drm/i915: Separate GEM context construction and registration to userspace

In later patches, it became apparent that userspace can see a partially
constructed GEM context and begin using it before it was ready, to much
hilarity. Close this window of opportunity by lifting the registration of
the context with userspace (the insertion of the context into the filp's
idr) to the very end of the CONTEXT_CREATE ioctl.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190321140711.11190-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_context.c

@@ -337,15 +337,13 @@ static u32 default_desc_template(const struct drm_i915_private *i915,
 }
 
 static struct i915_gem_context *
-__create_hw_context(struct drm_i915_private *dev_priv,
-		    struct drm_i915_file_private *file_priv)
+__create_context(struct drm_i915_private *dev_priv)
 {
 	struct i915_gem_context *ctx;
-	int ret;
 	int i;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
-	if (ctx == NULL)
+	if (!ctx)
 		return ERR_PTR(-ENOMEM);
 
 	kref_init(&ctx->ref);
@@ -362,29 +360,6 @@ __create_hw_context(struct drm_i915_private *dev_priv,
 	INIT_LIST_HEAD(&ctx->handles_list);
 	INIT_LIST_HEAD(&ctx->hw_id_link);
 
-	/* Default context will never have a file_priv */
-	ret = DEFAULT_CONTEXT_HANDLE;
-	if (file_priv) {
-		ret = idr_alloc(&file_priv->context_idr, ctx,
-				DEFAULT_CONTEXT_HANDLE, 0, GFP_KERNEL);
-		if (ret < 0)
-			goto err_lut;
-	}
-	ctx->user_handle = ret;
-
-	ctx->file_priv = file_priv;
-	if (file_priv) {
-		ctx->pid = get_task_pid(current, PIDTYPE_PID);
-		ctx->name = kasprintf(GFP_KERNEL, "%s[%d]/%x",
-				      current->comm,
-				      pid_nr(ctx->pid),
-				      ctx->user_handle);
-		if (!ctx->name) {
-			ret = -ENOMEM;
-			goto err_pid;
-		}
-	}
-
 	/* NB: Mark all slices as needing a remap so that when the context first
 	 * loads it will restore whatever remap state already exists. If there
 	 * is no remap info, it will be a NOP. */
@@ -401,25 +376,10 @@ __create_hw_context(struct drm_i915_private *dev_priv,
 		ctx->hang_timestamp[i] = jiffies - CONTEXT_FAST_HANG_JIFFIES;
 
 	return ctx;
-
-err_pid:
-	put_pid(ctx->pid);
-	idr_remove(&file_priv->context_idr, ctx->user_handle);
-err_lut:
-	context_close(ctx);
-	return ERR_PTR(ret);
-}
-
-static void __destroy_hw_context(struct i915_gem_context *ctx,
-				 struct drm_i915_file_private *file_priv)
-{
-	idr_remove(&file_priv->context_idr, ctx->user_handle);
-	context_close(ctx);
 }
 
 static struct i915_gem_context *
-i915_gem_create_context(struct drm_i915_private *dev_priv,
-			struct drm_i915_file_private *file_priv)
+i915_gem_create_context(struct drm_i915_private *dev_priv)
 {
 	struct i915_gem_context *ctx;
 
@@ -428,18 +388,18 @@ i915_gem_create_context(struct drm_i915_private *dev_priv,
 	/* Reap the most stale context */
 	contexts_free_first(dev_priv);
 
-	ctx = __create_hw_context(dev_priv, file_priv);
+	ctx = __create_context(dev_priv);
 	if (IS_ERR(ctx))
 		return ctx;
 
 	if (HAS_FULL_PPGTT(dev_priv)) {
 		struct i915_hw_ppgtt *ppgtt;
 
