drm/xe/vf: Redo LRC creation while in VF fixups

drm/xe/vf: Redo LRC creation while in VF fixups

If the xe module within a VM was creating a new LRC during save/
restore, this LRC will be invalid. The fixups procedure may not
be able to reach it, as there will be a race to add the new LRC
reference to an exec queue.

Even if the new LRC which was being created during VM migration is
added to EQ in time for fixups, said LRC may still remain damaged.
In a small percentage of specially crafted test cases, the resulting
LRC was still damaged and caused GPU hang.

Any LRC which could be created in such a situation, have to be
re-created.

Due to VM having arbitrarily set amount of CPU cores, it is possible
to limit the amount to 1. In such case, there is a possibility that
kernel will switch CPU contexts in a way which allows to miss
VF migration recovery running in parallel (by simply not switching
to the LRC creation thread during recovery). Therefore checking
if the migration is in progress just after LRC creation, is not
enough to ensure detection.

Free the incorrectly created LRC, and trigger a re-run of the
creation, but only after waiting for default LRC to get fixups.
Use additional atomic value increased after fixups, to ensure any VF
migration that avoided detection by just checking for recovery in
progress, will be caught.

v2: Merge marker and wait for default LRC, reducing amount of calls
  within xe_init_eq(). Alter the LRC creation loop to remove a race
  with post-migration fixups worker.
v3: Kerneldoc fixes. Rename fixups_complete_count.

Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patch.msgid.link/20260226212701.2937065-5-tomasz.lis@intel.com