From patchwork Wed May 30 05:34:21 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alex Williamson X-Patchwork-Id: 161864 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id EBED9B6FF4 for ; Wed, 30 May 2012 15:36:16 +1000 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756685Ab2E3Feo (ORCPT ); Wed, 30 May 2012 01:34:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42756 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753492Ab2E3Fem (ORCPT ); Wed, 30 May 2012 01:34:42 -0400 Received: from int-mx12.intmail.prod.int.phx2.redhat.com (int-mx12.intmail.prod.int.phx2.redhat.com [10.5.11.25]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q4U5YNJo013619 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Wed, 30 May 2012 01:34:23 -0400 Received: from bling.home (ovpn-113-39.phx2.redhat.com [10.3.113.39]) by int-mx12.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id q4U5YLvX028567; Wed, 30 May 2012 01:34:22 -0400 From: Alex Williamson Subject: [PATCH 2/4] vfio: Add documentation To: benh@kernel.crashing.org, aik@ozlabs.ru, david@gibson.dropbear.id.au, gregkh@linuxfoundation.org Cc: joerg.roedel@amd.com, dwmw2@infradead.org, chrisw@sous-sol.org, agraf@suse.de, benve@cisco.com, aafabbri@cisco.com, B08248@freescale.com, B07421@freescale.com, avi@redhat.com, konrad.wilk@oracle.com, kvm@vger.kernel.org, qemu-devel@nongnu.org, iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, bhelgaas@google.com, ddutile@redhat.com, alex.williamson@redhat.com Date: Tue, 29 May 2012 23:34:21 -0600 Message-ID: <20120530053421.1934.61469.stgit@bling.home> In-Reply-To: <20120530051317.1934.28218.stgit@bling.home> References: <20120530051317.1934.28218.stgit@bling.home> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.68 on 10.5.11.25 Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org Signed-off-by: Alex Williamson --- Documentation/vfio.txt | 315 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 315 insertions(+) create mode 100644 Documentation/vfio.txt -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt new file mode 100644 index 0000000..1240874 --- /dev/null +++ b/Documentation/vfio.txt @@ -0,0 +1,315 @@ +VFIO - "Virtual Function I/O"[1] +------------------------------------------------------------------------------- +Many modern system now provide DMA and interrupt remapping facilities +to help ensure I/O devices behave within the boundaries they've been +allotted. This includes x86 hardware with AMD-Vi and Intel VT-d, +POWER systems with Partitionable Endpoints (PEs) and embedded PowerPC +systems such as Freescale PAMU. The VFIO driver is an IOMMU/device +agnostic framework for exposing direct device access to userspace, in +a secure, IOMMU protected environment. In other words, this allows +safe[2], non-privileged, userspace drivers. + +Why do we want that? Virtual machines often make use of direct device +access ("device assignment") when configured for the highest possible +I/O performance. From a device and host perspective, this simply +turns the VM into a userspace driver, with the benefits of +significantly reduced latency, higher bandwidth, and direct use of +bare-metal device drivers[3]. + +Some applications, particularly in the high performance computing +field, also benefit from low-overhead, direct device access from +userspace. Examples include network adapters (often non-TCP/IP based) +and compute accelerators. Prior to VFIO, these drivers had to either +go through the full development cycle to become proper upstream +driver, be maintained out of tree, or make use of the UIO framework, +which has no notion of IOMMU protection, limited interrupt support, +and requires root privileges to access things like PCI configuration +space. + +The VFIO driver framework intends to unify these, replacing both the +KVM PCI specific device assignment code as well as provide a more +secure, more featureful userspace driver environment than UIO. + +Groups, Devices, and IOMMUs +------------------------------------------------------------------------------- + +Devices