Re: [PATCH v2 2/2] iommu: Probe right iommu_ops for device

[Robin Murphy]

On 2024-01-26 10:53 am, Lu Baolu wrote:
> Previously, in the iommu probe device path, __iommu_probe_device() gets
> the iommu_ops for the device from dev->iommu->fwspec if this field has
> been initialized before probing. Otherwise, it is assumed that only one
> of Intel, AMD, s390, PAMU or legacy SMMUv2 can be present, hence it's
> feasible to lookup the global iommu device list and use the iommu_ops of
> the first iommu device which has no dev->iommu->fwspec.
>
> The assumption mentioned above is no longer correct with the introduction
> of the IOMMUFD mock device on x86 platforms. There might be multiple
> instances of iommu drivers, none of which have the dev->iommu->fwspec
> field populated.
>
> Probe the right iommu_ops for device by iterating over all the global
> drivers and call their probe function to find a match.

This will now break several drivers which are no longer expecting to see 
a ->probe_device call without having seen the corresponding ->of_xlate 
call first.

Can we please just do the trivial fix to iommufd itself? At this point I 
don't mind if it's your v1, the even simpler one I proposed 2 months 
ago[1], or anything else similarly self-contained.

Thanks,
Robin.

[1] 
https://lore.kernel.org/linux-iommu/e365c08b21a8d0b60e6f5d1411be6701c1a06a53.1701165201.git.robin.murphy@xxxxxxx/

> Fixes: 17de3f5fdd35 ("iommu: Retire bus ops")
> Cc: Robin Murphy <robin.murphy@xxxxxxx>
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>   drivers/iommu/iommu.c | 76 +++++++++++++++++++++++++++----------------
>   1 file changed, 48 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 0af0b5544072..2cdb01e411fa 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -396,30 +396,69 @@ void dev_iommu_priv_set(struct device *dev, void *priv)
>   }
>   EXPORT_SYMBOL_GPL(dev_iommu_priv_set);
>   
> +static struct iommu_device *
> +__iommu_do_probe_device(struct device *dev, const struct iommu_ops *ops)
> +{
> +	struct iommu_device *iommu_dev;
> +
> +	if (!try_module_get(ops->owner))
> +		return ERR_PTR(-EINVAL);
> +
> +	iommu_dev = ops->probe_device(dev);
> +	if (IS_ERR(iommu_dev))
> +		module_put(ops->owner);
> +
> +	return iommu_dev;
> +}
> +
> +static struct iommu_device *iommu_probe_device_ops(struct device *dev)
> +{
> +	struct iommu_device *iter, *iommu_dev = ERR_PTR(-ENODEV);
> +	struct iommu_fwspec *fwspec;
> +
> +	/*
> +	 * For FDT-based systems and ACPI IORT/VIOT, drivers register IOMMU
> +	 * instances with non-NULL fwnodes, and client devices should have been
> +	 * identified with a fwspec by this point. Otherwise, we will iterate
> +	 * over all the global drivers and call their probe function to find a
> +	 * match.
> +	 */
> +	fwspec = dev_iommu_fwspec_get(dev);
> +	if (fwspec && fwspec->ops)
> +		return __iommu_do_probe_device(dev, fwspec->ops);
> +
> +	mutex_lock(&iommu_device_lock);
> +	list_for_each_entry(iter, &iommu_device_list, list) {
> +		iommu_dev = __iommu_do_probe_device(dev, iter->ops);
> +		if (!IS_ERR(iommu_dev))
> +			break;
> +	}
> +	mutex_unlock(&iommu_device_lock);
> +
> +	return iommu_dev;
> +}
> +
>   /*
>    * Init the dev->iommu and dev->iommu_group in the struct device and get the
>    * driver probed
>    */
> -static int iommu_init_device(struct device *dev, const struct iommu_ops *ops)
> +static int iommu_init_device(struct device *dev)
>   {
>   	struct iommu_device *iommu_dev;
> +	const struct iommu_ops *ops;
>   	struct iommu_group *group;
>   	int ret;
>   
>   	if (!dev_iommu_get(dev))
>   		return -ENOMEM;
>   
> -	if (!try_module_get(ops->owner)) {
> -		ret = -EINVAL;
> -		goto err_free;
> -	}
> -
> -	iommu_dev = ops->probe_device(dev);
> +	iommu_dev = iommu_probe_device_ops(dev);
>   	if (IS_ERR(iommu_dev)) {
>   		ret = PTR_ERR(iommu_dev);
> -		goto err_module_put;
> +		goto err_free;
>   	}
>   	dev->iommu->iommu_dev = iommu_dev;
> +	ops = dev_iommu_ops(dev);
>   
>   	ret = iommu_device_link(iommu_dev, dev);
>   	if (ret)
> @@ -444,7 +483,6 @@ static int iommu_init_device(struct device *dev, const struct iommu_ops *ops)
>   err_release:
>   	if (ops->release_device)
>   		ops->release_device(dev);
> -err_module_put:
>   	module_put(ops->owner);
>   err_free:
>   	dev->iommu->iommu_dev = NULL;
> @@ -499,28 +537,10 @@ DEFINE_MUTEX(iommu_probe_device_lock);
>   
>   static int __iommu_probe_device(struct device *dev, struct list_head *group_list)
>   {
> -	const struct iommu_ops *ops;
> -	struct iommu_fwspec *fwspec;
>   	struct iommu_group *group;
>   	struct group_device *gdev;
>   	int ret;
>   
> -	/*
> -	 * For FDT-based systems and ACPI IORT/VIOT, drivers register IOMMU
> -	 * instances with non-NULL fwnodes, and client devices should have been
> -	 * identified with a fwspec by this point. Otherwise, we can currently
> -	 * assume that only one of Intel, AMD, s390, PAMU or legacy SMMUv2 can
> -	 * be present, and that any of their registered instances has suitable
> -	 * ops for probing, and thus cheekily co-opt the same mechanism.
> -	 */
> -	fwspec = dev_iommu_fwspec_get(dev);
> -	if (fwspec && fwspec->ops)
> -		ops = fwspec->ops;
> -	else
> -		ops = iommu_ops_from_fwnode(NULL);
> -
> -	if (!ops)
> -		return -ENODEV;
>   	/*
>   	 * Serialise to avoid races between IOMMU drivers registering in
>   	 * parallel and/or the "replay" calls from ACPI/OF code via client
> @@ -534,7 +554,7 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list
>   	if (dev->iommu_group)
>   		return 0;
>   
> -	ret = iommu_init_device(dev, ops);
> +	ret = iommu_init_device(dev);
>   	if (ret)
>   		return ret;
>