On Sat, Feb 08, 2020 at 03:42:28AM +0800, Kirti Wankhede wrote:
> - Defined MIGRATION region type and sub-type.
>
> - Defined vfio_device_migration_info structure which will be placed at 0th
> offset of migration region to get/set VFIO device related information.
> Defined members of structure and usage on read/write access.
>
> - Defined device states and state transition details.
>
> - Defined sequence to be followed while saving and resuming VFIO device.
>
> Signed-off-by: Kirti Wankhede <kwankhede@xxxxxxxxxx>
> Reviewed-by: Neo Jia <cjia@xxxxxxxxxx>
> ---
> include/uapi/linux/vfio.h | 208 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 208 insertions(+)
>
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 9e843a147ead..572242620ce9 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -305,6 +305,7 @@ struct vfio_region_info_cap_type {
> #define VFIO_REGION_TYPE_PCI_VENDOR_MASK (0xffff)
> #define VFIO_REGION_TYPE_GFX (1)
> #define VFIO_REGION_TYPE_CCW (2)
> +#define VFIO_REGION_TYPE_MIGRATION (3)
>
> /* sub-types for VFIO_REGION_TYPE_PCI_* */
>
> @@ -379,6 +380,213 @@ struct vfio_region_gfx_edid {
> /* sub-types for VFIO_REGION_TYPE_CCW */
> #define VFIO_REGION_SUBTYPE_CCW_ASYNC_CMD (1)
>
> +/* sub-types for VFIO_REGION_TYPE_MIGRATION */
> +#define VFIO_REGION_SUBTYPE_MIGRATION (1)
> +
> +/*
> + * Structure vfio_device_migration_info is placed at 0th offset of
> + * VFIO_REGION_SUBTYPE_MIGRATION region to get/set VFIO device related migration
> + * information. Field accesses from this structure are only supported at their
> + * native width and alignment, otherwise the result is undefined and vendor
> + * drivers should return an error.
> + *
> + * device_state: (read/write)
> + * - User application writes this field to inform vendor driver about the
> + * device state to be transitioned to.
> + * - Vendor driver should take necessary actions to change device state.
> + * On successful transition to given state, vendor driver should return
> + * success on write(device_state, state) system call. If device state
> + * transition fails, vendor driver should return error, -EFAULT.
> + * - On user application side, if device state transition fails, i.e. if
> + * write(device_state, state) returns error, read device_state again to
> + * determine the current state of the device from vendor driver.
> + * - Vendor driver should return previous state of the device unless vendor
> + * driver has encountered an internal error, in which case vendor driver
> + * may report the device_state VFIO_DEVICE_STATE_ERROR.
> + * - User application must use the device reset ioctl in order to recover
> + * the device from VFIO_DEVICE_STATE_ERROR state. If the device is
> + * indicated in a valid device state via reading device_state, the user
> + * application may decide attempt to transition the device to any valid
> + * state reachable from the current state or terminate itself.
> + *
> + * device_state consists of 3 bits:
> + * - If bit 0 set, indicates _RUNNING state. When it's clear, that
> + * indicates _STOP state. When device is changed to _STOP, driver should
> + * stop device before write() returns.
> + * - If bit 1 set, indicates _SAVING state. When set, that indicates driver
> + * should start gathering device state information which will be provided
> + * to VFIO user application to save device's state.
> + * - If bit 2 set, indicates _RESUMING state. When set, that indicates
> + * prepare to resume device, data provided through migration region
> + * should be used to resume device.
> + * Bits 3 - 31 are reserved for future use. In order to preserve them,
> + * user application should perform read-modify-write operation on this
> + * field when modifying the specified bits.
> + *
> + * +------- _RESUMING
> + * |+------ _SAVING
> + * ||+----- _RUNNING
> + * |||
> + * 000b => Device Stopped, not saving or resuming
> + * 001b => Device running state, default state
> + * 010b => Stop Device & save device state, stop-and-copy state
> + * 011b => Device running and save device state, pre-copy state
> + * 100b => Device stopped and device state is resuming
> + * 101b => Invalid state
> + * 110b => Error state
> + * 111b => Invalid state
> + *
> + * State transitions:
> + *
> + * _RESUMING _RUNNING Pre-copy Stop-and-copy _STOP
> + * (100b) (001b) (011b) (010b) (000b)
> + * 0. Running or Default state
> + * |
> + *
> + * 1. Normal Shutdown (optional)
> + * |------------------------------------->|
> + *
> + * 2. Save state or Suspend
> + * |------------------------->|---------->|
> + *
> + * 3. Save state during live migration
> + * |----------->|------------>|---------->|
> + *
> + * 4. Resuming
> + * |<---------|
> + *
> + * 5. Resumed
> + * |--------->|
> + *
> + * 0. Default state of VFIO device is _RUNNNG when user application starts.
> + * 1. During normal user application shutdown, vfio device state changes
> + * from _RUNNING to _STOP. This is optional, user application may or may not
> + * perform this state transition and vendor driver may not need.
> + * 2. When user application save state or suspend application, device state
> + * transitions from _RUNNING to stop-and-copy state and then to _STOP.
> + * On state transition from _RUNNING to stop-and-copy, driver must
> + * stop device, save device state and send it to application through
> + * migration region. Sequence to be followed for such transition is given
> + * below.
> + * 3. In user application live migration, state transitions from _RUNNING
> + * to pre-copy to stop-and-copy to _STOP.
> + * On state transition from _RUNNING to pre-copy, driver should start
> + * gathering device state while application is still running and send device
> + * state data to application through migration region.
> + * On state transition from pre-copy to stop-and-copy, driver must stop
> + * device, save device state and send it to user application through
> + * migration region.
> + * Sequence to be followed for above two transitions is given below.
