drm/i915/gem: Implement object migration

Introduce an interface to migrate objects between regions.
This is primarily intended to migrate objects to LMEM for display and
to SYSTEM for dma-buf, but might be reused in one form or another for
performance-based migration.

v2:
- Verify that the memory region given as an id really exists.
  (Reported by Matthew Auld)
- Call i915_gem_object_{init,release}_memory_region() when switching region
  to handle also switching region lists. (Reported by Matthew Auld)
v3:
- Fix i915_gem_object_can_migrate() to return true if object is already in
  the correct region, even if the object ops doesn't have a migrate()
  callback.
- Update typo in commit message.
- Fix kerneldoc of i915_gem_object_wait_migration().
v4:
- Improve documentation (Suggested by Mattew Auld and Michael Ruhl)
- Always assume TTM migration hits a TTM move and unsets the pages through
  move_notify. (Reported by Matthew Auld)
- Add a dma_fence_might_wait() annotation to
  i915_gem_object_wait_migration() (Suggested by Daniel Vetter)
v5:
- Re-add might_sleep() instead of __dma_fence_might_wait(), Sent
  v4 with the wrong version, didn't compile and __dma_fence_might_wait()
  is not exported.
- Added an R-B.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210629151203.209465-2-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -513,6 +513,118 @@ bool i915_gem_object_has_iomem(const struct drm_i915_gem_object *obj)
 	return obj->mem_flags & I915_BO_FLAG_IOMEM;
 }
 
+/**
+ * i915_gem_object_can_migrate - Whether an object likely can be migrated
+ *
+ * @obj: The object to migrate
+ * @id: The region intended to migrate to
+ *
+ * Check whether the object backend supports migration to the
+ * given region. Note that pinning may affect the ability to migrate as
+ * returned by this function.
+ *
+ * This function is primarily intended as a helper for checking the
+ * possibility to migrate objects and might be slightly less permissive
+ * than i915_gem_object_migrate() when it comes to objects with the
+ * I915_BO_ALLOC_USER flag set.
+ *
+ * Return: true if migration is possible, false otherwise.
+ */
+bool i915_gem_object_can_migrate(struct drm_i915_gem_object *obj,
+				 enum intel_region_id id)
+{
+	struct drm_i915_private *i915 = to_i915(obj->base.dev);
+	unsigned int num_allowed = obj->mm.n_placements;
+	struct intel_memory_region *mr;
+	unsigned int i;
+
+	GEM_BUG_ON(id >= INTEL_REGION_UNKNOWN);
+	GEM_BUG_ON(obj->mm.madv != I915_MADV_WILLNEED);
+
+	mr = i915->mm.regions[id];
+	if (!mr)
+		return false;
+
+	if (obj->mm.region == mr)
+		return true;
+
+	if (!i915_gem_object_evictable(obj))
+		return false;
+
+	if (!obj->ops->migrate)
+		return false;
+
+	if (!(obj->flags & I915_BO_ALLOC_USER))
+		return true;
+
+	if (num_allowed == 0)
+		return false;
+
+	for (i = 0; i < num_allowed; ++i) {
+		if (mr == obj->mm.placements[i])
+			return true;
+	}
+
+	return false;
+}
+
+/**
+ * i915_gem_object_migrate - Migrate an object to the desired region id
+ * @obj: The object to migrate.
+ * @ww: An optional struct i915_gem_ww_ctx. If NULL, the backend may
+ * not be successful in evicting other objects to make room for this object.
+ * @id: The region id to migrate to.
+ *
+ * Attempt to migrate the object to the desired memory region. The
+ * object backend must support migration and the object may not be
+ * pinned, (explicitly pinned pages or pinned vmas). The object must
+ * be locked.
+ * On successful completion, the object will have pages pointing to
+ * memory in the new region, but an async migration task may not have
+ * completed yet, and to accomplish that, i915_gem_object_wait_migration()
+ * must be called.
+ *
+ * This function is a bit more permissive than i915_gem_object_can_migrate()
+ * to allow for migrating objects where the caller knows exactly what is
+ * happening. For example within selftests. More specifically this
+ * function allows migrating I915_BO_ALLOC_USER objects to regions
+ * that are not in the list of allowable regions.
+ *
+ * Note: the @ww parameter is not used yet, but included to make sure
+ * callers put some effort into obtaining a valid ww ctx if one is
+ * available.
+ *
+ * Return: 0 on success. Negative error code on failure. In particular may
+ * return -ENXIO on lack of region space, -EDEADLK for deadlock avoidance
+ * if @ww is set, -EINTR or -ERESTARTSYS if signal pending, and
+ * -EBUSY if the object is pinned.
+ */
+int i915_gem_object_migrate(struct drm_i915_gem_object *obj,
+			    struct i915_gem_ww_ctx *ww,
+			    enum intel_region_id id)
+{
+	struct drm_i915_private *i915 = to_i915(obj->base.dev);
+	struct intel_memory_region *mr;
+
+	GEM_BUG_ON(id >= INTEL_REGION_UNKNOWN);
+	GEM_BUG_ON(obj->mm.madv != I915_MADV_WILLNEED);
+	assert_object_held(obj);
+
+	mr = i915->mm.regions[id];
+	GEM_BUG_ON(!mr);
+
+	if (obj->mm.region == mr)
+		return 0;
+
+	if (!i915_gem_object_evictable(obj))
+		return -EBUSY;
+
+	if (!obj->ops->migrate)
+		return -EOPNOTSUPP;
+
+	return obj->ops->migrate(obj, mr);
+}
+
 void i915_gem_init__objects(struct drm_i915_private *i915)
 {
 	INIT_WORK(&i915->mm.free_work, __i915_gem_free_work);

