linux-kernel - Re: [PATCH v3 4/7] iommu: Switch __iommu_domain

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Message-ID: <e0a7969a-60e3-6b3c-4f74-592654d4407f@linux.intel.com>
Date:   Mon, 18 Sep 2023 14:10:58 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>, joro@...tes.org,
        will@...nel.org
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        jgg@...dia.com
Subject: Re: [PATCH v3 4/7] iommu: Switch __iommu_domain_alloc() to device ops

On 9/16/23 12:58 AM, Robin Murphy wrote:
> @@ -1997,16 +1995,13 @@ void iommu_set_fault_handler(struct iommu_domain *domain,
>   }
>   EXPORT_SYMBOL_GPL(iommu_set_fault_handler);
>   
> -static struct iommu_domain *__iommu_domain_alloc(const struct bus_type *bus,
> +static struct iommu_domain *__iommu_domain_alloc(struct device *dev,
>   						 unsigned type)
>   {
> -	const struct iommu_ops *ops = bus ? bus->iommu_ops : NULL;
> +	const struct iommu_ops *ops = dev_iommu_ops(dev);
>   	struct iommu_domain *domain;
>   	unsigned int alloc_type = type & IOMMU_DOMAIN_ALLOC_FLAGS;
>   
> -	if (!ops)
> -		return NULL;
> -
>   	domain = ops->domain_alloc(alloc_type);
>   	if (!domain)
>   		return NULL;
> @@ -2030,9 +2025,28 @@ static struct iommu_domain *__iommu_domain_alloc(const struct bus_type *bus,
>   	return domain;
>   }
>   
> +static int __iommu_domain_alloc_dev(struct device *dev, void *data)
> +{
> +	struct device **alloc_dev = data;
> +
> +	if (!dev_has_iommu(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(const struct bus_type *bus)
>   {
> -	return __iommu_domain_alloc(bus, IOMMU_DOMAIN_UNMANAGED);
> +	struct device *dev = NULL;
> +
> +	if (bus_for_each_dev(bus, NULL, &dev, __iommu_domain_alloc_dev))
> +		return NULL;

__iommu_domain_alloc_dev() always returns 0. Hence above if condition
will never be true. Perhaps, in __iommu_domain_alloc_dev(),

	if (WARN_ON(*alloc_dev && dev_iommu_ops(dev) !=
             dev_iommu_ops(*alloc_dev))
		return -EPERM;

?

> +
> +	return __iommu_domain_alloc(dev, IOMMU_DOMAIN_UNMANAGED);

Is it possible that all devices on this bus have dev_has_iommu() to be
false? If so, we probably need something like below:

	if (!dev_has_iommu(dev))
		return -ENODEV;

?

>   }
>   EXPORT_SYMBOL_GPL(iommu_domain_alloc);
>   
> @@ -3228,13 +3242,17 @@ static int __iommu_group_alloc_blocking_domain(struct iommu_group *group)
>   	if (group->blocking_domain)
>   		return 0;
>   
> -	group->blocking_domain = __iommu_domain_alloc(dev->bus, IOMMU_DOMAIN_BLOCKED);
> +	/* noiommu groups should never be here */
> +	if (WARN_ON(!dev_has_iommu(dev)))
> +		return -ENODEV;
> +
> +	group->blocking_domain = __iommu_domain_alloc(dev, IOMMU_DOMAIN_BLOCKED);
>   	if (!group->blocking_domain) {
>   		/*
>   		 * For drivers that do not yet understand IOMMU_DOMAIN_BLOCKED
>   		 * create an empty domain instead.
>   		 */
> -		group->blocking_domain = __iommu_domain_alloc(dev->bus, IOMMU_DOMAIN_UNMANAGED);
> +		group->blocking_domain = __iommu_domain_alloc(dev, IOMMU_DOMAIN_UNMANAGED);
>   		if (!group->blocking_domain)
>   			return -EINVAL;
>   	}

Best regards,
baolu