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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 EC625C010B4 for ; Tue, 5 Nov 2019 10:55:50 +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 BB7A82190F for ; Tue, 5 Nov 2019 10:55:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="DRiSBYA3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BB7A82190F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:42914 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iRwV3-0002xG-Qa for qemu-devel@archiver.kernel.org; Tue, 05 Nov 2019 05:55:49 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:38271) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iRwUM-0002RY-Ma for qemu-devel@nongnu.org; Tue, 05 Nov 2019 05:55:08 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iRwUJ-0002E6-Sv for qemu-devel@nongnu.org; Tue, 05 Nov 2019 05:55:05 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:23311 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iRwUJ-0002DM-Ha for qemu-devel@nongnu.org; Tue, 05 Nov 2019 05:55:03 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1572951302; 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; bh=sIQ1jZwoR2tUq12TbfN95oJSdxSRsIhx/PvNCM2nGQQ=; b=DRiSBYA3lXoj5RPHYc15/Be7Av5BHbKx8j1334nqsL+15uFn8MzhD2Z8BdZ9+FYDVd3PlP Omfuevo+xxZgI5JnXfi82iSOwc7cNcYqx8+7xKjIQYkROfGNJeTadJ67gXquP7dZGJ6ftb Ju547oOhIyrkkLzFsAmHex/Xz81xtyo= 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-220-q3y6bil_Nw-sp9D_30H07Q-1; Tue, 05 Nov 2019 05:55:00 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 45A818017DD; Tue, 5 Nov 2019 10:54:58 +0000 (UTC) Received: from sirius.home.kraxel.org (ovpn-116-69.ams2.redhat.com [10.36.116.69]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9130F46; Tue, 5 Nov 2019 10:54:57 +0000 (UTC) Received: by sirius.home.kraxel.org (Postfix, from userid 1000) id AB9F317535; Tue, 5 Nov 2019 11:54:56 +0100 (CET) Date: Tue, 5 Nov 2019 11:54:56 +0100 From: Gerd Hoffmann To: Keiichi Watanabe Subject: guest / host buffer sharing ... Message-ID: <20191105105456.7xbhtistnbp272lj@sirius.home.kraxel.org> MIME-Version: 1.0 User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: q3y6bil_Nw-sp9D_30H07Q-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 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: , Cc: geoff@hostfission.com, virtio-dev@lists.oasis-open.org, Alex Lau , Alexandre Courbot , qemu-devel@nongnu.org, Tomasz Figa , Hans Verkuil , David Stevens , Daniel Vetter , =?utf-8?B?U3TDqXBoYW5l?= Marchesin , Dylan Reid , Gurchetan Singh , Dmitry Morozov , Pawel Osciak , Linux Media Mailing List Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi folks, The issue of sharing buffers between guests and hosts keeps poping up again and again in different contexts. Most recently here: https://www.mail-archive.com/qemu-devel@nongnu.org/msg656685.html So, I'm grabbing the recipient list of the virtio-vdec thread and some more people I know might be interested in this, hoping to have everyone included. Reason is: Meanwhile I'm wondering whenever "just use virtio-gpu resources" is really a good answer for all the different use cases we have collected over time. Maybe it is better to have a dedicated buffer sharing virtio device? Here is the rough idea: (1) The virtio device =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Has a single virtio queue, so the guest can send commands to register and unregister buffers. Buffers are allocated in guest ram. Each buffer has a list of memory ranges for the data. Each buffer also has some properties to carry metadata, some fixed (id, size, application), but also allow free form (name =3D value, framebuffers would have width/height/stride/format for example). (2) The linux guest implementation =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D I guess I'd try to make it a drm driver, so we can re-use drm infrastructure (shmem helpers for example). Buffers are dumb drm buffers. dma-buf import and export is supported (shmem helpers get us that for free). Some device-specific ioctls to get/set properties and to register/unregister the buffers on the host. (3) The qemu host implementation =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D qemu (likewise other vmms) can use the udmabuf driver to create host-side dma-bufs for the buffers. The dma-bufs can be passed to anyone interested, inside and outside qemu. We'll need some protocol for communication between qemu and external users interested in those buffers, to receive dma-bufs (via unix file descriptor passing) and update notifications. Dispatching updates could be done based on the application property, which could be "virtio-vdec" or "wayland-proxy" for example. commments? cheers, Gerd