netdev - [PATCH RESEND v10 1/3] vhost: Add a new modparam to allow userspace select kthread

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Message-ID: <20250531095800.160043-2-lulu@redhat.com>
Date: Sat, 31 May 2025 17:57:26 +0800
From: Cindy Lu <lulu@...hat.com>
To: lulu@...hat.com,
	jasowang@...hat.com,
	mst@...hat.com,
	michael.christie@...cle.com,
	sgarzare@...hat.com,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	netdev@...r.kernel.org
Subject: [PATCH RESEND v10 1/3] vhost: Add a new modparam to allow userspace select kthread

The vhost now uses vhost_task and workers as a child of the owner thread.
While this aligns with containerization principles, it confuses some
legacy userspace applications, therefore, we are reintroducing kthread
API support.

Add a new module parameter to allow userspace to select behavior
between using kthread and task.

By default, this parameter is set to true (task mode). This means the
default behavior remains unchanged by this patch.

Signed-off-by: Cindy Lu <lulu@...hat.com>
---
 drivers/vhost/vhost.c |  5 +++++
 drivers/vhost/vhost.h | 10 ++++++++++
 2 files changed, 15 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3a5ebb973dba..240ba78b1e3f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -41,6 +41,10 @@ static int max_iotlb_entries = 2048;
 module_param(max_iotlb_entries, int, 0444);
 MODULE_PARM_DESC(max_iotlb_entries,
 	"Maximum number of iotlb entries. (default: 2048)");
+bool inherit_owner_default = true;
+module_param(inherit_owner_default, bool, 0444);
+MODULE_PARM_DESC(inherit_owner_default,
+		 "Set task mode as the default(default: Y)");
 
 enum {
 	VHOST_MEMORY_F_LOG = 0x1,
@@ -552,6 +556,7 @@ void vhost_dev_init(struct vhost_dev *dev,
 	dev->byte_weight = byte_weight;
 	dev->use_worker = use_worker;
 	dev->msg_handler = msg_handler;
+	dev->inherit_owner = inherit_owner_default;
 	init_waitqueue_head(&dev->wait);
 	INIT_LIST_HEAD(&dev->read_list);
 	INIT_LIST_HEAD(&dev->pending_list);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index bb75a292d50c..c1ff4a92b925 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -176,6 +176,16 @@ struct vhost_dev {
 	int byte_weight;
 	struct xarray worker_xa;
 	bool use_worker;
+	/*
+	 * If inherit_owner is true we use vhost_tasks to create
+	 * the worker so all settings/limits like cgroups, NPROC,
+	 * scheduler, etc are inherited from the owner. If false,
+	 * we use kthreads and only attach to the same cgroups
+	 * as the owner for compat with older kernels.
+	 * here we use true as default value.
+	 * The default value is set by modparam inherit_owner_default
+	 */
+	bool inherit_owner;
 	int (*msg_handler)(struct vhost_dev *dev, u32 asid,
 			   struct vhost_iotlb_msg *msg);
 };
-- 
2.45.0