From mboxrd@z Thu Jan 1 00:00:00 1970 From: Don Dutile Subject: Re: RFC: vfio / iommu driver for hardware with no iommu Date: Thu, 25 Apr 2013 18:23:36 -0400 Message-ID: <5179ACE8.2030506@redhat.com> References: <9F6FE96B71CF29479FF1CDC8046E15035BE0A3@039-SN1MPN1-002.039d.mgd.msft.net> <1366736189.2918.573.camel@bling.home> <9F6FE96B71CF29479FF1CDC8046E15035BE2BD@039-SN1MPN1-002.039d.mgd.msft.net> <1366746427.2918.650.camel@bling.home> <51783553.80202@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Sethi Varun-B16395 Cc: Yoder Stuart-B08248 , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" List-Id: iommu@lists.linux-foundation.org On 04/24/2013 10:49 PM, Sethi Varun-B16395 wrote: > > >> -----Original Message----- >> From: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org [mailto:iommu- >> bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org] On Behalf Of Don Dutile >> Sent: Thursday, April 25, 2013 1:11 AM >> To: Alex Williamson >> Cc: Yoder Stuart-B08248; iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org >> Subject: Re: RFC: vfio / iommu driver for hardware with no iommu >> >> On 04/23/2013 03:47 PM, Alex Williamson wrote: >>> On Tue, 2013-04-23 at 19:16 +0000, Yoder Stuart-B08248 wrote: >>>> >>>>> -----Original Message----- >>>>> From: Alex Williamson [mailto:alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org] >>>>> Sent: Tuesday, April 23, 2013 11:56 AM >>>>> To: Yoder Stuart-B08248 >>>>> Cc: Joerg Roedel; iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org >>>>> Subject: Re: RFC: vfio / iommu driver for hardware with no iommu >>>>> >>>>> On Tue, 2013-04-23 at 16:13 +0000, Yoder Stuart-B08248 wrote: >>>>>> Joerg/Alex, >>>>>> >>>>>> We have embedded systems where we use QEMU/KVM and have the >>>>>> requirement to do device assignment, but have no iommu. So we >>>>>> would like to get vfio-pci working on systems like this. >>>>>> >>>>>> We're aware of the obvious limitations-- no protection, DMA'able >>>>>> memory must be physically contiguous and will have no iova->phy >>>>>> translation. But there are use cases where all OSes involved are >>>>>> trusted and customers can >>>>>> live with those limitations. Virtualization is used >>>>>> here not to sandbox untrusted code, but to consolidate multiple >>>>>> OSes. >>>>>> >>>>>> We would like to get your feedback on the rough idea. There are >>>>>> two parts-- iommu driver and vfio-pci. >>>>>> >>>>>> 1. iommu driver >>>>>> >>>>>> First, we still need device groups created because vfio is based on >>>>>> that, so we envision a 'dummy' iommu driver that implements only >>>>>> the add/remove device ops. Something like: >>>>>> >>>>>> static struct iommu_ops fsl_none_ops = { >>>>>> .add_device = fsl_none_add_device, >>>>>> .remove_device = fsl_none_remove_device, >>>>>> }; >>>>>> >>>>>> int fsl_iommu_none_init() >>>>>> { >>>>>> int ret = 0; >>>>>> >>>>>> ret = iommu_init_mempool(); >>>>>> if (ret) >>>>>> return ret; >>>>>> >>>>>> bus_set_iommu(&platform_bus_type,&fsl_none_ops); >>>>>> bus_set_iommu(&pci_bus_type,&fsl_none_ops); >>>>>> >>>>>> return ret; >>>>>> } >>>>>> >>>>>> 2. vfio-pci >>>>>> >>>>>> For vfio-pci, we would ideally like to keep user space mostly >>>>>> unchanged. User space will have to follow the semantics of mapping >>>>>> only physically contiguous chunks...and iova will equal phys. >>>>>> >>>>>> So, we propose to implement a new vfio iommu type, called >>>>>> VFIO_TYPE_NONE_IOMMU. This implements any needed vfio interfaces, >>>>>> but there are no calls to the iommu layer...e.g. map_dma() is a >>>>>> noop. >>>>>> >>>>>> Would like your feedback. >>>>> >>>>> My first thought is that this really detracts from vfio and iommu >>>>> groups being a secure interface, so somehow this needs to be clearly >>>>> an insecure mode that requires an opt-in and maybe taints the >>>>> kernel. Any notion of unprivileged use needs to be blocked and it >>>>> should test CAP_COMPROMISE_KERNEL (or whatever it's called now) at >>>>> critical access points. We might even have interfaces exported that >>>>> would allow this to be an out-of-tree driver (worth a check). >>>>> >>>>> I would guess that you would probably want to do all the iommu group >>>>> setup from the vfio fake-iommu driver. In other words, that driver >>>>> both creates the fake groups and provides the dummy iommu backend for >> vfio. >>>>> That would be a nice way to compartmentalize this as a >>>>> vfio-noiommu-special. >>>> >>>> So you mean don't implement any of the iommu driver ops at all and >>>> keep everything in the vfio layer? >>>> >>>> Would you still have real iommu groups?...i.e. >>>> $ readlink /sys/bus/pci/devices/0000:06:0d.0/iommu_group >>>> ../../../../kernel/iommu_groups/26 >>>> >>>> ...and that is created by vfio-noiommu-special? >>> >>> I'm suggesting (but haven't checked if it's possible), to implement >>> the iommu driver ops as part of the vfio iommu backend driver. The >>> primary motivation for this would be to a) keep a fake iommu groups >>> interface out of the iommu proper (possibly containing it in an >>> external driver) and b) modularizing it so we don't have fake iommu >>> groups being created by default. It would have to populate the iommu >>> groups sysfs interfaces to be compatible with vfio. >>> >>>> Right now when the PCI and platform buses are probed, the iommu >>>> driver add-device callback gets called and that is where the >>>> per-device group gets created. Are you envisioning registering a >>>> callback for the PCI bus to do this in vfio-noiommu-special? >>> >>> Yes. It's just as easy to walk all the devices rather than doing >>> callbacks, iirc the group code does this when you register. In fact, >>> this noiommu interface may not want to add all devices, we may want to >>> be very selective and only add some. >>> >> Right. >> Sounds like a no-iommu driver is needed to leave vfio unaffected, and >> still leverage/use vfio for qemu's device assignment. >> Just not sure how to 'taint' it as 'not secure' if no-iommu driver put in >> place. >> >> btw -- qemu has the inherent assumption that pci cfg cycles are trapped, >> so assigned devices are 'remapped' from system-B:D.F to virt- >> machine's >> (virtualized) B:D.F of the assigned device. >> Are pci-cfg cycles trapped in freescale qemu model ? >> > The vfio-pci device would be visible (to a KVM guest) as a PCI device on the virtual PCI bus (emulated by qemu). > > -Varun > Understood, but as Alex stated, the whole purpose of VFIO is to be able to do _secure_, user-level-driven I/O. Since this would be 'unsecure', there should be a way to note that during configuration.