> + * 4. To start resuming phase, device state should be transitioned from
> + * _RUNNING to _RESUMING state.
> + * In _RESUMING state, driver should use received device state data through
> + * migration region to resume device.
> + * 5. On providing saved device data to driver, application should change state
> + * from _RESUMING to _RUNNING.
> + *
> + * pending bytes: (read only)
> + * Number of pending bytes yet to be migrated from vendor driver
> + *
> + * data_offset: (read only)
> + * User application should read data_offset in migration region from where
> + * user application should read device data during _SAVING state or write
> + * device data during _RESUMING state. See below for detail of sequence to
> + * be followed.
> + *
> + * data_size: (read/write)
> + * User application should read data_size to get size of data copied in
> + * bytes in migration region during _SAVING state and write size of data
> + * copied in bytes in migration region during _RESUMING state.
> + *
> + * Migration region looks like:
> + * ------------------------------------------------------------------
> + * |vfio_device_migration_info| data section |
> + * | | /////////////////////////////// |
> + * ------------------------------------------------------------------
> + * ^ ^
> + * offset 0-trapped part data_offset
> + *
> + * Structure vfio_device_migration_info is always followed by data section in
> + * the region, so data_offset will always be non-0. Offset from where data is
> + * copied is decided by kernel driver, data section can be trapped or mapped
> + * or partitioned, depending on how kernel driver defines data section.
> + * Data section partition can be defined as mapped by sparse mmap capability.
> + * If mmapped, then data_offset should be page aligned, where as initial section
> + * which contain vfio_device_migration_info structure might not end at offset
> + * which is page aligned. The user is not required to access via mmap regardless
> + * of the region mmap capabilities.
> + * Vendor driver should decide whether to partition data section and how to
> + * partition the data section. Vendor driver should return data_offset
> + * accordingly.
> + *
> + * Sequence to be followed for _SAVING|_RUNNING device state or pre-copy phase
> + * and for _SAVING device state or stop-and-copy phase:
> + * a. read pending_bytes, indicates start of new iteration to get device data.
> + * Repeatative read on pending_bytes at this stage should have no side
> + * effect.
if the data section is mmaped into user space, vendor driver is not able
to know when user application has finished reading of the data.
so, if user application reads pending_bytes repeatedly, vendor
driver actually does not know what value to return except by making
assumption that reading of data_size is a sign of data reading,
which is somewhat strange, as data_size is read before reading data.
e.g. vendor driver actually does not know how to handle below sequence
1. read pending_bytes
2. read data_offset
3. read pending_bytes
4. read data_size
and what if user space reads in below sequence but never launches a real
reading of data?
1. read pending_bytes
2. read data_offset
3. read data_size
Thanks
Yan
> + * If pending_bytes == 0, user application should not iterate to get data
> + * for that device.
> + * If pending_bytes > 0, go through below steps.
> + * b. read data_offset, indicates vendor driver to make data available through
> + * data section. Vendor driver should return this read operation only after
> + * data is available from (region + data_offset) to (region + data_offset +
> + * data_size).
> + * c. read data_size, amount of data in bytes available through migration
> + * region.
> + * Read on data_offset and data_size should return offset and size of current
> + * buffer if user application reads those more than once here.
> + * d. read data of data_size bytes from (region + data_offset) from migration
> + * region.
> + * e. process data.
> + * f. read pending_bytes, this read operation indicates data from previous
> + * iteration had read. If pending_bytes > 0, goto step b.
> + *
> + * If there is any error during the above sequence, vendor driver can return
> + * error code for next read()/write() operation, that will terminate the loop
> + * and user should take next necessary action, for example, fail migration or
> + * terminate user application.
> + *
> + * User application can transition from _SAVING|_RUNNING (pre-copy state) to
> + * _SAVING (stop-and-copy) state regardless of pending bytes.
> + * User application should iterate in _SAVING (stop-and-copy) until
> + * pending_bytes is 0.
> + *
> + * Sequence to be followed while _RESUMING device state:
> + * While data for this device is available, repeat below steps:
> + * a. read data_offset from where user application should write data.
> + * b. write data of data_size to migration region from data_offset. Data size
> + * should be data packet size at source during _SAVING.
> + * c. write data_size which indicates vendor driver that data is written in
> + * migration region. Vendor driver should read this data from migration
> + * region and resume device's state.
> + *
> + * For user application, data is opaque. User application should write data in
> + * the same order as received and should of same transaction size at source.
> + */
> +
> +struct vfio_device_migration_info {
> + __u32 device_state; /* VFIO device state */
> +#define VFIO_DEVICE_STATE_STOP (0)
> +#define VFIO_DEVICE_STATE_RUNNING (1 << 0)
> +#define VFIO_DEVICE_STATE_SAVING (1 << 1)
> +#define VFIO_DEVICE_STATE_RESUMING (1 << 2)
> +#define VFIO_DEVICE_STATE_MASK (VFIO_DEVICE_STATE_RUNNING | \
> + VFIO_DEVICE_STATE_SAVING | \
> + VFIO_DEVICE_STATE_RESUMING)
> +
> +#define VFIO_DEVICE_STATE_VALID(state) \
> + (state & VFIO_DEVICE_STATE_RESUMING ? \
> + (state & VFIO_DEVICE_STATE_MASK) == VFIO_DEVICE_STATE_RESUMING : 1)
> +
> +#define VFIO_DEVICE_STATE_ERROR \
> + (VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RESUMING)
> +
> + __u32 reserved;
> + __u64 pending_bytes;
> + __u64 data_offset;
> + __u64 data_size;
> +} __attribute__((packed));
> +
> /*
> * The MSIX mappable capability informs that MSIX data of a BAR can be mmapped
> * which allows direct access to non-MSIX registers which happened to be within
> --
> 2.7.0
>
