From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932344AbaHBWdj (ORCPT ); Sat, 2 Aug 2014 18:33:39 -0400 Received: from shards.monkeyblade.net ([149.20.54.216]:49678 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751578AbaHBWdi (ORCPT ); Sat, 2 Aug 2014 18:33:38 -0400 Date: Sat, 02 Aug 2014 15:33:37 -0700 (PDT) Message-Id: <20140802.153337.1399638752235662112.davem@davemloft.net> To: wei.liu2@citrix.com Cc: zoltan.kiss@citrix.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com, david.vrabel@citrix.com, Ian.Campbell@citrix.com, paul.durrant@citrix.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org Subject: Re: [PATCH] xen-netfront: Fix handling packets on compound pages with skb_segment From: David Miller In-Reply-To: <20140801110246.GB17947@zion.uk.xensource.com> References: <1406726730-17994-1-git-send-email-zoltan.kiss@citrix.com> <20140731.132520.1889577477638334755.davem@davemloft.net> <20140801110246.GB17947@zion.uk.xensource.com> X-Mailer: Mew version 6.5 on Emacs 24.1 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.7 (shards.monkeyblade.net [149.20.54.216]); Sat, 02 Aug 2014 15:33:38 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wei Liu Date: Fri, 1 Aug 2014 12:02:46 +0100 > On Thu, Jul 31, 2014 at 01:25:20PM -0700, David Miller wrote: >> If you were to have a 64-slot TX queue, you ought to be able to handle >> this theoretical 51 slot SKB. > > There's two problems: > 1. IIRC a single page ring has 256 slots, allowing 64 slots packet > yields 4 in-flight packets in worst case. > 2. Older netback could not handle this large number of slots and it's > likely to deem the frontend malicious. > > For #1, we don't actually care that much if guest screws itself by > generating 64 slot packets. #2 is more concerning. How many slots can the older netback handle?