drm/pagemap: Clear driver-provided PFNs from migration PFN array

drm/pagemap: Clear driver-provided PFNs from migration PFN array

DRM pagemap overloads the migration PFN array to store driver-provided
PFNs before calling migrate_vma_*() to finalize the migration. If an
error occurs during the incremental copy phase, the migration PFN
entries are reverted to their original state. After reverting the
device-folio mutations, clear any remaining driver-provided PFNs to
avoid confusing the migrate_vma_*() helpers.

Also clear any driver-provided PFNs if populate_devmem_pfn() fails, as
a precaution against stale entries being interpreted as migration PFNs.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: 3902846af36b ("drm/pagemap Fix error paths in drm_pagemap_migrate_to_devmem")
Fixes: ec265e1f1cfc ("drm/pagemap: Support source migration over interconnect")
Cc: stable@vger.kernel.org
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://patch.msgid.link/20260721204353.1082632-1-matthew.brost@intel.com