drm/i915: Add VM to context

Pretty straightforward so far except for the bit about the refcounting.
The PPGTT will potentially be shared amongst multiple contexts. Because
contexts themselves have a refcounted lifecycle, the easiest way to
manage this will be to refcount the PPGTT. To acheive this, we piggy
back off of the existing context refcount, and will increment and
decrement the PPGTT refcount with context creation, and destruction.

To put it more clearly, if context A, and context B both use PPGTT 0, we
can't free the PPGTT until both A, and B are destroyed.

Note that because the PPGTT is permanently pinned (for now), it really
just matters for the PPGTT destruction, as opposed to making space under
memory pressure.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -655,6 +655,7 @@ struct i915_gtt {
 
 struct i915_hw_ppgtt {
 	struct i915_address_space base;
+	struct kref ref;
 	struct drm_mm_node node;
 	unsigned num_pd_entries;
 	union {
@@ -704,6 +705,7 @@ struct i915_hw_context {
 	struct intel_ring_buffer *last_ring;
 	struct drm_i915_gem_object *obj;
 	struct i915_ctx_hang_stats hang_stats;
+	struct i915_address_space *vm;
 
 	struct list_head link;
 };
@@ -2292,6 +2294,12 @@ static inline bool intel_enable_ppgtt(struct drm_device *dev, bool full)
 	return HAS_ALIASING_PPGTT(dev);
 }
 
+static inline void ppgtt_release(struct kref *kref)
+{
+	struct i915_hw_ppgtt *ppgtt = container_of(kref, struct i915_hw_ppgtt, ref);
+
+	ppgtt->base.cleanup(&ppgtt->base);
+}
 
 
 /* i915_gem_evict.c */

drivers/gpu/drm/i915/i915_gem_context.c

@@ -141,9 +141,19 @@ void i915_gem_context_free(struct kref *ctx_ref)
 {
 	struct i915_hw_context *ctx = container_of(ctx_ref,
 						   typeof(*ctx), ref);
+	struct i915_hw_ppgtt *ppgtt = NULL;
 
-	list_del(&ctx->link);
+	/* We refcount even the aliasing PPGTT to keep the code symmetric */
+	if (USES_ALIASING_PPGTT(ctx->obj->base.dev))
+		ppgtt = container_of(ctx->vm, struct i915_hw_ppgtt, base);
+
+	/* XXX: Free up the object before tearing down the address space, in
+	 * case we're bound in the PPGTT */
 	drm_gem_object_unreference(&ctx->obj->base);
+
+	if (ppgtt)
+		kref_put(&ppgtt->ref, ppgtt_release);
+	list_del(&ctx->link);
 	kfree(ctx);
 }
 

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -902,9 +902,11 @@ int i915_gem_init_ppgtt(struct drm_device *dev, struct i915_hw_ppgtt *ppgtt)
 	else
 		BUG();
 
-	if (!ret)
+	if (!ret) {
+		kref_init(&ppgtt->ref);
 		drm_mm_init(&ppgtt->base.mm, ppgtt->base.start,
 			    ppgtt->base.total);
+	}
 
 	return ret;
 }
@@ -917,7 +919,8 @@ void i915_gem_cleanup_aliasing_ppgtt(struct drm_device *dev)
 	if (!ppgtt)
 		return;
 
-	ppgtt->base.cleanup(&ppgtt->base);
+	kref_put(&dev_priv->mm.aliasing_ppgtt->ref, ppgtt_release);
+
 	dev_priv->mm.aliasing_ppgtt = NULL;
 }