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 D88D2C46470 for ; Sun, 5 Aug 2018 21:27:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C993219A6 for ; Sun, 5 Aug 2018 21:27:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C993219A6 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 S1727591AbeHEXdU (ORCPT ); Sun, 5 Aug 2018 19:33:20 -0400 Received: from gate.crashing.org ([63.228.1.57]:33811 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726865AbeHEXdU (ORCPT ); Sun, 5 Aug 2018 19:33:20 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id w75LGmvM030309; Sun, 5 Aug 2018 16:16:49 -0500 Message-ID: Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices From: Benjamin Herrenschmidt To: Christoph Hellwig Cc: "Michael S. Tsirkin" , 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: Mon, 06 Aug 2018 07:16:47 +1000 In-Reply-To: <20180805072930.GB23288@infradead.org> References: <20180802200646-mutt-send-email-mst@kernel.org> <20180802225738-mutt-send-email-mst@kernel.org> <20180803070507.GA1344@infradead.org> <20180803160246.GA13794@infradead.org> <22310f58605169fe9de83abf78b59f593ff7fbb7.camel@kernel.crashing.org> <20180804082120.GB4421@infradead.org> <20180805072930.GB23288@infradead.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 Sun, 2018-08-05 at 00:29 -0700, Christoph Hellwig wrote: > On Sun, Aug 05, 2018 at 11:10:15AM +1000, Benjamin Herrenschmidt wrote: > > - One you have rejected, which is to have a way for "no-iommu" virtio > > (which still doesn't use an iommu on the qemu side and doesn't need > > to), to be forced to use some custom DMA ops on the VM side. > > > > - One, which sadly has more overhead and will require modifying more > > pieces of the puzzle, which is to make qemu uses an emulated iommu. > > Once we make qemu do that, we can then layer swiotlb on top of the > > emulated iommu on the guest side, and pass that as dma_ops to virtio. > > Or number three: have a a virtio feature bit that tells the VM > to use whatever dma ops the platform thinks are appropinquate for > the bus it pretends to be on. Then set a dma-range that is limited > to your secure memory range (if you really need it to be runtime > enabled only after a device reset that rescans) and use the normal > dma mapping code to bounce buffer. Who would set this bit ? qemu ? Under what circumstances ? What would be the effect of this bit while VIRTIO_F_IOMMU is NOT set, ie, what would qemu do and what would Linux do ? I'm not sure I fully understand your idea. I'm trying to understand because the limitation is not a device side limitation, it's not a qemu limitation, it's actually more of a VM limitation. It has most of its memory pages made inaccessible for security reasons. The platform from a qemu/KVM perspective is almost entirely normal. So I don't understand when would qemu set this bit, or should it be set by the VM at runtime ? 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: Mon, 06 Aug 2018 07:16:47 +1000 Message-ID: References: <20180802200646-mutt-send-email-mst@kernel.org> <20180802225738-mutt-send-email-mst@kernel.org> <20180803070507.GA1344@infradead.org> <20180803160246.GA13794@infradead.org> <22310f58605169fe9de83abf78b59f593ff7fbb7.camel@kernel.crashing.org> <20180804082120.GB4421@infradead.org> <20180805072930.GB23288@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180805072930.GB23288@infradead.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: Christoph Hellwig Cc: robh@kernel.org, srikar@linux.vnet.ibm.com, "Michael S. Tsirkin" , mpe@ellerman.id.au, Will Deacon , linux-kernel@vger.kernel.org, linuxram@us.ibm.com, virtualization@lists.linux-foundation.org, 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 Sun, 2018-08-05 at 00:29 -0700, Christoph Hellwig wrote: > On Sun, Aug 05, 2018 at 11:10:15AM +1000, Benjamin Herrenschmidt wrote: > > - One you have rejected, which is to have a way for "no-iommu" virtio > > (which still doesn't use an iommu on the qemu side and doesn't need > > to), to be forced to use some custom DMA ops on the VM side. > > > > - One, which sadly has more overhead and will require modifying more > > pieces of the puzzle, which is to make qemu uses an emulated iommu. > > Once we make qemu do that, we can then layer swiotlb on top of the > > emulated iommu on the guest side, and pass that as dma_ops to virtio. > > Or number three: have a a virtio feature bit that tells the VM > to use whatever dma ops the platform thinks are appropinquate for > the bus it pretends to be on. Then set a dma-range that is limited > to your secure memory range (if you really need it to be runtime > enabled only after a device reset that rescans) and use the normal > dma mapping code to bounce buffer. Who would set this bit ? qemu ? Under what circumstances ? What would be the effect of this bit while VIRTIO_F_IOMMU is NOT set, ie, what would qemu do and what would Linux do ? I'm not sure I fully understand your idea. I'm trying to understand because the limitation is not a device side limitation, it's not a qemu limitation, it's actually more of a VM limitation. It has most of its memory pages made inaccessible for security reasons. The platform from a qemu/KVM perspective is almost entirely normal. So I don't understand when would qemu set this bit, or should it be set by the VM at runtime ? Cheers, Ben.