Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 520 insertions, 0 deletions

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+==================================
+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_type1_info iommu_info = { .argsz = sizeof(iommu_info) };
+	struct vfio_iommu_type1_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, &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, &irq);
+
+		/* 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 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
+iommu_group of the specified dev and register the 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) On older systems (POWER7 with P5IOC2/IODA1) only one IOMMU group per
+   container is supported as an IOMMU table is allocated at the boot time,
+   one table per a IOMMU group which is a Partitionable Endpoint (PE)
+   (PE is often a PCI domain but not always).
+
+   Newer systems (POWER8 with IODA2) have improved hardware design which allows
+   to remove this limitation and have multiple IOMMU groups per a VFIO
+   container.
+
+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.
+
+4) According to sPAPR specification, A Partitionable Endpoint (PE) is an I/O
+   subtree that can be treated as a unit for the purposes of partitioning and
+   error recovery. A PE may be a single or multi-function IOA (IO Adapter), a
+   function of a multi-function IOA, or multiple IOAs (possibly including
+   switch and bridge structures above the multiple IOAs). PPC64 guests detect
+   PCI errors and recover from them via EEH RTAS services, which works on the
+   basis of additional ioctl commands.
+
+   So 4 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.
+
+	VFIO_EEH_PE_OP
+		provides an API for EEH setup, error detection and recovery.
+
+   The code flow from the example above should be slightly changed::
+
+	struct vfio_eeh_pe_op pe_op = { .argsz = sizeof(pe_op), .flags = 0 };
+
+	.....
+	/* 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);
+
+	/* Get a file descriptor for the device */
+	device = ioctl(group, VFIO_GROUP_GET_DEVICE_FD, "0000:06:0d.0");
+
+	....
+
+	/* Gratuitous device reset and go... */
+	ioctl(device, VFIO_DEVICE_RESET);
+
+	/* Make sure EEH is supported */
+	ioctl(container, VFIO_CHECK_EXTENSION, VFIO_EEH);
+
+	/* Enable the EEH functionality on the device */
+	pe_op.op = VFIO_EEH_PE_ENABLE;
+	ioctl(container, VFIO_EEH_PE_OP, &pe_op);
+
+	/* You're suggested to create additional data struct to represent
+	 * PE, and put child devices belonging to same IOMMU group to the
+	 * PE instance for later reference.
+	 */
+
+	/* Check the PE's state and make sure it's in functional state */
+	pe_op.op = VFIO_EEH_PE_GET_STATE;
+	ioctl(container, VFIO_EEH_PE_OP, &pe_op);
+
+	/* Save device state using pci_save_state().
+	 * EEH should be enabled on the specified device.
+	 */
+
+	....
+
+	/* Inject EEH error, which is expected to be caused by 32-bits
+	 * config load.
+	 */
+	pe_op.op = VFIO_EEH_PE_INJECT_ERR;
+	pe_op.err.type = EEH_ERR_TYPE_32;
+	pe_op.err.func = EEH_ERR_FUNC_LD_CFG_ADDR;
+	pe_op.err.addr = 0ul;
+	pe_op.err.mask = 0ul;
+	ioctl(container, VFIO_EEH_PE_OP, &pe_op);
+
+	....
+
+	/* When 0xFF's returned from reading PCI config space or IO BARs
+	 * of the PCI device. Check the PE's state to see if that has been
+	 * frozen.
+	 */
+	ioctl(container, VFIO_EEH_PE_OP, &pe_op);
+
+	/* Waiting for pending PCI transactions to be completed and don't
+	 * produce any more PCI traffic from/to the affected PE until
+	 * recovery is finished.
+	 */
+
+	/* Enable IO for the affected PE and collect logs. Usually, the
+	 * standard part of PCI config space, AER registers are dumped
+	 * as logs for further analysis.
+	 */
+	pe_op.op = VFIO_EEH_PE_UNFREEZE_IO;
+	ioctl(container, VFIO_EEH_PE_OP, &pe_op);
+
+	/*
+	 * Issue PE reset: hot or fundamental reset. Usually, hot reset
+	 * is enough. However, the firmware of some PCI adapters would
+	 * require fundamental reset.
+	 */
+	pe_op.op = VFIO_EEH_PE_RESET_HOT;
+	ioctl(container, VFIO_EEH_PE_OP, &pe_op);
+	pe_op.op = VFIO_EEH_PE_RESET_DEACTIVATE;
+	ioctl(container, VFIO_EEH_PE_OP, &pe_op);
+
+	/* Configure the PCI bridges for the affected PE */
+	pe_op.op = VFIO_EEH_PE_CONFIGURE;
+	ioctl(container, VFIO_EEH_PE_OP, &pe_op);
+
+	/* Restored state we saved at initialization time. pci_restore_state()
+	 * is good enough as an example.
+	 */
+
+	/* Hopefully, error is recovered successfully. Now, you can resume to
+	 * start PCI traffic to/from the affected PE.
+	 */
+
+	....
+
+5) There is v2 of SPAPR TCE IOMMU. It deprecates VFIO_IOMMU_ENABLE/
+   VFIO_IOMMU_DISABLE and implements 2 new ioctls:
+   VFIO_IOMMU_SPAPR_REGISTER_MEMORY and VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY
+   (which are unsupported in v1 IOMMU).
+
+   PPC64 paravirtualized guests generate a lot of map/unmap requests,
+   and the handling of those includes pinning/unpinning pages and updating
+   mm::locked_vm counter to make sure we do not exceed the rlimit.
+   The v2 IOMMU splits accounting and pinning into separate operations:
+
+   - VFIO_IOMMU_SPAPR_REGISTER_MEMORY/VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY ioctls
+     receive a user space address and size of the block to be pinned.
+     Bisecting is not supported and VFIO_IOMMU_UNREGISTER_MEMORY is expected to
+     be called with the exact address and size used for registering
+     the memory block. The userspace is not expected to call these often.
+     The ranges are stored in a linked list in a VFIO container.
+
+   - VFIO_IOMMU_MAP_DMA/VFIO_IOMMU_UNMAP_DMA ioctls only update the actual
+     IOMMU table and do not do pinning; instead these check that the userspace
+     address is from pre-registered range.
+
+   This separation helps in optimizing DMA for guests.
+
+6) sPAPR specification allows guests to have an additional DMA window(s) on
+   a PCI bus with a variable page size. Two ioctls have been added to support
+   this: VFIO_IOMMU_SPAPR_TCE_CREATE and VFIO_IOMMU_SPAPR_TCE_REMOVE.
+   The platform has to support the functionality or error will be returned to
+   the userspace. The existing hardware supports up to 2 DMA windows, one is
+   2GB long, uses 4K pages and called "default 32bit window"; the other can
+   be as big as entire RAM, use different page size, it is optional - guests
+   create those in run-time if the guest driver supports 64bit DMA.
+
+   VFIO_IOMMU_SPAPR_TCE_CREATE receives a page shift, a DMA window size and
+   a number of TCE table levels (if a TCE table is going to be big enough and
+   the kernel may not be able to allocate enough of physically contiguous
+   memory). It creates a new window in the available slot and returns the bus
+   address where the new window starts. Due to hardware limitation, the user
+   space cannot choose the location of DMA windows.
+
+   VFIO_IOMMU_SPAPR_TCE_REMOVE receives the bus start address of the window
+   and removes it.
+
+-------------------------------------------------------------------------------
+
+.. [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)