linux-kernel - Re: [PATCH v3 1/4] iommu: Check IOMMU_DEV_FEAT

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Date:   Wed, 29 Jul 2020 14:03:43 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v3 1/4] iommu: Check IOMMU_DEV_FEAT_AUX feature in aux
 api's

On Tue, 14 Jul 2020 13:57:00 +0800
Lu Baolu <baolu.lu@...ux.intel.com> wrote:

> The iommu aux-domain api's work only when IOMMU_DEV_FEAT_AUX is enabled
> for the device. Add this check to avoid misuse.

Shouldn't this really be the IOMMU driver's responsibility to test?  If
nothing else, iommu_dev_feature_enabled() needs to get the iommu_ops
from dev->bus->iommu_ops, which is presumably the same iommu_ops we're
then calling from domain->ops to attach/detach the device, so it'd be
more efficient for the IOMMU driver to error on devices that don't
support aux.  Thanks,

Alex

> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/iommu/iommu.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 1ed1e14a1f0c..e1fdd3531d65 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2725,11 +2725,13 @@ EXPORT_SYMBOL_GPL(iommu_dev_feature_enabled);
>   */
>  int iommu_aux_attach_device(struct iommu_domain *domain, struct device *dev)
>  {
> -	int ret = -ENODEV;
> +	int ret;
>  
> -	if (domain->ops->aux_attach_dev)
> -		ret = domain->ops->aux_attach_dev(domain, dev);
> +	if (!iommu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX) ||
> +	    !domain->ops->aux_attach_dev)
> +		return -ENODEV;
>  
> +	ret = domain->ops->aux_attach_dev(domain, dev);
>  	if (!ret)
>  		trace_attach_device_to_domain(dev);
>  
> @@ -2748,12 +2750,12 @@ EXPORT_SYMBOL_GPL(iommu_aux_detach_device);
>  
>  int iommu_aux_get_pasid(struct iommu_domain *domain, struct device *dev)
>  {
> -	int ret = -ENODEV;
> +	if (!iommu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX) ||
> +	    !domain->ops->aux_get_pasid)
> +		return -ENODEV;
>  
> -	if (domain->ops->aux_get_pasid)
> -		ret = domain->ops->aux_get_pasid(domain, dev);
> +	return domain->ops->aux_get_pasid(domain, dev);
>  
> -	return ret;
>  }
>  EXPORT_SYMBOL_GPL(iommu_aux_get_pasid);
>