forked from rrcarlosr/Jetpack
515 lines
21 KiB
Plaintext
515 lines
21 KiB
Plaintext
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, ®);
|
|
|
|
/* 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 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) 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)
|