From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752163AbaHCJL1 (ORCPT ); Sun, 3 Aug 2014 05:11:27 -0400 Received: from smtp.citrix.com ([66.165.176.89]:21529 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751305AbaHCJLZ (ORCPT ); Sun, 3 Aug 2014 05:11:25 -0400 X-IronPort-AV: E=Sophos;i="5.01,791,1400025600"; d="scan'208";a="158251362" Date: Sun, 3 Aug 2014 10:11:10 +0100 From: Wei Liu To: David Miller CC: , , , , , , , , , Subject: Re: [PATCH] xen-netfront: Fix handling packets on compound pages with skb_segment Message-ID: <20140803091110.GA7093@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> <20140802.153337.1399638752235662112.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20140802.153337.1399638752235662112.davem@davemloft.net> User-Agent: Mutt/1.5.23 (2014-03-12) X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 02, 2014 at 03:33:37PM -0700, David Miller wrote: > 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? I listed those two problems in the context "if we were to lift this limit in the latest net-next tree", so "older netback" actually refers to netback from 3.10 to 3.16. The current implementation allows the number of slots X: 1. X <= 18, valid packet 2. 18 < X < fatal_slot_count, dropped 3. X >= fatal_slot_count, malicious frontend fatal_slot_count has default value of 20. Wei. > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html