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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 D06C3C49ED7 for ; Thu, 19 Sep 2019 06:41:24 +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 A501321924 for ; Thu, 19 Sep 2019 06:41:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A501321924 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:38260 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iAq83-0004l6-T8 for qemu-devel@archiver.kernel.org; Thu, 19 Sep 2019 02:41:23 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47441) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iAq7J-0004Jy-A1 for qemu-devel@nongnu.org; Thu, 19 Sep 2019 02:40:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iAq7H-0008A1-Jw for qemu-devel@nongnu.org; Thu, 19 Sep 2019 02:40:37 -0400 Received: from mga02.intel.com ([134.134.136.20]:21396) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iAq7H-00089a-Bz for qemu-devel@nongnu.org; Thu, 19 Sep 2019 02:40:35 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Sep 2019 23:40:34 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,522,1559545200"; d="scan'208";a="181378596" Received: from joy-optiplex-7040.sh.intel.com (HELO joy-OptiPlex-7040) ([10.239.13.9]) by orsmga008.jf.intel.com with ESMTP; 18 Sep 2019 23:40:32 -0700 Date: Thu, 19 Sep 2019 02:32:49 -0400 From: Yan Zhao To: Jason Wang Message-ID: <20190919063249.GD18391@joy-OptiPlex-7040> References: <8302a4ae-1914-3046-b3b5-b3234d7dda02@redhat.com> <6d73572e-1e89-b04a-bdd6-98ac73798083@redhat.com> <204219fa-ee72-ca60-52a4-fb4bbc887773@redhat.com> <20190919052819.GA18391@joy-OptiPlex-7040> <7b6d6343-33de-ebd7-9846-af54a45a82a2@redhat.com> <20190919061756.GB18391@joy-OptiPlex-7040> <20190919062954.GC18391@joy-OptiPlex-7040> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190919062954.GC18391@joy-OptiPlex-7040> User-Agent: Mutt/1.9.4 (2018-02-28) X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 134.134.136.20 Subject: Re: [Qemu-devel] vhost, iova, and dirty page tracking 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: , Reply-To: Yan Zhao Cc: "Tian, Kevin" , 'Alex Williamson' , Peter Xu , "qemu-devel@nongnu.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Sep 19, 2019 at 02:29:54PM +0800, Yan Zhao wrote: > On Thu, Sep 19, 2019 at 02:32:03PM +0800, Jason Wang wrote: > > > > On 2019/9/19 下午2:17, Yan Zhao wrote: > > > On Thu, Sep 19, 2019 at 02:09:53PM +0800, Jason Wang wrote: > > >> On 2019/9/19 下午1:28, Yan Zhao wrote: > > >>> On Thu, Sep 19, 2019 at 09:05:12AM +0800, Jason Wang wrote: > > >>>> On 2019/9/18 下午4:37, Tian, Kevin wrote: > > >>>>>> From: Jason Wang [mailto:jasowang@redhat.com] > > >>>>>> Sent: Wednesday, September 18, 2019 2:10 PM > > >>>>>> > > >>>>>>>> Note that the HVA to GPA mapping is not an 1:1 mapping. One HVA > > >>>>>> range > > >>>>>>>> could be mapped to several GPA ranges. > > >>>>>>> This is fine. Currently vfio_dma maintains IOVA->HVA mapping. > > >>>>>>> > > >>>>>>> btw under what condition HVA->GPA is not 1:1 mapping? I didn't realize it. > > >>>>>> I don't remember the details e.g memory region alias? And neither kvm > > >>>>>> nor kvm API does forbid this if my memory is correct. > > >>>>>> > > >>>>> I checked https://qemu.weilnetz.de/doc/devel/memory.html, which > > >>>>> provides an example of aliased layout. However, its aliasing is all > > >>>>> 1:1, instead of N:1. From guest p.o.v every writable GPA implies an > > >>>>> unique location. Why would we hit the situation where multiple > > >>>>> write-able GPAs are mapped to the same HVA (i.e. same physical > > >>>>> memory location)? > > >>>> I don't know, just want to say current API does not forbid this. So we > > >>>> probably need to take care it. > > >>>> > > >>> yes, in KVM API level, it does not forbid two slots to have the same HVA(slot->userspace_addr). > > >>> But > > >>> (1) there's only one kvm instance for each vm for each qemu process. > > >>> (2) all ramblock->host (corresponds to HVA and slot->userspace_addr) in one qemu > > >>> process is non-overlapping as it's obtained from mmmap(). > > >>> (3) qemu ensures two kvm slots will not point to the same section of one ramblock. > > >>> > > >>> So, as long as kvm instance is not shared in two processes, and > > >>> there's no bug in qemu, we can assure that HVA to GPA is 1:1. > > >> > > >> Well, you leave this API for userspace, so you can't assume qemu is the > > >> only user or any its behavior. If you had you should limit it in the API > > >> level instead of open window for them. > > >> > > >> > > >>> But even if there are two processes operating on the same kvm instance > > >>> and manipulating on memory slots, adding an extra GPA along side current > > >>> IOVA & HVA to ioctl VFIO_IOMMU_MAP_DMA can still let driver knows the > > >>> right IOVA->GPA mapping, right? > > >> > > >> It looks fragile. Consider HVA was mapped to both GPA1 and GPA2. Guest > > >> maps IOVA to GPA2, so we have IOVA GPA2 HVA in the new ioctl and then > > >> log through GPA2. If userspace is trying to sync through GPA1, it will > > >> miss the dirty page. So for safety we need log both GPA1 and GPA2. (See > > >> what has been done in log_write_hva() in vhost.c). The only way to do > > >> that is to maintain an independent HVA to GPA mapping like what KVM or > > >> vhost did. > > >> > > > why GPA1 and GPA2 should be both dirty? > > > even they have the same HVA due to overlaping virtual address space in > > > two processes, they still correspond to two physical pages. > > > don't get what's your meaning :) > > > > > > The point is not leave any corner case that is hard to debug or fix in > > the future. > > > > Let's just start by a single process, the API allows userspace to maps > > HVA to both GPA1 and GPA2. Since it knows GPA1 and GPA2 are equivalent, > > it's ok to sync just through GPA1. That means if you only log GPA2, it > > won't work. > > > In that case, cannot log dirty according to HPA. sorry, it should be "cannot log dirty according to HVA". > because kvm cannot tell whether it's an valid case (the two GPAs are equivalent) > or an invalid case (the two GPAs are not equivalent, but with the same > HVA value). > > Right? > > Thanks > Yan > > > > Thanks > > > > > > > > > > Thanks > > > Yan > > > > > > > > >> Thanks > > >> > > >> > > >>> Thanks > > >>> Yan > > >>> > > >>>>> Is Qemu doing its own same-content memory > > >>>>> merging in GPA level, similar to KSM? > > >>>> AFAIK, it doesn't. > > >>>> > > >>>> Thanks > > >>>> > > >>>> > > >>>>> Thanks > > >>>>> Kevin > > >>>> >