linux-kernel - Re: [PATCH] vhost-vdpa: fail enabling virtqueue in certain conditions

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Date: Tue, 6 Feb 2024 10:56:50 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: virtualization@...ts.linux.dev, Shannon Nelson <shannon.nelson@....com>,
	Eugenio Pérez <eperezma@...hat.com>,
	kvm@...r.kernel.org, Kevin Wolf <kwolf@...hat.com>,
	Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost-vdpa: fail enabling virtqueue in certain conditions

better @subj: try late vq enable only if negotiated

On Tue, Feb 06, 2024 at 03:51:54PM +0100, Stefano Garzarella wrote:
> If VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK is not negotiated, we expect
> the driver to enable virtqueue before setting DRIVER_OK. If the driver
> tries anyway, better to fail right away as soon as we get the ioctl.
> Let's also update the documentation to make it clearer.
> 
> We had a problem in QEMU for not meeting this requirement, see
> https://lore.kernel.org/qemu-devel/20240202132521.32714-1-kwolf@redhat.com/
> 
> Fixes: 9f09fd6171fe ("vdpa: accept VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK backend feature")
> Cc: eperezma@...hat.com
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
>  include/uapi/linux/vhost_types.h | 3 ++-
>  drivers/vhost/vdpa.c             | 4 ++++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> index d7656908f730..5df49b6021a7 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -182,7 +182,8 @@ struct vhost_vdpa_iova_range {
>  /* Device can be resumed */
>  #define VHOST_BACKEND_F_RESUME  0x5
>  /* Device supports the driver enabling virtqueues both before and after
> - * DRIVER_OK
> + * DRIVER_OK. If this feature is not negotiated, the virtqueues must be
> + * enabled before setting DRIVER_OK.
>   */
>  #define VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK  0x6
>  /* Device may expose the virtqueue's descriptor area, driver area and
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index bc4a51e4638b..1fba305ba8c1 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -651,6 +651,10 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>  	case VHOST_VDPA_SET_VRING_ENABLE:
>  		if (copy_from_user(&s, argp, sizeof(s)))
>  			return -EFAULT;
> +		if (!vhost_backend_has_feature(vq,
> +			VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK) &&
> +		    (ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK))
> +			return -EINVAL;
>  		ops->set_vq_ready(vdpa, idx, s.num);
>  		return 0;
>  	case VHOST_VDPA_GET_VRING_GROUP:
> -- 
> 2.43.0