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -17,6 +17,8 @@
 #include "i915_gem_ww.h"
 #include "i915_vma_types.h"
 
+enum intel_region_id;
+
 /*
  * XXX: There is a prevalence of the assumption that we fit the
  * object's page count inside a 32bit _signed_ variable. Let's document
@@ -597,6 +599,16 @@ bool i915_gem_object_migratable(struct drm_i915_gem_object *obj);
 
 bool i915_gem_object_validates_to_lmem(struct drm_i915_gem_object *obj);
 
+int i915_gem_object_migrate(struct drm_i915_gem_object *obj,
+			    struct i915_gem_ww_ctx *ww,
+			    enum intel_region_id id);
+
+bool i915_gem_object_can_migrate(struct drm_i915_gem_object *obj,
+				 enum intel_region_id id);
+
+int i915_gem_object_wait_migration(struct drm_i915_gem_object *obj,
+				   unsigned int flags);
+
 #ifdef CONFIG_MMU_NOTIFIER
 static inline bool
 i915_gem_object_is_userptr(struct drm_i915_gem_object *obj)

drivers/gpu/drm/i915/gem/i915_gem_object_types.h

@@ -18,6 +18,7 @@
 
 struct drm_i915_gem_object;
 struct intel_fronbuffer;
+struct intel_memory_region;
 
 /*
  * struct i915_lut_handle tracks the fast lookups from handle to vma used
@@ -77,6 +78,14 @@ struct drm_i915_gem_object_ops {
 	 * delayed_free - Override the default delayed free implementation
 	 */
 	void (*delayed_free)(struct drm_i915_gem_object *obj);
+
+	/**
+	 * migrate - Migrate object to a different region either for
+	 * pinning or for as long as the object lock is held.
+	 */
+	int (*migrate)(struct drm_i915_gem_object *obj,
+		       struct intel_memory_region *mr);
+
 	void (*release)(struct drm_i915_gem_object *obj);
 
 	const struct vm_operations_struct *mmap_ops;

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

@@ -617,7 +617,8 @@ struct ttm_device_funcs *i915_ttm_driver(void)
 	return &i915_ttm_bo_driver;
 }
 
-static int i915_ttm_get_pages(struct drm_i915_gem_object *obj)
+static int __i915_ttm_get_pages(struct drm_i915_gem_object *obj,
+				struct ttm_placement *placement)
 {
 	struct ttm_buffer_object *bo = i915_gem_to_ttm(obj);
 	struct ttm_operation_ctx ctx = {
@@ -625,19 +626,12 @@ static int i915_ttm_get_pages(struct drm_i915_gem_object *obj)
 		.no_wait_gpu = false,
 	};
 	struct sg_table *st;
-	struct ttm_place requested, busy[I915_TTM_MAX_PLACEMENTS];
-	struct ttm_placement placement;
 	int real_num_busy;
 	int ret;
 
-	GEM_BUG_ON(obj->mm.n_placements > I915_TTM_MAX_PLACEMENTS);
-
-	/* Move to the requested placement. */
-	i915_ttm_placement_from_obj(obj, &requested, busy, &placement);
-
 	/* First try only the requested placement. No eviction. */
-	real_num_busy = fetch_and_zero(&placement.num_busy_placement);
-	ret = ttm_bo_validate(bo, &placement, &ctx);
+	real_num_busy = fetch_and_zero(&placement->num_busy_placement);
+	ret = ttm_bo_validate(bo, placement, &ctx);
 	if (ret) {
 		ret = i915_ttm_err_to_gem(ret);
 		/*
@@ -652,8 +646,8 @@ static int i915_ttm_get_pages(struct drm_i915_gem_object *obj)
 		 * If the initial attempt fails, allow all accepted placements,
 		 * evicting if necessary.
 		 */
-		placement.num_busy_placement = real_num_busy;
-		ret = ttm_bo_validate(bo, &placement, &ctx);
+		placement->num_busy_placement = real_num_busy;
+		ret = ttm_bo_validate(bo, placement, &ctx);
 		if (ret)
 			return i915_ttm_err_to_gem(ret);
 	}
@@ -668,6 +662,7 @@ static int i915_ttm_get_pages(struct drm_i915_gem_object *obj)
 		i915_ttm_adjust_gem_after_move(obj);
 	}
 
