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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 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 1177DC433E2 for ; Thu, 17 Sep 2020 18:23:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B352F2220A for ; Thu, 17 Sep 2020 18:23:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726600AbgIQSXo convert rfc822-to-8bit (ORCPT ); Thu, 17 Sep 2020 14:23:44 -0400 Received: from mga09.intel.com ([134.134.136.24]:17974 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726411AbgIQSXY (ORCPT ); Thu, 17 Sep 2020 14:23:24 -0400 IronPort-SDR: D1vz/kH3A5Uvl45qXjp+BvXYqM0FDtR9VclRL5RC4b2U+4YleD2VnDqOah7dvxcTTbNII8u61e f2Hkbo0EnLhw== X-IronPort-AV: E=McAfee;i="6000,8403,9747"; a="160689629" X-IronPort-AV: E=Sophos;i="5.77,271,1596524400"; d="scan'208";a="160689629" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Sep 2020 11:17:57 -0700 IronPort-SDR: lLeZ+Fj9HzGIdwJB/CGAkBh8htdhAwiJF5jEAiEwe0vmFBMC2bi6DYC5f7/W0jXsyCzaAjhco0 LJna/xBO4xwQ== X-IronPort-AV: E=Sophos;i="5.77,271,1596524400"; d="scan'208";a="303042892" Received: from jpan9-mobl2.amr.corp.intel.com (HELO localhost) ([10.212.182.111]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Sep 2020 11:17:56 -0700 Date: Thu, 17 Sep 2020 11:17:54 -0700 From: "Jacob Pan (Jun)" To: Jason Wang Cc: Jason Gunthorpe , "Raj, Ashok" , Alex Williamson , Jean-Philippe Brucker , Liu Yi L , eric.auger@redhat.com, baolu.lu@linux.intel.com, joro@8bytes.org, kevin.tian@intel.com, jun.j.tian@intel.com, yi.y.sun@intel.com, peterx@redhat.com, hao.wu@intel.com, stefanha@gmail.com, iommu@lists.linux-foundation.org, kvm@vger.kernel.org, "Michael S. Tsirkin" , jacob.jun.pan@linux.intel.com, jacob.jun.pan@intel.com Subject: Re: [PATCH v7 00/16] vfio: expose virtual Shared Virtual Addressing to VMs Message-ID: <20200917111754.00006bcc@intel.com> In-Reply-To: <69ec9537-460f-2351-fa90-c31aaeef3c4b@redhat.com> References: <20200915113341.GW904879@nvidia.com> <20200915181154.GA70770@otc-nc-03> <20200915184510.GB1573713@nvidia.com> <20200915150851.76436ca1@jacob-builder> <20200915235126.GK1573713@nvidia.com> <20200915171319.00003f59@linux.intel.com> <20200916150754.GE6199@nvidia.com> <20200916163343.GA76252@otc-nc-03> <20200916170113.GD3699@nvidia.com> <20200916112110.000024ee@intel.com> <20200916183841.GI6199@nvidia.com> <20200916160901.000046ec@intel.com> <69ec9537-460f-2351-fa90-c31aaeef3c4b@redhat.com> Organization: OTC X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; i686-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hi Jason, On Thu, 17 Sep 2020 11:53:49 +0800, Jason Wang wrote: > On 2020/9/17 上午7:09, Jacob Pan (Jun) wrote: > > Hi Jason, > > On Wed, 16 Sep 2020 15:38:41 -0300, Jason Gunthorpe > > wrote: > > > >> On Wed, Sep 16, 2020 at 11:21:10AM -0700, Jacob Pan (Jun) wrote: > >>> Hi Jason, > >>> On Wed, 16 Sep 2020 14:01:13 -0300, Jason Gunthorpe > >>> wrote: > >>> > >>>> On Wed, Sep 16, 2020 at 09:33:43AM -0700, Raj, Ashok wrote: > >>>>> On Wed, Sep 16, 2020 at 12:07:54PM -0300, Jason Gunthorpe > >>>>> wrote: > >>>>>> On Tue, Sep 15, 2020 at 05:22:26PM -0700, Jacob Pan (Jun) > >>>>>> wrote: > >>>>>>>> If user space wants to bind page tables, create the PASID > >>>>>>>> with /dev/sva, use ioctls there to setup the page table > >>>>>>>> the way it wants, then pass the now configured PASID to a > >>>>>>>> driver that can use it. > >>>>>>> Are we talking about bare metal SVA? > >>>>>> What a weird term. > >>>>> Glad you noticed it at v7 :-) > >>>>> > >>>>> Any suggestions on something less weird than > >>>>> Shared Virtual Addressing? There is a reason why we moved from > >>>>> SVM to SVA. > >>>> SVA is fine, what is "bare metal" supposed to mean? > >>>> > >>> What I meant here is sharing virtual address between DMA and host > >>> process. This requires devices perform DMA request with PASID and > >>> use IOMMU first level/stage 1 page tables. > >>> This