are the main target of any I/O driver. Devices typically +create a programming interface made up of I/O access, interrupts, +and DMA. Without going into the details of each of these, DMA is +by far the most critical aspect for maintaining a secure environment +as allowing a device read-write access to system memory imposes the +greatest risk to the overall system integrity. + +To help mitigate this risk, many modern IOMMUs now incorporate +isolation properties into what was, in many cases, an interface only +meant for translation (ie. solving the addressing problems of devices +with limited address spaces). With this, devices can now be isolated +from each other and from arbitrary memory access, thus allowing +things like secure direct assignment of devices into virtual machines. + +This isolation is not always at the granularity of a single device +though. Even when an IOMMU is capable of this, properties of devices, +interconnects, and IOMMU topologies can each reduce this isolation. +For instance, an individual device may be part of a larger multi- +function enclosure. While the IOMMU may be able to distinguish +between devices within the enclosure, the enclosure may not require +transactions between devices to reach the IOMMU. Examples of this +could be anything from a multi-function PCI device with backdoors +between functions to a non-PCI-ACS (Access Control Services) capable +bridge allowing redirection without reaching the IOMMU. Topology +can also play a factor in terms of hiding devices. A PCIe-to-PCI +bridge masks the devices behind it, making transaction appear as if +from the bridge itself. Obviously IOMMU design plays a major factor +as well. + +Therefore, while for the most part an IOMMU may have device level +granularity, any system is susceptible to reduced granularity. The +IOMMU API therefore supports a notion of IOMMU groups. A group is +a set of devices which is isolatable from all other devices in the +system. Groups are therefore the unit of ownership used by VFIO. + +While the group is the minimum granularity that must be used to +ensure secure user access, it's not necessarily the preferred +granularity. In IOMMUs which make use of page tables, it may be +possible to share a set of page tables between different groups, +reducing the overhead both to the platform (reduced TLB thrashing, +reduced duplicate page tables), and to the user (programming only +a single set of translations). For this reason, VFIO makes use of +a container class, which may hold one or more groups. A container +is created by simply opening the /dev/vfio/vfio character device. + +On its own, the container provides little functionality, with all +but a couple version and extension query interfaces locked away. +The user needs to add a group into the container for the next level +of functionality. To do this, the user first needs to identify the +group associated with the desired device. This can be done using +the sysfs links described in the example below. By unbinding the +device from the host driver and binding it to a VFIO driver, a new +VFIO group will appear for the group as /dev/vfio/$GROUP, where +$GROUP is the IOMMU group number of which the device is a member. +If the IOMMU group contains multiple devices, each will need to +be bound to a VFIO driver before operations on the VFIO group +are allowed (it's also sufficient to only unbind the device from +host drivers if a VFIO driver is unavailable; this will make the +group available, but not that particular device). TBD - interface +for disabling driver probing/locking a device. + +Once the group is ready, it may be added to the container by opening +the VFIO group character device (/dev/vfio/$GROUP) and using the +VFIO_GROUP_SET_CONTAINER ioctl, passing the file descriptor of the +previously opened container file. If desired and if the IOMMU driver +supports sharing the IOMMU context between groups, multiple groups may +be set to the same container. If a group fails to set to a container +with existing groups, a new empty container