Subject: Re: [PATCH v6 08/25] iommu: Reorganize iommu_get_default_domain_type() to respect def_domain_type()

From: Jason Gunthorpe <[email-masked]>
Date: Mon, 14 Aug 2023 14:25:46 -0300

On Sat, Aug 12, 2023 at 10:15:42AM +0800, Baolu Lu wrote:

> 
> How about consolidating above into a single helper?
> 
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1787,6 +1787,21 @@ __iommu_group_alloc_default_domain(struct iommu_group
> *group, int req_type)
>  	return __iommu_group_domain_alloc(group, req_type);
>  }
> 
> +/*
> + * Returns the iommu_ops for the devices in an iommu group.
> + *
> + * It is assumed that all devices in an iommu group are managed by a single
> + * IOMMU unit. Therefore, this returns the dev_iommu_ops of the first
> device
> + * in the group.
> + */
> +static const struct iommu_ops *group_iommu_ops(struct iommu_group *group)
> +{
> +	struct group_device *device;
> +
> +	device = list_first_entry(&group->devices, struct group_device, list);
> +	return dev_iommu_ops(device->dev);
> +}

Okay I did this, but it doesn't help as much..

> @@ -2124,13 +2134,9 @@ static struct iommu_domain
> *__iommu_domain_alloc(const struct iommu_ops *ops,
>  static struct iommu_domain *
>  __iommu_group_domain_alloc(struct iommu_group *group, unsigned int type)
>  {
> -	struct device *dev =
> -		list_first_entry(&group->devices, struct group_device, list)
> -			->dev;
> -
>  	lockdep_assert_held(&group->mutex);
> 
> -	return __iommu_domain_alloc(dev_iommu_ops(dev), dev, type);
> +	return __iommu_domain_alloc(group_iommu_ops(group), dev, type);
>  }

Since this is all still needed to calculate dev

> > +err:
> > +	if (target_type) {
> > +		dev_err_ratelimited(
> > +			gdev->dev,
> > +			"Device cannot be in %s domain - it is forcing %s\n",
> > +			iommu_domain_type_str(target_type),
> > +			iommu_domain_type_str(type));
> > +		return -1;
> > +	}
> > +
> > +	dev_warn(
> > +		gdev->dev,
> > +		"Device needs domain type %s, but device %s in the same iommu group requires type %s - using default\n",
> > +		iommu_domain_type_str(type), dev_name(last_dev),
> > +		iommu_domain_type_str(best_type));
> > +	return 0;
> 
> This doesn't match the commit message, where it states:
> 
> "Arrange things so that if the driver says it needs IDENTITY then
>  iommu_get_default_domain_type() either fails or returns IDENTITY.
> "
> 
> I saw that this change was made in the sequential patch. It is probably
> better to put that here?

Ah, I went over all this again and decided to try again, it is too
complicated. This patch can do what the commit message says and the
following patches are even simpler:

/*
 * Combine the driver's choosen def_domain_type across all the devices in a
 * group. Drivers must give a consistent result.
 */
static int iommu_get_def_domain_type(struct iommu_group *group,
				     struct device *dev, int cur_type)
{
	const struct iommu_ops *ops = group_iommu_ops(group);
	int type;

	if (!ops->def_domain_type)
		return cur_type;

	type = ops->def_domain_type(dev);
	if (!type || cur_type == type)
		return cur_type;
	if (!cur_type)
		return type;

	dev_err_ratelimited(
		dev,
		"IOMMU driver error, requesting conflicting def_domain_type, %s and %s, for devices in group %u.\n",
		iommu_domain_type_str(cur_type), iommu_domain_type_str(type),
		group->id);

	/*
	 * Try to recover, drivers are allowed to force IDENITY or DMA, IDENTITY
	 * takes precedence.
	 */
	if (cur_type || type == IOMMU_DOMAIN_IDENTITY)
		return IOMMU_DOMAIN_IDENTITY;
	return cur_type;
}

/*
 * A target_type of 0 will select the best domain type. 0 can be returned in
 * this case meaning the global default should be used.
 */
static int iommu_get_default_domain_type(struct iommu_group *group,
					 int target_type)
{
	struct device *untrusted = NULL;
	struct group_device *gdev;
	int driver_type = 0;

	lockdep_assert_held(&group->mutex);

	/*
	 * ARM32 drivers supporting CONFIG_ARM_DMA_USE_IOMMU can declare an
	 * identity_domain and it will automatically become their default
	 * domain. Later on ARM_DMA_USE_IOMMU will install its UNMANAGED domain.
	 * Override the selection to IDENTITY.
	 */
	if (IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)) {
		static_assert(!(IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU) &&
				IS_ENABLED(CONFIG_IOMMU_DMA)));
		driver_type = IOMMU_DOMAIN_IDENTITY;
	}

	for_each_group_device(group, gdev) {
		driver_type = iommu_get_def_domain_type(group, gdev->dev,
							driver_type);

		if (dev_is_pci(gdev->dev) && to_pci_dev(gdev->dev)->untrusted) {
			/*
			 * No ARM32 using systems will set untrusted, it cannot
			 * work.
			 */
			if (WARN_ON(IS_ENABLED(CONFIG_ARM_DMA_USE_IOMMU)))
				return -1;
			untrusted = gdev->dev;
		}
	}

	if (untrusted) {
		if (driver_type && driver_type != IOMMU_DOMAIN_DMA) {
			dev_err_ratelimited(
				untrusted,
				"Device is not trusted, but driver is overriding group %u to %s, refusing to probe.\n",
				group->id, iommu_domain_type_str(driver_type));
			return -1;
		}
		driver_type = IOMMU_DOMAIN_DMA;
	}

	if (target_type) {
		if (driver_type && target_type != driver_type)
			return -1;
		return target_type;
	}
	return driver_type;
}

Thanks,
Jason