This patch reintroduces kthread mode for vhost workers and provides
configuration to select between kthread and task worker.
- Add 'fork_owner' parameter to vhost_dev to let users select kthread
or task mode. Default mode is task mode(VHOST_FORK_OWNER_TASK).
- Reintroduce kthread mode support:
* Bring back the original vhost_worker() implementation,
and renamed to vhost_run_work_kthread_list().
* Add cgroup support for the kthread
* Introduce struct vhost_worker_ops:
- Encapsulates create / stop / wake‑up callbacks.
- vhost_worker_create() selects the proper ops according to
inherit_owner.
- Userspace configuration interface:
* New IOCTLs:
- VHOST_SET_FORK_FROM_OWNER lets userspace select task mode
(VHOST_FORK_OWNER_TASK) or kthread mode (VHOST_FORK_OWNER_KTHREAD)
- VHOST_GET_FORK_FROM_OWNER reads the current worker mode
* Expose module parameter 'fork_from_owner_default' to allow system
administrators to configure the default mode for vhost workers
* Kconfig option CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL controls whether
these IOCTLs and the parameter are available (for distros that may
want to disable them)
- The VHOST_NEW_WORKER functionality requires fork_owner to be set
to true, with validation added to ensure proper configuration
This partially reverts or improves upon:
commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")
commit 1cdaafa1b8b4 ("vhost: replace single worker pointer with xarray")
Signed-off-by: Cindy Lu <l...@redhat.com>
---
drivers/vhost/Kconfig | 17 +++
drivers/vhost/vhost.c | 244 ++++++++++++++++++++++++++++++++++---
drivers/vhost/vhost.h | 22 ++++
include/uapi/linux/vhost.h | 29 +++++
4 files changed, 294 insertions(+), 18 deletions(-)
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 020d4fbb947c..1b3602b1f8e2 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -95,4 +95,21 @@ config VHOST_CROSS_ENDIAN_LEGACY
If unsure, say "N".
+config VHOST_ENABLE_FORK_OWNER_CONTROL
+ bool "Enable 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, `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".
+
endif
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3a5ebb973dba..84c9bdf9aedd 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -22,6 +22,7 @@
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/kthread.h>
+#include <linux/cgroup.h>
#include <linux/module.h>
#include <linux/sort.h>
#include <linux/sched/mm.h>
@@ -41,6 +42,13 @@ 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)");
+static bool fork_from_owner_default = VHOST_FORK_OWNER_TASK;
+
+#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,
@@ -242,7 +250,7 @@ static void vhost_worker_queue(struct vhost_worker *worker,
* test_and_set_bit() implies a memory barrier.
*/
llist_add(&work->node, &worker->work_list);
- vhost_task_wake(worker->vtsk);
+ worker->ops->wakeup(worker);
}
}
@@ -388,6 +396,44 @@ static void vhost_vq_reset(struct vhost_dev *dev,
__vhost_vq_meta_reset(vq);
}
+static int vhost_run_work_kthread_list(void *data)
+{
+ struct vhost_worker *worker = data;
+ struct vhost_work *work, *work_next;
+ struct vhost_dev *dev = worker->dev;
+ struct llist_node *node;
+
+ kthread_use_mm(dev->mm);
+
+ for (;;) {
+ /* mb paired w/ kthread_stop */
+ set_current_state(TASK_INTERRUPTIBLE);
+
+ if (kthread_should_stop()) {
+ __set_current_state(TASK_RUNNING);
+ break;
+ }
+ node = llist_del_all(&worker->work_list);
+ if (!node)
+ schedule();
+
+ node = llist_reverse_order(node);
+ /* make sure flag is seen after deletion */
+ smp_wmb();
+ llist_for_each_entry_safe(work, work_next, node, node) {
+ clear_bit(VHOST_WORK_QUEUED, &work->flags);
+ __set_current_state(TASK_RUNNING);
+ kcov_remote_start_common(worker->kcov_handle);
+ work->fn(work);
+ kcov_remote_stop();
+ cond_resched();
+ }
+ }
+ kthread_unuse_mm(dev->mm);
