netdev - Re: [PATCH] vhost-vdpa: print error when vhost_vdpa_alloc

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Date:   Wed, 1 Feb 2023 10:52:35 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alvaro Karsz <alvaro.karsz@...id-run.com>
Cc:     jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, netdev@...r.kernel.org,
        Eugenio Perez Martin <eperezma@...hat.com>
Subject: Re: [PATCH] vhost-vdpa: print error when vhost_vdpa_alloc_domain
 fails

On Wed, Feb 01, 2023 at 05:20:18PM +0200, Alvaro Karsz wrote:
> Add a print explaining why vhost_vdpa_alloc_domain failed if the device
> is not IOMMU cache coherent capable.
> 
> Without this print, we have no hint why the operation failed.
> 
> For example:
> 
> $ virsh start <domain>
> 	error: Failed to start domain <domain>
> 	error: Unable to open '/dev/vhost-vdpa-<idx>' for vdpa device:
> 	       Unknown error 524
> 
> Suggested-by: Eugenio Perez Martin <eperezma@...hat.com>
> Signed-off-by: Alvaro Karsz <alvaro.karsz@...id-run.com>

I'm not sure this is a good idea. Userspace is not supposed to be
able to trigger dev_err.

> ---
>  drivers/vhost/vdpa.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 23db92388393..56287506aa0d 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -1151,8 +1151,11 @@ static int vhost_vdpa_alloc_domain(struct vhost_vdpa *v)
>  	if (!bus)
>  		return -EFAULT;
>  
> -	if (!device_iommu_capable(dma_dev, IOMMU_CAP_CACHE_COHERENCY))
> +	if (!device_iommu_capable(dma_dev, IOMMU_CAP_CACHE_COHERENCY)) {
> +		dev_err(&v->dev,
> +			"Failed to allocate domain, device is not IOMMU cache coherent capable\n");
>  		return -ENOTSUPP;
> +	}
>  
>  	v->domain = iommu_domain_alloc(bus);
>  	if (!v->domain)
> -- 
> 2.34.1