From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 29124C433DB for ; Fri, 15 Jan 2021 16:38:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D1B2A238EE for ; Fri, 15 Jan 2021 16:38:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728477AbhAOQiE (ORCPT ); Fri, 15 Jan 2021 11:38:04 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:31563 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726137AbhAOQiD (ORCPT ); Fri, 15 Jan 2021 11:38:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610728596; 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=fOKUS7S2hYkjSxN1bA51IXrlqQyUlOoQEgDCV7xGvu8=; b=ih7W8f/i74ImGUCHWBzxmT+ik35YMBrzB5BoVepD3+8ZFUQAd4P/WxCc8bhOtpWObKLrJS YIrgXFWdFBqGNHv2od4UuPq+df+JnHUf4z72iYcyyaD19ia4liiqVPpMI0PXGceOZG0vq1 raKGHXnJDv5ieJZB4PLe8NqJtFvijEo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-155-gFwPazXdOKye8lXf0xK5Ng-1; Fri, 15 Jan 2021 11:36:27 -0500 X-MC-Unique: gFwPazXdOKye8lXf0xK5Ng-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 76C1C806661; Fri, 15 Jan 2021 16:36:26 +0000 (UTC) Received: from [10.36.113.143] (ovpn-113-143.ams2.redhat.com [10.36.113.143]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0DAB819C45; Fri, 15 Jan 2021 16:36:24 +0000 (UTC) From: "Eelco Chaudron" To: "Maciej Fijalkowski" , "Alexei Starovoitov" , "Daniel Borkmann" Cc: "Lorenzo Bianconi" , bpf@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH v5 bpf-next 13/14] bpf: add new frame_length field to the XDP ctx Date: Fri, 15 Jan 2021 17:36:23 +0100 Message-ID: <5A8FDDE5-3022-4FD7-BA71-9ACB4374BDB9@redhat.com> In-Reply-To: <54E66B9D-4677-436F-92A1-E70977E869FA@redhat.com> References: <0547d6f752e325f56a8e5f6466b50e81ff29d65f.1607349924.git.lorenzo@kernel.org> <20201208221746.GA33399@ranger.igk.intel.com> <96C89134-A747-4E05-AA11-CB6EA1420900@redhat.com> <20201209111047.GB36812@ranger.igk.intel.com> <170BF39B-894D-495F-93E0-820EC7880328@redhat.com> <38C60760-4F8C-43AC-A5DE-7FAECB65C310@redhat.com> <20201215180638.GB23785@ranger.igk.intel.com> <54E66B9D-4677-436F-92A1-E70977E869FA@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 16 Dec 2020, at 15:08, Eelco Chaudron wrote: > On 15 Dec 2020, at 19:06, Maciej Fijalkowski wrote: > >> On Tue, Dec 15, 2020 at 02:28:39PM +0100, Eelco Chaudron wrote: >>> >>> >>> On 9 Dec 2020, at 13:07, Eelco Chaudron wrote: >>> >>>> On 9 Dec 2020, at 12:10, Maciej Fijalkowski wrote: >>> >>> >>> >>>>>>>> + >>>>>>>> + ctx_reg = (si->src_reg == si->dst_reg) ? scratch_reg - 1 : >>>>>>>> si->src_reg; >>>>>>>> + while (dst_reg == ctx_reg || scratch_reg == ctx_reg) >>>>>>>> + ctx_reg--; >>>>>>>> + >>>>>>>> + /* Save scratch registers */ >>>>>>>> + if (ctx_reg != si->src_reg) { >>>>>>>> + *insn++ = BPF_STX_MEM(BPF_DW, si->src_reg, ctx_reg, >>>>>>>> + offsetof(struct xdp_buff, >>>>>>>> + tmp_reg[1])); >>>>>>>> + >>>>>>>> + *insn++ = BPF_MOV64_REG(ctx_reg, si->src_reg); >>>>>>>> + } >>>>>>>> + >>>>>>>> + *insn++ = BPF_STX_MEM(BPF_DW, ctx_reg, scratch_reg, >>>>>>>> + offsetof(struct xdp_buff, tmp_reg[0])); >>>>>>> >>>>>>> Why don't you push regs to stack, use it and then pop it >>>>>>> back? That way >>>>>>> I >>>>>>> suppose you could avoid polluting xdp_buff with tmp_reg[2]. >>>>>> >>>>>> There is no “real” stack in eBPF, only a read-only frame >>>>>> pointer, and as we >>>>>> are replacing a single instruction, we have no info on what we >>>>>> can use as >>>>>> scratch space. >>>>> >>>>> Uhm, what? You use R10 for stack operations. Verifier tracks the >>>>> stack >>>>> depth used by programs and then it is passed down to JIT so that >>>>> native >>>>> asm will create a properly sized stack frame. >>>>> >>>>> From the top of my head I would let know xdp_convert_ctx_access of >>>>> a >>>>> current stack depth and use it for R10 stores, so your scratch >>>>> space >>>>> would >>>>> be R10 + (stack depth + 8), R10 + (stack_depth + 16). >>>> >>>> Other instances do exactly the same, i.e. put some scratch >>>> registers in >>>> the underlying data structure, so I reused this approach. From the >>>> current information in the callback, I was not able to determine >>>> the >>>> current stack_depth. With "real" stack above, I meant having a >>>> pop/push >>>> like instruction. >>>> >>>> I do not know the verifier code well enough, but are you suggesting >>>> I >>>> can get the current stack_depth from the verifier in the >>>> xdp_convert_ctx_access() callback? If so any pointers? >>> >>> Maciej any feedback on the above, i.e. getting the stack_depth in >>> xdp_convert_ctx_access()? >> >> Sorry. I'll try to get my head around it. If i recall correctly stack >> depth is tracked per subprogram whereas convert_ctx_accesses is >> iterating >> through *all* insns (so a prog that is not chunked onto subprogs), >> but >> maybe we could dig up the subprog based on insn idx. >> >> But at first, you mentioned that you took the approach from other >> instances, can you point me to them? > > Quick search found the following two (sure there is one more with two > regs): > > https://elixir.bootlin.com/linux/v5.10.1/source/kernel/bpf/cgroup.c#L1718 > https://elixir.bootlin.com/linux/v5.10.1/source/net/core/filter.c#L8977 > >> I'd also like to hear from Daniel/Alexei/John and others their >> thoughts. > > Please keep me in the loop… Any thoughts/update on the above so I can move this patchset forward?