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=-0.7 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 CFCE3C432C0 for ; Mon, 18 Nov 2019 10:21:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9866C20748 for ; Mon, 18 Nov 2019 10:21:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="pZUgrpV4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726686AbfKRKVH (ORCPT ); Mon, 18 Nov 2019 05:21:07 -0500 Received: from mail-qk1-f196.google.com ([209.85.222.196]:43600 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726460AbfKRKVG (ORCPT ); Mon, 18 Nov 2019 05:21:06 -0500 Received: by mail-qk1-f196.google.com with SMTP id z23so13848046qkj.10 for ; Mon, 18 Nov 2019 02:21:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=p9A0HQCTWo8IkEueIZ8gvaKdgMnDvJwnr6rC9+7dHTk=; b=pZUgrpV46Ejm0ly4g2aa4VANJRCg3njcAsKTWBbzIkV7v9jrgEa/PHjr/+JzVDC8XX xoXyCSlhJE0y1crHp0Q5hKtD3Md0iRErVhRhpa/5F7yWbVv4QN/kqYwuZkcDOAyc+6lX KIhrHYNvx9YB/+5SrEffvrOHh9LtC9awGCoJwh2KTULBsXA0Bgs4167r9HXcoIfvKzdL ppOh4RO1J6+dHQS4xGdYKEicbzBI1I7fRTame0sJT1y613dkEEB28MEMh12MUmCWrfTt PIKw2rYNgqGh1eU9ZNGBpo5WNmqblA0HGiqysXDym0ap0j1STzqEaSSoMU3lUXu8NMlN p8HQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=p9A0HQCTWo8IkEueIZ8gvaKdgMnDvJwnr6rC9+7dHTk=; b=jVdye0CQeBKpF0j3j+ZBADXeZNXYkWpZ8xrq/E9z73vUyQPwTlx4qY6TUOcvXxMqdA XEQlwlCLlVucL6b6hJe0ZpRW48DUfMi/O6xEYhdh3WNjcZf9yzhe5EzCxOFBgBvwrBhR tbYgV1FZYRGe4RFgZaUoOPRXdMXiG7Rp5WjkO+AUoBE2cJ6G5FgGUOynIIOtgkIJ3jQ0 xt8UuONXOZKNRyi2/Z/N3l3Tf1dP5P+NhLr0FcAxQ5CjezU9fAbPobPfpab2iAKO/kkt W/nFa/NEBiNI3HPTpN7ruSr9Ld6BUa6/vGjxclDHO8kez3bIHGN+2EdlvHMQYu7gAVwj ztQQ== X-Gm-Message-State: APjAAAXBxGweG6Jmmhci4VdpNRP5JbkyovtweupTKgM0BWzC2VKmsbKx Bj+LJN5386hYs2fgdXl78EIboEbpCHJ8g9ZE/MQ= X-Google-Smtp-Source: APXvYqz48LbupXsRKsNJSGUqZn5aPb6LZVEB2oQg4AmlOsDZF8A3gLq6CbqzGhMwrDu+IyOPXG6rlv01vOsPaMddWxA= X-Received: by 2002:a05:620a:14a2:: with SMTP id x2mr23572703qkj.236.1574072465398; Mon, 18 Nov 2019 02:21:05 -0800 (PST) MIME-Version: 1.0 References: <20191105105456.7xbhtistnbp272lj@sirius.home.kraxel.org> <20191106084344.GB189998@stefanha-x1.localdomain> <20191106095122.jju7eo57scfoat6a@sirius.home.kraxel.org> <20191106125023.uhdhtqisybilxasr@sirius.home.kraxel.org> <20191108072210.ywyneaoc2y4slth6@sirius.home.kraxel.org> In-Reply-To: From: Stefan Hajnoczi Date: Mon, 18 Nov 2019 10:20:54 +0000 Message-ID: Subject: Re: guest / host buffer sharing ... To: Tomasz Figa Cc: =?UTF-8?Q?St=C3=A9phane_Marchesin?= , Gerd Hoffmann , geoff@hostfission.com, virtio-dev@lists.oasis-open.org, Alex Lau , Daniel Vetter , Alexandre Courbot , qemu-devel , Keiichi Watanabe , David Stevens , Hans Verkuil , Dylan Reid , Gurchetan Singh , Dmitry Morozov , Pawel Osciak , Linux Media Mailing List Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Sat, Nov 9, 2019 at 3:12 PM Tomasz Figa wrote: > > On Sat, Nov 9, 2019 at 9:08 PM Stefan Hajnoczi wrote= : > > > > On Sat, Nov 9, 2019 at 12:17 PM Tomasz Figa wrote: > > > On Sat, Nov 9, 2019 at 7:12 PM Stefan Hajnoczi w= rote: > > > > On Sat, Nov 9, 2019 at 2:41 AM St=C3=A9phane Marchesin wrote: > > > > > On Thu, Nov 7, 2019 at 11:35 PM Stefan Hajnoczi wrote: > > > > > > On Fri, Nov 8, 2019 at 8:22 AM Gerd Hoffmann wrote: > > > > > > > > > Adding a list of common properties to the spec certainly = makes sense, > > > > > > > > > so everybody uses the same names. Adding struct-ed prope= rties for > > > > > > > > > common use cases might be useful too. > > > > > > > > > > > > > > > > Why not define VIRTIO devices for wayland and