From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-175.mta1.migadu.com (out-175.mta1.migadu.com [95.215.58.175]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DEE2C1E7C27 for ; Tue, 5 Nov 2024 19:22:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.175 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730834548; cv=none; b=SFDnO28gs5yBQZLMxUiuNiACAvxzDTDxWOqv5MVuee/fjxn+vmXTK9Oe0sKMqkv+2DvlIwvekDSWplNB4Xo8StX3x/4hkklxUoegX0jXrlJJARHxSBmZla1a2sgjseC0UBbGAexP/TlvDB49iFECNplFCWUl0PYu1o51eF2ND+I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730834548; c=relaxed/simple; bh=EK18a9GsAaNuMbsMBX+mlEU/2y8NCZMLplGvJ8fchqQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=TDblYgIXKqHs0bvKQYzN79tl0mqJ3xVgaPuxGkjyThDLWhYM+I30R0mc86ctnhyVzM/zhluCuAG7TeZ75YtqqEIk0eRPgBOCZEtzl76vshzn+PbHZNke/mcF1o1xh0GRTSGLxoum1KNCp42+JUFqWKEhVQVRxXgOeBjc2jjBuJ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=t0rDGiu4; arc=none smtp.client-ip=95.215.58.175 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="t0rDGiu4" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1730834540; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=e/lV56qOFekIpTJ0243xyhBPojpFxY1cI7kHvI1Dc0Y=; b=t0rDGiu4kcbJWqqnIp1eA7/ABUJPfcWEp5oyLZuXDW+rbTi7nHHV/7C3fiWSJKBi/Kq0IC NmpulbcAq4Kfkh+dheC5mcgNpNkf23CBbXtBl31wLa+ilqOZc026f7L7LKel4CbptMdDBd fJLAtaj+9cbQBOtIubOmLtRx18mnDSA= Date: Tue, 5 Nov 2024 11:22:09 -0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH net-next v3 02/14] net-timestamp: allow two features to work parallelly To: Jason Xing Cc: Willem de Bruijn , willemb@google.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, dsahern@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, 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, shuah@kernel.org, ykolal@fb.com, bpf@vger.kernel.org, netdev@vger.kernel.org, Jason Xing References: <20241028110535.82999-1-kerneljasonxing@gmail.com> <67219e5562f8c_37251929465@willemb.c.googlers.com.notmuch> <3c7c5f25-593f-4b48-9274-a18a9ea61e8f@linux.dev> <672269c08bcd5_3c834029423@willemb.c.googlers.com.notmuch> <67237877cd08d_b246b2942b@willemb.c.googlers.com.notmuch> <65968a5c-2c67-4b66-8fe0-0cebd2bf9c29@linux.dev> <6724d85d8072_1a157829475@willemb.c.googlers.com.notmuch> <1c8ebc16-f8e7-4a98-9518-865db3952f8f@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 11/4/24 10:22 PM, Jason Xing wrote: > On Tue, Nov 5, 2024 at 10:09 AM Martin KaFai Lau wrote: >> >> On 11/1/24 6:32 AM, Willem de Bruijn wrote: >>>> In udp/raw/..., I don't know how likely is the user space having "cork->tx_flags >>>> & SKBTX_ANY_TSTAMP" set but has neither "READ_ONCE(sk->sk_tsflags) & >>>> SOF_TIMESTAMPING_OPT_ID" nor "cork->flags & IPCORK_TS_OPT_ID" set. >>> This is not something to rely on. OPT_ID was added relatively recently. >>> Older applications, or any that just use the most straightforward API, >>> will not set this. >> >> Good point that the OPT_ID per cmsg is very new. >> >> The datagram support on SOF_TIMESTAMPING_OPT_ID in sk->sk_tsflags had >> been there for quite some time now. Is it a safe assumption that >> most applications doing udp tx timestamping should have >> the SOF_TIMESTAMPING_OPT_ID set to be useful? >> >>> >>>> If it is >>>> unlikely, may be we can just disallow bpf prog from directly setting >>>> skb_shinfo(skb)->tskey for this particular skb. >>>> >>>> For all other cases, in __ip[6]_append_data, directly call a bpf prog and also >>>> pass the kernel decided tskey to the bpf prog. >>>> >>>> The kernel passed tskey could be 0 (meaning the user space has not used it). The >>>> bpf prog can give one for the kernel to use. The bpf prog can store the >>>> sk_tskey_bpf in the bpf_sk_storage now. Meaning no need to add one to the struct >>>> sock. The bpf prog does not have to start from 0 (e.g. start from U32_MAX >>>> instead) if it helps. >>>> >>>> If the kernel passed tskey is not 0, the bpf prog can just use that one >>>> (assuming the user space is doing something sane, like the value in >>>> SCM_TS_OPT_ID won't be jumping back and front between 0 to U32_MAX). I hope this >>>> is very unlikely also (?) but the bpf prog can probably detect this and choose >>>> to ignore this sk. >>> If an applications uses OPT_ID, it is unlikely that they will toggle >>> the feature on and off on a per-packet basis. So in the common case >>> the program could use the user-set counter or use its own if userspace >>> does not enable the feature. In the rare case that an application does >>> intermittently set an OPT_ID, the numbering would be erratic. This >>> does mean that an actively malicious application could mess with admin >>> measurements. >> >> All make sense. Given it is reasonable to assume the user space should either >> has SOF_TIMESTAMPING_OPT_ID always on or always off. When it is off, the bpf >> prog can directly provide its own tskey to be used in shinfo->tskey. The bpf >> prog can generate the id itself without using the sk->sk_tskey, e.g. store an >> atomic int in the bpf_sk_storage. > > I wonder, how can we correlate the key with each skb in the bpf > program for non-TCP type without implementing a bpf extension for > SCM_TS_OPT_ID? Every time the timestamp is reported, we cannot know > which sendmsg() the skb belongs to for non-TCP cases. SCM_TS_OPT_ID is eventually setting the shinfo->tskey. If the shinfo->tskey is not set by the user space, the bpf prog can directly set the shinfo->tskey. There is no need to use the sk->sk_tskey as the ID generator also. The bpf prog can have its own id generator. If the user space has already set the shinfo->tskey (either by sk->sk_tskey or SCM_TS_OPT_ID), the bpf prog can just use the user space one. If there is a weird application that flips flops between OPT_ID on/off, the bpf prog will get confused which is fine. The bpf prog can detect this and choose to ignore measuring this sk/skb. The bpf prog can also choose to be on the very safe side and ignore all skb with SKBTX_ANY_TSTAMP set in txflags but with no OPT_ID. The bpf prog can look into the details of the sk and skb to decide what makes the most sense for its deployment. I don't know whether it makes more sense to call the bpf prog to decide the shinfo->{tx_flags,tskey} just before the "while (length > 0)" in __ip[6]_append_data or it is better to call the bpf prog in ip[6]_setup_cork. I admittedly less familiar with this code path than the tcp one.