linux-kernel - Re: [PATCH 4/8] iommu: Switch __iommu_domain

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Message-ID: <Y8mZbh56MzXWpbi9@nvidia.com>
Date:   Thu, 19 Jan 2023 15:26:38 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     joro@...tes.org, will@...nel.org, hch@....de,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] iommu: Switch __iommu_domain_alloc() to device ops

On Thu, Jan 19, 2023 at 07:18:22PM +0000, Robin Murphy wrote:

> -static struct iommu_domain *__iommu_domain_alloc(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;
>  
> -	if (!ops)
> -		return NULL;
> -
>  	domain = ops->domain_alloc(type);
>  	if (!domain)
>  		return NULL;
> @@ -1970,9 +1968,28 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
>  	return domain;
>  }
>  
> +static int __iommu_domain_alloc_dev(struct device *dev, void *data)
> +{
> +	struct device **alloc_dev = data;
> +
> +	if (!device_iommu_mapped(dev))
> +		return 0;

Is 0 the right thing? see below

> +
> +	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. This may not work as expected, sorry!\n");

if (WARN_ONCE(..))
   return -EINVAL

So that iommu_domain_alloc fails?

> +	*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;
> +
> +	if (bus_for_each_dev(bus, NULL, &dev, __iommu_domain_alloc_dev))
> +		return NULL;

eg shouldn't iommu_domain_alloc() return NULL if any devices are
!device_iommu_mapped ?

Jason