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Message-ID: <20250609073430.442159-4-lulu@redhat.com>
Date: Mon, 9 Jun 2025 15:33:09 +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 v11 3/3] vhost: Add configuration controls for vhost worker's mode
This patch introduces functionality to control the vhost worker mode:
- Add two new IOCTLs:
* VHOST_SET_FORK_FROM_OWNER: Allows userspace to select between
task mode (fork_owner=1) and kthread mode (fork_owner=0)
* VHOST_GET_FORK_FROM_OWNER: Retrieves the current thread mode
setting
- Expose module parameter 'fork_from_owner_default' to allow system
administrators to configure the default mode for vhost workers
- Add KConfig option CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL to
control the availability of these IOCTLs and parameter, allowing
distributions to disable them if not needed
- The VHOST_NEW_WORKER functionality requires fork_owner to be set
to true, with validation added to ensure proper configuration
Signed-off-by: Cindy Lu <lulu@...hat.com>
---
drivers/vhost/Kconfig | 17 +++++++++++++++
drivers/vhost/vhost.c | 44 ++++++++++++++++++++++++++++++++++++++
include/uapi/linux/vhost.h | 25 ++++++++++++++++++++++
3 files changed, 86 insertions(+)
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 020d4fbb947c..49e1d9dc92b7 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -96,3 +96,20 @@ config VHOST_CROSS_ENDIAN_LEGACY
If unsure, say "N".
endif
+
+config CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL
+ bool "Enable CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL"
+ default n
+ help
+ This option enables two IOCTLs: VHOST_SET_FORK_FROM_OWNER and
+ VHOST_GET_FORK_FROM_OWNER. These allow userspace applications
+ to modify the vhost worker mode for vhost devices.
+
+ Also expose module parameter 'fork_from_owner_default' to allow users
+ to configure the default mode for vhost workers.
+
+ By default, `CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL` is set to `n`,
+ which disables the IOCTLs and parameter.
+ When enabled (y), users can change the worker thread mode as needed.
+
+ If unsure, say "N".
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 37d3ed8be822..903d9c3f6784 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -43,6 +43,11 @@ module_param(max_iotlb_entries, int, 0444);
MODULE_PARM_DESC(max_iotlb_entries,
"Maximum number of iotlb entries. (default: 2048)");
static bool fork_from_owner_default = true;
+#ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL
+module_param(fork_from_owner_default, bool, 0444);
+MODULE_PARM_DESC(fork_from_owner_default,
+ "Set task mode as the default(default: Y)");
+#endif
enum {
VHOST_MEMORY_F_LOG = 0x1,
@@ -1019,6 +1024,13 @@ long vhost_worker_ioctl(struct vhost_dev *dev, unsigned int ioctl,
switch (ioctl) {
/* dev worker ioctls */
case VHOST_NEW_WORKER:
+ /*
+ * vhost_tasks will account for worker threads under the parent's
+ * NPROC value but kthreads do not. To avoid userspace overflowing
+ * the system with worker threads fork_owner must be true.
+ */
+ if (!dev->fork_owner)
+ return -EFAULT;
ret = vhost_new_worker(dev, &state);
if (!ret && copy_to_user(argp, &state, sizeof(state)))
ret = -EFAULT;
@@ -1136,6 +1148,7 @@ void vhost_dev_reset_owner(struct vhost_dev *dev, struct vhost_iotlb *umem)
vhost_dev_cleanup(dev);
+ dev->fork_owner = fork_from_owner_default;
dev->umem = umem;
/* We don't need VQ locks below since vhost_dev_cleanup makes sure
* VQs aren't running.
@@ -2289,6 +2302,37 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
goto done;
}
+#ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL
+ u8 fork_owner;
+
+ if (ioctl == VHOST_SET_FORK_FROM_OWNER) {
+ /*fork_owner can only be modified before owner is set*/
+ if (vhost_dev_has_owner(d)) {
+ r = -EBUSY;
+ goto done;
+ }
+ if (copy_from_user(&fork_owner, argp, sizeof(u8))) {
+ r = -EFAULT;
+ goto done;
+ }
+ if (fork_owner > 1) {
+ r = -EINVAL;
+ goto done;
+ }
+ d->fork_owner = (bool)fork_owner;
+ r = 0;
+ goto done;
+ }
+ if (ioctl == VHOST_GET_FORK_FROM_OWNER) {
+ fork_owner = d->fork_owner;
+ if (copy_to_user(argp, &fork_owner, sizeof(u8))) {
+ r = -EFAULT;
+ goto done;
+ }
+ r = 0;
+ goto done;
+ }
+#endif
/* You must be the owner to do anything else */
r = vhost_dev_check_owner(d);
if (r)
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index d4b3e2ae1314..e51d6a347607 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -235,4 +235,29 @@
*/
#define VHOST_VDPA_GET_VRING_SIZE _IOWR(VHOST_VIRTIO, 0x82, \
struct vhost_vring_state)
+
+/**
+ * VHOST_SET_FORK_FROM_OWNER - Set the fork_owner flag for the vhost device,
+ * This ioctl must called before VHOST_SET_OWNER.
+ * Only available when CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL=y
+ *
+ * @param fork_owner: An 8-bit value that determines the vhost thread mode
+ *
+ * When fork_owner is set to 1(default value):
+ * - Vhost will create vhost worker as tasks forked from the owner,
+ * inheriting all of the owner's attributes.
+ *
+ * When fork_owner is set to 0:
+ * - Vhost will create vhost workers as kernel threads.
+ */
+#define VHOST_SET_FORK_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, __u8)
+
+/**
+ * VHOST_GET_FORK_OWNER - Get the current fork_owner flag for the vhost device.
+ * Only available when CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL=y
+ *
+ * @return: An 8-bit value indicating the current thread mode.
+ */
+#define VHOST_GET_FORK_FROM_OWNER _IOR(VHOST_VIRTIO, 0x84, __u8)
+
#endif
--
2.45.0
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