-		ppgtt = i915_ppgtt_create(dev_priv, file_priv);
+		ppgtt = i915_ppgtt_create(dev_priv);
 		if (IS_ERR(ppgtt)) {
 			DRM_DEBUG_DRIVER("PPGTT setup failed (%ld)\n",
 					 PTR_ERR(ppgtt));
-			__destroy_hw_context(ctx, file_priv);
+			context_close(ctx);
 			return ERR_CAST(ppgtt);
 		}
 
@@ -475,7 +435,7 @@ 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 = i915_gem_create_context(to_i915(dev));
 	if (IS_ERR(ctx))
 		goto out;
 
@@ -511,7 +471,7 @@ i915_gem_context_create_kernel(struct drm_i915_private *i915, int prio)
 	struct i915_gem_context *ctx;
 	int err;
 
-	ctx = i915_gem_create_context(i915, NULL);
+	ctx = i915_gem_create_context(i915);
 	if (IS_ERR(ctx))
 		return ctx;
 
@@ -625,25 +585,74 @@ static int context_idr_cleanup(int id, void *p, void *data)
 	return 0;
 }
 
+static int gem_context_register(struct i915_gem_context *ctx,
+				struct drm_i915_file_private *fpriv)
+{
+	int ret;
+
+	ctx->file_priv = fpriv;
+	if (ctx->ppgtt)
+		ctx->ppgtt->vm.file = fpriv;
+
+	ctx->pid = get_task_pid(current, PIDTYPE_PID);
+	ctx->name = kasprintf(GFP_KERNEL, "%s[%d]",
+			      current->comm, pid_nr(ctx->pid));
+	if (!ctx->name) {
+		ret = -ENOMEM;
+		goto err_pid;
+	}
+
+	/* And finally expose ourselves to userspace via the idr */
+	ret = idr_alloc(&fpriv->context_idr, ctx,
+			DEFAULT_CONTEXT_HANDLE, 0, GFP_KERNEL);
+	if (ret < 0)
+		goto err_name;
+
+	ctx->user_handle = ret;
+
+	return 0;
+
+err_name:
+	kfree(fetch_and_zero(&ctx->name));
+err_pid:
+	put_pid(fetch_and_zero(&ctx->pid));
+	return ret;
+}
+
 int i915_gem_context_open(struct drm_i915_private *i915,
 			  struct drm_file *file)
 {
 	struct drm_i915_file_private *file_priv = file->driver_priv;
 	struct i915_gem_context *ctx;
+	int err;
 
 	idr_init(&file_priv->context_idr);
 
 	mutex_lock(&i915->drm.struct_mutex);
-	ctx = i915_gem_create_context(i915, file_priv);
-	mutex_unlock(&i915->drm.struct_mutex);
+
+	ctx = i915_gem_create_context(i915);
 	if (IS_ERR(ctx)) {
-		idr_destroy(&file_priv->context_idr);
-		return PTR_ERR(ctx);
+		err = PTR_ERR(ctx);
+		goto err;
 	}
 
+	err = gem_context_register(ctx, file_priv);
+	if (err)
+		goto err_ctx;
+
+	GEM_BUG_ON(ctx->user_handle != DEFAULT_CONTEXT_HANDLE);
 	GEM_BUG_ON(i915_gem_context_is_kernel(ctx));
 
+	mutex_unlock(&i915->drm.struct_mutex);
+
 	return 0;
+
+err_ctx:
+	context_close(ctx);
+err:
+	mutex_unlock(&i915->drm.struct_mutex);
+	idr_destroy(&file_priv->context_idr);
+	return PTR_ERR(ctx);
 }
 
 void i915_gem_context_close(struct drm_file *file)
@@ -835,17 +844,28 @@ int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
 	if (ret)
 		return ret;
 
-	ctx = i915_gem_create_context(i915, file_priv);
-	mutex_unlock(&dev->struct_mutex);
-	if (IS_ERR(ctx))
-		return PTR_ERR(ctx);
+	ctx = i915_gem_create_context(i915);
+	if (IS_ERR(ctx)) {
+		ret = PTR_ERR(ctx);
+		goto err_unlock;
+	}
 
