From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f50.google.com (mail-wm1-f50.google.com [209.85.128.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 78A752BE051 for ; Mon, 20 Jul 2026 10:24:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.50 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784543091; cv=none; b=SYschnWYFh4Gup8LGOTeme11g3G3xxOdFSFpoHNsLdgCVE5LlUs00u64M+Xi7Qm+OM/Idv4G51mIGZuY2XRIiH+ChCPVzJbKUFPhjkh8DAyMDRnCny5FpgfAulUgsdDWQwxzy7RQQWVvinitGewLESluxeQzMFREao7FfrCntbU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784543091; c=relaxed/simple; bh=ZQZICDYgbRgiUxmzpxgAJ9erLVWkdQLc9nJ8avEn+Vk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=RnLtgMggiLV7BLl6Xpc4IST81tBRe0kFkzm3/Uz9CR5v0vIdJEbW9/iYlo1y0Pl/ZN5SQluL7j0j01nVinExGA/t+P497IRdOoNFjOmkvMontM2eQA9mMtv4s+gV+J6KVEzBeJ5reyC4bvKRzD4txKQfsulV8eyvHwRmlj98kqg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=readmodwrite.com; spf=none smtp.mailfrom=readmodwrite.com; dkim=pass (2048-bit key) header.d=readmodwrite-com.20251104.gappssmtp.com header.i=@readmodwrite-com.20251104.gappssmtp.com header.b=vg5IcwTi; arc=none smtp.client-ip=209.85.128.50 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=readmodwrite.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=readmodwrite.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=readmodwrite-com.20251104.gappssmtp.com header.i=@readmodwrite-com.20251104.gappssmtp.com header.b="vg5IcwTi" Received: by mail-wm1-f50.google.com with SMTP id 5b1f17b1804b1-4954df200ddso14271685e9.0 for ; Mon, 20 Jul 2026 03:24:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=readmodwrite-com.20251104.gappssmtp.com; s=20251104; t=1784543089; x=1785147889; darn=vger.kernel.org; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to:content-type; bh=zd72l0RJ8ftcCUHhUbD81aNG9YQZtgyyjQP2cHWS9d4=; b=vg5IcwTim6+mko0v5reuGZG8ZIxKuY1jOOnPyegZZKYzqPyESW98Bgse4+tZfyjsUH BbDmk4bVMjgg5CUux2RYjSz5Wn27waC+NHp03PutvJNlJFCjKawqL3ijk3ub29LTAb/6 42l4ly/okxkVmher7uYz/dIQo3upJKc+8jgjpR3jwbweagqO+nRqSWZcHmc3i3BVD9yz q1TrdfydVJOjMs2X+ki17sOllSYUumDeDL59nuwir1oahVIPQnRaBDA5bgAk+4yr9Vbh /2pj1R6+BPN/HQAkDAV2hrGxMyMxCvVb/GpxNMOp9lC5lq7d+OpfQTa8vab3BZFthzQ5 vXWg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1784543089; x=1785147889; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to:content-type; bh=zd72l0RJ8ftcCUHhUbD81aNG9YQZtgyyjQP2cHWS9d4=; b=OgsO01ejZbTkuWcHdcnuNj4dCGxOxmIpjsKkIDbE2jbekKyfr8u5StVOfy34UQBhZ7 wrc9G0cyetnfcGmOYbcD692Eg/SVHGmpUDLRrRnPYS+ItR0LSQq5A4Vd73YwZLWKSOje sACMeqK8qlMYi2BBPRKVB0jltG2WAQH/VL43vJ/O9nGS5MZYowRV3hlQaiMx0dOn9gRE 5VY+QueZNh4B8/43EQpef+8kNr028eVTt/WcxYSWRgh000RRcz9/if359jC9vEzZAQe+ J79TIFuJpFWnSh0WH2WoBjsqOBMAu1nfDVoBWQMTuXjq06uhsWnCBcSKTaCiY6zObHKI IQ1g== X-Forwarded-Encrypted: i=1; AHgh+RqZtLLXEeI00vugQmY68l9nFROQFvz97bomQmd2s1dXN0wZAP11ZfvjRL/NzOloseAV7E413+0=@vger.kernel.org X-Gm-Message-State: AOJu0YyCFJa508jAK8EUgDbITHiUuk83Sopb82y+cwKmUz+q7pmBHmhq JkXEmKPufzSsaNCeLyG3FMf9Sy6rhdaV2aT/PYQDB4JMTqvXEOB81G8eLY6Nv8hpXn8= X-Gm-Gg: AfdE7cmJVMWIJgNB2oAf4hfaiB6DOJZp+gDYQv5WpyRRCP04yHZbxO37BHlWfpEztMX TgDXz//zFrAshhTuKIXwRbr4dwFMIhnFPcdIHMT6KG1592rwo7NTK7llAFv2tb50T8GmSa7GPEP EOCQ9guuxvNk3KAWxqU9fMcF0sgdMBs3E/En8WABONM/NgHERsm4VfKB1Fjl+v+kd9jxs4ZuekY Kt2hSvFav+Eup+AWfLk1rk01ixNpY13eSJAIfwZefUFILAh2MsohA9hhNdbxIQgH3rPeJ5TNBKA cG3qChhaJklsIaiFvSCOU3b/Xs+VbRHwxfZVyWUyfSs9vJ80jTlAzgFNesO/dUCtxNbp/WUpSXs bv77mEOmNS8DKLn6N2Vagzw5MWZxddP3RAlr/2nAtxquJPBrCc5R+8kyMPVFQ0pSQ X-Received: by 2002:a05:600c:4f09:b0:495:5b32:df72 with SMTP id 5b1f17b1804b1-4955b32e0c7mr61903515e9.35.1784543088526; Mon, 20 Jul 2026 03:24:48 -0700 (PDT) Received: from localhost ([2a09:bac6:37a8:1cdc::2e0:ea]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49549c96fecsm318116205e9.11.2026.07.20.03.24.