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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 8790DC43142 for ; Thu, 2 Aug 2018 17:54:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4943021530 for ; Thu, 2 Aug 2018 17:54:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4943021530 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732285AbeHBTrH (ORCPT ); Thu, 2 Aug 2018 15:47:07 -0400 Received: from gate.crashing.org ([63.228.1.57]:49248 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726318AbeHBTrF (ORCPT ); Thu, 2 Aug 2018 15:47:05 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id w72HrfJP026998; Thu, 2 Aug 2018 12:53:42 -0500 Message-ID: Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices From: Benjamin Herrenschmidt To: "Michael S. Tsirkin" Cc: Christoph Hellwig , Will Deacon , Anshuman Khandual , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, aik@ozlabs.ru, robh@kernel.org, joe@perches.com, elfring@users.sourceforge.net, david@gibson.dropbear.id.au, jasowang@redhat.com, mpe@ellerman.id.au, linuxram@us.ibm.com, haren@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com, robin.murphy@arm.com, jean-philippe.brucker@arm.com, marc.zyngier@arm.com Date: Thu, 02 Aug 2018 12:53:41 -0500 In-Reply-To: <20180802200646-mutt-send-email-mst@kernel.org> References: <20180730125100-mutt-send-email-mst@kernel.org> <20180730111802.GA9830@infradead.org> <20180730155633-mutt-send-email-mst@kernel.org> <20180731173052.GA17153@infradead.org> <3d6e81511571260de1c8047aaffa8ac4df093d2e.camel@kernel.crashing.org> <20180801081637.GA14438@arm.com> <20180801083639.GF26378@infradead.org> <26c1d3d50d8e081eed44fe9940fbefed34598cbd.camel@kernel.crashing.org> <20180802182959-mutt-send-email-mst@kernel.org> <82ccef6ec3d95ee43f3990a4a2d0aea87eb45e89.camel@kernel.crashing.org> <20180802200646-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.4 (3.28.4-1.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2018-08-02 at 20:19 +0300, Michael S. Tsirkin wrote: > > I see. So yes, given that device does not know or care, using > virtio features is an awkward fit. > > So let's say as a quick fix for you maybe we could generalize the > xen_domain hack, instead of just checking xen_domain check some static > branch. Then teach xen and others to enable that.> > OK but problem then becomes this: if you do this and virtio device appears > behind a vIOMMU and it does not advertize the IOMMU flag, the > code will try to use the vIOMMU mappings and fail. > > It does look like even with trick above, you need a special version of > DMA ops that does just swiotlb but not any of the other things DMA API > might do. > > Thoughts? Yes, this is the purpose of Anshuman original patch (I haven't looked at the details of the patch in a while but that's what I told him to implement ;-) : - Make virtio always use DMA ops to simplify the code path (with a set of "transparent" ops for legacy) and - Provide an arch hook allowing us to "override" those "transparent" DMA ops with some custom ones that do the appropriate swiotlb gunk. Cheers, Ben. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Date: Thu, 02 Aug 2018 12:53:41 -0500 Message-ID: References: <20180730125100-mutt-send-email-mst@kernel.org> <20180730111802.GA9830@infradead.org> <20180730155633-mutt-send-email-mst@kernel.org> <20180731173052.GA17153@infradead.org> <3d6e81511571260de1c8047aaffa8ac4df093d2e.camel@kernel.crashing.org> <20180801081637.GA14438@arm.com> <20180801083639.GF26378@infradead.org> <26c1d3d50d8e081eed44fe9940fbefed34598cbd.camel@kernel.crashing.org> <20180802182959-mutt-send-email-mst@kernel.org> <82ccef6ec3d95ee43f3990a4a2d0aea87eb45e89.camel@kernel.crashing.org> <20180802200646-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180802200646-mutt-send-email-mst@kernel.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: robh@kernel.org, srikar@linux.vnet.ibm.com, mpe@ellerman.id.au, Will Deacon , linux-kernel@vger.kernel.org, linuxram@us.ibm.com, virtualization@lists.linux-foundation.org, Christoph Hellwig , paulus@samba.org, marc.zyngier@arm.com, joe@perches.com, robin.murphy@arm.com, david@gibson.dropbear.id.au, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net, haren@linux.vnet.ibm.com, Anshuman Khandual List-Id: virtualization@lists.linuxfoundation.org On Thu, 2018-08-02 at 20:19 +0300, Michael S. Tsirkin wrote: > > I see. So yes, given that device does not know or care, using > virtio features is an awkward fit. > > So let's say as a quick fix for you maybe we could generalize the > xen_domain hack, instead of just checking xen_domain check some static > branch. Then teach xen and others to enable that.> > OK but problem then becomes this: if you do this and virtio device appears > behind a vIOMMU and it does not advertize the IOMMU flag, the > code will try to use the vIOMMU mappings and fail. > > It does look like even with trick above, you need a special version of > DMA ops that does just swiotlb but not any of the other things DMA API > might do. > > Thoughts? Yes, this is the purpose of Anshuman original patch (I haven't looked at the details of the patch in a while but that's what I told him to implement ;-) : - Make virtio always use DMA ops to simplify the code path (with a set of "transparent" ops for legacy) and - Provide an arch hook allowing us to "override" those "transparent" DMA ops with some custom ones that do the appropriate swiotlb gunk. Cheers, Ben.