drm/i915: Only refcount ppgtt if it actually is one

This essentially unbreaks non-ppgtt operation where we'd scribble over
random memory.

While at it give the vm_to_ppgtt function a proper prefix and make it
a bit more paranoid.
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -2512,6 +2512,15 @@ static inline bool i915_is_ggtt(struct i915_address_space *vm)
 	return vm == ggtt;
 }
 
+static inline struct i915_hw_ppgtt *
+i915_vm_to_ppgtt(struct i915_address_space *vm)
+{
+	WARN_ON(i915_is_ggtt(vm));
+
+	return container_of(vm, struct i915_hw_ppgtt, base);
+}
+
+
 static inline bool i915_gem_obj_ggtt_bound(struct drm_i915_gem_object *obj)
 {
 	return i915_gem_obj_bound(obj, obj_to_ggtt(obj));
@@ -2547,7 +2556,6 @@ void i915_gem_object_ggtt_unpin(struct drm_i915_gem_object *obj);
 
 /* i915_gem_context.c */
 #define ctx_to_ppgtt(ctx) container_of((ctx)->vm, struct i915_hw_ppgtt, base)
-#define vm_to_ppgtt(vm) container_of(vm, struct i915_hw_ppgtt, base)
 int __must_check i915_gem_context_init(struct drm_device *dev);
 void i915_gem_context_fini(struct drm_device *dev);
 void i915_gem_context_reset(struct drm_device *dev);

drivers/gpu/drm/i915/i915_gem.c

@@ -4485,7 +4485,8 @@ void i915_gem_vma_destroy(struct i915_vma *vma)
 
 	vm = vma->vm;
 
-	i915_ppgtt_put(vm_to_ppgtt(vm));
+	if (!i915_is_ggtt(vm))
+		i915_ppgtt_put(i915_vm_to_ppgtt(vm));
 
 	list_del(&vma->vma_link);
 

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -2187,7 +2187,8 @@ i915_gem_obj_lookup_or_create_vma(struct drm_i915_gem_object *obj,
 	if (!vma)
 		vma = __i915_gem_vma_create(obj, vm);
 
-	i915_ppgtt_get(vm_to_ppgtt(vm));
+	if (!i915_is_ggtt(vm))
+		i915_ppgtt_get(i915_vm_to_ppgtt(vm));
 
 	return vma;
 }