* Yan Zhao (yan.y.zhao@xxxxxxxxx) wrote:
> This patchset enables VFIO devices to have live migration capability.
> Currently it does not support post-copy phase.
>
> It follows Alex's comments on last version of VFIO live migration patches,
> including device states, VFIO device state region layout, dirty bitmap's
> query.
Hi,
I've sent minor comments to later patches; but some minor general
comments:
a) Never trust the incoming migrations stream - it might be corrupt,
so check when you can.
b) How do we detect if we're migrating from/to the wrong device or
version of device? Or say to a device with older firmware or perhaps
a device that has less device memory ?
c) Consider using the trace_ mechanism - it's really useful to
add to loops writing/reading data so that you can see when it fails.
Dave
(P.S. You have a few typo's grep your code for 'devcie', 'devie' and
'migrtion'
> Device Data
> -----------
> Device data is divided into three types: device memory, device config,
> and system memory dirty pages produced by device.
>
> Device config: data like MMIOs, page tables...
> Every device is supposed to possess device config data.
> Usually device config's size is small (no big than 10M), and it
> needs to be loaded in certain strict order.
> Therefore, device config only needs to be saved/loaded in
> stop-and-copy phase.
> The data of device config is held in device config region.
> Size of device config data is smaller than or equal to that of
> device config region.
>
> Device Memory: device's internal memory, standalone and outside system
> memory. It is usually very big.
> This kind of data needs to be saved / loaded in pre-copy and
> stop-and-copy phase.
> The data of device memory is held in device memory region.
> Size of devie memory is usually larger than that of device
> memory region. qemu needs to save/load it in chunks of size of
> device memory region.
> Not all device has device memory. Like IGD only uses system memory.
>
> System memory dirty pages: If a device produces dirty pages in system
> memory, it is able to get dirty bitmap for certain range of system
> memory. This dirty bitmap is queried in pre-copy and stop-and-copy
> phase in .log_sync callback. By setting dirty bitmap in .log_sync
> callback, dirty pages in system memory will be save/loaded by ram's
> live migration code.
> The dirty bitmap of system memory is held in dirty bitmap region.
> If system memory range is larger than that dirty bitmap region can
> hold, qemu will cut it into several chunks and get dirty bitmap in
> succession.
>
>
> Device State Regions
> --------------------
> Vendor driver is required to expose two mandatory regions and another two
> optional regions if it plans to support device state management.
>
> So, there are up to four regions in total.
> One control region: mandatory.
> Get access via read/write system call.
> Its layout is defined in struct vfio_device_state_ctl
> Three data regions: mmaped into qemu.
> device config region: mandatory, holding data of device config
> device memory region: optional, holding data of device memory
> dirty bitmap region: optional, holding bitmap of system memory
> dirty pages
>
> (The reason why four seperate regions are defined is that the unit of mmap
> system call is PAGE_SIZE, i.e. 4k bytes. So one read/write region for
> control and three mmaped regions for data seems better than one big region
> padded and sparse mmaped).
>
>
> kernel device state interface [1]
> --------------------------------------
> #define VFIO_DEVICE_STATE_INTERFACE_VERSION 1
> #define VFIO_DEVICE_DATA_CAP_DEVICE_MEMORY 1
> #define VFIO_DEVICE_DATA_CAP_SYSTEM_MEMORY 2
>
> #define VFIO_DEVICE_STATE_RUNNING 0
> #define VFIO_DEVICE_STATE_STOP 1
> #define VFIO_DEVICE_STATE_LOGGING 2
>
> #define VFIO_DEVICE_DATA_ACTION_GET_BUFFER 1
> #define VFIO_DEVICE_DATA_ACTION_SET_BUFFER 2
> #define VFIO_DEVICE_DATA_ACTION_GET_BITMAP 3
>
> struct vfio_device_state_ctl {
> __u32 version; /* ro */
> __u32 device_state; /* VFIO device state, wo */
> __u32 caps; /* ro */
> struct {
> __u32 action; /* wo, GET_BUFFER or SET_BUFFER */
> __u64 size; /*rw*/
> } device_config;
> struct {
> __u32 action; /* wo, GET_BUFFER or SET_BUFFER */
> __u64 size; /* rw */
> __u64 pos; /*the offset in total buffer of device memory*/
> } device_memory;
> struct {
> __u64 start_addr; /* wo */
> __u64 page_nr; /* wo */
> } system_memory;
> };
>
> Devcie States
> -------------
> After migration is initialzed, it will set device state via writing to
> device_state field of control region.
