From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-1.mimecast.com ([205.139.110.61]:38225 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728109AbgFSJVJ (ORCPT ); Fri, 19 Jun 2020 05:21:09 -0400 Date: Fri, 19 Jun 2020 11:20:51 +0200 From: Cornelia Huck Subject: Re: [PATCH v3 1/1] s390: virtio: let arch accept devices without IOMMU feature Message-ID: <20200619112051.74babdb1.cohuck@redhat.com> In-Reply-To: <20200618002956.5f179de4.pasic@linux.ibm.com> References: <1592390637-17441-1-git-send-email-pmorel@linux.ibm.com> <1592390637-17441-2-git-send-email-pmorel@linux.ibm.com> <20200618002956.5f179de4.pasic@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Halil Pasic Cc: Pierre Morel , linux-kernel@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, mst@redhat.com, jasowang@redhat.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org, virtualization@lists.linux-foundation.org, thomas.lendacky@amd.com, david@gibson.dropbear.id.au, linuxram@us.ibm.com, heiko.carstens@de.ibm.com, gor@linux.ibm.com On Thu, 18 Jun 2020 00:29:56 +0200 Halil Pasic wrote: > On Wed, 17 Jun 2020 12:43:57 +0200 > Pierre Morel wrote: > > > An architecture protecting the guest memory against unauthorized host > > access may want to enforce VIRTIO I/O device protection through the > > use of VIRTIO_F_IOMMU_PLATFORM. > > > > Let's give a chance to the architecture to accept or not devices > > without VIRTIO_F_IOMMU_PLATFORM. > > > [..] > > > I'm still not really satisfied with your commit message, furthermore > I did some thinking about the abstraction you introduce here. I will > give a short analysis of that, but first things first. Your patch does > the job of preventing calamity, and the details can be changed any time, > thus: > > Acked-by: Halil Pasic > > Regarding the interaction of architecture specific code with virtio core, > I believe we could have made the interface more generic. > > One option is to introduce virtio_arch_finalize_features(), a hook that > could reject any feature that is inappropriate. s/any feature/any combination of features/ This sounds like a good idea (for a later update). > > Another option would be to find a common name for is_prot_virt_guest() > (arch/s390) sev_active() (arch/x86) and is_secure_guest() (arch/powerpc) > and use that instead of arch_needs_virtio_iommu_platform() and where-ever > appropriate. Currently we seem to want this info in driver code only for > virtio, but if the virtio driver has a legitimate need to know, other > drivers may as well have a legitimate need to know. For example if we > wanted to protect ourselves in ccw device drivers from somebody > setting up a vfio-ccw device and attach it to the prot-virt guest (AFAICT > we only lack guest enablement for this) such a function could be useful. I'm not really sure if we can find enough commonality between architectures, unless you propose to have a function for checking things like device memory only. > > But since this can be rewritten any time, let's go with the option > people already agree with, instead of more discussion. Yes, there's nothing wrong with the patch as-is. Acked-by: Cornelia Huck Which tree should this go through? Virtio? s390? > > Just another question. Do we want this backported? Do we need cc stable? It does change behaviour of virtio-ccw devices; but then, it only fences off configurations that would not have worked anyway. Distributions should probably pick this; but I do not consider it strictly a "fix" (more a mitigation for broken configurations), so I'm not sure whether stable applies. > [..] > > > > int virtio_finalize_features(struct virtio_device *dev) > > { > > int ret = dev->config->finalize_features(dev); > > @@ -179,6 +194,13 @@ int virtio_finalize_features(struct virtio_device *dev) > > if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) > > return 0; > > > > + if (arch_needs_virtio_iommu_platform(dev) && > > + !virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) { > > + dev_warn(&dev->dev, > > + "virtio: device must provide VIRTIO_F_IOMMU_PLATFORM\n"); > > I'm not sure, divulging the current Linux name of this feature bit is a > good idea, but if everybody else is fine with this, I don't care that Not sure if that feature name will ever change, as it is exported in headers. At most, we might want to add the new ACCESS_PLATFORM define and keep the old one, but that would still mean some churn. > much. An alternative would be: > "virtio: device falsely claims to have full access to the memory, > aborting the device" "virtio: device does not work with limited memory access" ? But no issue with keeping the current message.