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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 B97CAC46472 for ; Mon, 6 Aug 2018 17:41:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C34D21A03 for ; Mon, 6 Aug 2018 17:41:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6C34D21A03 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=davemloft.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732930AbeHFTv6 (ORCPT ); Mon, 6 Aug 2018 15:51:58 -0400 Received: from shards.monkeyblade.net ([23.128.96.9]:55122 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732363AbeHFTv5 (ORCPT ); Mon, 6 Aug 2018 15:51:57 -0400 Received: from localhost (c-24-20-22-31.hsd1.or.comcast.net [24.20.22.31]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 91BAB133E98F1; Mon, 6 Aug 2018 10:41:49 -0700 (PDT) Date: Mon, 06 Aug 2018 10:41:48 -0700 (PDT) Message-Id: <20180806.104148.1576759632957723909.davem@davemloft.net> To: jasowang@redhat.com Cc: mst@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next V2] vhost: switch to use new message format From: David Miller In-Reply-To: <1533525467-17787-1-git-send-email-jasowang@redhat.com> References: <1533525467-17787-1-git-send-email-jasowang@redhat.com> X-Mailer: Mew version 6.7 on Emacs 26 / 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-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Mon, 06 Aug 2018 10:41:49 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jason Wang Date: Mon, 6 Aug 2018 11:17:47 +0800 > We use to have message like: > > struct vhost_msg { > int type; > union { > struct vhost_iotlb_msg iotlb; > __u8 padding[64]; > }; > }; > > Unfortunately, there will be a hole of 32bit in 64bit machine because > of the alignment. This leads a different formats between 32bit API and > 64bit API. What's more it will break 32bit program running on 64bit > machine. > > So fixing this by introducing a new message type with an explicit > 32bit reserved field after type like: > > struct vhost_msg_v2 { > __u32 type; > __u32 reserved; > union { > struct vhost_iotlb_msg iotlb; > __u8 padding[64]; > }; > }; > > We will have a consistent ABI after switching to use this. To enable > this capability, introduce a new ioctl (VHOST_SET_BAKCEND_FEATURE) for > userspace to enable this feature (VHOST_BACKEND_F_IOTLB_V2). > > Fixes: 6b1e6cc7855b ("vhost: new device IOTLB API") > Signed-off-by: Jason Wang > --- > Changes from V1: > - use __u32 instead of int for type Applied, thanks Jason.