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Tue, 13 Oct 2026 01:32:03 -0700 (PDT) Date: Tue, 13 Oct 2026 10:32:03 +0200 From: Lorenzo Bianconi To: Nicolai Buchwitz 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 Message-ID: References: <20261012-stmmac-rx-mb-v6-0-2225050915c1@oss.qualcomm.com> <20261012-stmmac-rx-mb-v6-3-2225050915c1@oss.qualcomm.com> <3a483a6fbd86f50a02435932fe4a7ea3@tipi-net.de> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="3qwKvKFoaOiXYisH" Content-Disposition: inline In-Reply-To: <3a483a6fbd86f50a02435932fe4a7ea3@tipi-net.de> X-Proofpoint-GUID: RU1vuv3KO2SQNdGTRITNPeAirvEesTnx X-Authority-Analysis: v=2.4 cv=JJuuIMKb c=1 sm=1 tr=0 ts=6acdec86 cx=c_pps a=HLyN3IcIa5EE8TELMZ618Q==:117 a=WpTaRW6qxYHRGzLzQsVYzg==:17 a=660iZSQnnn4A:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yx91gb_oNiZeI1HMLzn7:22 a=VeR9IiojQdXVVGmY0-kA:9 a=CjuIK1q_8ugA:10 a=hNWK7rNVVTdq26VXPtYA:9 a=bTQJ7kPSJx9SKPbeHEYW:22 X-Proofpoint-Spam-Info: AW1haW4tMjYxMDEzMDAzMyBTYWx0ZWRfX0BtXJtDUWu8i bBUNJCLoN8ITdMPoH8gjDAUjRPnwasWk7VCo+Yz2U06/9dEPfVmOxIfuToB41XKlFOY7gLzjvwb JcZmjWKh9nxQU8z8WMIpPaL7RVU4rpo= X-Proofpoint-ORIG-GUID: RU1vuv3KO2SQNdGTRITNPeAirvEesTnx X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDEzMDAzMyBTYWx0ZWRfXzfJHkr8YGhCc 86CSag9OBjjkAoYqOqGzEEkDNHhHp7t166hGprmqsP3ZvJlP8AjcoW7c4t7fUNsyuW+TZpCyrDs AIfsF1qG6YPfTaZavyWgfDpi+yJDDEjWeYAp5oSaS/khjSuBNR6lyyeFdv66oA9eAn17aO3Enrc Dcg9JEtY07czIoUH0m0kMIVs3+D82eqVGz10O6PEQ6yRZSxPRTUSS9OqkaguSI8PFOA9dBZLiYr vXkU0WImv4rla1a37IF18SVswki51PADlG5hxttaRcxwjDKFQGs4IYprZWZg6KfsB7orxgXRraw 8tEsiGLikw+XBKfxXdPAmhTL63Uoyr4x5wb78bm60vp7Czx0+t1YOgSWnqTVTV8N+6fVrZSnriq N0XexUaZod1VnFvhEnocbiks151SWTg9Ok9RcxUy3IulNo7yzn/sX5qCmLxoKM5OSjX4nXqhdxE mGNgcI4kub/+BvGVBfA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-10-13_01,2026-10-09_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 clxscore=1015 malwarescore=0 lowpriorityscore=0 impostorscore=0 adultscore=0 phishscore=0 priorityscore=1501 spamscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610080000 definitions=main-2610130033 --3qwKvKFoaOiXYisH Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Oct 13, Nicolai Buchwitz wrote: > Hi Lorenzo >=20 > On 13.10.2026 10:17, Lorenzo Bianconi wrote: > > On Oct 12, Nicolai Buchwitz wrote: >=20 > > [...] >=20 > > > > 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 *pr= iv, > > > > int limit, u32 queue) > > > > > > > > if (priv->extend_desc) > > > > stmmac_rx_extended_status(priv, &priv->xstats, rx_q->dma_erx + > > > > entry); > > > > - if (unlikely(status =3D=3D discard_frame)) { > > > > - page_pool_put_page(rx_q->page_pool, buf->page, 0, true); > > > > - buf->page =3D NULL; > > > > + > > > > + if (unlikely(!error && status =3D=3D discard_frame)) { > > > > error =3D 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 =3D 1; > > > > + } > > >=20 > > > 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? > > >=20 > > > 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. > > >=20 > > > 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? > >=20 > > Hi Nicolai, > >=20 > > 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: > >=20 > > ... > > buf2_len =3D stmmac_rx_buf2_len(priv, p, status, len); > > len +=3D buf2_len; > >=20 > > if (unlikely(stmmac_xdp_is_enabled(priv) && buf2_len)) { > > rx_dropped++; > > dev_kfree_skb(skb); > > goto next; > > } > > ... > >=20 > > Is my understanding correct? >=20 > Yes, exactly. >=20 > 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. >=20 > Maybe extend the "We do not support SG in XDP mode" comment to cover > this case too. ack, thx for the review. I will fix it in v7. Regards, Lorenzo >=20 > > [...] >=20 > Thanks, > Nicolai --3qwKvKFoaOiXYisH Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTquNwa3Txd3rGGn7Y6cBh0uS2trAUCas3sgwAKCRA6cBh0uS2t rEjBAP9gErlRqvxFcDyFsfPFSFOkj0MTST4iWeXLN6NZgNjN7wD8DWWqfrjLXqPl Dp1q1qQAQUSjZYRFz2ogR2tzHG0Eeg4= =mHzj -----END PGP SIGNATURE----- --3qwKvKFoaOiXYisH--