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 F24FECA9ED2 for ; Mon, 12 Oct 2026 21:04:28 +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=ATDlnVkVpmBsbQi4Z42Xo1+upTwPMCBzGpQyazaRSrc=; b=vntFgbhNg4ASCEDc+lUoX65uxh MCk3LIqX5UuVfp7RlTxQcVzDzh1dbjr/SC2WiMwx2lP3eJHZU7/0GMYbIGHVzmEESTn7yeFnJFV19 QieyHG5F/hpcAqS/H+Ahd1ZrPmGkD2IXKKpAxnxRvIRXDns6g1gTrVTVp0nSYkYp1FHFWs5rHRVcx vVapdQHXW1y1OIwT4tD1WM6opZdTWScugOQ3jVcZjL8eOWujCAPaHTm3GQa6lWYbnyJ9wR+21eMl1 naHse62rvd9eNNpup6hcHrw9zCLnMyBLHPkSZUldb5XA3Jix1pYlkeSjC/yU35FkogNJUsK8tg4Da 3nrLwWjA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGNC1-0000000BWIs-26J0; Mon, 12 Oct 2026 21:04:21 +0000 Received: from mail.tipi-net.de ([2a03:4000:43:185::1]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xGNBx-0000000BWIE-0N42 for linux-arm-kernel@lists.infradead.org; Mon, 12 Oct 2026 21:04:19 +0000 Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id D0919A1310; Mon, 12 Oct 2026 23:04:11 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tipi-net.de; s=dkim; t=1791839054; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=ATDlnVkVpmBsbQi4Z42Xo1+upTwPMCBzGpQyazaRSrc=; b=k9r/oLnDGvjr3FmAMuH3CPaV+y2P+c3qben785WrqLhJh6pNaTakZQNJ2ky9wt6Fs+bsOj 3WSgg2NAc5OKhJX23eXNt1jiABziDNN2fCCMwcKeqME3fBwIqAJt440qMlGsOU+rpzeAH7 72lLMvjBBi1UQli8/iGnDKkwSWxF9EaTsEf90YetDK4Z4v07vpGCsTx0cIggwISc/JSVRH IYn3lkSC16pe8NfQCQ5/N024S+AMypBUpNCWml7VEbP06nEbjB/JCOittk0yd1IxPN9CZb CeNkg8TM8nk2zYFMHSgeS3CamxRvBPKWzjCjMl6V2M/99r7QGb8ry4VxOKAINA== MIME-Version: 1.0 Date: Mon, 12 Oct 2026 23:04:11 +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: <20261012-stmmac-rx-mb-v6-3-2225050915c1@oss.qualcomm.com> References: <20261012-stmmac-rx-mb-v6-0-2225050915c1@oss.qualcomm.com> <20261012-stmmac-rx-mb-v6-3-2225050915c1@oss.qualcomm.com> 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-20261012_140418_557850_CDA73479 X-CRM114-Status: GOOD ( 28.92 ) 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 Hi Lorenzo On 12.10.2026 18:44, Lorenzo Bianconi wrote: > stmmac_rx() runs the XDP program once per descriptor buffer and uses > skb == NULL as the only marker for the start of a frame. A frame larger > than one buffer is split by the hardware across several descriptors; > GMAC4 enables jumbo frames unconditionally (GMAC_CONFIG_JE in > GMAC_CORE_INIT), so an on-link peer can deliver such a frame even when > the interface MTU is left at 1500. > > When an XDP verdict ends a non-last descriptor, skb is cleared and the > next descriptor of the same hardware frame is parsed as a new frame. > For XDP_CONSUMED this happens via read_again with len preserved, so > stmmac_rx_buf1_len() then returns min(dma_buf_sz, plen - len) for the > last descriptor, which can be as small as 0-3 bytes. buf1_len -= > ETH_FCS_LEN underflows and xdp_prepare_buff() puts data_end far past > data; on XDP_PASS this produces an skb whose length is close to 4G that > reaches the network stack (skb->tail and skb->len are 32-bit and wrap > below skb->end, so skb_over_panic() does not fire). A 4+ byte tail is > instead offered to the XDP program and delivered as a standalone > mid-payload Ethernet frame on XDP_PASS. XDP_TX/XDP_REDIRECT instead > falls through to the next iteration, resetting the running length, so > the tail is re-parsed as a full-size new frame. > > XDP does not support scatter-gather frames until the multi-buffer > rework, so drop the whole frame instead: mark it as errored as soon as > a non-last descriptor is seen while an XDP program is attached, drain > and release every descriptor - including the last - and account the > frame once in rx_dropped. Removing the re-parse lets both XDP verdict > branches simply complete the packet via next. > > Note: the subsequent "net: stmmac: rework stmmac_rx to support XDP rx > multi-buff" accumulates the whole frame into a single xdp_buff and > supersedes this patch; the fix is kept so the net portion of the series > stands on its own. > > Fixes: 5fabb01207a2 ("net: stmmac: Add initial XDP support") > Signed-off-by: Lorenzo Bianconi > --- > drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 28 > ++++++++++------------- > 1 file changed, 12 insertions(+), 16 deletions(-) > > 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? > [...] Thanks, Nicolai