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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 0E534C433E0 for ; Wed, 1 Jul 2020 17:34:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D6365207BB for ; Wed, 1 Jul 2020 17:34:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593624897; bh=7gRGt637RJr7xqh8m9IFhKHH4colOY8f4NtES4RwwhY=; h=Date:From:To:cc:Subject:In-Reply-To:References:List-ID:From; b=dX0OXV2/xGkTkqPkm2654wZO6nA+67k03Kqpl9RmM6NkuD19cmrtKSXEY2DCbTdew gOs1Km1buEgpPYqY+eWDI0E9hDvu04zj+BtiWNC7Ec6hp0/lIKskevWRs5TaTT6QwI CHXOe9Ml2JigSoExrAxuMS7ANiKArTMeTKmw08ek= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732597AbgGARe4 (ORCPT ); Wed, 1 Jul 2020 13:34:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:40520 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726432AbgGARez (ORCPT ); Wed, 1 Jul 2020 13:34:55 -0400 Received: from localhost (c-67-164-102-47.hsd1.ca.comcast.net [67.164.102.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5CDCB20781; Wed, 1 Jul 2020 17:34:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593624894; bh=7gRGt637RJr7xqh8m9IFhKHH4colOY8f4NtES4RwwhY=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=s4JTo+sHZ5kueHTuTEAo2QGy2uhqmeAHdidNDEG2j3pV3VxRg5Xv6wKav2TR+6t4b XUiS73u1pvO97HpBjUcfEuJ+XpBhQ0M0mFiLtwwqKmYcxdiCP4RGhschpBHp6VSQJP m93SVv9K90jHvPW8nUrDpWPn4XcEaTHFUj4sKDZM= Date: Wed, 1 Jul 2020 10:34:53 -0700 (PDT) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-T480s To: Christoph Hellwig cc: Stefano Stabellini , jgross@suse.com, Peng Fan , x86@kernel.org, konrad.wilk@oracle.com, jasowang@redhat.com, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, iommu@lists.linux-foundation.org, linux-imx@nxp.com, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] xen: introduce xen_vring_use_dma In-Reply-To: <20200701133456.GA23888@infradead.org> Message-ID: 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> <20200701133456.GA23888@infradead.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 1 Jul 2020, Christoph Hellwig wrote: > 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. Lots of broken virtio implementations out there it would seem :-( > > 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.. Would you be in favor of a more flexible check along the lines of the one proposed in the patch that started this thread: if (xen_vring_use_dma()) return true; xen_vring_use_dma would be implemented so that it returns true when xen_swiotlb is required and false otherwise. 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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 B6087C433DF for ; Wed, 1 Jul 2020 17:34:59 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (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 7D00720781 for ; Wed, 1 Jul 2020 17:34:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="s4JTo+sH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7D00720781 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 5417C8AD3F; Wed, 1 Jul 2020 17:34:59 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 3ar+RwzBkn1D; Wed, 1 Jul 2020 17:34:58 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id B26038AAF4; Wed, 1 Jul 2020 17:34:58 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id A1BB8C0890; Wed, 1 Jul 2020 17:34:58 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 9599AC0733; Wed, 1 Jul 2020 17:34:56 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 75BE38BD7E; Wed, 1 Jul 2020 17:34:56 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id aIzjPfczqmQJ; Wed, 1 Jul 2020 17:34:55 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by whitealder.osuosl.org (Postfix) with ESMTPS id 2C9818BD86; Wed, 1 Jul 2020 17:34:55 +0000 (UTC) Received: from localhost (c-67-164-102-47.hsd1.ca.comcast.net [67.164.102.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5CDCB20781; Wed, 1 Jul 2020 17:34:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593624894; bh=7gRGt637RJr7xqh8m9IFhKHH4colOY8f4NtES4RwwhY=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=s4JTo+sHZ5kueHTuTEAo2QGy2uhqmeAHdidNDEG2j3pV3VxRg5Xv6wKav2TR+6t4b XUiS73u1pvO97HpBjUcfEuJ+XpBhQ0M0mFiLtwwqKmYcxdiCP4RGhschpBHp6VSQJP m93SVv9K90jHvPW8nUrDpWPn4XcEaTHFUj4sKDZM= Date: Wed, 1 Jul 2020 10:34:53 -0700 (PDT) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-T480s To: Christoph Hellwig Subject: Re: [PATCH] xen: introduce xen_vring_use_dma In-Reply-To: <20200701133456.GA23888@infradead.org> Message-ID: 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> <20200701133456.GA23888@infradead.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Cc: jgross@suse.com, Peng Fan , Stefano Stabellini , konrad.wilk@oracle.com, jasowang@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, iommu@lists.linux-foundation.org, "Michael S. Tsirkin" , linux-imx@nxp.com, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com, linux-arm-kernel@lists.infradead.org X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Wed, 1 Jul 2020, Christoph Hellwig wrote: > 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. Lots of broken virtio implementations out there it would seem :-( > > 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.. Would you be in favor of a more flexible check along the lines of the one proposed in the patch that started this thread: if (xen_vring_use_dma()) return true; xen_vring_use_dma would be implemented so that it returns true when xen_swiotlb is required and false otherwise. