From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net] virtio-net: alloc big buffers also when guest can receive UFO Date: Thu, 13 Feb 2014 07:15:59 +0200 Message-ID: <20140213051559.GB31352@redhat.com> References: <1392183808-16789-1-git-send-email-jasowang@redhat.com> <20140212115901.GC23006@redhat.com> <52FC35B5.6000900@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <52FC35B5.6000900@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Jason Wang Cc: virtio-dev@lists.oasis-open.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Sridhar Samudrala List-Id: virtualization@lists.linuxfoundation.org On Thu, Feb 13, 2014 at 11:02:13AM +0800, Jason Wang wrote: > On 02/12/2014 07:59 PM, Michael S. Tsirkin wrote: > > On Wed, Feb 12, 2014 at 01:43:28PM +0800, Jason Wang wrote: > >> > We should alloc big buffers also when guest can receive UFO > >> > pakcets. Otherwise the big packets will be truncated when mergeable rx > >> > buffer is disabled. > > Not truncated, they will be dropped. > > > > Why dropped? We enable the ufo on tap0 if VIRTIO_NET_F_GUEST_UFO is > negotiated. So skb was queued on the receive queue. But since the > receive buffer is small, it will be truncated during tun_put_user(). Hypervisor shouldn't truncate packets silently - if it does it's a hypervisor bug. Passing malformed packets to guest is a bad idea. -- MST From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752436AbaBMFLJ (ORCPT ); Thu, 13 Feb 2014 00:11:09 -0500 Received: from mx1.redhat.com ([209.132.183.28]:29682 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751089AbaBMFLH (ORCPT ); Thu, 13 Feb 2014 00:11:07 -0500 Date: Thu, 13 Feb 2014 07:15:59 +0200 From: "Michael S. Tsirkin" To: Jason Wang Cc: rusty@rustcorp.com.au, virtio-dev@lists.oasis-open.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Sridhar Samudrala Subject: Re: [PATCH net] virtio-net: alloc big buffers also when guest can receive UFO Message-ID: <20140213051559.GB31352@redhat.com> References: <1392183808-16789-1-git-send-email-jasowang@redhat.com> <20140212115901.GC23006@redhat.com> <52FC35B5.6000900@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <52FC35B5.6000900@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 13, 2014 at 11:02:13AM +0800, Jason Wang wrote: > On 02/12/2014 07:59 PM, Michael S. Tsirkin wrote: > > On Wed, Feb 12, 2014 at 01:43:28PM +0800, Jason Wang wrote: > >> > We should alloc big buffers also when guest can receive UFO > >> > pakcets. Otherwise the big packets will be truncated when mergeable rx > >> > buffer is disabled. > > Not truncated, they will be dropped. > > > > Why dropped? We enable the ufo on tap0 if VIRTIO_NET_F_GUEST_UFO is > negotiated. So skb was queued on the receive queue. But since the > receive buffer is small, it will be truncated during tun_put_user(). Hypervisor shouldn't truncate packets silently - if it does it's a hypervisor bug. Passing malformed packets to guest is a bad idea. -- MST