path: root/Documentation
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authorLinus Torvalds <torvalds@linux-foundation.org>2012-07-31 19:17:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-07-31 19:17:27 -0700
commita40a1d3d0a2fd613fdec6d89d3c053268ced76ed (patch)
treeed8ea274f82e0cb645632c9b1ddcd1a6afc40bad /Documentation
parent3e9a97082fa639394e905e1fc4a0a7f719ca7644 (diff)
parent89e1f7d4c66d85f42c3d52ea3866eb10cadf6153 (diff)
Merge tag 'vfio-for-v3.6' of git://github.com/awilliam/linux-vfio
Pull VFIO core from Alex Williamson: "This series includes the VFIO userspace driver interface for the 3.6 kernel merge window. This driver is intended to provide a secure interface for device access using IOMMU protection for applications like assignment of physical devices to virtual machines. Qemu will be the first user of this interface, enabling assignment of PCI devices to Qemu guests. This interface is intended to eventually replace the x86-specific assignment mechanism currently available in KVM. This interface has the advantage of being more secure, by working with IOMMU groups to ensure device isolation and providing it's own filtered resource access mechanism, and also more flexible, in not being x86 or KVM specific (extensions to enable POWER are already working). This driver is originally the work of Tom Lyon, but has since been handed over to me and gone through a complete overhaul thanks to the input from David Gibson, Ben Herrenschmidt, Chris Wright, Joerg Roedel, and others. This driver has been available in linux-next for the last month." Paul Mackerras says: "I would be glad to see it go in since we want to use it with KVM on PowerPC. If possible we'd like the PowerPC bits for it to go in as well." * tag 'vfio-for-v3.6' of git://github.com/awilliam/linux-vfio: vfio: Add PCI device driver vfio: Type1 IOMMU implementation vfio: Add documentation vfio: VFIO core
Diffstat (limited to 'Documentation')
2 files changed, 315 insertions, 0 deletions
diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index 915f28c470e9..849b771c5e03 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -88,6 +88,7 @@ Code Seq#(hex) Include File Comments
and kernel/power/user.c
'8' all SNP8023 advanced NIC card
+';' 64-7F linux/vfio.h
'@' 00-0F linux/radeonfb.h conflict!
'@' 00-0F drivers/video/aty/aty128fb.c conflict!
'A' 00-1F linux/apm_bios.h conflict!
diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt
new file mode 100644
index 000000000000..0cb6685c8029
--- /dev/null
+++ b/Documentation/vfio.txt
@@ -0,0 +1,314 @@
+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
+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/$GROUP) and using the
+VFIO_GROUP_SET_CONTAINER ioctl, passing the file descriptor of the
+previously opened container file. If desired and if the IOMMU driver
+supports sharing the IOMMU context between groups, multiple groups may
+be set to the same container. If a group fails to set to a container
+with existing groups, a new empty container will need to be used
+With a group (or groups) attached to a container, the remaining
+ioctls become available, enabling access to the VFIO IOMMU interfaces.
+Additionally, it now becomes possible to get file descriptors for each
+device within a group using an ioctl on the VFIO group file descriptor.
+The VFIO device API includes ioctls for describing the device, the I/O
+regions and their read/write/mmap offsets on the device descriptor, as
+well as mechanisms for describing and registering interrupt
+VFIO Usage Example
+Assume user wants to access PCI device 0000:06:0d.0
+$ readlink /sys/bus/pci/devices/0000:06:0d.0/iommu_group
+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
+# 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
+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,
+ dma_map.size = 1024 * 1024;
+ dma_map.iova = 0; /* 1MB starting at 0x0 from device view */
+ 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, &reg);
+ /* 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, &reg);
+ /* Setup IRQs... eventfds, VFIO_DEVICE_SET_IRQS */
+ }
+ /* Gratuitous device reset and go... */
+ ioctl(device, VFIO_DEVICE_RESET);
+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()
+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
+[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:
+ \-0d.1
+00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 90)