Re: [PATCH v3 3/6] drm/i915 Implement LMEM backup and restore for suspend / resume

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On 14/09/2021 20:31, 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.

v3:
- Fix a potential use-after-free (Matthew Auld)
- Use i915_gem_object_create_shmem() instead of
   i915_gem_object_create_region (Matthew Auld)
- Minor simplifications (Matthew Auld)
- Fix up kerneldoc for i195_ttm_restore_region().
- Final lmem_suspend() call moved to i915_gem_backup_suspend from
   i915_gem_suspend_late, since the latter gets called at driver unload
   and we don't unnecessarily want to run it at that time.

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

<snip>

+
+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 (!backup)
+		return 0;
+
+	if (!pm_apply->allow_gpu && (obj->flags & I915_BO_ALLOC_USER))
+		return 0;

Hmm, do we ever hit this? I would presume anything that userspace directly allocated in lmem can be kicked out with ttm_bo_validate(sys) i.e backup == NULL?

+
+	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);
+
+	if (!err)
+		i915_gem_object_put(backup);
+
+	return err;
+}
+



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