can be further divided into 1) user SVA 2) supervisor SVA > >>> (sharing init_mm) > >>> > >>> My point is that /dev/sva is not useful here since the driver can > >>> perform PASID allocation while doing SVA bind. > >> No, you are thinking too small. > >> > >> Look at VDPA, it has a SVA uAPI. Some HW might use PASID for the > >> SVA. > > Could you point to me the SVA UAPI? I couldn't find it in the > > mainline. Seems VDPA uses VHOST interface? > > > It's the vhost_iotlb_msg defined in uapi/linux/vhost_types.h. > Thanks for the pointer, for complete vSVA functionality we would need 1 TLB flush (IOTLB and PASID cache etc.) 2 PASID alloc/free 3 bind/unbind page tables or PASID tables 4 Page request service Seems vhost_iotlb_msg can be used for #1 partially. And the proposal is to pluck out the rest into /dev/sda? Seems awkward as Alex pointed out earlier for similar situation in VFIO. > > > > >> When VDPA is used by DPDK it makes sense that the PASID will be SVA > >> and 1:1 with the mm_struct. > >> > > I still don't see why bare metal DPDK needs to get a handle of the > > PASID. > > > My understanding is that it may: > > - have a unified uAPI with vSVA: alloc, bind, unbind, free Got your point, but vSVA needs more than these > - leave the binding policy to userspace instead of the using a > implied one in the kenrel > Only if necessary. > > > Perhaps the SVA patch would explain. Or are you talking about > > vDPA DPDK process that is used to support virtio-net-pmd in the > > guest? > >> When VDPA is used by qemu it makes sense that the PASID will be an > >> arbitary IOVA map constructed to be 1:1 with the guest vCPU > >> physical map. /dev/sva allows a single uAPI to do this kind of > >> setup, and qemu can support it while supporting a range of SVA > >> kernel drivers. VDPA and vfio-mdev are obvious initial targets. > >> > >> *BOTH* are needed. > >> > >> In general any uAPI for PASID should have the option to use either > >> the mm_struct SVA PASID *OR* a PASID from /dev/sva. It costs > >> virtually nothing to implement this in the driver as PASID is just > >> a number, and gives so much more flexability. > >> > > Not really nothing in terms of PASID life cycles. For example, if > > user uses uacce interface to open an accelerator, it gets an > > FD_acc. Then it opens /dev/sva to allocate PASID then get another > > FD_pasid. Then we pass FD_pasid to the driver to bind page tables, > > perhaps multiple drivers. Now we have to worry about If FD_pasid > > gets closed before FD_acc(s) closed and all these race conditions. > > > I'm not sure I understand this. But this demonstrates the flexibility > of an unified uAPI. E.g it allows vDPA and VFIO device to use the > same PAISD which can be shared with a process in the guest. > This is for user DMA not for vSVA. I was contending that /dev/sva creates unnecessary steps for such usage. For vSVA, I think vDPA and VFIO can potentially share but I am not seeing convincing benefits. If a guest process wants to do SVA with a VFIO assigned device and a vDPA-backed virtio-net at the same time, it might be a limitation if PASID is not managed via a common interface. But I am not sure how vDPA SVA support will look like, does it support gIOVA? need virtio IOMMU? > For the race condition, it could be probably solved with refcnt. > Agreed but the best solution might be not to have the problem in the first place :) > Thanks > > > > > > If we do not expose FD_pasid to the user, the teardown is much > > simpler and streamlined. Following each FD_acc close, PASID unbind > > is performed. > >>> Yi can correct me but this set is is about VFIO-PCI, VFIO-mdev > >>> will be introduced later. > >> Last patch is: > >> > >> vfio/type1: Add vSVA support for IOMMU-backed mdevs > >> > >> So pretty hard to see how this is not about vfio-mdev, at least a > >> little.. > >> > >> Jason > > > > Thanks, > > > > Jacob > > > Thanks, Jacob