This patch introduces a new UAPI that allows the vhost device to select
in kthread mode. Userspace applications can utilize IOCTL
VHOST_FORK_FROM_OWNER to select between task and kthread modes, which
must be invoked before IOCTL VHOST_SET_OWNER, as the worker will be
created during that call.
The VHOST_NEW_WORKER requires the inherit_owner setting to be true, and
a check has been added to ensure proper configuration.
Additionally, a new KConfig option, CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL,
is introduced to control the availability of the IOCTL
VHOST_FORK_FROM_OWNER. When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is set
to n, the IOCTL is disabled, and any attempt to use it will result in a
failure.
Signed-off-by: Cindy Lu <l...@redhat.com>
---
drivers/vhost/Kconfig | 13 +++++++++++++
drivers/vhost/vhost.c | 30 +++++++++++++++++++++++++++++-
include/uapi/linux/vhost.h | 16 ++++++++++++++++
3 files changed, 58 insertions(+), 1 deletion(-)
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 020d4fbb947c..300e474b60fd 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -96,3 +96,16 @@ config VHOST_CROSS_ENDIAN_LEGACY
If unsure, say "N".
endif
+
+config VHOST_ENABLE_FORK_OWNER_IOCTL
+ bool "Enable IOCTL VHOST_FORK_FROM_OWNER"
+ default n
+ help
+ This option enables the IOCTL VHOST_FORK_FROM_OWNER, allowing
+ userspace applications to modify the thread mode for vhost devices.
+
+ By default, `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL` is set to `n`,
+ which disables the IOCTL. When enabled (y), the IOCTL allows
+ users to set the mode as needed.
+
+ If unsure, say "N".
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2d2909be1bb2..673c2dc8607b 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1022,6 +1022,13 @@ 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 inherit_owner must be true.
+ */
+ if (!dev->inherit_owner)
+ return -EFAULT;
ret = vhost_new_worker(dev, &state);
if (!ret && copy_to_user(argp, &state, sizeof(state)))
ret = -EFAULT;
@@ -1138,7 +1145,7 @@ void vhost_dev_reset_owner(struct vhost_dev *dev, struct
vhost_iotlb *umem)
int i;
vhost_dev_cleanup(dev);
-
+ dev->inherit_owner = true;
dev->umem = umem;
/* We don't need VQ locks below since vhost_dev_cleanup makes sure
* VQs aren't running.
@@ -2292,6 +2299,27 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int
ioctl, void __user *argp)
goto done;
}
+#ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL
+ if (ioctl == VHOST_FORK_FROM_OWNER) {
+ u8 inherit_owner;
+ /*inherit_owner can only be modified before owner is set*/
+ if (vhost_dev_has_owner(d)) {
+ r = -EBUSY;
+ goto done;
+ }
+ if (copy_from_user(&inherit_owner, argp, sizeof(u8))) {
+ r = -EFAULT;
+ goto done;
+ }
+ if (inherit_owner > 1) {
+ r = -EINVAL;
+ goto done;
+ }
+ d->inherit_owner = (bool)inherit_owner;
+ 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..d2692c7ef450 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -235,4 +235,20 @@
*/
#define VHOST_VDPA_GET_VRING_SIZE _IOWR(VHOST_VIRTIO, 0x82, \
struct vhost_vring_state)
+
+/**
+ * VHOST_FORK_FROM_OWNER - Set the inherit_owner flag for the vhost device,
+ * This ioctl must called before VHOST_SET_OWNER.
+ *
+ * @param inherit_owner: An 8-bit value that determines the vhost thread mode
+ *
+ * When inherit_owner is set to 1(default value):
+ * - Vhost will create tasks similar to processes forked from the owner,
+ * inheriting all of the owner's attributes.
+ *
+ * When inherit_owner is set to 0:
+ * - Vhost will create tasks as kernel thread.
+ */
+#define VHOST_FORK_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, __u8)
+
#endif
--
2.45.0
