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diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt deleted file mode 100644 index d7993dcf8537..000000000000 --- a/Documentation/vfio.txt +++ /dev/null @@ -1,377 +0,0 @@ -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-pci/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_TYPE1_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_TYPE1_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. - - -PPC64 sPAPR implementation note -------------------------------------------------------------------------------- - -This implementation has some specifics: - -1) Only one IOMMU group per container is supported as an IOMMU group -represents the minimal entity which isolation can be guaranteed for and -groups are allocated statically, one per a Partitionable Endpoint (PE) -(PE is often a PCI domain but not always). - -2) The hardware supports so called DMA windows - the PCI address range -within which DMA transfer is allowed, any attempt to access address space -out of the window leads to the whole PE isolation. - -3) PPC64 guests are paravirtualized but not fully emulated. There is an API -to map/unmap pages for DMA, and it normally maps 1..32 pages per call and -currently there is no way to reduce the number of calls. In order to make things -faster, the map/unmap handling has been implemented in real mode which provides -an excellent performance which has limitations such as inability to do -locked pages accounting in real time. - -So 3 additional ioctls have been added: - - VFIO_IOMMU_SPAPR_TCE_GET_INFO - returns the size and the start - of the DMA window on the PCI bus. - - VFIO_IOMMU_ENABLE - enables the container. The locked pages accounting - is done at this point. This lets user first to know what - the DMA window is and adjust rlimit before doing any real job. - - VFIO_IOMMU_DISABLE - disables the container. - - -The code flow from the example above should be slightly changed: - - ..... - /* 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_SPAPR_TCE_IOMMU) - - /* Get addition sPAPR IOMMU info */ - vfio_iommu_spapr_tce_info spapr_iommu_info; - ioctl(container, VFIO_IOMMU_SPAPR_TCE_GET_INFO, &spapr_iommu_info); - - if (ioctl(container, VFIO_IOMMU_ENABLE)) - /* Cannot enable container, may be low rlimit */ - - /* 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; - - /* Check here is .iova/.size are within DMA window from spapr_iommu_info */ - - ioctl(container, VFIO_IOMMU_MAP_DMA, &dma_map); - ..... - -------------------------------------------------------------------------------- - -[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) |