drm/xe: handle pinned memory in PM notifier

Userspace is still alive and kicking at this point so actually moving
pinned stuff here is tricky. However, we can instead pre-allocate the
backup storage upfront from the notifier, such that we scoop up as much
as we can, and then leave the final .suspend() to do the actual copy (or
allocate anything that we missed). That way the bulk of our allocations
will hopefully be done outside the more restrictive .suspend().

We do need to be extra careful though, since the pinned handling can now
race with PM notifier, like something becoming unpinned after we prepare
it from the notifier.

v2 (Thomas):
  - Fix kernel doc and drop the pin as soon as we are done with the
    restore, instead of deferring to later.

Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://lore.kernel.org/r/20250416150913.434369-8-matthew.auld@intel.com

Author: matt-auld

drivers/gpu/drm/xe/xe_bo.c

@@ -1084,6 +1084,80 @@ long xe_bo_shrink(struct ttm_operation_ctx *ctx, struct ttm_buffer_object *bo,
 	return lret;
 }
 
+/**
+ * xe_bo_notifier_prepare_pinned() - Prepare a pinned VRAM object to be backed
+ * up in system memory.
+ * @bo: The buffer object to prepare.
+ *
+ * On successful completion, the object backup pages are allocated. Expectation
+ * is that this is called from the PM notifier, prior to suspend/hibernation.
+ *
+ * Return: 0 on success. Negative error code on failure.
+ */
+int xe_bo_notifier_prepare_pinned(struct xe_bo *bo)
+{
+	struct xe_device *xe = ttm_to_xe_device(bo->ttm.bdev);
+	struct xe_bo *backup;
+	int ret = 0;
+
+	xe_bo_lock(bo, false);
+
+	xe_assert(xe, !bo->backup_obj);
+
+	/*
+	 * Since this is called from the PM notifier we might have raced with
+	 * someone unpinning this after we dropped the pinned list lock and
+	 * grabbing the above bo lock.
+	 */
+	if (!xe_bo_is_pinned(bo))
+		goto out_unlock_bo;
+
+	if (!xe_bo_is_vram(bo))
+		goto out_unlock_bo;
+
+	if (bo->flags & XE_BO_FLAG_PINNED_NORESTORE)
+		goto out_unlock_bo;
+
+	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 */
+	ttm_bo_pin(&backup->ttm);
+	bo->backup_obj = backup;
+
+out_unlock_bo:
+	xe_bo_unlock(bo);
+	return ret;
+}
+
+/**
+ * xe_bo_notifier_unprepare_pinned() - Undo the previous prepare operation.
+ * @bo: The buffer object to undo the prepare for.
+ *
+ * Always returns 0. The backup object is removed, if still present. Expectation
+ * it that this called from the PM notifier when undoing the prepare step.
+ *
+ * Return: Always returns 0.
+ */
+int xe_bo_notifier_unprepare_pinned(struct xe_bo *bo)
+{
+	xe_bo_lock(bo, false);
+	if (bo->backup_obj) {
+		ttm_bo_unpin(&bo->backup_obj->ttm);
+		xe_bo_put(bo->backup_obj);
+		bo->backup_obj = NULL;
+	}
+	xe_bo_unlock(bo);
+
+	return 0;
+}
+
 /**
  * xe_bo_evict_pinned() - Evict a pinned VRAM object to system memory
  * @bo: The buffer object to move.
@@ -1098,7 +1172,8 @@ long xe_bo_shrink(struct ttm_operation_ctx *ctx, struct ttm_buffer_object *bo,
 int xe_bo_evict_pinned(struct xe_bo *bo)
 {
 	struct xe_device *xe = ttm_to_xe_device(bo->ttm.bdev);
-	struct xe_bo *backup;
+	struct xe_bo *backup = bo->backup_obj;
+	bool backup_created = false;
 	bool unmap = false;
 	int ret = 0;
 
