drm/i915: Force CPU relocations if not GTT mapped

Move the decision on whether we need to have a mappable object during
execbuffer to the fore and then reuse that decision by propagating the
flag through to reservation. As a corollary, before doing the actual
relocation through the GTT, we can make sure that we do have a GTT
mapping through which to operate.

Note that the key to make this work is to ditch the
obj->map_and_fenceable unbind optimization - with full ppgtt it
doesn't make a lot of sense any more anyway.

v2: Revamp and resend to ease future patches.
v3: Refresh patch rationale

References: https://bugs.freedesktop.org/show_bug.cgi?id=81094
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ben Widawsky <benjamin.widawsky@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
[danvet: Explain why obj->map_and_fenceable is key and split out the
secure batch fix.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -2928,9 +2928,8 @@ int i915_vma_unbind(struct i915_vma *vma)
 	vma->unbind_vma(vma);
 
 	list_del_init(&vma->mm_list);
-	/* Avoid an unnecessary call to unbind on rebind. */
 	if (i915_is_ggtt(vma->vm))
-		obj->map_and_fenceable = true;
+		obj->map_and_fenceable = false;
 
 	drm_mm_remove_node(&vma->node);
 	i915_gem_vma_destroy(vma);
@@ -3282,6 +3281,9 @@ i915_gem_object_get_fence(struct drm_i915_gem_object *obj)
 			return 0;
 		}
 	} else if (enable) {
+		if (WARN_ON(!obj->map_and_fenceable))
+			return -EINVAL;
+
 		reg = i915_find_fence_reg(dev);
 		if (IS_ERR(reg))
 			return PTR_ERR(reg);
@@ -4331,8 +4333,6 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
 
 	obj->fence_reg = I915_FENCE_REG_NONE;
 	obj->madv = I915_MADV_WILLNEED;
-	/* Avoid an unnecessary call to unbind on the first bind. */
-	obj->map_and_fenceable = true;
 
 	i915_gem_info_add_obj(obj->base.dev->dev_private, obj->base.size);
 }