-	GEM_BUG_ON(i915_gem_context_is_kernel(ctx));
+	ret = gem_context_register(ctx, file_priv);
+	if (ret)
+		goto err_ctx;
+
+	mutex_unlock(&dev->struct_mutex);
 
 	args->ctx_id = ctx->user_handle;
 	DRM_DEBUG("HW context %d created\n", args->ctx_id);
 
 	return 0;
+
+err_ctx:
+	context_close(ctx);
+err_unlock:
+	mutex_unlock(&dev->struct_mutex);
+	return ret;
 }
 
 int i915_gem_context_destroy_ioctl(struct drm_device *dev, void *data,
@@ -870,7 +890,9 @@ int i915_gem_context_destroy_ioctl(struct drm_device *dev, void *data,
 	if (ret)
 		goto out;
 
-	__destroy_hw_context(ctx, file_priv);
+	idr_remove(&file_priv->context_idr, ctx->user_handle);
+	context_close(ctx);
+
 	mutex_unlock(&dev->struct_mutex);
 
 out:

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -2069,8 +2069,7 @@ __hw_ppgtt_create(struct drm_i915_private *i915)
 }
 
 struct i915_hw_ppgtt *
-i915_ppgtt_create(struct drm_i915_private *i915,
-		  struct drm_i915_file_private *fpriv)
+i915_ppgtt_create(struct drm_i915_private *i915)
 {
 	struct i915_hw_ppgtt *ppgtt;
 
@@ -2078,8 +2077,6 @@ i915_ppgtt_create(struct drm_i915_private *i915,
 	if (IS_ERR(ppgtt))
 		return ppgtt;
 
-	ppgtt->vm.file = fpriv;
-
 	trace_i915_ppgtt_create(&ppgtt->vm);
 
 	return ppgtt;
@@ -2657,7 +2654,7 @@ int i915_gem_init_aliasing_ppgtt(struct drm_i915_private *i915)
 	struct i915_hw_ppgtt *ppgtt;
 	int err;
 
-	ppgtt = i915_ppgtt_create(i915, ERR_PTR(-EPERM));
+	ppgtt = i915_ppgtt_create(i915);
 	if (IS_ERR(ppgtt))
 		return PTR_ERR(ppgtt);
 

drivers/gpu/drm/i915/i915_gem_gtt.h

@@ -603,15 +603,17 @@ int i915_gem_init_ggtt(struct drm_i915_private *dev_priv);
 void i915_ggtt_cleanup_hw(struct drm_i915_private *dev_priv);
 
 int i915_ppgtt_init_hw(struct drm_i915_private *dev_priv);
-void i915_ppgtt_release(struct kref *kref);
-struct i915_hw_ppgtt *i915_ppgtt_create(struct drm_i915_private *dev_priv,
-					struct drm_i915_file_private *fpriv);
+
+struct i915_hw_ppgtt *i915_ppgtt_create(struct drm_i915_private *dev_priv);
 void i915_ppgtt_close(struct i915_address_space *vm);
+void i915_ppgtt_release(struct kref *kref);
+
 static inline void i915_ppgtt_get(struct i915_hw_ppgtt *ppgtt)
 {
 	if (ppgtt)
 		kref_get(&ppgtt->ref);
 }
+
 static inline void i915_ppgtt_put(struct i915_hw_ppgtt *ppgtt)
 {
 	if (ppgtt)

drivers/gpu/drm/i915/selftests/huge_pages.c

@@ -1713,7 +1713,7 @@ int i915_gem_huge_page_mock_selftests(void)
 	mkwrite_device_info(dev_priv)->ppgtt_size = 48;
 
 	mutex_lock(&dev_priv->drm.struct_mutex);
-	ppgtt = i915_ppgtt_create(dev_priv, ERR_PTR(-ENODEV));
+	ppgtt = i915_ppgtt_create(dev_priv);
 	if (IS_ERR(ppgtt)) {
 		err = PTR_ERR(ppgtt);
 		goto out_unlock;

