Re: [PATCH v12 21/24] vfio: Determine noiommu device in __vfio_register_dev()

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Jun 14, 2023 at 01:12:50PM +0000, Liu, Yi L wrote:
> diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> index 41a09a2df690..c2e0128323a7 100644
> --- a/drivers/vfio/group.c
> +++ b/drivers/vfio/group.c
> @@ -687,16 +687,6 @@ static struct vfio_group *vfio_group_find_or_alloc(struct device *dev)
>  	if (!iommu_group)
>  		return ERR_PTR(-EINVAL);
>  
> -	/*
> -	 * VFIO always sets IOMMU_CACHE because we offer no way for userspace to
> -	 * restore cache coherency. It has to be checked here because it is only
> -	 * valid for cases where we are using iommu groups.
> -	 */
> -	if (!device_iommu_capable(dev, IOMMU_CAP_CACHE_COHERENCY)) {
> -		iommu_group_put(iommu_group);
> -		return ERR_PTR(-EINVAL);
> -	}
> -
>  	mutex_lock(&vfio.group_lock);
>  	group = vfio_group_find_from_iommu(iommu_group);
>  	if (group) {
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 51c80eb32af6..ffb4585b7f0e 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -292,6 +292,17 @@ static int __vfio_register_dev(struct vfio_device *device,
>  	if (ret)
>  		return ret;
>  
> +	/*
> +	 * VFIO always sets IOMMU_CACHE because we offer no way for userspace to
> +	 * restore cache coherency. It has to be checked here because it is only
> +	 * valid for cases where we are using iommu groups.
> +	 */
> +	if (type == VFIO_IOMMU && !vfio_device_is_noiommu(device) &&
> +	    !device_iommu_capable(device->dev, IOMMU_CAP_CACHE_COHERENCY)) {
> +		ret = -EINVAL;
> +		goto err_out;
> +	}
> +
>  	ret = vfio_device_add(device);
>  	if (ret)
>  		goto err_out;

Yes that looks right

> 
> > I prefer the idea that vfio_device_is_noiommu() works in all the
> > kconfig scenarios rather than adding #ifdefs.
> 
> But the vfio_group would be empty when CONFIG_VFIO_GROUP is unset.
> From what I got now, when CONFIG_VFIO_GROUP is unset, the stub
> function always returns false.

It seems fine, you could also put the ifdef inside the stub

Jason