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=-10.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 26340C433E6 for ; Thu, 31 Dec 2020 02:51:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ED8732222D for ; Thu, 31 Dec 2020 02:51:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726524AbgLaCvU (ORCPT ); Wed, 30 Dec 2020 21:51:20 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:43715 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726289AbgLaCvT (ORCPT ); Wed, 30 Dec 2020 21:51:19 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1609382992; 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=jaBXRn3R6xRNQg/4syGGTAnxznRs8q7smaQWSZzeHto=; b=GxasZsPPGYUoOKgBPat+tWoYUIorRH6VqV5t8JJF0u95qN7dp9W/YZXqo2kWcnIGZwNPQQ Jzx78Ty0nrvAjr+M3FDh/PwpqicXTlrWdh4yy/JikkSrG8ZxAx1Eb7YZ/64egRmrjnwEiM u+c2/eAWHJdOtZcQs6l+j6ttqjeizCs= 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-284-Lh-HFYLCMCCg_MhT9L4ufA-1; Wed, 30 Dec 2020 21:49:49 -0500 X-MC-Unique: Lh-HFYLCMCCg_MhT9L4ufA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B4A4210054FF; Thu, 31 Dec 2020 02:49:46 +0000 (UTC) Received: from [10.72.12.236] (ovpn-12-236.pek2.redhat.com [10.72.12.236]) by smtp.corp.redhat.com (Postfix) with ESMTP id 25DE572161; Thu, 31 Dec 2020 02:49:34 +0000 (UTC) Subject: Re: [RFC v2 09/13] vduse: Add support for processing vhost iotlb message To: Yongji Xie Cc: "Michael S. Tsirkin" , Stefan Hajnoczi , sgarzare@redhat.com, Parav Pandit , akpm@linux-foundation.org, Randy Dunlap , Matthew Wilcox , viro@zeniv.linux.org.uk, axboe@kernel.dk, bcrl@kvack.org, corbet@lwn.net, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org References: <20201222145221.711-1-xieyongji@bytedance.com> <0e6faf9c-117a-e23c-8d6d-488d0ec37412@redhat.com> <2b24398c-e6d9-14ec-2c0d-c303d528e377@redhat.com> <1356137727.40748805.1609233068675.JavaMail.zimbra@redhat.com> <3fc6a132-9fc2-c4e2-7fb1-b5a8bfb771fa@redhat.com> From: Jason Wang Message-ID: Date: Thu, 31 Dec 2020 10:49:33 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2020/12/30 下午6:12, Yongji Xie wrote: > On Wed, Dec 30, 2020 at 4:41 PM Jason Wang wrote: >> >> On 2020/12/30 下午3:09, Yongji Xie wrote: >>> On Wed, Dec 30, 2020 at 2:11 PM Jason Wang wrote: >>>> On 2020/12/29 下午6:26, Yongji Xie wrote: >>>>> On Tue, Dec 29, 2020 at 5:11 PM Jason Wang wrote: >>>>>> ----- Original Message ----- >>>>>>> On Mon, Dec 28, 2020 at 4:43 PM Jason Wang wrote: >>>>>>>> On 2020/12/28 下午4:14, Yongji Xie wrote: >>>>>>>>>> I see. So all the above two questions are because VHOST_IOTLB_INVALIDATE >>>>>>>>>> is expected to be synchronous. This need to be solved by tweaking the >>>>>>>>>> current VDUSE API or we can re-visit to go with descriptors relaying >>>>>>>>>> first. >>>>>>>>>> >>>>>>>>> Actually all vdpa related operations are synchronous in current >>>>>>>>> implementation. The ops.set_map/dma_map/dma_unmap should not return >>>>>>>>> until the VDUSE_UPDATE_IOTLB/VDUSE_INVALIDATE_IOTLB message is replied >>>>>>>>> by userspace. Could it solve this problem? >>>>>>>> I was thinking whether or not we need to generate IOTLB_INVALIDATE >>>>>>>> message to VDUSE during dma_unmap (vduse_dev_unmap_page). >>>>>>>> >>>>>>>> If we don't, we're probably fine. >>>>>>>> >>>>>>> It seems not feasible. This message will be also used in the >>>>>>> virtio-vdpa case to notify userspace to unmap some pages during >>>>>>> consistent dma unmapping. Maybe we can document it to make sure the >>>>>>> users can handle the message correctly. >>>>>> Just to make sure I understand your point. >>>>>> >>>>>> Do you mean you plan to notify the unmap of 1) streaming DMA or 2) >>>>>> coherent DMA? >>>>>> >>>>>> For 1) you probably need a workqueue to do that since dma unmap can >>>>>> be done in irq or bh context. And if usrspace does't do the unmap, it >>>>>> can still access the bounce buffer (if you don't zap pte)? >>>>>> >>>>> I plan to do it in the coherent DMA case. >>>> Any reason for treating coherent DMA differently? >>>> >>> Now the memory of the bounce buffer is allocated page by page in the >>> page fault handler. So it can't be used in coherent DMA mapping case >>> which needs some memory with contiguous virtual addresses. I can use >>> vmalloc() to do allocation for the bounce buffer instead. But it might >>> cause some memory waste. Any suggestion? >> >> I may miss something. But I don't see a relationship between the >> IOTLB_UNMAP and vmalloc(). >> > In the vmalloc() case, the coherent DMA page will be taken from the > memory allocated by vmalloc(). So IOTLB_UNMAP is not needed anymore > during coherent DMA unmapping because those vmalloc'ed memory which > has been mapped into userspace address space during initialization can > be reused. And userspace should not unmap the region until we destroy > the device. Just to make sure I understand. My understanding is that IOTLB_UNMAP is only needed when there's a change the mapping from IOVA to page. So if we stick to the mapping, e.g during dma_unmap, we just put IOVA to free list to be used by the next IOVA allocating. IOTLB_UNMAP could be avoided. So we are not limited by how the pages are actually allocated? Thanks > >>>>> It's true that userspace can >>>>> access the dma buffer if userspace doesn't do the unmap. But the dma >>>>> pages would not be freed and reused unless user space called munmap() >>>>> for them. >>>> I wonder whether or not we could recycle IOVA in this case to avoid the >>>> IOTLB_UMAP message. >>>> >>> We can achieve that if we use vmalloc() to do allocation for the >>> bounce buffer which can be used in coherent DMA mapping case. But >>> looks like we still have no way to avoid the IOTLB_UMAP message in >>> vhost-vdpa case. >> >> I think that's fine. For virtio-vdpa, from VDUSE userspace perspective, >> it works like a driver that is using SWIOTLB in this case. >> > OK, will do it in v3. > > Thanks, > Yongji >