linux-kernel - Re: [PATCH v2 7/7] vhost: Add new UAPI to support change to task mode

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Message-ID: <20241015061702-mutt-send-email-mst@kernel.org>
Date: Tue, 15 Oct 2024 06:19:22 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Mike Christie <michael.christie@...cle.com>
Cc: Cindy Lu <lulu@...hat.com>, jasowang@...hat.com,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 7/7] vhost: Add new UAPI to support change to task mode

On Mon, Oct 14, 2024 at 03:56:33PM -0500, Mike Christie wrote:
> On 10/3/24 8:58 PM, Cindy Lu wrote:
> > Add a new UAPI to support setting the vhost device to
> > use task mode. The user space application needs to use
> > VHOST_SET_INHERIT_FROM_OWNER to set the mode.
> > This setting must be set before VHOST_SET_OWNER is set.
> > 
> > Signed-off-by: Cindy Lu <lulu@...hat.com>
> > ---
> >  drivers/vhost/vhost.c      | 18 +++++++++++++++++-
> >  include/uapi/linux/vhost.h |  2 ++
> >  2 files changed, 19 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 08c9e77916ca..0e5c81026acd 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -2341,8 +2341,24 @@ 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;
> > +	bool inherit_owner;
> > +
> > +	if (ioctl == VHOST_SET_INHERIT_FROM_OWNER) {
> 
> Maybe instead of a modparam and this ioctl we just want a new ioctl:
> 
> /*
>  * This will setup the owner based on the calling thread instead of
>  * using kthread.
>  */
> #define VHOST_INHERIT_OWNER _IO(VHOST_VIRTIO, 0x83)

I feel this is not good because it is insecure -
process should not normally have a say in whether
namespaces work correctly.
So we want the system admin to be able to block the
old mode.

> It would initially be used by vhost-scsi when worker_per_virtqueue=true
> since that is a new use case and there will be no regressions.
> 
> For the other cases we default to VHOST_SET_OWNER. Other QEMU cases or
> tool XYZ can use the new ioctl when they are ready.

I do not like it that we switched default now we apparently will be
switching it back. Will break some userspace whatever we do.

-- 
MST