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=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 1CE7AC4321A for ; Fri, 28 Jun 2019 01:59:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E2D7B2064A for ; Fri, 28 Jun 2019 01:59:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726487AbfF1B7K (ORCPT ); Thu, 27 Jun 2019 21:59:10 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:17808 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725770AbfF1B7K (ORCPT ); Thu, 27 Jun 2019 21:59:10 -0400 Received: from pps.filterd (m0098409.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x5S1vDtd041017; Thu, 27 Jun 2019 21:58:49 -0400 Received: from ppma01wdc.us.ibm.com (fd.55.37a9.ip4.static.sl-reverse.com [169.55.85.253]) by mx0a-001b2d01.pphosted.com with ESMTP id 2td76ad7mt-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 27 Jun 2019 21:58:49 -0400 Received: from pps.filterd (ppma01wdc.us.ibm.com [127.0.0.1]) by ppma01wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x5S1tCOI009374; Fri, 28 Jun 2019 01:58:48 GMT Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by ppma01wdc.us.ibm.com with ESMTP id 2t9by7ajaw-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 28 Jun 2019 01:58:48 +0000 Received: from b03ledav005.gho.boulder.ibm.com (b03ledav005.gho.boulder.ibm.com [9.17.130.236]) by b03cxnp07029.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5S1wklw29294852 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 28 Jun 2019 01:58:46 GMT Received: from b03ledav005.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 989EABE04F; Fri, 28 Jun 2019 01:58:46 +0000 (GMT) Received: from b03ledav005.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C8451BE051; Fri, 28 Jun 2019 01:58:42 +0000 (GMT) Received: from morokweng.localdomain (unknown [9.85.218.134]) by b03ledav005.gho.boulder.ibm.com (Postfix) with ESMTPS; Fri, 28 Jun 2019 01:58:42 +0000 (GMT) References: <20190129134750-mutt-send-email-mst@kernel.org> <877eefxvyb.fsf@morokweng.localdomain> <20190204144048-mutt-send-email-mst@kernel.org> <87ef71seve.fsf@morokweng.localdomain> <20190320171027-mutt-send-email-mst@kernel.org> <87tvfvbwpb.fsf@morokweng.localdomain> <20190323165456-mutt-send-email-mst@kernel.org> <87a7go71hz.fsf@morokweng.localdomain> <20190520090939-mutt-send-email-mst@kernel.org> <877ea26tk8.fsf@morokweng.localdomain> <20190603211528-mutt-send-email-mst@kernel.org> User-agent: mu4e 1.2.0; emacs 26.2 From: Thiago Jung Bauermann To: "Michael S. Tsirkin" Cc: virtualization@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Jason Wang , Christoph Hellwig , David Gibson , Alexey Kardashevskiy , Paul Mackerras , Benjamin Herrenschmidt , Ram Pai , Jean-Philippe Brucker , Michael Roth , Mike Anderson Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted In-reply-to: <20190603211528-mutt-send-email-mst@kernel.org> Date: Thu, 27 Jun 2019 22:58:40 -0300 Message-ID: <877e96qxm7.fsf@morokweng.localdomain> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-27_15:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906280014 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Michael S. Tsirkin writes: > On Mon, Jun 03, 2019 at 10:13:59PM -0300, Thiago Jung Bauermann wrote: >> >> >> Michael S. Tsirkin writes: >> >> > On Wed, Apr 17, 2019 at 06:42:00PM -0300, Thiago Jung Bauermann wrote: >> >> I rephrased it in terms of address translation. What do you think of >> >> this version? The flag name is slightly different too: >> >> >> >> >> >> VIRTIO_F_ACCESS_PLATFORM_NO_TRANSLATION This feature has the same >> >> meaning as VIRTIO_F_ACCESS_PLATFORM both when set and when not set, >> >> with the exception that address translation is guaranteed to be >> >> unnecessary when accessing memory addresses supplied to the device >> >> by the driver. Which is to say, the device will always use physical >> >> addresses matching addresses used by the driver (typically meaning >> >> physical addresses used by the CPU) and not translated further. This >> >> flag should be set by the guest if offered, but to allow for >> >> backward-compatibility device implementations allow for