Re: [PATCH v8 6/8] vhost: uapi to control task mode (owner vs kthread)

Stefano Garzarella
2025-04-01T13:57:42Z

On Fri, Mar 28, 2025 at 06:02:50PM +0800, Cindy Lu wrote:
>Add a new UAPI to configure the vhost device to use the kthread mode

nit: missing . at the end

>The userspace application can use IOCTL VHOST_FORK_FROM_OWNER
>to choose between owner and kthread mode if necessary

Ditto

>This setting must be applied before VHOST_SET_OWNER, as the worker
>will be created in the VHOST_SET_OWNER function

Ditto.

>
>Signed-off-by: Cindy Lu <lulu@redhat.com>
>---
> drivers/vhost/vhost.c | 22 ++++++++++++++++++++--
> include/uapi/linux/vhost.h | 16 ++++++++++++++++
> 2 files changed, 36 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>index be97028a8baf..ff930c2e5b78 100644
>--- a/drivers/vhost/vhost.c
>+++ b/drivers/vhost/vhost.c
>@@ -1134,7 +1134,7 @@ 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.
>@@ -2287,7 +2287,25 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> r = vhost_dev_set_owner(d);
> goto done;
> }
>-

As I mentioned, I'll add the Kconfig in this patch to avoid bisection
issues.

The rest LGTM.

Thanks,
Stefano

>+ 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;
>+ }
> /* 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 b95dd84eef2d..1ae0917bfeca 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
>