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Jul 2026 03:24:47 -0700 (PDT) Date: Mon, 20 Jul 2026 11:24:47 +0100 From: Matt Fleming To: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= Cc: Alexei Starovoitov , Daniel Borkmann , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Lorenzo Bianconi , bpf@vger.kernel.org, netdev@vger.kernel.org, stable@vger.kernel.org, kernel-team@cloudflare.com, Matt Fleming Subject: Re: [PATCH bpf] veth: convert frag_list skbs before running XDP Message-ID: References: <20260716100605.939654-1-matt@readmodwrite.com> <87jyquj5wm.fsf@toke.dk> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87jyquj5wm.fsf@toke.dk> On Fri, Jul 17, 2026 at 11:56:41AM +0200, Toke Høiland-Jørgensen wrote: > Matt Fleming writes: > > > diff --git a/drivers/net/veth.c b/drivers/net/veth.c > > index 1c5142149175..efb24aae1f26 100644 > > --- a/drivers/net/veth.c > > +++ b/drivers/net/veth.c > > @@ -756,7 +756,7 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq, > > u32 frame_sz; > > > > if (skb_shared(skb) || skb_head_is_locked(skb) || > > - skb_shinfo(skb)->nr_frags || > > + skb_shinfo(skb)->nr_frags || skb_has_frag_list(skb) || > > Isn't 'skb_shinfo(skb)->nr_frags || skb_has_frag_list(skb)' basically > the same as 'skb_is_nonlinear(skb)'? Which, incidentally, is what > generic XDP uses in the check that guards calling into the > skb_pp_cow_data() path. Yeah, you're right. I tested that expression and it still fixes the bug. I'll update v2 to use skb_is_nonlinear(). > Looking at those two places, generic XDP checks for 'skb_cloned(skb)', > while veth checks 'skb_shared(skb) || skb_head_is_locked(skb)'. AFAICT, > the latter is stricter; should we update the generic XDP check? Possibly, but the surrounding code isn't set up to deal with skb_shared() SKBs so that'd be a larger change. I can take a look at that too but I'm going to need more time to get my head around making that change correctly given that there's different fallback rules than veth. > > skb_headroom(skb) < XDP_PACKET_HEADROOM) { > > if (skb_pp_cow_data(rq->page_pool, pskb, XDP_PACKET_HEADROOM)) > > goto drop; > > @@ -771,7 +771,7 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq, > > xdp_prepare_buff(xdp, skb->head, skb_headroom(skb), > > skb_headlen(skb), true); > > > > - if (skb_is_nonlinear(skb)) { > > + if (skb_shinfo(skb)->nr_frags) { > > skb_shinfo(skb)->xdp_frags_size = skb->data_len; > > xdp_buff_set_frags_flag(xdp); > > } else { > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > index 18dabb4e9cfa..1e837d01a908 100644 > > --- a/net/core/skbuff.c > > +++ b/net/core/skbuff.c > > @@ -936,12 +936,11 @@ int skb_pp_cow_data(struct page_pool *pool, struct sk_buff **pskb, > > int err, i, head_off; > > void *data; > > > > - /* XDP does not support fraglist so we need to linearize > > - * the skb. > > + /* > > + * skb_copy_bits() handles both frags[] and frag_list input. If the > > + * copied skb remains non-linear, it uses frags[], which is the > > + * representation used by XDP multi-buffer. > > */ > > This comment sorta reads like a function documentation comment, but it > ends up sitting weirdly in the middle of the function body. The comment > you're replacing was tied to the statement below, but this one isn't, > really. Should we turn it into an actual function doc comment instead? Good point. I'll make this a function doc comment. Thanks, Matt