will need to be used +instead. + +With a group (or groups) attached to a container, the remaining +ioctls become available, enabling access to the VFIO IOMMU interfaces. +Additionally, it now becomes possible to get file descriptors for each +device within a group using an ioctl on the VFIO group file descriptor. + +The VFIO device API includes ioctls for describing the device, the I/O +regions and their read/write/mmap offsets on the device descriptor, as +well as mechanisms for describing and registering interrupt +notifications. + +VFIO Usage Example +------------------------------------------------------------------------------- + +Assume user wants to access PCI device 0000:06:0d.0 + +$ readlink /sys/bus/pci/devices/0000:06:0d.0/iommu_group +../../../../kernel/iommu_groups/26 + +This device is therefore in IOMMU group 26. This device is on the +pci bus, therefore the user will make use of vfio-pci to manage the +group: + +# modprobe vfio-pci + +Binding this device to the vfio-pci driver creates the VFIO group +character devices for this group: + +$ lspci -n -s 0000:06:0d.0 +06:0d.0 0401: 1102:0002 (rev 08) +# echo 0000:06:0d.0 > /sys/bus/pci/devices/0000:06:0d.0/driver/unbind +# echo 1102 0002 > /sys/bus/pci/drivers/vfio/new_id +# echo 0000:06:0d.0 > /sys/bus/pci/drivers/vfio/bind + +Now we need to look at what other devices are in the group to free +it for use by VFIO: + +$ ls -l /sys/bus/pci/devices/0000:06:0d.0/iommu_group/devices +total 0 +lrwxrwxrwx. 1 root root 0 Apr 23 16:13 0000:00:1e.0 -> + ../../../../devices/pci0000:00/0000:00:1e.0 +lrwxrwxrwx. 1 root root 0 Apr 23 16:13 0000:06:0d.0 -> + ../../../../devices/pci0000:00/0000:00:1e.0/0000:06:0d.0 +lrwxrwxrwx. 1 root root 0 Apr 23 16:13 0000:06:0d.1 -> + ../../../../devices/pci0000:00/0000:00:1e.0/0000:06:0d.1 + +This device is behind a PCIe-to-PCI bridge[4], therefore we also +need to add device 0000:06:0d.1 to the group following the same +procedure as above. Device 0000:00:1e.0 is a bridge that does +not currently have a host driver, therefore it's not required to +bind this device to the vfio-pci driver (vfio-pci does not currently +support PCI bridges). + +The final step is to provide the user with access to the group if +unprivileged operation is desired (note that /dev/vfio/vfio provides +no capabilities on its own and is therefore expected to be set to +mode 0666 by the system). + +# chown user:user /dev/vfio/26 + +The user now has full access to all the devices and the iommu for this +group and can access them as follows: + + int container, group, device, i; + struct vfio_group_status group_status = + { .argsz = sizeof(group_status) }; + struct vfio_iommu_x86_info iommu_info = { .argsz = sizeof(iommu_info) }; + struct vfio_iommu_x86_dma_map dma_map = { .argsz = sizeof(dma_map) }; + struct vfio_device_info device_info = { .argsz = sizeof(device_info) }; + + /* Create a new container */ + container = open("/dev/vfio/vfio, O_RDWR); + + if (ioctl(container, VFIO_GET_API_VERSION) != VFIO_API_VERSION) + /* Unknown API version */ + + if (!ioctl(container, VFIO_CHECK_EXTENSION, VFIO_X86_IOMMU)) + /* Doesn't support the IOMMU driver we want. */ + + /* Open the group */ + group = open("/dev/vfio/26", O_RDWR); + + /* Test the group is viable and available */ + ioctl(group, VFIO_GROUP_GET_STATUS, &group_status); + + if (!(group_status.flags & VFIO_GROUP_FLAGS_VIABLE)) + /* Group is not viable (ie, not all devices bound for vfio) */ + + /* Add the group to the container */ + ioctl(group, VFIO_GROUP_SET_CONTAINER, &container); + + /* Enable the IOMMU model we want */ + ioctl(container, VFIO_SET_IOMMU, VFIO_X86_IOMMU) + + /* Get addition IOMMU info */ + ioctl(container, VFIO_IOMMU_GET_INFO, &iommu_info); + + /* Allocate some space and setup a DMA mapping */ + dma_map.vaddr = mmap(0, 1024 * 1024, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, 0, 0); + dma_map.size = 1024 * 1024; + dma_map.iova = 0; /* 1MB starting at 0x0 from device view */ + dma_map.flags = VFIO_DMA_MAP_FLAG_READ | VFIO_DMA_MAP_FLAG_WRITE; + + ioctl(container, VFIO_IOMMU_MAP_DMA, &dma_map); + + /* Get a file descriptor for the device */ + device = ioctl(group, VFIO_GROUP_GET_DEVICE_FD, "0000:06:0d.0"); + + /* Test and setup the device */ + ioctl(device, VFIO_DEVICE_GET_INFO, &device_info); + + for (i = 0; i < device_info.num_regions; i++) { + struct vfio_region_info reg = { .argsz = sizeof(reg) }; + + reg.index = i; + + ioctl(device, VFIO_DEVICE_GET_REGION_INFO, ®); + + /* Setup mappings... read/write offsets, mmaps + * For PCI devices, config space is a region */ + } + + for (i = 0; i < device_info.num_irqs; i++) { + struct vfio_irq_info irq = { .argsz = sizeof(irq) }; + + irq.index = i; + + ioctl(device, VFIO_DEVICE_GET_IRQ_INFO, ®); + + /* Setup IRQs... eventfds, VFIO_DEVICE_SET_IRQS */ + } + + /* Gratuitous device reset and go... */ + ioctl(device, VFIO_DEVICE_RESET); + +VFIO User API +------------------------------------------------------------------------------- + +Please see include/linux/vfio.h for complete API documentation. + +VFIO bus driver API +------------------------------------------------------------------------------- + +VFIO bus drivers, such as vfio-pci make use of only a few interfaces +into VFIO core. When devices are bound and unbound to the driver, +the driver should call vfio_add_group_dev() and vfio_del_group_dev() +respectively: + +extern int vfio_add_group_dev(struct iommu_group *iommu_group, + struct device *dev, + const struct vfio_device_ops *ops, + void *device_data); + +extern void *vfio_del_group_dev(struct device *dev); + +vfio_add_group_dev() indicates to the core to begin tracking the +specified iommu_group and register the specified dev as owned by +a VFIO bus driver. The driver provides an ops structure for callbacks +similar to a file operations structure: + +struct vfio_device_ops { + int (*open)(void *device_data); + void (*release)(void *device_data); + ssize_t (*read)(void *device_data, char __user *buf, + size_t count, loff_t *ppos); + ssize_t (*write)(void *device_data, const char __user *buf, + size_t size, loff_t *ppos); + long (*ioctl)(void *device_data, unsigned int cmd, + unsigned long arg); + int (*mmap)(void *device_data, struct vm_area_struct *vma); +}; + +Each function is passed the device_data that was originally registered +in the vfio_add_group_dev() call above. This allows the bus driver +an easy place to store its opaque, private data. The open/release +callbacks are issued when a new file descriptor is created for a +device (via VFIO_GROUP_GET_DEVICE_FD). The ioctl interface provides +a direct pass through for VFIO_DEVICE_* ioctls. The read/write/mmap +interfaces implement the device region access defined by the device's +own VFIO_DEVICE_GET_REGION_INFO ioctl. + +------------------------------------------------------------------------------- + +[1] VFIO was originally an acronym for "Virtual Function I/O" in its +initial implementation by Tom Lyon while as Cisco. We've since +outgrown the acronym, but it's catchy. + +[2] "safe" also depends upon a device being "well behaved". It's +possible for multi-function devices to have backdoors between +functions and even for single function devices to have alternative +access to things like PCI config space through MMIO registers. To +guard against the former we can include additional precautions in the +IOMMU driver to group multi-function PCI devices together +(iommu=group_mf). The latter we can't prevent, but the IOMMU should +still provide isolation. For PCI, SR-IOV Virtual Functions are the +best indicator of "well behaved", as these are designed for +virtualization usage models. + +[3] As always there are trade-offs to virtual machine device +assignment that are beyond the scope of VFIO. It's expected that +future IOMMU technologies will reduce some, but maybe not all, of +these trade-offs. + +[4] In this case the device is below a PCI bridge, so transactions +from either function of the device are indistinguishable to the iommu: + +-[0000:00]-+-1e.0-[06]--+-0d.0 + \-0d.1 + +00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 90)