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=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 64965C433DF for ; Wed, 1 Jul 2020 13:35:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D08B20760 for ; Wed, 1 Jul 2020 13:35:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="hlKDnjFX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731146AbgGANfM (ORCPT ); Wed, 1 Jul 2020 09:35:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42344 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730916AbgGANfM (ORCPT ); Wed, 1 Jul 2020 09:35:12 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1793DC08C5C1 for ; Wed, 1 Jul 2020 06:35:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=6o0bqYA9UibQkqr/MmLZIfw1Phn9yQ8zQ1ln3u9Cm/E=; b=hlKDnjFXs/Y5WjrWNNgSQ+2Cvd RvsmfMbhXkV1KC+OK+5x7CGESEtA1Qk4HZeAu6Yaz/UH9zEAUbNa9FVjAhV4Duiv/yAyXRv3/1ni3 CSmwa08RJtybgECUGXsj6t5Ikz9WU8jXnEjZhSsiO4Cce5bMLn+ryrsvUEQAfHt3Y/kj2M4b29Xj0 2lORXLltD3a0Za4R4fVC/+lv0bptUhSUEHkFmEDfSV3phIa7QD/g3Q2Zle+t27uSL2Zcfg1ARrlES xPbJ0Leq9BQuYJ3vQmrkn81G/oqYWCgAUIa51MwnCk73e/oMjUpHEK7/k+Ajj3vJC3XBgczD+ReMg 1fAQgQbQ==; Received: from hch by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqct6-0006Qi-2K; Wed, 01 Jul 2020 13:34:56 +0000 Date: Wed, 1 Jul 2020 14:34:56 +0100 From: Christoph Hellwig To: Stefano Stabellini Cc: "Michael S. Tsirkin" , Peng Fan , boris.ostrovsky@oracle.com, jgross@suse.com, konrad.wilk@oracle.com, jasowang@redhat.com, x86@kernel.org, xen-devel@lists.xenproject.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, virtualization@lists.linux-foundation.org, linux-imx@nxp.com Subject: Re: [PATCH] xen: introduce xen_vring_use_dma Message-ID: <20200701133456.GA23888@infradead.org> References: <20200624091732.23944-1-peng.fan@nxp.com> <20200624050355-mutt-send-email-mst@kernel.org> <20200624163940-mutt-send-email-mst@kernel.org> <20200624181026-mutt-send-email-mst@kernel.org> <20200626110629-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 29, 2020 at 04:46:09PM -0700, Stefano Stabellini wrote: > > I could imagine some future Xen hosts setting a flag somewhere in the > > platform capability saying "no xen specific flag, rely on > > "VIRTIO_F_ACCESS_PLATFORM". Then you set that accordingly in QEMU. > > How about that? > > Yes, that would be fine and there is no problem implementing something > like that when we get virtio support in Xen. Today there are still no > virtio interfaces provided by Xen to ARM guests (no virtio-block/net, > etc.) > > In fact, in both cases we are discussing virtio is *not* provided by > Xen; it is a firmware interface to something entirely different: > > 1) virtio is used to talk to a remote AMP processor (RPMesg) > 2) virtio is used to talk to a secure-world firmware/OS (Trusty) > > VIRTIO_F_ACCESS_PLATFORM is not set by Xen in these cases but by RPMesg > and by Trusty respectively. I don't know if Trusty should or should not > set VIRTIO_F_ACCESS_PLATFORM, but I think Linux should still work > without issues. > Any virtio implementation that is not in control of the memory map (aka not the hypervisor) absolutely must set VIRTIO_F_ACCESS_PLATFORM, else it is completely broken. > The xen_domain() check in Linux makes it so that vring_use_dma_api > returns the opposite value on native Linux compared to Linux as Xen/ARM > DomU by "accident". By "accident" because there is no architectural > reason why Linux Xen/ARM DomU should behave differently compared to > native Linux in this regard. > > I hope that now it is clearer why I think the if (xen_domain()) check > needs to be improved anyway, even if we fix generic dma_ops with virtio > interfaces missing VIRTIO_F_ACCESS_PLATFORM. IMHO that Xen quirk should never have been added in this form..