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 83259C43387 for ; Fri, 11 Jan 2019 08:59:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 516DA20657 for ; Fri, 11 Jan 2019 08:59:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731214AbfAKI7W (ORCPT ); Fri, 11 Jan 2019 03:59:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44902 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725779AbfAKI7W (ORCPT ); Fri, 11 Jan 2019 03:59:22 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BA96192A57; Fri, 11 Jan 2019 08:59:21 +0000 (UTC) Received: from [10.72.12.143] (ovpn-12-143.pek2.redhat.com [10.72.12.143]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D0CA25D9C8; Fri, 11 Jan 2019 08:59:16 +0000 (UTC) Subject: Re: [RFC PATCH V3 0/5] Hi: From: Jason Wang To: "Michael S. Tsirkin" Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, davem@davemloft.net References: <20181229124656.3900-1-jasowang@redhat.com> <20190104163516-mutt-send-email-mst@kernel.org> <68727e1b-1d51-0596-29c3-931475dd5dab@redhat.com> <20190107094516-mutt-send-email-mst@kernel.org> <682d520e-00e3-cdaa-d51e-23524ae48854@redhat.com> Message-ID: <303660e9-5ad4-975d-535d-bd158d99884e@redhat.com> Date: Fri, 11 Jan 2019 16:59:13 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <682d520e-00e3-cdaa-d51e-23524ae48854@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Fri, 11 Jan 2019 08:59:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/1/8 下午6:12, Jason Wang wrote: > > On 2019/1/7 下午10:47, Michael S. Tsirkin wrote: >> On Mon, Jan 07, 2019 at 02:58:08PM +0800, Jason Wang wrote: >>> On 2019/1/5 上午5:41, Michael S. Tsirkin wrote: >>>> On Sat, Dec 29, 2018 at 08:46:51PM +0800, Jason Wang wrote: >>>>> This series tries to access virtqueue metadata through kernel virtual >>>>> address instead of copy_user() friends since they had too much >>>>> overheads like checks, spec barriers or even hardware feature >>>>> toggling. >>>> I think it's a reasonable approach. >>>> However I need to look at whether and which mmu notifiers are >>>> invoked before >>>> writeback. Do you know? >>> >>> I don't know but just looking at the MMU notifier ops definition, >>> there's no >>> such callback if my understanding is correct. >>> >>> Thanks >> In that case how are you making sure used ring updates are written back? >> If they aren't guest will crash ... > > > I think this is the writeback issue you mentioned early. I don't do a > followup on the pointer but it looks to me some work is ongoing to fix > the issue. > > I can investigate it more, but it's not something new, consider the > case of VFIO. > > Thanks Ok, after some investigation. The GUP + dirty pages issue is not easy to be fixed so it may still take a while. An idea is switch back to copy_user() friends if we find the metadata page is not anonymous. Does this sound good to you? Thanks