+
+ return 0;
+}
+
static bool vhost_run_work_list(void *data)
{
struct vhost_worker *worker = data;
@@ -552,6 +598,7 @@ void vhost_dev_init(struct vhost_dev *dev,
dev->byte_weight = byte_weight;
dev->use_worker = use_worker;
dev->msg_handler = msg_handler;
+ dev->fork_owner = fork_from_owner_default;
init_waitqueue_head(&dev->wait);
INIT_LIST_HEAD(&dev->read_list);
INIT_LIST_HEAD(&dev->pending_list);
@@ -581,6 +628,46 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
}
EXPORT_SYMBOL_GPL(vhost_dev_check_owner);
+struct vhost_attach_cgroups_struct {
+ struct vhost_work work;
+ struct task_struct *owner;
+ int ret;
+};
+
+static void vhost_attach_cgroups_work(struct vhost_work *work)
+{
+ struct vhost_attach_cgroups_struct *s;
+
+ s = container_of(work, struct vhost_attach_cgroups_struct, work);
+ s->ret = cgroup_attach_task_all(s->owner, current);
+}
+
+static int vhost_attach_task_to_cgroups(struct vhost_worker *worker)
+{
+ struct vhost_attach_cgroups_struct attach;
+ int saved_cnt;
+
+ attach.owner = current;
+
+ vhost_work_init(&attach.work, vhost_attach_cgroups_work);
+ vhost_worker_queue(worker, &attach.work);
+
+ mutex_lock(&worker->mutex);
+
+ /*
+ * Bypass attachment_cnt check in __vhost_worker_flush:
+ * Temporarily change it to INT_MAX to bypass the check
+ */
+ saved_cnt = worker->attachment_cnt;
+ worker->attachment_cnt = INT_MAX;
+ __vhost_worker_flush(worker);
+ worker->attachment_cnt = saved_cnt;
+
+ mutex_unlock(&worker->mutex);
+
+ return attach.ret;
+}
+
/* Caller should have device mutex */
bool vhost_dev_has_owner(struct vhost_dev *dev)
{
@@ -626,7 +713,7 @@ static void vhost_worker_destroy(struct vhost_dev *dev,
WARN_ON(!llist_empty(&worker->work_list));
xa_erase(&dev->worker_xa, worker->id);
- vhost_task_stop(worker->vtsk);
+ worker->ops->stop(worker);
kfree(worker);
}
@@ -649,42 +736,115 @@ static void vhost_workers_free(struct vhost_dev *dev)
xa_destroy(&dev->worker_xa);
}
+static void vhost_task_wakeup(struct vhost_worker *worker)
+{
+ return vhost_task_wake(worker->vtsk);
+}
+
+static void vhost_kthread_wakeup(struct vhost_worker *worker)
+{
+ wake_up_process(worker->kthread_task);
+}
+
+static void vhost_task_do_stop(struct vhost_worker *worker)
+{
+ return vhost_task_stop(worker->vtsk);
+}
+
+static void vhost_kthread_do_stop(struct vhost_worker *worker)
+{
+ kthread_stop(worker->kthread_task);
+}
+
+static int vhost_task_worker_create(struct vhost_worker *worker,
+ struct vhost_dev *dev, const char *name)
+{
+ struct vhost_task *vtsk;
+ u32 id;
+ int ret;
+
+ vtsk = vhost_task_create(vhost_run_work_list, vhost_worker_killed,
+ worker, name);
+ if (IS_ERR(vtsk))
+ return PTR_ERR(vtsk);
+
+ worker->vtsk = vtsk;
+ vhost_task_start(vtsk);
+ ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
+ if (ret < 0) {
+ vhost_task_do_stop(worker);
+ return ret;
+ }
+ worker->id = id;
+ return 0;
+}
+
+static int vhost_kthread_worker_create(struct vhost_worker *worker,
+ struct vhost_dev *dev, const char *name)
+{
+ struct task_struct *task;
+ u32 id;
+ int ret;
+
+ task = kthread_create(vhost_run_work_kthread_list, worker, "%s", name);
+ if (IS_ERR(task))
+ return PTR_ERR(task);
+
+ worker->kthread_task = task;
+ wake_up_process(task);
+ ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
+ if (ret < 0)
+ goto stop_worker;
+
+ ret = vhost_attach_task_to_cgroups(worker);
+ if (ret)
+ goto stop_worker;
+
+ worker->id = id;
+ return 0;
+
+stop_worker:
+ vhost_kthread_do_stop(worker);
+ return ret;
+}
+
+static const struct vhost_worker_ops kthread_ops = {
+ .create = vhost_kthread_worker_create,
+ .stop = vhost_kthread_do_stop,
+ .wakeup = vhost_kthread_wakeup,
+};
+
+static const struct vhost_worker_ops vhost_task_ops = {
+ .create = vhost_task_worker_create,
+ .stop = vhost_task_do_stop,
