linux-kernel - Re: [PATCH v3 7/9] vhost: Add new UAPI to support change to task mode

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Message-ID: <6dtic6ld6p6kyzbjjewj4cxkc6h6r5t6y2ztazrgozdanz6gkm@vlj3ubpam6ih>
Date: Tue, 5 Nov 2024 11:31:57 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Cindy Lu <lulu@...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 v3 7/9] vhost: Add new UAPI to support change to task mode

On Tue, Nov 05, 2024 at 03:25:26PM +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      | 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...

> 	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?

>@@ -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.

>+			break;

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

>+
>+		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

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