+	GEM_WARN_ON(obj->mm.pages);
 	/* Object either has a page vector or is an iomem object */
 	st = bo->ttm ? i915_ttm_tt_get_st(bo->ttm) : obj->ttm.cached_io_st;
 	if (IS_ERR(st))
@@ -678,6 +673,63 @@ static int i915_ttm_get_pages(struct drm_i915_gem_object *obj)
 	return ret;
 }
 
+static int i915_ttm_get_pages(struct drm_i915_gem_object *obj)
+{
+	struct ttm_place requested, busy[I915_TTM_MAX_PLACEMENTS];
+	struct ttm_placement placement;
+
+	GEM_BUG_ON(obj->mm.n_placements > I915_TTM_MAX_PLACEMENTS);
+
+	/* Move to the requested placement. */
+	i915_ttm_placement_from_obj(obj, &requested, busy, &placement);
+
+	return __i915_ttm_get_pages(obj, &placement);
+}
+
+/**
+ * DOC: Migration vs eviction
+ *
+ * GEM migration may not be the same as TTM migration / eviction. If
+ * the TTM core decides to evict an object it may be evicted to a
+ * TTM memory type that is not in the object's allowable GEM regions, or
+ * in fact theoretically to a TTM memory type that doesn't correspond to
+ * a GEM memory region. In that case the object's GEM region is not
+ * updated, and the data is migrated back to the GEM region at
+ * get_pages time. TTM may however set up CPU ptes to the object even
+ * when it is evicted.
+ * Gem forced migration using the i915_ttm_migrate() op, is allowed even
+ * to regions that are not in the object's list of allowable placements.
+ */
+static int i915_ttm_migrate(struct drm_i915_gem_object *obj,
+			    struct intel_memory_region *mr)
+{
+	struct ttm_place requested;
+	struct ttm_placement placement;
+	int ret;
+
+	i915_ttm_place_from_region(mr, &requested, obj->flags);
+	placement.num_placement = 1;
+	placement.num_busy_placement = 1;
+	placement.placement = &requested;
+	placement.busy_placement = &requested;
+
+	ret = __i915_ttm_get_pages(obj, &placement);
+	if (ret)
+		return ret;
+
+	/*
+	 * Reinitialize the region bindings. This is primarily
+	 * required for objects where the new region is not in
+	 * its allowable placements.
+	 */
+	if (obj->mm.region != mr) {
+		i915_gem_object_release_memory_region(obj);
+		i915_gem_object_init_memory_region(obj, mr);
+	}
+
+	return 0;
+}
+
 static void i915_ttm_put_pages(struct drm_i915_gem_object *obj,
 			       struct sg_table *st)
 {
@@ -814,6 +866,7 @@ static const struct drm_i915_gem_object_ops i915_gem_ttm_obj_ops = {
 	.truncate = i915_ttm_purge,
 	.adjust_lru = i915_ttm_adjust_lru,
 	.delayed_free = i915_ttm_delayed_free,
+	.migrate = i915_ttm_migrate,
 	.mmap_offset = i915_ttm_mmap_offset,
 	.mmap_ops = &vm_ops_ttm,
 };

drivers/gpu/drm/i915/gem/i915_gem_wait.c

@@ -290,3 +290,22 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 	i915_gem_object_put(obj);
 	return ret;
 }
+
+/**
+ * i915_gem_object_wait_migration - Sync an accelerated migration operation
+ * @obj: The migrating object.
+ * @flags: waiting flags. Currently supports only I915_WAIT_INTERRUPTIBLE.
+ *
+ * Wait for any pending async migration operation on the object,
+ * whether it's explicitly (i915_gem_object_migrate()) or implicitly
+ * (swapin, initial clearing) initiated.
+ *
+ * Return: 0 if successful, -ERESTARTSYS if a signal was hit during waiting.
+ */
+int i915_gem_object_wait_migration(struct drm_i915_gem_object *obj,
+				   unsigned int flags)
+{
+	might_sleep();
+	/* NOP for now. */
+	return 0;
+}