it to be >> >> left unset by the guest. It is an error to set both this flag and >> >> VIRTIO_F_ACCESS_PLATFORM. >> > >> > >> > OK so VIRTIO_F_ACCESS_PLATFORM is designed to allow unpriveledged >> > drivers. This is why devices fail when it's not negotiated. >> >> Just to clarify, what do you mean by unprivileged drivers? Is it drivers >> implemented in guest userspace such as with VFIO? Or unprivileged in >> some other sense such as needing to use bounce buffers for some reason? > > I had drivers in guest userspace in mind. Great. Thanks for clarifying. I don't think this flag would work for guest userspace drivers. Should I add a note about that in the flag definition? >> > This confuses me. >> > If driver is unpriveledged then what happens with this flag? >> > It can supply any address it wants. Will that corrupt kernel >> > memory? >> >> Not needing address translation doesn't necessarily mean that there's no >> IOMMU. On powerpc we don't use VIRTIO_F_ACCESS_PLATFORM but there's >> always an IOMMU present. And we also support VFIO drivers. The VFIO API >> for pseries (sPAPR section in Documentation/vfio.txt) has extra ioctls >> to program the IOMMU. >> >> For our use case, we don't need address translation because we set up an >> identity mapping in the IOMMU so that the device can use guest physical >> addresses. > > And can it access any guest physical address? Sorry, I was mistaken. We do support VFIO in guests but not for virtio devices, only for regular PCI devices. In which case they will use address translation. >> If the guest kernel is concerned that an unprivileged driver could >> jeopardize its integrity it should not negotiate this feature flag. > > Unfortunately flag negotiation is done through config space > and so can be overwritten by the driver. Ok, so the guest kernel has to forbid VFIO access on devices where this flag is advertised. >> Perhaps there should be a note about this in the flag definition? This >> concern is platform-dependant though. I don't believe it's an issue in >> pseries. > > Again ACCESS_PLATFORM has a pretty open definition. It does actually > say it's all up to the platform. > > Specifically how will VIRTIO_F_ACCESS_PLATFORM_NO_TRANSLATION be > implemented portably? virtio has no portable way to know > whether DMA API bypasses translation. The fact that VIRTIO_F_ACCESS_PLATFORM_NO_TRANSLATION is set communicates that knowledge to virtio. There is a shared understanding between the guest and the host about what this flag being set means. -- Thiago Jung Bauermann IBM Linux Technology Center 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=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 A791FC4321A for ; Fri, 28 Jun 2019 02:01:04 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 302262064A for ; Fri, 28 Jun 2019 02:01:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 302262064A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 45Zg3L0QkgzDqkX for ; Fri, 28 Jun 2019 12:01:02 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=linux.ibm.com (client-ip=148.163.156.1; helo=mx0a-001b2d01.pphosted.com; envelope-from=bauerman@linux.ibm.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.ibm.com Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 45Zg131Kz4zDqVR for ; Fri, 28 Jun 2019 11:59:02 +1000 (AEST) Received: from pps.filterd (m0098409.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x5S1vDtd041017; Thu, 27 Jun 2019 21:58:49 -0400 Received: from ppma01wdc.us.ibm.com (fd.55.37a9.ip4.static.sl-reverse.com [169.55.85.253]) by mx0a-001b2d01.pphosted.com with ESMTP id 2td76ad7mt-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 27 Jun 2019 21:58:49 -0400 Received: from pps.filterd (ppma01wdc.us.ibm.com [127.0.0.1]) by ppma01wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x5S1tCOI009374; Fri, 28 Jun 2019 01:58:48 GMT Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by ppma01wdc.us.ibm.com with ESMTP id 2t9by7ajaw-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 28 Jun 2019 01:58:48 +0000 Received: from b03ledav005.gho.boulder.ibm.com (b03ledav005.gho.boulder.ibm.com [9.17.130.236]) by b03cxnp07029.