refill() reuses them, so nothing leaks. Maybe extend the "We do not support SG in XDP mode" comment to cover this case too. > [...] Thanks, Nicolai