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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 86194C2D0CE for ; Tue, 21 Jan 2020 08:35:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4F01B24683 for ; Tue, 21 Jan 2020 08:35:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="J90SFnPa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729021AbgAUIfx (ORCPT ); Tue, 21 Jan 2020 03:35:53 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:45457 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728708AbgAUIfw (ORCPT ); Tue, 21 Jan 2020 03:35:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579595751; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=N7dpAEkIwYs7qlTREqwW6WdsBkWtgFDA0vfOaVMiY7c=; b=J90SFnPaoC+Z+0CeBym/O2aFOCBXsUpeCj1zzkIyd7cWux3LPvCrr0ELxh0YCXvD/Q8cnM y823NBaHy0e/4Cn611n/Lm95m2CxKztLoYFaWwS8myKK1EFU9+1J8oGAyoRKdxNCVgfEBL Hj/z6GdsN2gyUlvxoBfNGXTxA57cvsU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-183-bBs492L5PM6Oe7SbmYwpXw-1; Tue, 21 Jan 2020 03:35:50 -0500 X-MC-Unique: bBs492L5PM6Oe7SbmYwpXw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 80F95107ACC4; Tue, 21 Jan 2020 08:35:47 +0000 (UTC) Received: from [10.72.12.103] (ovpn-12-103.pek2.redhat.com [10.72.12.103]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0429F63148; Tue, 21 Jan 2020 08:35:28 +0000 (UTC) Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus To: "Michael S. Tsirkin" Cc: Jason Gunthorpe , Shahaf Shuler , Rob Miller , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , Netdev , "Bie, Tiwei" , "maxime.coquelin@redhat.com" , "Liang, Cunming" , "Wang, Zhihong" , "Wang, Xiao W" , "haotian.wang@sifive.com" , "Zhu, Lingshan" , "eperezma@redhat.com" , "lulu@redhat.com" , Parav Pandit , "Tian, Kevin" , "stefanha@redhat.com" , "rdunlap@infradead.org" , "hch@infradead.org" , Ariel Adam , Jiri Pirko , "hanand@xilinx.com" , "mhabets@solarflare.com" References: <20200116124231.20253-4-jasowang@redhat.com> <20200117070324-mutt-send-email-mst@kernel.org> <239b042c-2d9e-0eec-a1ef-b03b7e2c5419@redhat.com> <20200120174933.GB3891@mellanox.com> <2a324cec-2863-58f4-c58a-2414ee32c930@redhat.com> <20200121004047-mutt-send-email-mst@kernel.org> <20200121031506-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <028ed448-a948-79d9-f224-c325029b17ab@redhat.com> Date: Tue, 21 Jan 2020 16:35:27 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20200121031506-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/1/21 =E4=B8=8B=E5=8D=884:15, Michael S. Tsirkin wrote: > On Tue, Jan 21, 2020 at 04:00:38PM +0800, Jason Wang wrote: >> On 2020/1/21 =E4=B8=8B=E5=8D=881:47, Michael S. Tsirkin wrote: >>> On Tue, Jan 21, 2020 at 12:00:57PM +0800, Jason Wang wrote: >>>> On 2020/1/21 =E4=B8=8A=E5=8D=881:49, Jason Gunthorpe wrote: >>>>> On Mon, Jan 20, 2020 at 04:43:53PM +0800, Jason Wang wrote: >>>>>> This is similar to the design of platform IOMMU part of vhost-vdpa= . We >>>>>> decide to send diffs to platform IOMMU there. If it's ok to do tha= t in >>>>>> driver, we can replace set_map with incremental API like map()/unm= ap(). >>>>>> >>>>>> Then driver need to maintain rbtree itself. >>>>> I think we really need to see two modes, one where there is a fixed >>>>> translation without dynamic vIOMMU driven changes and one that >>>>> supports vIOMMU. >>>> I think in this case, you meant the method proposed by Shahaf that s= ends >>>> diffs of "fixed translation" to device? >>>> >>>> It would be kind of tricky to deal with the following case for examp= le: >>>> >>>> old map [4G, 16G) new map [4G, 8G) >>>> >>>> If we do >>>> >>>> 1) flush [4G, 16G) >>>> 2) add [4G, 8G) >>>> >>>> There could be a window between 1) and 2). >>>> >>>> It requires the IOMMU that can do >>>> >>>> 1) remove [8G, 16G) >>>> 2) flush [8G, 16G) >>>> 3) change [4G, 8G) >>>> >>>> .... >>> Basically what I had in mind is something like qemu memory api >>> >>> 0. begin >>> 1. remove [8G, 16G) >>> 2. add [4G, 8G) >>> 3. commit >> >> This sounds more flexible e.g driver may choose to implement static ma= pping >> one through commit. But a question here, it looks to me this still req= uires >> the DMA to be synced with at least commit here. Otherwise device may g= et DMA >> fault? Or device is expected to be paused DMA during begin? >> >> Thanks > For example, commit might switch one set of tables for another, > without need to pause DMA. Yes, I think that works but need confirmation from Shahaf or Jason. Thanks > >>> Anyway, I'm fine with a one-shot API for now, we can >>> improve it later. >>> >>>>> There are different optimization goals in the drivers for these two >>>>> configurations. >>>>> >>>>>>> If the first one, then I think memory hotplug is a heavy flow >>>>>>> regardless. Do you think the extra cycles for the tree traverse >>>>>>> will be visible in any way? >>>>>> I think if the driver can pause the DMA during the time for settin= g up new >>>>>> mapping, it should be fine. >>>>> This is very tricky for any driver if the mapping change hits the >>>>> virtio rings. :( >>>>> >>>>> Even a IOMMU using driver is going to have problems with that.. >>>>> >>>>> Jason >>>> Or I wonder whether ATS/PRI can help here. E.g during I/O page fault= , >>>> driver/device can wait for the new mapping to be set and then replay= the >>>> DMA. >>>> >>>> Thanks >>>>