>
> Four states are defined for a VFIO device:
> RUNNING, RUNNING & LOGGING, STOP & LOGGING, STOP
>
> RUNNING: In this state, a VFIO device is in active state ready to receive
> commands from device driver.
> It is the default state that a VFIO device enters initially.
>
> STOP: In this state, a VFIO device is deactivated to interact with
> device driver.
>
> LOGGING: a special state that it CANNOT exist independently. It must be
> set alongside with state RUNNING or STOP (i.e. RUNNING & LOGGING,
> STOP & LOGGING).
> Qemu will set LOGGING state on in .save_setup callbacks, then vendor
> driver can start dirty data logging for device memory and system
> memory.
> LOGGING only impacts device/system memory. They return whole
> snapshot outside LOGGING and dirty data since last get operation
> inside LOGGING.
> Device config should be always accessible and return whole config
> snapshot regardless of LOGGING state.
>
> Note:
> The reason why RUNNING is the default state is that device's active state
> must not depend on device state interface.
> It is possible that region vfio_device_state_ctl fails to get registered.
> In that condition, a device needs be in active state by default.
>
> Get Version & Get Caps
> ----------------------
> On migration init phase, qemu will probe the existence of device state
> regions of vendor driver, then get version of the device state interface
> from the r/w control region.
>
> Then it will probe VFIO device's data capability by reading caps field of
> control region.
> #define VFIO_DEVICE_DATA_CAP_DEVICE_MEMORY 1
> #define VFIO_DEVICE_DATA_CAP_SYSTEM_MEMORY 2
> If VFIO_DEVICE_DATA_CAP_DEVICE_MEMORY is on, it will save/load data of
> device memory in pre-copy and stop-and-copy phase. The data of
> device memory is held in device memory region.
> If VFIO_DEVICE_DATA_CAP_SYSTEM_MEMORY is on, it will query of dirty pages
> produced by VFIO device during pre-copy and stop-and-copy phase.
> The dirty bitmap of system memory is held in dirty bitmap region.
>
> If failing to find two mandatory regions and optional data regions
> corresponding to data caps or version mismatching, it will setup a
> migration blocker and disable live migration for VFIO device.
>
>
> Flows to call device state interface for VFIO live migration
> ------------------------------------------------------------
>
> Live migration save path:
>
> (QEMU LIVE MIGRATION STATE --> DEVICE STATE INTERFACE --> DEVICE STATE)
>
> MIGRATION_STATUS_NONE --> VFIO_DEVICE_STATE_RUNNING
> |
> MIGRATION_STATUS_SAVE_SETUP
> |
> .save_setup callback -->
> get device memory size (whole snapshot size)
> get device memory buffer (whole snapshot data)
> set device state --> VFIO_DEVICE_STATE_RUNNING & VFIO_DEVICE_STATE_LOGGING
> |
> MIGRATION_STATUS_ACTIVE
> |
> .save_live_pending callback --> get device memory size (dirty data)
> .save_live_iteration callback --> get device memory buffer (dirty data)
> .log_sync callback --> get system memory dirty bitmap
> |
> (vcpu stops) --> set device state -->
> VFIO_DEVICE_STATE_STOP & VFIO_DEVICE_STATE_LOGGING
> |
> .save_live_complete_precopy callback -->
> get device memory size (dirty data)
> get device memory buffer (dirty data)
> get device config size (whole snapshot size)
> get device config buffer (whole snapshot data)
> |
> .save_cleanup callback --> set device state --> VFIO_DEVICE_STATE_STOP
> MIGRATION_STATUS_COMPLETED
>
> MIGRATION_STATUS_CANCELLED or
> MIGRATION_STATUS_FAILED
> |
> (vcpu starts) --> set device state --> VFIO_DEVICE_STATE_RUNNING
>
>
> Live migration load path:
>
> (QEMU LIVE MIGRATION STATE --> DEVICE STATE INTERFACE --> DEVICE STATE)
>
> MIGRATION_STATUS_NONE --> VFIO_DEVICE_STATE_RUNNING
> |
> (vcpu stops) --> set device state --> VFIO_DEVICE_STATE_STOP
> |
> MIGRATION_STATUS_ACTIVE
> |
> .load state callback -->
> set device memory size, set device memory buffer, set device config size,
> set device config buffer
> |
> (vcpu starts) --> set device state --> VFIO_DEVICE_STATE_RUNNING
> |
> MIGRATION_STATUS_COMPLETED
>
>
>
> In source VM side,
> In precopy phase,
> if a device has VFIO_DEVICE_DATA_CAP_DEVICE_MEMORY on,
> qemu will first get whole snapshot of device memory in .save_setup
> callback, and then it will get total size of dirty data in device memory in
> .save_live_pending callback by reading device_memory.size field of control
> region.
