mm/migrate: Trylock device page in do_swap_page

mm/migrate: Trylock device page in do_swap_page

Avoid multiple CPU page faults to the same device page racing by trying
to lock the page in do_swap_page before taking an extra reference to the
page. This prevents scenarios where multiple CPU page faults each take
an extra reference to a device page, which could abort migration in
folio_migrate_mapping. With the device page being locked in
do_swap_page, the migrate_vma_* functions need to be updated to avoid
locking the fault_page argument.

Prior to this change, a livelock scenario could occur in Xe's (Intel GPU
DRM driver) SVM implementation if enough threads faulted the same device
page.

v3:
 - Put page after unlocking page (Alistair)
 - Warn on spliting a TPH which is fault page (Alistair)
 - Warn on dst page == fault page (Alistair)
v6:
 - Add more verbose comment around THP (Alistair)
v7:
 - Fix migrate_device_finalize alignment (Checkpatch)

Cc: Alistair Popple <apopple@nvidia.com>
Cc: Philip Yang <Philip.Yang@amd.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Simona Vetter <simona.vetter@ffwll.ch>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Tested-by: Alistair Popple <apopple@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250306012657.3505757-4-matthew.brost@intel.com