linux-kernel - Re: [PATCH 6/6] vduse: Update api version to 1

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Date:   Wed, 29 Jun 2022 04:33:35 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Xie Yongji <xieyongji@...edance.com>
Cc:     jasowang@...hat.com, xiaodong.liu@...el.com,
        maxime.coquelin@...hat.com, stefanha@...hat.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] vduse: Update api version to 1

On Wed, Jun 29, 2022 at 04:25:41PM +0800, Xie Yongji wrote:
> Let's update api version to 1 since we introduced
> some new ioctls to support registering userspace
> memory for IOTLB.
> 
> Signed-off-by: Xie Yongji <xieyongji@...edance.com>


Adding new ioctls does not justify things like this.

Besides, adding UAPI then changing it is not nice
since it makes git bisect behave incorrectly.

> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 12 ++++++++++++
>  include/uapi/linux/vduse.h         |  8 +++++++-
>  2 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 7b2ea7612da9..2795785ca6a2 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -1206,6 +1206,10 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
>  	case VDUSE_IOTLB_GET_INFO: {
>  		struct vduse_iotlb_info iotlb;
>  
> +		ret = -EPERM;


Almost for sure a wrong error code.

> +		if (dev->api_version < 1)
> +			break;
> +
>  		iotlb.bounce_iova = 0;
>  		iotlb.bounce_size = dev->domain->bounce_size;
>  


Wait a second. so you are intentionally breaking any userspace
that called VDUSE_SET_API_VERSION with version 0?

Please don't.


> @@ -1219,6 +1223,10 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
>  	case VDUSE_IOTLB_REG_UMEM: {
>  		struct vduse_iotlb_umem umem;
>  
> +		ret = -EPERM;
> +		if (dev->api_version < 1)
> +			break;
> +
>  		ret = -EFAULT;
>  		if (copy_from_user(&umem, argp, sizeof(umem)))
>  			break;
> @@ -1230,6 +1238,10 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
>  	case VDUSE_IOTLB_DEREG_UMEM: {
>  		struct vduse_iotlb_umem umem;
>  
> +		ret = -EPERM;
> +		if (dev->api_version < 1)
> +			break;
> +
>  		ret = -EFAULT;
>  		if (copy_from_user(&umem, argp, sizeof(umem)))
>  			break;
> diff --git a/include/uapi/linux/vduse.h b/include/uapi/linux/vduse.h
> index 1b17391e228f..902ea19cd9e0 100644
> --- a/include/uapi/linux/vduse.h
> +++ b/include/uapi/linux/vduse.h
> @@ -8,7 +8,13 @@
>  
>  /* The ioctls for control device (/dev/vduse/control) */
>  
> -#define VDUSE_API_VERSION	0
> +/*
> + * v0 -> v1:
> + *  - Introduce VDUSE_IOTLB_GET_INFO ioctl
> + *  - Introduce VDUSE_VDUSE_IOTLB_REG_UMEM ioctl
> + *  - Introduce VDUSE_IOTLB_DEREG_UMEM ioctl
> + */
> +#define VDUSE_API_VERSION	1
>  
>  /*
>   * Get the version of VDUSE API that kernel supported (VDUSE_API_VERSION).
> -- 
> 2.20.1