drm/xe: share bo dma-resv with backup object

We end up needing to grab both locks together anyway and keep them held
until we complete the copy or add the fence. Plus the backup_obj is
short lived and tied to the parent object, so seems reasonable to share
the same dma-resv. This will simplify the locking here, and in follow
up patches.

v2:
  - Hold reference to the parent bo to be sure the shared dma-resv can't
    go out of scope too soon. (Thomas)

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://lore.kernel.org/r/20250416150913.434369-7-matthew.auld@intel.com

Author: matt-auld

drivers/gpu/drm/xe/xe_bo.c

@@ -1120,13 +1120,15 @@ int xe_bo_evict_pinned(struct xe_bo *bo)
 	if (bo->flags & XE_BO_FLAG_PINNED_NORESTORE)
 		goto out_unlock_bo;
 
-	backup = xe_bo_create_locked(xe, NULL, NULL, bo->size, ttm_bo_type_kernel,
-				     XE_BO_FLAG_SYSTEM | XE_BO_FLAG_NEEDS_CPU_ACCESS |
-				     XE_BO_FLAG_PINNED);
+	backup = ___xe_bo_create_locked(xe, NULL, NULL, bo->ttm.base.resv, NULL, bo->size,
+					DRM_XE_GEM_CPU_CACHING_WB, ttm_bo_type_kernel,
+					XE_BO_FLAG_SYSTEM | XE_BO_FLAG_NEEDS_CPU_ACCESS |
+					XE_BO_FLAG_PINNED);
 	if (IS_ERR(backup)) {
 		ret = PTR_ERR(backup);
 		goto out_unlock_bo;
 	}
+	backup->parent_obj = xe_bo_get(bo); /* Released by bo_destroy */
 
 	if (xe_bo_is_user(bo) || (bo->flags & XE_BO_FLAG_PINNED_LATE_RESTORE)) {
 		struct xe_migrate *migrate;
@@ -1177,7 +1179,6 @@ int xe_bo_evict_pinned(struct xe_bo *bo)
 
 out_backup:
 	xe_bo_vunmap(backup);
-	xe_bo_unlock(backup);
 	if (ret)
 		xe_bo_put(backup);
 out_unlock_bo:
@@ -1212,17 +1213,12 @@ int xe_bo_restore_pinned(struct xe_bo *bo)
 	if (!backup)
 		return 0;
 
-	xe_bo_lock(backup, false);
+	xe_bo_lock(bo, false);
 
 	ret = ttm_bo_validate(&backup->ttm, &backup->placement, &ctx);
 	if (ret)
 		goto out_backup;
 
-	if (WARN_ON(!dma_resv_trylock(bo->ttm.base.resv))) {
-		ret = -EBUSY;
-		goto out_backup;
-	}
-
 	if (xe_bo_is_user(bo) || (bo->flags & XE_BO_FLAG_PINNED_LATE_RESTORE)) {
 		struct xe_migrate *migrate;
 		struct dma_fence *fence;
@@ -1271,15 +1267,14 @@ int xe_bo_restore_pinned(struct xe_bo *bo)
 
 	bo->backup_obj = NULL;
 
-out_unlock_bo:
-	if (unmap)
-		xe_bo_vunmap(bo);
-	xe_bo_unlock(bo);
 out_backup:
 	xe_bo_vunmap(backup);
-	xe_bo_unlock(backup);
 	if (!bo->backup_obj)
 		xe_bo_put(backup);
+out_unlock_bo:
+	if (unmap)
+		xe_bo_vunmap(bo);
+	xe_bo_unlock(bo);
 	return ret;
 }
 
@@ -1532,6 +1527,9 @@ static void xe_ttm_bo_destroy(struct ttm_buffer_object *ttm_bo)
 	if (bo->vm && xe_bo_is_user(bo))
 		xe_vm_put(bo->vm);
 
+	if (bo->parent_obj)
+		xe_bo_put(bo->parent_obj);
+
 	mutex_lock(&xe->mem_access.vram_userfault.lock);
 	if (!list_empty(&bo->vram_userfault_link))
 		list_del(&bo->vram_userfault_link);

drivers/gpu/drm/xe/xe_bo_types.h

@@ -30,6 +30,8 @@ struct xe_bo {
 	struct ttm_buffer_object ttm;
 	/** @backup_obj: The backup object when pinned and suspended (vram only) */
 	struct xe_bo *backup_obj;
+	/** @parent_obj: Ref to parent bo if this a backup_obj */
+	struct xe_bo *parent_obj;
 	/** @size: Size of this buffer object */
 	size_t size;
 	/** @flags: flags for this buffer object */