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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham 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 271F0C4360F for ; Wed, 3 Apr 2019 07:18:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F2FFE20830 for ; Wed, 3 Apr 2019 07:18:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728625AbfDCHSh (ORCPT ); Wed, 3 Apr 2019 03:18:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49116 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726360AbfDCHSh (ORCPT ); Wed, 3 Apr 2019 03:18:37 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 21BF6C0BFBBB; Wed, 3 Apr 2019 07:18:37 +0000 (UTC) Received: from carbon (ovpn-200-46.brq.redhat.com [10.40.200.46]) by smtp.corp.redhat.com (Postfix) with ESMTP id 91069600D4; Wed, 3 Apr 2019 07:18:32 +0000 (UTC) Date: Wed, 3 Apr 2019 09:18:30 +0200 From: Jesper Dangaard Brouer To: Matteo Croce Cc: brouer@redhat.com, netdev@vger.kernel.org, Sunil Goutham , Robert Richter , linux-arm-kernel@lists.infradead.org, Ilias Apalodimas Subject: Re: [PATCH net] net: thunderx: don't allow jumbo frames with XDP Message-ID: <20190403091830.5fa867aa@carbon> In-Reply-To: <20190402231136.15156-1-mcroce@redhat.com> References: <20190402231136.15156-1-mcroce@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Wed, 03 Apr 2019 07:18:37 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, 3 Apr 2019 01:11:36 +0200 Matteo Croce wrote: > The thunderx driver forbids to load an eBPF program if the MTU is higher > than 1500 bytes, but this can be circumvented by first loading the eBPF, > and then raising the MTU. > > XDP assumes that SKBs are linear and fit in a single page, this can lead > to undefined behaviours. > Fix this by limiting the MTU to 1500 bytes if an eBPF program is loaded. I find this 1500 bytes limit strange. While XDP does not support frames that is split over multiple pages, it does support larger frames, as long as it can fit within one (e.g 4K) page, minus XDP_PACKET_HEADROOM (256B) and have tail-room for skb_shared_info (320 bytes), which is 4096-256-320 = 3520 bytes. A quick look at this driver it seems you are limited to 2176 bytes (RCV_FRAG_LEN=1536+64+320 + 256) based on how the dma mapping is done. I think the drivers intent is to limit to 1536 bytes, but the DMA mapping area include more. It seems rather suboptimal that the skb_shared_info is included as part of the DMA mapping. > Fixes: 05c773f52b96e ("net: thunderx: Add basic XDP support") > Signed-off-by: Matteo Croce > --- > drivers/net/ethernet/cavium/thunder/nicvf_main.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/net/ethernet/cavium/thunder/nicvf_main.c b/drivers/net/ethernet/cavium/thunder/nicvf_main.c > index aa2be4807191..fe1d7513f01d 100644 > --- a/drivers/net/ethernet/cavium/thunder/nicvf_main.c > +++ b/drivers/net/ethernet/cavium/thunder/nicvf_main.c > @@ -1578,6 +1578,13 @@ static int nicvf_change_mtu(struct net_device *netdev, int new_mtu) > struct nicvf *nic = netdev_priv(netdev); > int orig_mtu = netdev->mtu; > > + /* For now just support only the usual MTU sized frames */ > + if (nic->xdp_prog && new_mtu > 1500) { > + netdev_warn(netdev, "Jumbo frames not yet supported with XDP, current MTU %d.\n", > + netdev->mtu); > + return -EOPNOTSUPP; > + } > + > netdev->mtu = new_mtu; > > if (!netif_running(netdev)) -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer