mirror of
https://github.com/torvalds/linux.git
synced 2024-11-10 22:21:40 +00:00
vfio.txt: standardize document format
Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: - adjust title marks; - use footnote marks; - mark literal blocks; - adjust identation. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab
Jonathan Corbet
parent
2a26ed8e4a
commit
c6f4d41338
@ -1,5 +1,7 @@
|
||||
VFIO - "Virtual Function I/O"[1]
|
||||
-------------------------------------------------------------------------------
|
||||
==================================
|
||||
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,
|
||||
@ -7,14 +9,14 @@ 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.
|
||||
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].
|
||||
bare-metal device drivers [3]_.
|
||||
|
||||
Some applications, particularly in the high performance computing
|
||||
field, also benefit from low-overhead, direct device access from
|
||||
@ -31,7 +33,7 @@ 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,
|
||||
@ -114,40 +116,40 @@ well as mechanisms for describing and registering interrupt
|
||||
notifications.
|
||||
|
||||
VFIO Usage Example
|
||||
-------------------------------------------------------------------------------
|
||||
------------------
|
||||
|
||||
Assume user wants to access PCI device 0000:06:0d.0
|
||||
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
|
||||
$ 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:
|
||||
group::
|
||||
|
||||
# modprobe vfio-pci
|
||||
# modprobe vfio-pci
|
||||
|
||||
Binding this device to the vfio-pci driver creates the VFIO group
|
||||
character devices for this 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
|
||||
$ 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:
|
||||
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
|
||||
$ 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
|
||||
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
|
||||
@ -157,12 +159,12 @@ 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).
|
||||
mode 0666 by the system)::
|
||||
|
||||
# chown user:user /dev/vfio/26
|
||||
# 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:
|
||||
group and can access them as follows::
|
||||
|
||||
int container, group, device, i;
|
||||
struct vfio_group_status group_status =
|
||||
@ -248,31 +250,31 @@ 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:
|
||||
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 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);
|
||||
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:
|
||||
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);
|
||||
};
|
||||
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
|
||||
@ -285,50 +287,55 @@ 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.
|
||||
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.
|
||||
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.
|
||||
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.
|
||||
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:
|
||||
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_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
|
||||
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_IOMMU_DISABLE
|
||||
disables the container.
|
||||
|
||||
VFIO_EEH_PE_OP - provides an API for EEH setup, error detection and recovery.
|
||||
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:
|
||||
The code flow from the example above should be slightly changed::
|
||||
|
||||
struct vfio_eeh_pe_op pe_op = { .argsz = sizeof(pe_op), .flags = 0 };
|
||||
|
||||
@ -442,73 +449,73 @@ The code flow from the example above should be slightly changed:
|
||||
....
|
||||
|
||||
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).
|
||||
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:
|
||||
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_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.
|
||||
- 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.
|
||||
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.
|
||||
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_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.
|
||||
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.
|
||||
.. [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.
|
||||
.. [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.
|
||||
.. [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:
|
||||
.. [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
|
||||
-[0000:00]-+-1e.0-[06]--+-0d.0
|
||||
\-0d.1
|
||||
|
||||
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 90)
|
||||
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 90)
|
||||
|
||||
Loading…
Reference in New Issue
Block a user