linux-kernel - Re: [PATCH v7 8/8] vhost: Add a KConfig knob to enable IOCTL VHOST_FORK_FROM

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Message-ID: <20250321153829-mutt-send-email-mst@kernel.org>
Date: Fri, 21 Mar 2025 15:39:31 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Cindy Lu <lulu@...hat.com>, michael.christie@...cle.com,
	sgarzare@...hat.com, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH v7 8/8] vhost: Add a KConfig knob to enable IOCTL
 VHOST_FORK_FROM_OWNER

On Mon, Mar 03, 2025 at 01:52:06PM +0800, Jason Wang wrote:
> On Sun, Mar 2, 2025 at 10:34 PM Cindy Lu <lulu@...hat.com> wrote:
> >
> > Introduce a new config knob `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL`,
> > to control the availability of the `VHOST_FORK_FROM_OWNER` ioctl.
> > When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is set to n, the ioctl
> > is disabled, and any attempt to use it will result in failure.
> >
> > Signed-off-by: Cindy Lu <lulu@...hat.com>
> > ---
> >  drivers/vhost/Kconfig | 15 +++++++++++++++
> >  drivers/vhost/vhost.c | 11 +++++++++++
> >  2 files changed, 26 insertions(+)
> >
> > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> > index b455d9ab6f3d..e5b9dcbf31b6 100644
> > --- a/drivers/vhost/Kconfig
> > +++ b/drivers/vhost/Kconfig
> > @@ -95,3 +95,18 @@ 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, which allows
> > +         userspace applications to modify the thread mode for vhost devices.
> > +
> > +          By default, `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL` is set to `n`,
> > +          meaning the ioctl is disabled and any operation using this ioctl
> > +          will fail.
> > +          When the configuration is enabled (y), the ioctl becomes
> > +          available, allowing users to set the mode if needed.
> > +
> > +         If unsure, say "N".
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index fb0c7fb43f78..09e5e44dc516 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -2294,6 +2294,8 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> >                 r = vhost_dev_set_owner(d);
> >                 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*/
> > @@ -2313,6 +2315,15 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
> >                 r = 0;
> >                 goto done;
> >         }
> > +
> > +#else
> > +       if (ioctl == VHOST_FORK_FROM_OWNER) {
> > +               /* When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is 'n', return error */
> > +               r = -ENOTTY;
> > +               goto done;
> > +       }
> > +#endif
> > +
> >         /* You must be the owner to do anything else */
> >         r = vhost_dev_check_owner(d);
> >         if (r)
> > --
> > 2.45.0
> 
> Do we need to change the default value of the inhert_owner? For example:
> 
> #ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL
> inherit_owner = false;
> #else
> inherit_onwer = true;
> #endif
> 
> ?
> 
> Other patches look good to me.
> 
> Thanks


I think I agree with Cindy. kconfig just tells us whether the
ioctl is allowed. should not affect the default, if we want
a kconfig for default, it should be separate, but I doubt it.

> >