linux-kernel - Re: [PATCH v2 5/8] iommu: Switch __iommu_domain

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Date:   Thu, 26 Jan 2023 15:22:37 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     joro@...tes.org, will@...nel.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, hch@....de, jgg@...dia.com,
        baolu.lu@...ux.intel.com, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 5/8] iommu: Switch __iommu_domain_alloc() to device
 ops

Hi Robin,

On Thu, 26 Jan 2023 18:26:20 +0000, Robin Murphy <robin.murphy@....com>
wrote:

>  
> +static int __iommu_domain_alloc_dev(struct device *dev, void *data)
> +{
> +	struct device **alloc_dev = data;
> +
> +	if (!dev_iommu_ops_valid(dev))
> +		return 0;
> +
> +	WARN_ONCE(*alloc_dev && dev_iommu_ops(dev) !=
> dev_iommu_ops(*alloc_dev),
> +		"Multiple IOMMU drivers present, which the public IOMMU
> API can't fully support yet. You may still need to disable one or more to
> get the expected result here, sorry!\n"); +
> +	*alloc_dev = dev;
> +	return 0;
> +}
> +
>  struct iommu_domain *iommu_domain_alloc(struct bus_type *bus)
>  {
> -	return __iommu_domain_alloc(bus, IOMMU_DOMAIN_UNMANAGED);
> +	struct device *dev = NULL;
> +
> +	/* We always check the whole bus, so the return value isn't
> useful */
> +	bus_for_each_dev(bus, NULL, &dev, __iommu_domain_alloc_dev);
> +	if (!dev)
> +		return NULL;
Since __iommu_domain_alloc_dev() will always return 0, bus_for_each_dev()
will never breakout until the whole dev list is iterated over. If so, would
dev only record the last one? i.e. prior results get overwritten.  Maybe a
misunderstood the logic.

> +	return __iommu_domain_alloc(dev, IOMMU_DOMAIN_UNMANAGED);
>  }
>  EXPORT_SYMBOL_GPL(iommu_domain_alloc);

Thanks,

Jacob