Re: [PATCH 2/2] vhost-scsi: reject invalid max_io_vqs module parameter

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jul 31, 2026 at 03:10:24PM -0700, Dongli Zhang wrote:
> max_io_vqs is currently validated only when a vhost-scsi device is opened.
> This allows sysfs to show values larger than the driver will actually use,
> e.g. writing 2048 succeeds even though vhost_scsi_open() later clamps it to
> VHOST_SCSI_MAX_IO_VQ. This makes the sysfs value differ from the value that
> will actually be used.
> 
> hv# echo 2048 > /sys/module/vhost_scsi/parameters/max_io_vqs
> 
> hv# cat /sys/module/vhost_scsi/parameters/max_io_vqs
> 2048
> 
> [  315.630495] Invalid max_io_vqs of 2048. Using 1024.
> 
> Use a module parameter callback to reject out-of-range updates when the
> parameter is written. This keeps the visible parameter value consistent
> with the effective queue limit.
> 
> With the parameter value kept in range, remove the duplicate validation
> from vhost_scsi_open().
> 
> Invalid values now fail with -EINVAL at write/load time instead of being
> accepted and silently adjusted later when the device is opened.
> 
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>

why should we change userspace visible behaviour now?

> ---
>  drivers/vhost/scsi.c | 27 ++++++++++++++++-----------
>  1 file changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index 0c0634eea144..c138c29ce3dd 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -210,7 +210,20 @@ static const int vhost_scsi_bits[] = {
>  #define VHOST_SCSI_MAX_EVENT	128
>  
>  static unsigned vhost_scsi_max_io_vqs = 128;
> -module_param_named(max_io_vqs, vhost_scsi_max_io_vqs, uint, 0644);
> +
> +static int vhost_scsi_set_max_io_vqs(const char *val,
> +				     const struct kernel_param *kp)
> +{
> +	return param_set_uint_minmax(val, kp, 1, VHOST_SCSI_MAX_IO_VQ);
> +}
> +
> +static const struct kernel_param_ops vhost_scsi_max_io_vqs_op = {
> +	.set = vhost_scsi_set_max_io_vqs,
> +	.get = param_get_uint,
> +};
> +
> +module_param_cb(max_io_vqs, &vhost_scsi_max_io_vqs_op,
> +		&vhost_scsi_max_io_vqs, 0644);
>  MODULE_PARM_DESC(max_io_vqs, "Set the max number of IO virtqueues a vhost scsi device can support. The default is 128. The max is 1024.");
>  
>  struct vhost_scsi_virtqueue {
> @@ -2273,22 +2286,14 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
>  	struct vhost_scsi_virtqueue *svq;
>  	struct vhost_scsi *vs;
>  	struct vhost_virtqueue **vqs;
> -	int r = -ENOMEM, i, nvqs = vhost_scsi_max_io_vqs;
> +	int r = -ENOMEM, i, nvqs;
>  
>  	vs = kvzalloc_obj(*vs);
>  	if (!vs)
>  		goto err_vs;
>  	vs->inline_sg_cnt = vhost_scsi_inline_sg_cnt;
>  
> -	if (nvqs > VHOST_SCSI_MAX_IO_VQ) {
> -		pr_err("Invalid max_io_vqs of %d. Using %d.\n", nvqs,
> -		       VHOST_SCSI_MAX_IO_VQ);
> -		nvqs = VHOST_SCSI_MAX_IO_VQ;
> -	} else if (nvqs == 0) {
> -		pr_err("Invalid max_io_vqs of %d. Using 1.\n", nvqs);
> -		nvqs = 1;
> -	}
> -	nvqs += VHOST_SCSI_VQ_IO;
> +	nvqs = vhost_scsi_max_io_vqs + VHOST_SCSI_VQ_IO;
>  
>  	vs->old_inflight = kmalloc_objs(*vs->old_inflight, nvqs,
>  					GFP_KERNEL | __GFP_ZERO);
> -- 
> 2.43.5