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=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 7EC18C010A2 for ; Tue, 5 Nov 2019 10:55:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5138421929 for ; Tue, 5 Nov 2019 10:55:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Zqx/YjJL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727339AbfKEKzF (ORCPT ); Tue, 5 Nov 2019 05:55:05 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:48071 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727262AbfKEKzF (ORCPT ); Tue, 5 Nov 2019 05:55:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1572951303; 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=Zqx/YjJL72Y+/Y99P4pUosfASu8QX76Bu9AWI3DslZmObASFLkyVz6hDhrjDr/Tv1Nf/Ds bG+63b3EYEeaUlSUm0q1lkWOqvTodR5GqCxT9i8Tl8OgV2Ct9/ervFHU0Qi4alhAuIov1i LCxkhpHo0kzAsA2O4OFFkEHES1hd9G8= 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 Cc: David Stevens , Tomasz Figa , Dmitry Morozov , Alexandre Courbot , Alex Lau , Dylan Reid , =?utf-8?B?U3TDqXBoYW5l?= Marchesin , Pawel Osciak , Hans Verkuil , Daniel Vetter , geoff@hostfission.com, Gurchetan Singh , Linux Media Mailing List , virtio-dev@lists.oasis-open.org, qemu-devel@nongnu.org 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 Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org 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