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vfio/migration: Multifd device state transfer support - send side

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Implement the multifd device state transfer via additional per-device
thread inside save_live_complete_precopy_thread handler.

Switch between doing the data transfer in the new handler and doing it
in the old save_state handler depending if VFIO multifd transfer is enabled
or not.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/4d727e2e0435e0022d50004e474077632830e08d.1741124640.git.maciej.szmigiero@oracle.com
[ clg: - Reordered savevm_vfio_handlers
       - Updated save_live_complete_precopy* documentation ]
Signed-off-by: Cédric Le Goater <clg@redhat.com>
This commit is contained in:
Maciej S. Szmigiero 2025-03-04 23:03:57 +01:00 • committed by Cédric Le Goater
parent b659c07c53
commit 6d644baef2
6 changed files with 189 additions and 8 deletions
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19
docs/devel/migration/vfio.rst
View file

@ -71,11 +71,23 @@ VFIO implements the device hooks for the iterative approach as follows:
reassembles the multifd received data and loads it in-order into the device.
In the non-multifd mode this function is a NOP.
* A ``save_state`` function to save the device config space if it is present.
* A ``save_state`` function to save the device config space if it is present
in the non-multifd mode.
In the multifd mode it just emits either a dummy EOS marker.
* A ``save_live_complete_precopy`` function that sets the VFIO device in
_STOP_COPY state and iteratively copies the data for the VFIO device until
the vendor driver indicates that no data remains.
In the multifd mode it just emits a dummy EOS marker.
* A ``save_live_complete_precopy_thread`` function that in the multifd mode
provides thread handler performing multifd device state transfer.
It sets the VFIO device to _STOP_COPY state, iteratively reads the data
from the VFIO device and queues it for multifd transmission until the vendor
driver indicates that no data remains.
After that, it saves the device config space and queues it for multifd
transfer too.
In the non-multifd mode this thread is a NOP.
* A ``load_state`` function that loads the config section and the data
sections that are generated by the save functions above.
@ -184,8 +196,11 @@ Live migration save path
Then the VFIO device is put in _STOP_COPY state
(FINISH_MIGRATE, _ACTIVE, _STOP_COPY)
.save_live_complete_precopy() is called for each active device
For the VFIO device, iterate in .save_live_complete_precopy() until
For the VFIO device: in the non-multifd mode iterate in
.save_live_complete_precopy() until
pending data is 0
In the multifd mode this iteration is done in
.save_live_complete_precopy_thread() instead.
|
(POSTMIGRATE, _COMPLETED, _STOP_COPY)
Migraton thread schedules cleanup bottom half and exits