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5S1wklw29294852 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 28 Jun 2019 01:58:46 GMT Received: from b03ledav005.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 989EABE04F; Fri, 28 Jun 2019 01:58:46 +0000 (GMT) Received: from b03ledav005.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C8451BE051; Fri, 28 Jun 2019 01:58:42 +0000 (GMT) Received: from morokweng.localdomain (unknown [9.85.218.134]) by b03ledav005.gho.boulder.ibm.com (Postfix) with ESMTPS; Fri, 28 Jun 2019 01:58:42 +0000 (GMT) References: <20190129134750-mutt-send-email-mst@kernel.org> <877eefxvyb.fsf@morokweng.localdomain> <20190204144048-mutt-send-email-mst@kernel.org> <87ef71seve.fsf@morokweng.localdomain> <20190320171027-mutt-send-email-mst@kernel.org> <87tvfvbwpb.fsf@morokweng.localdomain> <20190323165456-mutt-send-email-mst@kernel.org> <87a7go71hz.fsf@morokweng.localdomain> <20190520090939-mutt-send-email-mst@kernel.org> <877ea26tk8.fsf@morokweng.localdomain> <20190603211528-mutt-send-email-mst@kernel.org> User-agent: mu4e 1.2.0; emacs 26.2 From: Thiago Jung Bauermann To: "Michael S. Tsirkin" Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted In-reply-to: <20190603211528-mutt-send-email-mst@kernel.org> Date: Thu, 27 Jun 2019 22:58:40 -0300 Message-ID: <877e96qxm7.fsf@morokweng.localdomain> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-06-27_15:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906280014 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mike Anderson , Michael Roth , Jean-Philippe Brucker , Jason Wang , Alexey Kardashevskiy , Ram Pai , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Christoph Hellwig , David Gibson Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Michael S. Tsirkin writes: > On Mon, Jun 03, 2019 at 10:13:59PM -0300, Thiago Jung Bauermann wrote: >> >> >> Michael S. Tsirkin writes: >> >> > On Wed, Apr 17, 2019 at 06:42:00PM -0300, Thiago Jung Bauermann wrote: >> >> I rephrased it in terms of address translation. What do you think of >> >> this version? The flag name is slightly different too: >> >> >> >> >> >> VIRTIO_F_ACCESS_PLATFORM_NO_TRANSLATION This feature has the same >> >> meaning as VIRTIO_F_ACCESS_PLATFORM both when set and when not set, >> >> with the exception that address translation is guaranteed to be >> >> unnecessary when accessing memory addresses supplied to the device >> >> by the driver. Which is to say, the device will always use physical >> >> addresses matching addresses used by the driver (typically meaning >> >> physical addresses used by the CPU) and not translated further. This >> >> flag should be set by the guest if offered, but to allow for >> >> backward-compatibility device implementations allow for it to be >> >> left unset by the guest. It is an error to set both this flag and >> >> VIRTIO_F_ACCESS_PLATFORM. >> > >> > >> > OK so VIRTIO_F_ACCESS_PLATFORM is designed to allow unpriveledged >> > drivers. This is why devices fail when it's not negotiated. >> >> Just to clarify, what do you mean by unprivileged drivers? Is it drivers >> implemented in guest userspace such as with VFIO? Or unprivileged in >> some other sense such as needing to use bounce buffers for some reason? > > I had drivers in guest userspace in mind. Great. Thanks for clarifying. I don't think this flag would work for guest userspace drivers. Should I add a note about that in the flag definition? >> > This confuses me. >> > If driver is unpriveledged then what happens with this flag? >> > It can supply any address it wants. Will that corrupt kernel >> > memory? >> >> Not needing address translation doesn't necessarily mean that there's no >> IOMMU. On powerpc we don't use VIRTIO_F_ACCESS_PLATFORM but there's >> always an IOMMU present. And we also support VFIO drivers. The VFIO API >> for pseries (sPAPR section in Documentation/vfio.txt) has extra ioctls >> to program the IOMMU. >> >> For our use case, we don't need address translation because we set up an >> identity mapping in the IOMMU so that the device can use guest