drivers/gpu/drm/i915/selftests/i915_gem_context.c

@@ -76,7 +76,7 @@ static int live_nop_switch(void *arg)
 	}
 
 	for (n = 0; n < nctx; n++) {
-		ctx[n] = i915_gem_create_context(i915, file->driver_priv);
+		ctx[n] = live_context(i915, file);
 		if (IS_ERR(ctx[n])) {
 			err = PTR_ERR(ctx[n]);
 			goto out_unlock;
@@ -513,7 +513,7 @@ static int igt_ctx_exec(void *arg)
 		struct i915_gem_context *ctx;
 		unsigned int id;
 
-		ctx = i915_gem_create_context(i915, file->driver_priv);
+		ctx = live_context(i915, file);
 		if (IS_ERR(ctx)) {
 			err = PTR_ERR(ctx);
 			goto out_unlock;
@@ -962,7 +962,7 @@ __igt_ctx_sseu(struct drm_i915_private *i915,
 
 	mutex_lock(&i915->drm.struct_mutex);
 
-	ctx = i915_gem_create_context(i915, file->driver_priv);
+	ctx = live_context(i915, file);
 	if (IS_ERR(ctx)) {
 		ret = PTR_ERR(ctx);
 		goto out_unlock;
@@ -1072,7 +1072,7 @@ static int igt_ctx_readonly(void *arg)
 	if (err)
 		goto out_unlock;
 
-	ctx = i915_gem_create_context(i915, file->driver_priv);
+	ctx = live_context(i915, file);
 	if (IS_ERR(ctx)) {
 		err = PTR_ERR(ctx);
 		goto out_unlock;
@@ -1397,13 +1397,13 @@ static int igt_vm_isolation(void *arg)
 	if (err)
 		goto out_unlock;
 
-	ctx_a = i915_gem_create_context(i915, file->driver_priv);
+	ctx_a = live_context(i915, file);
 	if (IS_ERR(ctx_a)) {
 		err = PTR_ERR(ctx_a);
 		goto out_unlock;
 	}
 
-	ctx_b = i915_gem_create_context(i915, file->driver_priv);
+	ctx_b = live_context(i915, file);
 	if (IS_ERR(ctx_b)) {
 		err = PTR_ERR(ctx_b);
 		goto out_unlock;

drivers/gpu/drm/i915/selftests/i915_gem_gtt.c

@@ -1010,7 +1010,7 @@ static int exercise_ppgtt(struct drm_i915_private *dev_priv,
 		return PTR_ERR(file);
 
 	mutex_lock(&dev_priv->drm.struct_mutex);
-	ppgtt = i915_ppgtt_create(dev_priv, file->driver_priv);
+	ppgtt = i915_ppgtt_create(dev_priv);
 	if (IS_ERR(ppgtt)) {
 		err = PTR_ERR(ppgtt);
 		goto out_unlock;

drivers/gpu/drm/i915/selftests/mock_context.c

@@ -88,9 +88,24 @@ void mock_init_contexts(struct drm_i915_private *i915)
 struct i915_gem_context *
 live_context(struct drm_i915_private *i915, struct drm_file *file)
 {
+	struct i915_gem_context *ctx;
+	int err;
+
 	lockdep_assert_held(&i915->drm.struct_mutex);
 
-	return i915_gem_create_context(i915, file->driver_priv);
+	ctx = i915_gem_create_context(i915);
+	if (IS_ERR(ctx))
+		return ctx;
+
+	err = gem_context_register(ctx, file->driver_priv);
+	if (err)
+		goto err_ctx;
+
+	return ctx;
+
+err_ctx:
+	context_close(ctx);
+	return ERR_PTR(err);
 }
 
 struct i915_gem_context *