Re: [PATCH RFC 09/11] iommu: Add iommu_get_domain_for_dev_pasid()

[Jason Gunthorpe]

On Sun, Mar 20, 2022 at 02:40:28PM +0800, Lu Baolu wrote:
> @@ -3098,7 +3101,16 @@ int iommu_attach_device_pasid(struct iommu_domain *domain,
>  	if (iommu_group_device_count(group) != 1)
>  		goto out_unlock;
>  
> +	xa_lock(&group->pasid_array);
> +	curr = __xa_cmpxchg(&group->pasid_array, pasid, NULL,
> +			    domain, GFP_KERNEL);
> +	xa_unlock(&group->pasid_array);
> +	if (curr)

curr can be an xa_err that should be propogated.

> +		goto out_unlock;
> +
>  	ret = domain->ops->attach_dev_pasid(domain, dev, pasid);
> +	if (ret)
> +		xa_erase(&group->pasid_array, pasid);
>  
>  out_unlock:
>  	mutex_unlock(&group->mutex);
> @@ -3118,6 +3130,25 @@ void iommu_detach_device_pasid(struct iommu_domain *domain,
>  
>  	mutex_lock(&group->mutex);
>  	domain->ops->detach_dev_pasid(domain, dev, pasid);
> +	xa_erase(&group->pasid_array, pasid);
> +	mutex_unlock(&group->mutex);
> +	iommu_group_put(group);
> +}
> +
> +struct iommu_domain *
> +iommu_get_domain_for_dev_pasid(struct device *dev, ioasid_t pasid)
> +{
> +	struct iommu_domain *domain;
> +	struct iommu_group *group;
> +
> +	group = iommu_group_get(dev);
> +	if (!group)
> +		return NULL;
> +
> +	mutex_lock(&group->mutex);
> +	domain = xa_load(&group->pasid_array, pasid);
>  	mutex_unlock(&group->mutex);
>  	iommu_group_put(group);

This whole API seems sketchy - what is the lifecycle of the returned
iommu_domain and what prevents it from being concurrently freed after
unlocking?

Jason