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu 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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 C98FFC433DF for ; Wed, 1 Jul 2020 17:36:29 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 9684120780 for ; Wed, 1 Jul 2020 17:36:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Imc6z6+e"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="s4JTo+sH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9684120780 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:References:Message-ID:In-Reply-To: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=uz2QxUVwuIDjRc8OsHbrbE+Kv4bsI1jQ0tM5MZyC1F8=; b=Imc6z6+e1hJt0VHIWCTWaWnkf Sot670dlJuDDs5WbMY6PxU7QGCSkwvQehEbDaGQw3v52vtEp/xij70QB6cbq1430UyIRBpJc0EuRw NsSVWClBSS81Kpx38ztigfCjqihLJWkwwHFMRDXkJCgeDdo4wOzJfO7VgpblFtOjNy/AZFjTlOtJy kw3ApFDDeN/5EACZvflqbFoe08lYcKIzgO6vZQT4W526KnMSb1LfssCLXws5lSkDKWd8bkTSzAypK tFRNQiS4ZefGHSBsedAR77SKoX1YP9/znH8KojgIOTgYUyzQ6UsAWhYiD4yyi5YlDAV9ux4BCXtFS QU6NtLk9w==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqgdQ-0001Yx-7U; Wed, 01 Jul 2020 17:35:00 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqgdM-0001Vj-Db for linux-arm-kernel@lists.infradead.org; Wed, 01 Jul 2020 17:34:58 +0000 Received: from localhost (c-67-164-102-47.hsd1.ca.comcast.net [67.164.102.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5CDCB20781; Wed, 1 Jul 2020 17:34:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593624894; bh=7gRGt637RJr7xqh8m9IFhKHH4colOY8f4NtES4RwwhY=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=s4JTo+sHZ5kueHTuTEAo2QGy2uhqmeAHdidNDEG2j3pV3VxRg5Xv6wKav2TR+6t4b XUiS73u1pvO97HpBjUcfEuJ+XpBhQ0M0mFiLtwwqKmYcxdiCP4RGhschpBHp6VSQJP m93SVv9K90jHvPW8nUrDpWPn4XcEaTHFUj4sKDZM= Date: Wed, 1 Jul 2020 10:34:53 -0700 (PDT) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-T480s To: Christoph Hellwig Subject: Re: [PATCH] xen: introduce xen_vring_use_dma In-Reply-To: <20200701133456.GA23888@infradead.org> Message-ID: 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> <20200701133456.GA23888@infradead.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200701_133456_641809_E36DBD39 X-CRM114-Status: GOOD ( 24.85 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: jgross@suse.com, Peng Fan , Stefano Stabellini , konrad.wilk@oracle.com, jasowang@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, iommu@lists.linux-foundation.org, "Michael S. Tsirkin" , linux-imx@nxp.com, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, 1 Jul 2020, Christoph Hellwig wrote: > 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. Lots of broken virtio implementations out there it would seem :-( > > 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.. Would you be in favor of a more flexible check along the lines of the one proposed in the patch that started this thread: if (xen_vring_use_dma()) return true; xen_vring_use_dma would be implemented so that it returns true when xen_swiotlb is required and false otherwise. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 DAB3CC433E0 for ; Wed, 1 Jul 2020 17:36:01 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 A735E20780 for ; Wed, 1 Jul 2020 17:36:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="s4JTo+sH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A735E20780 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jqgdN-00005x-Ge; Wed, 01 Jul 2020 17:34:57 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jqgdM-00005s-8c for xen-devel@lists.xenproject.org; Wed, 01 Jul 2020 17:34:56 +0000 X-Inumbo-ID: 2d5a53fc-bbc1-11ea-874c-12813bfff9fa Received: from mail.kernel.org (unknown [198.145.29.99]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 2d5a53fc-bbc1-11ea-874c-12813bfff9fa; Wed, 01 Jul 2020 17:34:55 +0000 (UTC) Received: from localhost (c-67-164-102-47.hsd1.ca.comcast.net [67.164.102.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5CDCB20781; Wed, 1 Jul 2020 17:34:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593624894; bh=7gRGt637RJr7xqh8m9IFhKHH4colOY8f4NtES4RwwhY=; h=Date:From:To:cc:Subject:In-Reply-To:References:From; b=s4JTo+sHZ5kueHTuTEAo2QGy2uhqmeAHdidNDEG2j3pV3VxRg5Xv6wKav2TR+6t4b XUiS73u1pvO97HpBjUcfEuJ+XpBhQ0M0mFiLtwwqKmYcxdiCP4RGhschpBHp6VSQJP m93SVv9K90jHvPW8nUrDpWPn4XcEaTHFUj4sKDZM= Date: Wed, 1 Jul 2020 10:34:53 -0700 (PDT) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-T480s To: Christoph Hellwig Subject: Re: [PATCH] xen: introduce xen_vring_use_dma In-Reply-To: <20200701133456.GA23888@infradead.org> Message-ID: 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> <20200701133456.GA23888@infradead.org> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: jgross@suse.com, Peng Fan , Stefano Stabellini , konrad.wilk@oracle.com, jasowang@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, iommu@lists.linux-foundation.org, "Michael S. Tsirkin" , linux-imx@nxp.com, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com, linux-arm-kernel@lists.infradead.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On Wed, 1 Jul 2020, Christoph Hellwig wrote: > 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. Lots of broken virtio implementations out there it would seem :-( > > 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.. Would you be in favor of a more flexible check along the lines of the one proposed in the patch that started this thread: if (xen_vring_use_dma()) return true; xen_vring_use_dma would be implemented so that it returns true when xen_swiotlb is required and false otherwise.