From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sowmini Varadhan Subject: Re: [RFC] Kernel unaligned access at __skb_flow_dissect Date: Fri, 29 Jan 2016 16:09:00 -0500 Message-ID: <20160129210900.GD17127@oracle.com> References: <20160129180651.GA17127@oracle.com> <1454092428.7627.52.camel@edumazet-glaptop2.roam.corp.google.com> <1454093642.7627.57.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Dumazet , mwdalton@google.com, Linux Kernel Network Developers To: Tom Herbert Return-path: Received: from userp1040.oracle.com ([156.151.31.81]:28547 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751394AbcA2VJJ (ORCPT ); Fri, 29 Jan 2016 16:09:09 -0500 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On (01/29/16 13:00), Tom Herbert wrote: > Doesn't every IP/VXLAN packet contains unaligned headers? Why don't > those create alignment issues (like when stack looks at addresses)? They do. http://comments.gmane.org/gmane.linux.network/370672 some of it was fixed in https://lkml.org/lkml/2015/7/20/63. There's still some NET_IP_ALIGN missing. IIRC, I was seeing this for mldv3, but the fix has to be done carefully, by someone who knows how to fully regression test it. I dont know if other tunneling methods manage to get the NET_IP_ALIGN correct in every case. Also, while sparc complains about unaligned access in most cases, some sins may pass under the radar, and other platforms dont even generate traps, so it's easy to not know that there's a problem, a lot of the time. --Sowmini