linux-kernel - Re: [PATCH v6 5/6] vhost: Add new UAPI to support change to task mode

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Message-ID: <CACLfguU8-F=i3N6cyouBxwneM1Fr0oNs9ac3+c5xoHr_zcZW6A@mail.gmail.com>
Date: Wed, 26 Feb 2025 14:13:27 +0800
From: Cindy Lu <lulu@...hat.com>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: jasowang@...hat.com, mst@...hat.com, michael.christie@...cle.com, 
	linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH v6 5/6] vhost: Add new UAPI to support change to task mode

On Tue, Feb 25, 2025 at 7:31 PM Stefano Garzarella <sgarzare@...hat.com> wrote:
>
> On Sun, Feb 23, 2025 at 11:36:20PM +0800, Cindy Lu wrote:
> >Add a new UAPI to enable setting the vhost device to task mode.
> >The userspace application can use VHOST_SET_INHERIT_FROM_OWNER
> >to configure the mode if necessary.
> >This setting must be applied before VHOST_SET_OWNER, as the worker
> >will be created in the VHOST_SET_OWNER function
> >
> >Signed-off-by: Cindy Lu <lulu@...hat.com>
> >---
> > drivers/vhost/vhost.c      | 24 ++++++++++++++++++++++--
> > include/uapi/linux/vhost.h | 18 ++++++++++++++++++
> > 2 files changed, 40 insertions(+), 2 deletions(-)
> >
> >diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> >index d8c0ea118bb1..45d8f5c5bca9 100644
> >--- a/drivers/vhost/vhost.c
> >+++ b/drivers/vhost/vhost.c
> >@@ -1133,7 +1133,7 @@ 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.
> >@@ -2278,15 +2278,35 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> > {
> >       struct eventfd_ctx *ctx;
> >       u64 p;
> >-      long r;
> >+      long r = 0;
> >       int i, fd;
> >+      u8 inherit_owner;
> >
> >       /* If you are not the owner, you can become one */
> >       if (ioctl == VHOST_SET_OWNER) {
> >               r = vhost_dev_set_owner(d);
> >               goto done;
> >       }
> >+      if (ioctl == VHOST_FORK_FROM_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;
> >+              }
> >+              /* Validate the inherit_owner value, ensuring it is either 0 or 1 */
> >+              if (inherit_owner > 1) {
> >+                      r = -EINVAL;
> >+                      goto done;
> >+              }
> >+
> >+              d->inherit_owner = (bool)inherit_owner;
> >
> >+              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..8f558b433536 100644
> >--- a/include/uapi/linux/vhost.h
> >+++ b/include/uapi/linux/vhost.h
> >@@ -235,4 +235,22 @@
> >  */
> > #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
> >+ *
> >+ * @param inherit_owner: An 8-bit value that determines the vhost thread mode
> >+ *
> >+ * When inherit_owner is set to 1:
> >+ *   - The VHOST worker threads inherit its values/checks from
> >+ *     the thread that owns the VHOST device, The vhost threads will
> >+ *     be counted in the nproc rlimits.
> >+ *
> >+ * When inherit_owner is set to 0:
> >+ *   - The VHOST worker threads will use the traditional kernel thread (kthread)
> >+ *     implementation, which may be preferred by older userspace applications that
> >+ *     do not utilize the newer vhost_task concept.
> >+ */
> >+#define VHOST_FORK_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, __u8)
>
> I don't think we really care of the size of the parameter, so can we
> just use `bool` or `unsigned int` or `int` for this IOCTL?
>
> As we did for other IOCTLs where we had to enable/disable something (e.g
> VHOST_VSOCK_SET_RUNNING, VHOST_VDPA_SET_VRING_ENABLE).
>
hi Stefano
I initially used it as a boolean, but during the code review, the
maintainers considered it was unsuitable for the bool use as the
interface in ioctl (I think in version 3 ?). So I changed it to u8,
then will check if this is 1/0 in ioctl and the u8 should be
sufficient for us to use
Thanks
cindy
> Thanks,
> Stefano
>