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[35.245.46.111]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5ec69bba011sm8346081e0c.5.2026.11.01.07.12.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 01 Nov 2026 07:12:30 -0800 (PST) Date: Sun, 01 Nov 2026 10:12:30 -0500 From: Willem de Bruijn To: Steffen Trumtrar , "Michael S. Tsirkin" , Xuan Zhuo , "David S. Miller" , Jakub Kicinski , Paolo Abeni , Richard Cochran , Willem de Bruijn , Andrew Lunn , =?UTF-8?B?RXVnZW5pbyBQw6lyZXo=?= , Jason Wang , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Eric Dumazet Cc: Steffen Trumtrar , virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kvm@vger.kernel.org Message-ID: In-Reply-To: <20261026-v6-7-topic-virtio-net-ptp-v4-5-008af03cd43b@pengutronix.de> References: <20261026-v6-7-topic-virtio-net-ptp-v4-0-008af03cd43b@pengutronix.de> <20261026-v6-7-topic-virtio-net-ptp-v4-5-008af03cd43b@pengutronix.de> Subject: Re: [PATCH RFC v4 5/6] virtio-net: add XDP rx timestamp metadata X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Steffen Trumtrar wrote: > For the skb, the timestamp is read from the header before the XDP > program runs, so XDP_PASS keeps it even if the program changes the > packet. XDP therefore works with rx timestamping enabled. > = > Add xmo_rx_timestamp so XDP programs can read the timestamp with > bpf_xdp_metadata_rx_timestamp(). It returns -ENODATA if timestamping > is not enabled or the device did not timestamp the packet. Install the > metadata ops also if only VIRTIO_NET_F_RX_TSTAMP is negotiated; > rx_hash returns -ENODATA then. > = > Like virtnet_xdp_rx_hash(), the callback finds the header relative to > xdp->data, so it has to be called before bpf_xdp_adjust_head(). > = > Signed-off-by: Steffen Trumtrar > Assisted-by: Claude:claude-opus-5-5 > --- > drivers/net/virtio_net.c | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > = > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 23af10c613b48..e79b65653fad7 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -6848,8 +6848,30 @@ static int virtnet_xdp_rx_hash(const struct xdp_= md *_ctx, u32 *hash, > return 0; > } > = > +static int virtnet_xdp_rx_timestamp(const struct xdp_md *_ctx, u64 *ti= mestamp) > +{ > + const struct xdp_buff *xdp =3D (void *)_ctx; > + const struct virtio_net_common_hdr *hdr; > + struct virtnet_info *vi; > + u64 tstamp; > + > + vi =3D netdev_priv(xdp->rxq->dev); > + if (!READ_ONCE(vi->hwts_rx_en)) > + return -ENODATA; > + > + hdr =3D (const struct virtio_net_common_hdr *)(xdp->data - vi->hdr_le= n); Reading `hdr->tstamp` in place from `xdp->data - vi->hdr_len` violate= s the XDP metadata area contract (`Documentation/networking/xdp-rx-metadata.rst= `: drivers must copy device-reserved metadata out of `[data_hard_start, data)` b= efore presenting the frame to XDP) and breaks standard XDP metadata consume= rs: - `hdr->tstamp` sits at `[xdp->data - 8, xdp->data)`. Standard XDP pr= ograms=E2=80=94such as `tools/testing/selftests/bpf/progs/xdp_hw_metadata.c`=E2=80=94ca= ll `bpf_xdp_adjust_meta(ctx, -(int)sizeof(struct xdp_meta))` first, in= itialize fields in `meta` (e.g. `meta->hint_valid =3D 0` at `[xdp->data - 4,= xdp->data)`), and only then call `bpf_xdp_metadata_rx_timestamp(ctx, &meta->rx_ti= mestamp)`. Initializing `meta` overwrites `hdr->tstamp` (and `hdr->hash_v1_hdr= `) before this kfunc runs. - Calling `bpf_xdp_adjust_head()` before reading metadata also shifts= `xdp->data`, reading arbitrary bytes at `xdp->data - vi->hdr_len`. Wrap `struct xdp_buff` in a driver struct on the stack (`container_of= `, and in `struct xdp_buff_xsk`'s `cb` verified with `XSK_CHECK_PRIV_TYPE()` fo= r AF_XDP, matching `gve`/`igc`/`ice`/`mlx5`) and stash `tstamp` (already extrac= ted in `receive_buf()` and `virtnet_receive_xsk_buf()` before XDP runs) and = the hash fields before `bpf_prog_run_xdp()`.