physical >> addresses. > > And can it access any guest physical address? Sorry, I was mistaken. We do support VFIO in guests but not for virtio devices, only for regular PCI devices. In which case they will use address translation. >> If the guest kernel is concerned that an unprivileged driver could >> jeopardize its integrity it should not negotiate this feature flag. > > Unfortunately flag negotiation is done through config space > and so can be overwritten by the driver. Ok, so the guest kernel has to forbid VFIO access on devices where this flag is advertised. >> Perhaps there should be a note about this in the flag definition? This >> concern is platform-dependant though. I don't believe it's an issue in >> pseries. > > Again ACCESS_PLATFORM has a pretty open definition. It does actually > say it's all up to the platform. > > Specifically how will VIRTIO_F_ACCESS_PLATFORM_NO_TRANSLATION be > implemented portably? virtio has no portable way to know > whether DMA API bypasses translation. The fact that VIRTIO_F_ACCESS_PLATFORM_NO_TRANSLATION is set communicates that knowledge to virtio. There is a shared understanding between the guest and the host about what this flag being set means. -- Thiago Jung Bauermann IBM Linux Technology Center 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=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 69008C4321A for ; Fri, 28 Jun 2019 01:59:02 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 433C82064A for ; Fri, 28 Jun 2019 01:59:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 433C82064A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id CDE7CAA5; Fri, 28 Jun 2019 01:59:01 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 4F8019EE; Fri, 28 Jun 2019 01:59:00 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id AF5B413A; Fri, 28 Jun 2019 01:58:59 +0000 (UTC) Received: from pps.filterd (m0098409.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x5S1vDtd041017; Thu, 27 Jun 2019 21:58:49 -0400 Received: from ppma01wdc.us.ibm.com (fd.55.37a9.ip4.static.sl-reverse.com [169.55.85.253]) by mx0a-001b2d01.pphosted.com with ESMTP id 2td76ad7mt-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 27 Jun 2019 21:58:49 -0400 Received: from pps.filterd (ppma01wdc.us.ibm.com [127.0.0.1]) by ppma01wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x5S1tCOI009374; Fri, 28 Jun 2019 01:58:48 GMT Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by ppma01wdc.us.ibm.com with ESMTP id 2t9by7ajaw-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 28 Jun 2019 01:58:48 +0000 Received: from b03ledav005.gho.boulder.ibm.com (b03ledav005.gho.boulder.ibm.com [9.17.130.236]) by b03cxnp07029.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5S1wklw29294852 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 28 Jun 2019 01:58:46 GMT Received: from b03ledav005.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 989EABE04F; Fri, 28 Jun 2019 01:58:46 +0000 (GMT) Received: from b03ledav005.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C8451BE051; Fri, 28 Jun 2019 01:58:42 +0000 (GMT) Received: from morokweng.localdomain (unknown [9.85.218.134]) by b03ledav005.gho.boulder.ibm.com (Postfix) with ESMTPS; Fri, 28 Jun 2019 01:58:42 +0000 (GMT) References: <20190129134750-mutt-send-email-mst@kernel.org> <877eefxvyb.fsf@morokweng.localdomain> <20190204144048-mutt-send-email-mst@kernel.org> <87ef71seve.fsf@morokweng.localdomain> <20190320171027-mutt-send-email-mst@kernel.org> <87tvfvbwpb.fsf@morokweng.localdomain> <20190323165456-mutt-send-email-mst@kernel.org> <87a7go71hz.fsf@morokweng.localdomain> <20190520090939-mutt-send-email-mst@kernel.org> <877ea26tk8.fsf@morokweng.localdomain> <20190603211528-mutt-send-email-mst@kernel.org> User-agent: mu4e 1.2.0; emacs 26.2 From: Thiago Jung Bauermann To: "Michael S. Tsirkin" Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted In-reply-to: <20190603211528-mutt-send-email-mst@kernel.org> Date: Thu, 27 Jun 2019 22:58:40 -0300 Message-ID: <877e96qxm7.fsf@morokweng.localdomain> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-06-27_15:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906280014 Cc: Mike Anderson , Michael Roth , Jean-Philippe Brucker , Benjamin Herrenschmidt , Jason Wang , Alexey Kardashevskiy , Ram Pai , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Paul Mackerras , iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Christoph Hellwig , David Gibson X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 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 Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org Michael S. Tsirkin writes: > On Mon, Jun 03, 2019 at 10:13:59PM -0300, Thiago Jung Bauermann wrote: >> >> >> Michael S. Tsirkin writes: >> >> > On Wed, Apr 17, 2019 at 06:42:00PM -0300, Thiago Jung Bauermann wrote: >> >> I rephrased it in terms of address translation. What do you think of >> >> this version? The flag name is slightly different too: >> >> >> >> >> >> VIRTIO_F_ACCESS_PLATFORM_NO_TRANSLATION This feature has the same >> >> meaning as VIRTIO_F_ACCESS_PLATFORM both when set and when not set, >> >> with the exception that address translation is guaranteed to be >> >> unnecessary when accessing memory addresses supplied to the device >> >> by the driver. Which is to say, the device will always use physical >> >> addresses matching addresses used by the driver (typically meaning >> >> physical addresses used by the CPU) and not translated further. This >> >> flag should be set by the guest if offered, but to allow for >> >> backward-compatibility device implementations allow for it to be >> >> left unset by the guest. It is an error to set both this flag and >> >> VIRTIO_F_ACCESS_PLATFORM. >> > >> > >> > OK so VIRTIO_F_ACCESS_PLATFORM is designed to allow unpriveledged >> > drivers. This is why devices fail when it's not negotiated. >> >> Just to clarify, what do you mean by unprivileged drivers? Is it drivers >> implemented in guest userspace such as with VFIO? Or unprivileged in >> some other sense such as needing to use bounce buffers for some reason? > > I had drivers in guest userspace in mind. Great. Thanks for clarifying. I don't think this flag would work for guest userspace drivers. Should I add a note about that in the flag definition? >> > This confuses me. >> > If driver is unpriveledged then what happens with this flag? >> > It can supply any address it wants. Will that corrupt kernel >> > memory? >> >> Not needing address translation doesn't necessarily mean that there's no >> IOMMU. On powerpc we don't use VIRTIO_F_ACCESS_PLATFORM but there's >> always an IOMMU present. And we also support VFIO drivers. The VFIO API >> for pseries (sPAPR section in Documentation/vfio.txt) has extra ioctls >> to program the IOMMU. >> >> For our use case, we don't need address translation because we set up an >> identity mapping in the IOMMU so that the device can use guest physical >> addresses. > > And can it access any guest physical address? Sorry, I was mistaken. We do support VFIO in guests but not for virtio devices, only for regular PCI devices. In which case they will use address translation. >> If the guest kernel is concerned that an unprivileged driver could >> jeopardize its integrity it should not negotiate this feature flag. > > Unfortunately flag negotiation is done through config space > and so can be overwritten by the driver. Ok, so the guest kernel has to forbid VFIO access on devices where this flag is advertised. >> Perhaps there should be a note about this in the flag definition? This >> concern is platform-dependant though. I don't believe it's an issue in >> pseries. > > Again ACCESS_PLATFORM has a pretty open definition. It does actually > say it's all up to the platform. > > Specifically how will VIRTIO_F_ACCESS_PLATFORM_NO_TRANSLATION be > implemented portably? virtio has no portable way to know > whether DMA API bypasses translation. The fact that VIRTIO_F_ACCESS_PLATFORM_NO_TRANSLATION is set communicates that knowledge to virtio. There is a shared understanding between the guest and the host about what this flag being set means. -- Thiago Jung Bauermann IBM Linux Technology Center _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu