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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 96735C54EEB for ; Mon, 23 Mar 2020 17:55:39 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 67FDE20722 for ; Mon, 23 Mar 2020 17:55:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="JEdFcmiR" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 67FDE20722 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:37824 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jGRIY-00071m-J3 for qemu-devel@archiver.kernel.org; Mon, 23 Mar 2020 13:55:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55862) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jGRHr-0006ay-7z for qemu-devel@nongnu.org; Mon, 23 Mar 2020 13:54:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jGRHo-0004Uw-Bv for qemu-devel@nongnu.org; Mon, 23 Mar 2020 13:54:53 -0400 Received: from hqnvemgate25.nvidia.com ([216.228.121.64]:14974) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jGRHo-0004U6-56 for qemu-devel@nongnu.org; Mon, 23 Mar 2020 13:54:52 -0400 Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate25.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Mon, 23 Mar 2020 10:54:05 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Mon, 23 Mar 2020 10:54:49 -0700 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Mon, 23 Mar 2020 10:54:49 -0700 Received: from [10.40.103.10] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Mon, 23 Mar 2020 17:54:41 +0000 Subject: Re: [PATCH v15 Kernel 4/7] vfio iommu: Implementation of ioctl for dirty pages tracking. To: Alex Williamson References: <1584649004-8285-1-git-send-email-kwankhede@nvidia.com> <1584649004-8285-5-git-send-email-kwankhede@nvidia.com> <20200319165704.1f4eb36a@w520.home> <20200320120137.6acd89ee@x1.home> <20200320125910.028d7af5@w520.home> X-Nvconfidentiality: public From: Kirti Wankhede Message-ID: <7062f72a-bf06-a8cd-89f0-9e729699a454@nvidia.com> Date: Mon, 23 Mar 2020 23:24:37 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200320125910.028d7af5@w520.home> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1584986045; bh=S7OjFSz+PEtu+8vSTfjUUz/0UFh7RJGfe9S7guSjScc=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=JEdFcmiRF0bsEbgSV8NPZQX3m05jhahCFNI/AxnaiohSjZjWdykgJGEjfvrKcEEis de01YeAy3K1GOLhmrQcvrP6rES6xZZmCBoBjW2jhFosc3jZn1ZT+wuSIFrZ4ZhxMQE fBFb49lNGD+NFQA474mYPKxyAlUHRexniIeRzw69YTHkKcF3HSBUXINQH5yV0jjglw RK/9roALz2ZFqDq/10FkeetjZAve9cE0XmbwfjOHZPCsrpNGi6ncsXRvzeQJDEHw7X 3o1g6AUls25m10zaqCymh5N7QkqZL/iLLCisQAxdjEydl7TSUfO8+ULA/kTQ4YsCfh E6LJl1ivq+ecQ== X-detected-operating-system: by eggs.gnu.org: Windows 7 or 8 [fuzzy] X-Received-From: 216.228.121.64 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Zhengxiao.zx@Alibaba-inc.com, kevin.tian@intel.com, yi.l.liu@intel.com, cjia@nvidia.com, kvm@vger.kernel.org, eskultet@redhat.com, ziye.yang@intel.com, qemu-devel@nongnu.org, cohuck@redhat.com, shuangtai.tst@alibaba-inc.com, dgilbert@redhat.com, zhi.a.wang@intel.com, mlevitsk@redhat.com, pasic@linux.ibm.com, aik@ozlabs.ru, eauger@redhat.com, felipe@nutanix.com, jonathan.davies@nutanix.com, yan.y.zhao@intel.com, changpeng.liu@intel.com, Ken.Xue@amd.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/21/2020 12:29 AM, Alex Williamson wrote: > On Sat, 21 Mar 2020 00:12:04 +0530 > Kirti Wankhede wrote: > >> On 3/20/2020 11:31 PM, Alex Williamson wrote: >>> On Fri, 20 Mar 2020 23:19:14 +0530 >>> Kirti Wankhede wrote: >>> >>>> On 3/20/2020 4:27 AM, Alex Williamson wrote: >>>>> On Fri, 20 Mar 2020 01:46:41 +0530 >>>>> Kirti Wankhede wrote: >>>>> >> >> >> >>>>>> +static int vfio_iova_dirty_bitmap(struct vfio_iommu *iommu, dma_addr_t iova, >>>>>> + size_t size, uint64_t pgsize, >>>>>> + u64 __user *bitmap) >>>>>> +{ >>>>>> + struct vfio_dma *dma; >>>>>> + unsigned long pgshift = __ffs(pgsize); >>>>>> + unsigned int npages, bitmap_size; >>>>>> + >>>>>> + dma = vfio_find_dma(iommu, iova, 1); >>>>>> + >>>>>> + if (!dma) >>>>>> + return -EINVAL; >>>>>> + >>>>>> + if (dma->iova != iova || dma->size != size) >>>>>> + return -EINVAL; >>>>>> + >>>>>> + npages = dma->size >> pgshift; >>>>>> + bitmap_size = DIRTY_BITMAP_BYTES(npages); >>>>>> + >>>>>> + /* mark all pages dirty if all pages are pinned and mapped. */ >>>>>> + if (dma->iommu_mapped) >>>>>> + bitmap_set(dma->bitmap, 0, npages); >>>>>> + >>>>>> + if (copy_to_user((void __user *)bitmap, dma->bitmap, bitmap_size)) >>>>>> + return -EFAULT; >>>>> >>>>> We still need to reset the bitmap here, clearing and re-adding the >>>>> pages that are still pinned. >>>>> >>>>> https://lore.kernel.org/kvm/20200319070635.2ff5db56@x1.home/ >>>>> >>>> >>>> I thought you agreed on my reply to it >>>> https://lore.kernel.org/kvm/31621b70-02a9-2ea5-045f-f72b671fe703@nvidia.com/ >>>> >>>> > Why re-populate when there will be no change since >>>> > vfio_iova_dirty_bitmap() is called holding iommu->lock? If there is any >>>> > pin request while vfio_iova_dirty_bitmap() is still working, it will >>>> > wait till iommu->lock is released. Bitmap will be populated when page is >>>> > pinned. >>> >>> As coded, dirty bits are only ever set in the bitmap, never cleared. >>> If a page is unpinned between iterations of the user recording the >>> dirty bitmap, it should be marked dirty in the iteration immediately >>> after the unpinning and not marked dirty in the following iteration. >>> That doesn't happen here. We're reporting cumulative dirty pages since >>> logging was enabled, we need to be reporting dirty pages since the user >>> last retrieved the dirty bitmap. The bitmap should be cleared and >>> currently pinned pages re-added after copying to the user. Thanks, >>> >> >> Does that mean, we have to track every iteration? do we really need that >> tracking? >> >> Generally the flow is: >> - vendor driver pin x pages >> - Enter pre-copy-phase where vCPUs are running - user starts dirty pages >> tracking, then user asks dirty bitmap, x pages reported dirty by >> VFIO_IOMMU_DIRTY_PAGES ioctl with _GET flag >> - In pre-copy phase, vendor driver pins y more pages, now bitmap >> consists of x+y bits set >> - In pre-copy phase, vendor driver unpins z pages, but bitmap is not >> updated, so again bitmap consists of x+y bits set. >> - Enter in stop-and-copy phase, vCPUs are stopped, mdev devices are stopped >> - user asks dirty bitmap - Since here vCPU and mdev devices are stopped, >> pages should not get dirty by guest driver or the physical device. >> Hence, x+y dirty pages would be reported. >> >> I don't think we need to track every iteration of bitmap reporting. > > Yes, once a bitmap is read, it's reset. In your example, after > unpinning z pages the user should still see a bitmap with x+y pages, > but once they've read that bitmap, the next bitmap should be x+y-z. > Userspace can make decisions about when to switch from pre-copy to > stop-and-copy based on convergence, ie. the slope of the line recording > dirty pages per iteration. The implementation here never allows an > inflection point, dirty pages reported through vfio would always either > be flat or climbing. There might also be a case that an iommu backed > device could start pinning pages during the course of a migration, how > would the bitmap ever revert from fully populated to only tracking the > pinned pages? Thanks, > At KVM forum we discussed this - if guest driver pins say 1024 pages before migration starts, during pre-copy phase device can dirty 0 pages in best case and 1024 pages in worst case. In that case, user will transfer content of 1024 pages during pre-copy phase and in stop-and-copy phase also, that will be pages will be copied twice. So we decided to only get dirty pages bitmap at stop-and-copy phase. If user is going to get dirty pages in stop-and-copy phase only, then that will be single iteration. There aren't any devices yet that can track sys memory dirty pages. So we can go ahead with this patch and support for dirty pages tracking during pre-copy phase can be added later when there will be consumers of that functionality. Thanks, Kirti