On Thu, Nov 07, 2024 at 03:12:49PM +0800, Cindy Lu wrote:

On Tue, Nov 5, 2024 at 6:32 PM Stefano Garzarella [off-list ref] wrote:

quoted

On Tue, Nov 05, 2024 at 03:25:26PM +0800, Cindy Lu wrote:

quoted

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 <redacted>
---
drivers/vhost/vhost.c      | 15 ++++++++++++++-
include/uapi/linux/vhost.h |  2 ++
2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c17dc01febcc..70c793b63905 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -2274,8 +2274,9 @@ 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;

I don't know if something is missing in this patch, but I am confused:

`r` is set few lines below...

quoted

      int i, fd;
+      bool inherit_owner;

      /* If you are not the owner, you can become one */
      if (ioctl == VHOST_SET_OWNER) {

...

        /* You must be the owner to do anything else */
        r = vhost_dev_check_owner(d);
        if (r)
                goto done;

So, why we are now initializing it to 0?

r = 0 mean return successfully here.
Therefore, in the case VHOST_SET_INHERIT_FROM_OWNER function, I don't
need to set it again and can simply return.
....
   if (vhost_dev_has_owner(d))
      break;
.....

Okay, but vhost_dev_check_owner() already set it to 0, so we can avoid 
that, no?

quoted

quoted

@@ -2332,6 +2333,18 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
              if (ctx)
                      eventfd_ctx_put(ctx);
              break;
+      case VHOST_SET_INHERIT_FROM_OWNER:
+              /*inherit_owner can only be modified before owner is set*/
+              if (vhost_dev_has_owner(d))

And here, how this check can be false, if at the beginning of the
function we call vhost_dev_check_owner()?

Maybe your intention was to add this code before the
`vhost_dev_check_owner()` call, so this should explain why initialize
`r` to 0, but I'm not sure.

Yes, in the function beginning, the code is
if (ioctl == VHOST_SET_OWNER) {
r = vhost_dev_set_owner(d);
goto done;
}
if the ioctl is not VHOST_SET_OWNER,  then the  code will not run the
function vhost_dev_set_owner.

Sorry, I meant vhost_dev_check_owner(), not vhost_dev_set_owner().

I'll try to explain again.

After applying this series we have this code:

long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
{
	struct eventfd_ctx *ctx;
	u64 p;
	long r = 0;
	int i, fd;
	bool 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;
	}

	/* You must be the owner to do anything else */
	r = vhost_dev_check_owner(d);
	if (r)
		goto done;

	switch (ioctl) {
	...
     	case VHOST_SET_INHERIT_FROM_OWNER:
		/*inherit_owner can only be modified before owner is 
		 * set*/
		if (vhost_dev_has_owner(d))
			break;

IIUC this check is always true, so we always call `break` because at
the beginning of this function we call vhost_dev_check_owner() which
if `dev->mm != current->mm` (so it can't be null I guess) jumps directly
into `done`, returning an error.

So I still don't understand in which condition we can run the code after
this check.

Thanks,
Stefano

		if (copy_from_user(&inherit_owner, argp,
				   sizeof(inherit_owner))) {
			r = -EFAULT;
			break;
		}
		d->inherit_owner = inherit_owner;
		break;

This ioctl is used by userspace applications, so we cannot be certain
of the type and sequence of their calls; therefore, I added this
check.

quoted

quoted

+                      break;

Should we return an error (e.g. -EPERM) in this case?

sure，will add this back
thanks
Cindy

quoted

quoted

+
+              if (copy_from_user(&inherit_owner, argp,
+                                 sizeof(inherit_owner))) {
+                      r = -EFAULT;
+                      break;
+              }
+              d->inherit_owner = inherit_owner;
+              break;
      default:
              r = -ENOIOCTLCMD;
              break;

diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index b95dd84eef2d..1e192038633d 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h

@@ -235,4 +235,6 @@
 */

#define VHOST_VDPA_GET_VRING_SIZE     _IOWR(VHOST_VIRTIO, 0x82,       \
                                            struct vhost_vring_state)
+

Please add a documentation here, this is UAPI, so the user should
know what this ioctl does based on the parameter.

Thanks,
Stefano

quoted

+#define VHOST_SET_INHERIT_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, bool)
#endif
--
2.45.0