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[34.86.60.15]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c07c6088aesm602311185a.48.2025.02.17.17.45.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Feb 2025 17:45:44 -0800 (PST) Date: Mon, 17 Feb 2025 20:45:44 -0500 From: Willem de Bruijn To: Marcus Wichelmann , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: willemdebruijn.kernel@gmail.com, jasowang@redhat.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, mykolal@fb.com, shuah@kernel.org, hawk@kernel.org, marcus.wichelmann@hetzner-cloud.de Message-ID: <67b3e64856f5d_c0e2529442@willemb.c.googlers.com.notmuch> In-Reply-To: <20250217172308.3291739-3-marcus.wichelmann@hetzner-cloud.de> References: <20250217172308.3291739-1-marcus.wichelmann@hetzner-cloud.de> <20250217172308.3291739-3-marcus.wichelmann@hetzner-cloud.de> Subject: Re: [PATCH bpf-next v2 2/6] net: tun: enable transfer of XDP metadata to skb Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Marcus Wichelmann wrote: > When the XDP metadata area was used, it is expected that the same > metadata can also be accessed from TC, as can be read in the description > of the bpf_xdp_adjust_meta helper function. In the tun driver, this was > not yet implemented. > > To make this work, the skb that is being built on XDP_PASS should know > of the current size of the metadata area. This is ensured by adding > calls to skb_metadata_set. For the tun_xdp_one code path, an additional > check is necessary to handle the case where the externally initialized > xdp_buff has no metadata support (xdp->data_meta == xdp->data + 1). > > More information about this feature can be found in the commit message > of commit de8f3a83b0a0 ("bpf: add meta pointer for direct access"). > > Signed-off-by: Marcus Wichelmann > --- > drivers/net/tun.c | 21 ++++++++++++++++++--- > 1 file changed, 18 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index c95ab9c46bd2..3dde6cd29a84 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -1604,7 +1604,8 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile, > > static struct sk_buff *__tun_build_skb(struct tun_file *tfile, > struct page_frag *alloc_frag, char *buf, > - int buflen, int len, int pad) > + int buflen, int len, int pad, > + int metasize) > { > struct sk_buff *skb = build_skb(buf, buflen); > > @@ -1613,6 +1614,8 @@ static struct sk_buff *__tun_build_skb(struct tun_file *tfile, > > skb_reserve(skb, pad); > skb_put(skb, len); > + if (metasize) > + skb_metadata_set(skb, metasize); > skb_set_owner_w(skb, tfile->socket.sk); > > get_page(alloc_frag->page); > @@ -1672,6 +1675,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun, > char *buf; > size_t copied; > int pad = TUN_RX_PAD; > + int metasize = 0; > int err = 0; > > rcu_read_lock(); > @@ -1699,7 +1703,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun, > if (hdr->gso_type || !xdp_prog) { > *skb_xdp = 1; > return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, > - pad); > + pad, metasize); > } > > *skb_xdp = 0; > @@ -1734,12 +1738,18 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun, > > pad = xdp.data - xdp.data_hard_start; > len = xdp.data_end - xdp.data; > + > + /* It is known that the xdp_buff was prepared with metadata > + * support, so no additional check is necessary. > + */ > + metasize = xdp.data - xdp.data_meta; > } > bpf_net_ctx_clear(bpf_net_ctx); > rcu_read_unlock(); > local_bh_enable(); > > - return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, pad); > + return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, pad, > + metasize); > > out: > bpf_net_ctx_clear(bpf_net_ctx); > @@ -2456,6 +2466,7 @@ static int tun_xdp_one(struct tun_struct *tun, > struct sk_buff_head *queue; > u32 rxhash = 0, act; > int buflen = hdr->buflen; > + int metasize = 0; > int ret = 0; > bool skb_xdp = false; > struct page *page; > @@ -2510,6 +2521,10 @@ static int tun_xdp_one(struct tun_struct *tun, > skb_reserve(skb, xdp->data - xdp->data_hard_start); > skb_put(skb, xdp->data_end - xdp->data); > > + metasize = max(xdp->data - xdp->data_meta, 0); Is it ever possible for xdp->data_meta to be greater than xdp->data? This is pointer arithmetic, which is a bit complex wrt type. This is likely ptrdiff_t, which is signed. But may want to use max_t(int, to make this more explicit. > + if (metasize) > + skb_metadata_set(skb, metasize); > + Technically not needed as skb_metadata_clear is just skb_metadata_set(skb, 0). But fine to test and elide. > if (virtio_net_hdr_to_skb(skb, gso, tun_is_lttle_endian(tun))) { > atomic_long_inc(&tun->rx_frame_errors); > kfree_skb(skb); > -- > 2.43.0 >