@@ -1120,15 +1195,18 @@ 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->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;
+	if (!backup) {
+		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 */
+		backup_created = true;
 	}
-	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;
@@ -1175,11 +1253,12 @@ int xe_bo_evict_pinned(struct xe_bo *bo)
 				   bo->size);
 	}
 
-	bo->backup_obj = backup;
+	if (!bo->backup_obj)
+		bo->backup_obj = backup;
 
 out_backup:
 	xe_bo_vunmap(backup);
-	if (ret)
+	if (ret && backup_created)
 		xe_bo_put(backup);
 out_unlock_bo:
 	if (unmap)
@@ -1215,9 +1294,11 @@ int xe_bo_restore_pinned(struct xe_bo *bo)
 
 	xe_bo_lock(bo, false);
 
-	ret = ttm_bo_validate(&backup->ttm, &backup->placement, &ctx);
-	if (ret)
-		goto out_backup;
+	if (!xe_bo_is_pinned(backup)) {
+		ret = ttm_bo_validate(&backup->ttm, &backup->placement, &ctx);
+		if (ret)
+			goto out_unlock_bo;
+	}
 
 	if (xe_bo_is_user(bo) || (bo->flags & XE_BO_FLAG_PINNED_LATE_RESTORE)) {
 		struct xe_migrate *migrate;
@@ -1257,7 +1338,7 @@ int xe_bo_restore_pinned(struct xe_bo *bo)
 		if (iosys_map_is_null(&bo->vmap)) {
 			ret = xe_bo_vmap(bo);
 			if (ret)
-				goto out_unlock_bo;
+				goto out_backup;
 			unmap = true;
 		}
 
@@ -1269,8 +1350,11 @@ int xe_bo_restore_pinned(struct xe_bo *bo)
 
 out_backup:
 	xe_bo_vunmap(backup);
-	if (!bo->backup_obj)
+	if (!bo->backup_obj) {
+		if (xe_bo_is_pinned(backup))
+			ttm_bo_unpin(&backup->ttm);
 		xe_bo_put(backup);
+	}
 out_unlock_bo:
 	if (unmap)
 		xe_bo_vunmap(bo);
@@ -2304,6 +2388,13 @@ void xe_bo_unpin(struct xe_bo *bo)
 		xe_assert(xe, !list_empty(&bo->pinned_link));
 		list_del_init(&bo->pinned_link);
 		spin_unlock(&xe->pinned.lock);
+
+		if (bo->backup_obj) {
+			if (xe_bo_is_pinned(bo->backup_obj))
+				ttm_bo_unpin(&bo->backup_obj->ttm);
+			xe_bo_put(bo->backup_obj);
+			bo->backup_obj = NULL;
+		}
 	}
 	ttm_bo_unpin(&bo->ttm);
 	if (bo->ttm.ttm && ttm_tt_is_populated(bo->ttm.ttm))

drivers/gpu/drm/xe/xe_bo.h

@@ -277,6 +277,8 @@ int xe_bo_migrate(struct xe_bo *bo, u32 mem_type);
 int xe_bo_evict(struct xe_bo *bo, bool force_alloc);
 
 int xe_bo_evict_pinned(struct xe_bo *bo);
+int xe_bo_notifier_prepare_pinned(struct xe_bo *bo);
+int xe_bo_notifier_unprepare_pinned(struct xe_bo *bo);
 int xe_bo_restore_pinned(struct xe_bo *bo);
 
 int xe_bo_dma_unmap_pinned(struct xe_bo *bo);

drivers/gpu/drm/xe/xe_bo_evict.c

@@ -34,7 +34,13 @@ static int xe_bo_apply_to_pinned(struct xe_device *xe,
 		ret = pinned_fn(bo);
 		if (ret && pinned_list != new_list) {
 			spin_lock(&xe->pinned.lock);
-			list_move(&bo->pinned_link, pinned_list);
+			/*
+			 * We might no longer be pinned, since PM notifier can
+			 * call this. If the pinned link is now empty, keep it
+			 * that way.
+			 */
+			if (!list_empty(&bo->pinned_link))
+				list_move(&bo->pinned_link, pinned_list);
 			spin_unlock(&xe->pinned.lock);
 		}
 		xe_bo_put(bo);
@@ -46,6 +52,49 @@ static int xe_bo_apply_to_pinned(struct xe_device *xe,
 	return ret;
 }
 
