drm/i915: Simplify testing for am-I-the-kernel-context?

The kernel context (dev_priv->kernel_context) is unique in that it is
not associated with any user filp - it is the only one with
ctx->file_priv == NULL. This is a simpler test than comparing it against
dev_priv->kernel_context which involves some pointer dancing.

In checking that this is true, we notice that the gvt context is
allocating itself a i915_hw_ppgtt it doesn't use and not flagging that
its file_priv should be invalid.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170106152013.24684-5-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -4230,7 +4230,7 @@ static void assert_kernel_context_is_current(struct drm_i915_private *dev_priv)
 	enum intel_engine_id id;
 
 	for_each_engine(engine, dev_priv, id)
-		GEM_BUG_ON(engine->last_retired_context != dev_priv->kernel_context);
+		GEM_BUG_ON(!i915_gem_context_is_kernel(engine->last_retired_context));
 }
 
 int i915_gem_suspend(struct drm_i915_private *dev_priv)

drivers/gpu/drm/i915/i915_gem_context.c

@@ -413,14 +413,17 @@ i915_gem_context_create_gvt(struct drm_device *dev)
 	if (ret)
 		return ERR_PTR(ret);
 
-	ctx = i915_gem_create_context(to_i915(dev), NULL);
+	ctx = __create_hw_context(to_i915(dev), NULL);
 	if (IS_ERR(ctx))
 		goto out;
 
+	ctx->file_priv = ERR_PTR(-EBADF);
 	i915_gem_context_set_closed(ctx); /* not user accessible */
 	i915_gem_context_clear_bannable(ctx);
 	i915_gem_context_set_force_single_submission(ctx);
 	ctx->ring_size = 512 * PAGE_SIZE; /* Max ring buffer size */
+
+	GEM_BUG_ON(i915_gem_context_is_kernel(ctx));
 out:
 	mutex_unlock(&dev->struct_mutex);
 	return ctx;
@@ -472,6 +475,8 @@ int i915_gem_context_init(struct drm_i915_private *dev_priv)
 	ctx->priority = I915_PRIORITY_MIN; /* lowest priority; idle task */
 	dev_priv->kernel_context = ctx;
 
+	GEM_BUG_ON(!i915_gem_context_is_kernel(ctx));
+
 	DRM_DEBUG_DRIVER("%s context support initialized\n",
 			i915.enable_execlists ? "LR" :
 			dev_priv->hw_context_size ? "HW" : "fake");
@@ -524,6 +529,8 @@ void i915_gem_context_fini(struct drm_i915_private *dev_priv)
 
 	lockdep_assert_held(&dev_priv->drm.struct_mutex);
 
+	GEM_BUG_ON(!i915_gem_context_is_kernel(dctx));
+
 	context_close(dctx);
 	dev_priv->kernel_context = NULL;
 
@@ -549,6 +556,8 @@ int i915_gem_context_open(struct drm_device *dev, struct drm_file *file)
 	ctx = i915_gem_create_context(to_i915(dev), file_priv);
 	mutex_unlock(&dev->struct_mutex);
 
+	GEM_BUG_ON(i915_gem_context_is_kernel(ctx));
+
 	if (IS_ERR(ctx)) {
 		idr_destroy(&file_priv->context_idr);
 		return PTR_ERR(ctx);
@@ -968,6 +977,8 @@ int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 
+	GEM_BUG_ON(i915_gem_context_is_kernel(ctx));
+
 	args->ctx_id = ctx->user_handle;
 	DRM_DEBUG("HW context %d created\n", args->ctx_id);
 

drivers/gpu/drm/i915/i915_gem_context.h

@@ -246,6 +246,11 @@ static inline bool i915_gem_context_is_default(const struct i915_gem_context *c)
 	return c->user_handle == DEFAULT_CONTEXT_HANDLE;
 }
 
+static inline bool i915_gem_context_is_kernel(struct i915_gem_context *ctx)
+{
+	return !ctx->file_priv;
+}
+
 /* i915_gem_context.c */
 int __must_check i915_gem_context_init(struct drm_i915_private *dev_priv);
 void i915_gem_context_lost(struct drm_i915_private *dev_priv);

drivers/gpu/drm/i915/intel_lrc.c

@@ -786,7 +786,7 @@ static int execlists_context_pin(struct intel_engine_cs *engine,
 	flags = PIN_GLOBAL;
 	if (ctx->ggtt_offset_bias)
 		flags |= PIN_OFFSET_BIAS | ctx->ggtt_offset_bias;
-	if (ctx == ctx->i915->kernel_context)
+	if (i915_gem_context_is_kernel(ctx))
 		flags |= PIN_HIGH;
 
 	ret = i915_vma_pin(ce->state, 0, GEN8_LR_CONTEXT_ALIGN, flags);

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1974,7 +1974,7 @@ static int intel_ring_context_pin(struct intel_engine_cs *engine,
 		unsigned int flags;
 
 		flags = 0;
-		if (ctx == ctx->i915->kernel_context)
+		if (i915_gem_context_is_kernel(ctx))
 			flags = PIN_HIGH;
 
 		ret = context_pin(ctx, flags);
@@ -1989,7 +1989,7 @@ static int intel_ring_context_pin(struct intel_engine_cs *engine,
 	 * as during eviction we cannot allocate and pin the renderstate in
 	 * order to initialise the context.
 	 */
-	if (ctx == ctx->i915->kernel_context)
+	if (i915_gem_context_is_kernel(ctx))
 		ce->initialised = true;
 
 	i915_gem_context_get(ctx);