Re: [PATCH v2 3/6] drm/i915 Implement LMEM backup and restore for suspend / resume

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On 06/09/2021 17:55, Thomas Hellström wrote:
Just evict unpinned objects to system. For pinned LMEM objects,
make a backup system object and blit the contents to that.

Backup is performed in three steps,
1: Opportunistically evict evictable objects using the gpu blitter.
2: After gt idle, evict evictable objects using the gpu blitter. This will
be modified in an upcoming patch to backup pinned objects that are not used
by the blitter itself.
3: Backup remaining pinned objects using memcpy.

Also move uC suspend to after 2) to make sure we have a functional GuC
during 2) if using GuC submission.

v2:
- Major refactor to make sure gem_exec_suspend@hang-SX subtests work, and
   suspend / resume works with a slightly modified GuC submission enabling
   patch series.

Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>

<snip>

+
+static int i915_ttm_backup(struct i915_gem_apply_to_region *apply,
+			   struct drm_i915_gem_object *obj)
+{
+	struct i915_gem_ttm_pm_apply *pm_apply =
+		container_of(apply, typeof(*pm_apply), base);
+	struct ttm_buffer_object *bo = i915_gem_to_ttm(obj);
+	struct ttm_buffer_object *backup_bo;
+	struct drm_i915_private *i915 =
+		container_of(bo->bdev, typeof(*i915), bdev);
+	struct intel_memory_region *sys_region;
+	struct drm_i915_gem_object *backup;
+	struct ttm_operation_ctx ctx = {};
+	int err = 0;
+
+	if (bo->resource->mem_type == I915_PL_SYSTEM || obj->ttm.backup)
+		return 0;
+
+	if (pm_apply->allow_gpu && i915_gem_object_evictable(obj))
+		return ttm_bo_validate(bo, i915_ttm_sys_placement(), &ctx);
+
+	if (!pm_apply->backup_pinned)
+		return 0;
+
+	sys_region = i915->mm.regions[INTEL_REGION_SMEM];
+	backup = i915_gem_object_create_region(sys_region,
+					       obj->base.size,
+					       0, 0);

create_shmem()?

+	if (IS_ERR(backup))
+		return PTR_ERR(backup);
+
+	err = i915_gem_object_lock(backup, apply->ww);
+	if (err)
+		goto out_no_lock;
+
+	backup_bo = i915_gem_to_ttm(backup);
+	err = ttm_tt_populate(backup_bo->bdev, backup_bo->ttm, &ctx);
+	if (err)
+		goto out_no_populate;
+
+	err = i915_gem_obj_copy_ttm(backup, obj, pm_apply->allow_gpu, false);
+	GEM_WARN_ON(err);
+
+	obj->ttm.backup = backup;
+	return 0;
+
+out_no_populate:
+	i915_gem_ww_unlock_single(backup);
+out_no_lock:
+	i915_gem_object_put(backup);
+
+	return err;
+}
+
+static int i915_ttm_recover(struct i915_gem_apply_to_region *apply,
+			    struct drm_i915_gem_object *obj)
+{
+	i915_ttm_backup_free(obj);
+	return 0;
+}
+
+/**
+ * i915_ttm_recover_region - Free the backup of all objects of a region
+ * @mr: The memory region
+ *
+ * Checks all objects of a region if there is backup attached and if so
+ * frees that backup. Typically this is called to recover after a partially
+ * performed backup.
+ */
+void i915_ttm_recover_region(struct intel_memory_region *mr)
+{
+	static const struct i915_gem_apply_to_region_ops recover_ops = {
+		.process_obj = i915_ttm_recover,
+	};
+	struct i915_gem_apply_to_region apply = {.ops = &recover_ops};
+	int ret;
+
+	ret = i915_gem_process_region(mr, &apply);
+	GEM_WARN_ON(ret);
+}
+
+/**
+ * i915_ttm_backup_region - Back up all objects of a region to smem.
+ * @mr: The memory region
+ * @allow_gpu: Whether to allow the gpu blitter for this backup.
+ * @backup_pinned: Backup also pinned objects.
+ *
+ * Loops over all objects of a region and either evicts them if they are
+ * evictable or backs them up using a backup object if they are pinned.
+ *
+ * Return: Zero on success. Negative error code on error.
+ */
+int i915_ttm_backup_region(struct intel_memory_region *mr, bool allow_gpu,
+			   bool backup_pinned)
+{
+	static const struct i915_gem_apply_to_region_ops backup_ops = {
+		.process_obj = i915_ttm_backup,
+	};
+	struct i915_gem_ttm_pm_apply pm_apply = {
+		.base = {.ops = &backup_ops},
+		.allow_gpu = allow_gpu,
+		.backup_pinned = backup_pinned,
+	};
+
+	return i915_gem_process_region(mr, &pm_apply.base);
+}
+
+static int i915_ttm_restore(struct i915_gem_apply_to_region *apply,
+			    struct drm_i915_gem_object *obj)
+{
+	struct i915_gem_ttm_pm_apply *pm_apply =
+		container_of(apply, typeof(*pm_apply), base);
+	struct drm_i915_gem_object *backup = obj->ttm.backup;
+	struct ttm_buffer_object *backup_bo = i915_gem_to_ttm(backup);
+	struct ttm_operation_ctx ctx = {};
+	int err;
+
+	if (!obj->ttm.backup)

if (!backup)

+		return 0;
+
+	if (!pm_apply->allow_gpu && (obj->flags & I915_BO_ALLOC_USER))
+		return 0;
+
+	err = i915_gem_object_lock(backup, apply->ww);
+	if (err)
+		return err;
+
+	/* Content may have been swapped. */
+	err = ttm_tt_populate(backup_bo->bdev, backup_bo->ttm, &ctx);
+	if (!err) {
+		err = i915_gem_obj_copy_ttm(obj, backup, pm_apply->allow_gpu,
+					    false);
+		GEM_WARN_ON(err);
+
+		obj->ttm.backup = NULL;
+		err = 0;
+	}
+
+	i915_gem_ww_unlock_single(backup);
+	i915_gem_object_put(backup);

I assume we need to set ttm.backup = NULL somewhere here on the failure path, or don't drop the ref? Or at least it looks like potential uaf later?

+
+	return err;
+}
+



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