+ .wakeup = vhost_task_wakeup,
+};
+
static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
{
struct vhost_worker *worker;
- struct vhost_task *vtsk;
char name[TASK_COMM_LEN];
int ret;
- u32 id;
+ const struct vhost_worker_ops *ops = dev->fork_owner ? &vhost_task_ops :
+ &kthread_ops;
worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
if (!worker)
return NULL;
worker->dev = dev;
+ worker->ops = ops;
snprintf(name, sizeof(name), "vhost-%d", current->pid);
- vtsk = vhost_task_create(vhost_run_work_list, vhost_worker_killed,
- worker, name);
- if (IS_ERR(vtsk))
- goto free_worker;
-
mutex_init(&worker->mutex);
init_llist_head(&worker->work_list);
worker->kcov_handle = kcov_common_handle();
- worker->vtsk = vtsk;
-
- vhost_task_start(vtsk);
-
- ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
+ ret = ops->create(worker, dev, name);
if (ret < 0)
- goto stop_worker;
- worker->id = id;
+ goto free_worker;
return worker;
-stop_worker:
- vhost_task_stop(vtsk);
free_worker:
kfree(worker);
return NULL;
@@ -865,6 +1025,14 @@ 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;
@@ -982,6 +1150,7 @@ 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.
@@ -2135,6 +2304,45 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int
ioctl, void __user *argp)
goto done;
}
+#ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL
+ if (ioctl == VHOST_SET_FORK_FROM_OWNER) {
+ /* Only allow modification before owner is set */
+ if (vhost_dev_has_owner(d)) {
+ r = -EBUSY;
+ goto done;
+ }
+ u8 fork_owner_val;
+
+ if (get_user(fork_owner_val, (u8 __user *)argp)) {
+ r = -EFAULT;
+ goto done;
+ }
+ if (fork_owner_val != VHOST_FORK_OWNER_TASK &&
+ fork_owner_val != VHOST_FORK_OWNER_KTHREAD) {
+ r = -EINVAL;
+ goto done;
+ }
+ d->fork_owner = !!fork_owner_val;
+ r = 0;
+ goto done;
+ }
+ if (ioctl == VHOST_GET_FORK_FROM_OWNER) {
+ u8 fork_owner_val = d->fork_owner;
+
+ if (fork_owner_val != VHOST_FORK_OWNER_TASK &&
+ fork_owner_val != VHOST_FORK_OWNER_KTHREAD) {
+ r = -EINVAL;
+ goto done;
+ }
+ if (put_user(fork_owner_val, (u8 __user *)argp)) {
+ 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/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index bb75a292d50c..ab704d84fb34 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -26,7 +26,18 @@ struct vhost_work {
unsigned long flags;
};
+struct vhost_worker;
+struct vhost_dev;
+
+struct vhost_worker_ops {
+ int (*create)(struct vhost_worker *worker, struct vhost_dev *dev,
+ const char *name);
+ void (*stop)(struct vhost_worker *worker);
+ void (*wakeup)(struct vhost_worker *worker);
+};
+
struct vhost_worker {
+ struct task_struct *kthread_task;
struct vhost_task *vtsk;
struct vhost_dev *dev;
/* Used to serialize device wide flushing with worker swapping. */
@@ -36,6 +47,7 @@ struct vhost_worker {
u32 id;
int attachment_cnt;
bool killed;
+ const struct vhost_worker_ops *ops;
};
/* Poll a file (eventfd or socket) */
@@ -176,6 +188,16 @@ struct vhost_dev {
int byte_weight;
struct xarray worker_xa;
bool use_worker;
+ /*
+ * If fork_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 fork_from_owner_default
+ */
+ bool fork_owner;
int (*msg_handler)(struct vhost_dev *dev, u32 asid,
struct vhost_iotlb_msg *msg);
};
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index d4b3e2ae1314..e72f2655459e 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -235,4 +235,33 @@
*/
#define VHOST_VDPA_GET_VRING_SIZE _IOWR(VHOST_VIRTIO, 0x82, \
struct vhost_vring_state)
+
+/* fork_owner values for vhost */
+#define VHOST_FORK_OWNER_KTHREAD 0
+#define VHOST_FORK_OWNER_TASK 1
+
+/**
+ * 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 VHOST_FORK_OWNER_TASK(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 VHOST_FORK_OWNER_KTHREAD:
+ * - 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