+/**
+ * xe_bo_notifier_prepare_all_pinned() - Pre-allocate the backing pages for all
+ * pinned VRAM objects which need to be saved.
+ * @xe: xe device
+ *
+ * Should be called from PM notifier when preparing for s3/s4.
+ *
+ * Return: 0 on success, negative error code on error.
+ */
+int xe_bo_notifier_prepare_all_pinned(struct xe_device *xe)
+{
+	int ret;
+
+	ret = xe_bo_apply_to_pinned(xe, &xe->pinned.early.kernel_bo_present,
+				    &xe->pinned.early.kernel_bo_present,
+				    xe_bo_notifier_prepare_pinned);
+	if (!ret)
+		ret = xe_bo_apply_to_pinned(xe, &xe->pinned.late.kernel_bo_present,
+					    &xe->pinned.late.kernel_bo_present,
+					    xe_bo_notifier_prepare_pinned);
+
+	return ret;
+}
+
+/**
+ * xe_bo_notifier_unprepare_all_pinned() - Remove the backing pages for all
+ * pinned VRAM objects which have been restored.
+ * @xe: xe device
+ *
+ * Should be called from PM notifier after exiting s3/s4 (either on success or
+ * failure).
+ */
+void xe_bo_notifier_unprepare_all_pinned(struct xe_device *xe)
+{
+	(void)xe_bo_apply_to_pinned(xe, &xe->pinned.early.kernel_bo_present,
+				    &xe->pinned.early.kernel_bo_present,
+				    xe_bo_notifier_unprepare_pinned);
+
+	(void)xe_bo_apply_to_pinned(xe, &xe->pinned.late.kernel_bo_present,
+				    &xe->pinned.late.kernel_bo_present,
+				    xe_bo_notifier_unprepare_pinned);
+}
+
 /**
  * xe_bo_evict_all_user - evict all non-pinned user BOs from VRAM
  * @xe: xe device

drivers/gpu/drm/xe/xe_bo_evict.h

@@ -10,6 +10,8 @@ struct xe_device;
 
 int xe_bo_evict_all(struct xe_device *xe);
 int xe_bo_evict_all_user(struct xe_device *xe);
+int xe_bo_notifier_prepare_all_pinned(struct xe_device *xe);
+void xe_bo_notifier_unprepare_all_pinned(struct xe_device *xe);
 int xe_bo_restore_early(struct xe_device *xe);
 int xe_bo_restore_late(struct xe_device *xe);
 

drivers/gpu/drm/xe/xe_pm.c

@@ -297,9 +297,22 @@ static int xe_pm_notifier_callback(struct notifier_block *nb,
 	case PM_SUSPEND_PREPARE:
 		xe_pm_runtime_get(xe);
 		err = xe_bo_evict_all_user(xe);
-		xe_pm_runtime_put(xe);
-		if (err)
+		if (err) {
 			drm_dbg(&xe->drm, "Notifier evict user failed (%d)\n", err);
+			xe_pm_runtime_put(xe);
+			break;
+		}
+
+		err = xe_bo_notifier_prepare_all_pinned(xe);
+		if (err) {
+			drm_dbg(&xe->drm, "Notifier prepare pin failed (%d)\n", err);
+			xe_pm_runtime_put(xe);
+		}
+		break;
+	case PM_POST_HIBERNATION:
+	case PM_POST_SUSPEND:
+		xe_bo_notifier_unprepare_all_pinned(xe);
+		xe_pm_runtime_put(xe);
 		break;
 	}