friends? > > > > > > > > > > > > > > There is an out-of-tree implementation of that, so yes, that = surely is > > > > > > > an option. > > > > > > > > > > > > > > Wayland needs (a) shared buffers, mostly for gfx data, and (b= ) a stream > > > > > > > pipe as control channel. Pretty much the same for X11, excep= t that > > > > > > > shared buffers are optional because the X protocol can also s= queeze all > > > > > > > display updates through the stream pipe. > > > > > > > > > > > > > > So, if you want allow guests talk to the host display server = you can run > > > > > > > the stream pipe over vsock. But there is nothing for the sha= red > > > > > > > buffers ... > > > > > > > > > > > > > > We could replicate vsock functionality elsewhere. I think th= at happened > > > > > > > in the out-of-tree virtio-wayland implementation. There also= was some > > > > > > > discussion about adding streams to virtio-gpu, slightly pimpe= d up so you > > > > > > > can easily pass around virtio-gpu resource references for buf= fer > > > > > > > sharing. But given that getting vsock right isn't exactly tr= ivial > > > > > > > (consider all the fairness issues when multiplexing multiple = streams > > > > > > > over a virtqueue for example) I don't think this is a good pl= an. > > > > > > > > > > > > I also think vsock isn't the right fit. > > > > > > > > > > > > > > > > +1 we are using vsock right now and we have a few pains because o= f it. > > > > > > > > > > I think the high-level problem is that because it is a side chann= el, > > > > > we don't see everything that happens to the buffer in one place > > > > > (rendering + display) and we can't do things like reallocate the > > > > > format accordingly if needed, or we can't do flushing etc. on tha= t > > > > > buffer where needed. > > > > > > > > Do you think a VIRTIO device designed for your use case is an > > > > appropriate solution? > > > > > > > > I have been arguing that these use cases should be addressed with > > > > dedicated VIRTIO devices, but I don't understand the use cases of > > > > everyone on the CC list so maybe I'm missing something :). If ther= e > > > > are reasons why having a VIRTIO device for your use case does not m= ake > > > > sense then it would be good to discuss them. Blockers like "VIRTIO= is > > > > too heavyweight/complex for us because ...", "Our application can't > > > > make use of VIRTIO devices because ...", etc would be important to > > > > hear. > > > > > > Do you have any idea on how to model Wayland as a VIRTIO device? > > > > > > Stephane mentioned that we use vsock, but in fact we have our own > > > VIRTIO device, except that it's semantically almost the same as vsock= , > > > with a difference being the ability to pass buffers and pipes across > > > the VM boundary. > > > > I know neither Wayland nor your use case :). > > > > But we can discuss the design of your VIRTIO device. Please post a > > link to the code. > > The guest-side driver: > https://chromium.googlesource.com/chromiumos/third_party/kernel/+/chromeo= s-4.19/drivers/virtio/virtio_wl.c > > Protocol definitions: > https://chromium.googlesource.com/chromiumos/third_party/kernel/+/chromeo= s-4.19/include/uapi/linux/virtio_wl.h > > crosvm device implementation: > https://chromium.googlesource.com/chromiumos/platform/crosvm/+/refs/heads= /master/devices/src/virtio/wl.rs Thanks, Tomasz! Unfortunately I haven't had a chance to look or catch up on this email thread due to other work that will keep me away for at least another week :(. Stefan