Revert "drm/pagemap: Disable device-to-device migration"

With commit
a69d1ab ("mm: Fix a hmm_range_fault() livelock / starvation problem")
device-to-device migration is not functional again and the
disabling can be reverted.

Add the above commit as a Fixes: tag in order for the revert to not
take place unless that commit is present.

This reverts commit 10dd1ea.

Cc: Matthew Brost <matthew.brost@intel.com>
Fixes: b570f37 ("mm: Fix a hmm_range_fault() livelock / starvation problem")
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260211104159.114947-1-thomas.hellstrom@linux.intel.com
(cherry picked from commit 1a3c004)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[Rodrigo updated Fixes tag]

Author: Thomas Hellström

drivers/gpu/drm/drm_pagemap.c

@@ -480,18 +480,8 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
 		.start		= start,
 		.end		= end,
 		.pgmap_owner	= pagemap->owner,
-		/*
-		 * FIXME: MIGRATE_VMA_SELECT_DEVICE_PRIVATE intermittently
-		 * causes 'xe_exec_system_allocator --r *race*no*' to trigger aa
-		 * engine reset and a hard hang due to getting stuck on a folio
-		 * lock. This should work and needs to be root-caused. The only
-		 * downside of not selecting MIGRATE_VMA_SELECT_DEVICE_PRIVATE
-		 * is that device-to-device migrations won’t work; instead,
-		 * memory will bounce through system memory. This path should be
-		 * rare and only occur when the madvise attributes of memory are
-		 * changed or atomics are being used.
-		 */
-		.flags		= MIGRATE_VMA_SELECT_SYSTEM | MIGRATE_VMA_SELECT_DEVICE_COHERENT,
+		.flags		= MIGRATE_VMA_SELECT_SYSTEM | MIGRATE_VMA_SELECT_DEVICE_COHERENT |
+		MIGRATE_VMA_SELECT_DEVICE_PRIVATE,
 	};
 	unsigned long i, npages = npages_in_range(start, end);
 	unsigned long own_pages = 0, migrated_pages = 0;