> Then in .save_live_iteration callback, it will get buffer of device memory's
> dirty data chunk by chunk from device memory region by writing pos &
> action (GET_BUFFER) to device_memory.pos & device_memory.action fields of
> control region. (size of each chunk is the size of device memory data
> region).
> .save_live_pending and .save_live_iteration may be called several times in
> precopy phase to get dirty data in device memory.
>
> If VFIO_DEVICE_DATA_CAP_DEVICE_MEMORY is off, callbacks in precopy phase
> like .save_setup, .save_live_pending, .save_live_iteration will not call
> vendor driver's device state interface to get data from devcie memory.
>
> In precopy phase, if a device has VFIO_DEVICE_DATA_CAP_SYSTEM_MEMORY on,
> .log_sync callback will get system memory dirty bitmap from dirty bitmap
> region by writing system memory's start address, page count and action
> (GET_BITMAP) to "system_memory.start_addr", "system_memory.page_nr", and
> "system_memory.action" fields of control region.
> If page count passed in .log_sync callback is larger than the bitmap size
> the dirty bitmap region supports, Qemu will cut it into chunks and call
> vendor driver's get system memory dirty bitmap interface.
> If VFIO_DEVICE_DATA_CAP_SYSTEM_MEMORY is off, .log_sync callback just
> returns without call to vendor driver.
>
> In stop-and-copy phase, device state will be set to STOP & LOGGING first.
> in save_live_complete_precopy callback,
> If VFIO_DEVICE_DATA_CAP_SYSTEM_MEMORY is on,
> get device memory size and get device memory buffer will be called again.
> After that,
> device config data is get from device config region by reading
> devcie_config.size of control region and writing action (GET_BITMAP) to
> device_config.action of control region.
> Then after migration completes, in cleanup handler, LOGGING state will be
> cleared (i.e. deivce state is set to STOP).
> Clearing LOGGING state in cleanup handler is in consideration of the case
> of "migration failed" and "migration cancelled". They can also leverage
> the cleanup handler to unset LOGGING state.
>
>
> References
> ----------
> 1. kernel side implementation of Device state interfaces:
> https://patchwork.freedesktop.org/series/56876/
>
>
> Yan Zhao (5):
> vfio/migration: define kernel interfaces
> vfio/migration: support device of device config capability
> vfio/migration: tracking of dirty page in system memory
> vfio/migration: turn on migration
> vfio/migration: support device memory capability
>
> hw/vfio/Makefile.objs | 2 +-
> hw/vfio/common.c | 26 ++
> hw/vfio/migration.c | 858 ++++++++++++++++++++++++++++++++++++++++++
> hw/vfio/pci.c | 10 +-
> hw/vfio/pci.h | 26 +-
> include/hw/vfio/vfio-common.h | 1 +
> linux-headers/linux/vfio.h | 260 +++++++++++++
> 7 files changed, 1174 insertions(+), 9 deletions(-)
> create mode 100644 hw/vfio/migration.c
>
> --
> 2.7.4
>
--
Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK
