Re: [PATCH v2 06/17] iommu: Add iommu_fwspec_alloc/dealloc()

[Hector Martin <marcan@marcan.st>]

On 2023/11/15 23:05, Jason Gunthorpe wrote:
> Allow fwspec to exist independently from the dev->iommu by providing
> functions to allow allocating and freeing the raw struct iommu_fwspec.
> 
> Reflow the existing paths to call the new alloc/dealloc functions.
> 
> Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  drivers/iommu/iommu.c | 82 ++++++++++++++++++++++++++++++++-----------
>  include/linux/iommu.h | 11 +++++-
>  2 files changed, 72 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 18a82a20934d53..86bbb9e75c7e03 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -361,10 +361,8 @@ static void dev_iommu_free(struct device *dev)
>  	struct dev_iommu *param = dev->iommu;
>  
>  	dev->iommu = NULL;
> -	if (param->fwspec) {
> -		fwnode_handle_put(param->fwspec->iommu_fwnode);
> -		kfree(param->fwspec);
> -	}
> +	if (param->fwspec)
> +		iommu_fwspec_dealloc(param->fwspec);
>  	kfree(param);
>  }
>  
> @@ -2920,10 +2918,61 @@ const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
>  	return ops;
>  }
>  
> +static int iommu_fwspec_assign_iommu(struct iommu_fwspec *fwspec,
> +				     struct device *dev,
> +				     struct fwnode_handle *iommu_fwnode)
> +{
> +	const struct iommu_ops *ops;
> +
> +	if (fwspec->iommu_fwnode) {
> +		/*
> +		 * fwspec->iommu_fwnode is the first iommu's fwnode. In the rare
> +		 * case of multiple iommus for one device they must point to the
> +		 * same driver, checked via same ops.
> +		 */
> +		ops = iommu_ops_from_fwnode(iommu_fwnode);

This carries over a related bug from the original code: If a device has
two IOMMUs and the first one probes but the second one defers, ops will
be NULL here and the check will fail with EINVAL.

Adding a check for that case here fixes it:

		if (!ops)
			return driver_deferred_probe_check_state(dev);

With that, for the whole series:

Tested-by: Hector Martin <marcan@marcan.st>

I can't specifically test for the probe races the series intends to fix
though, since that bug we only hit extremely rarely. I'm just testing
that nothing breaks.

> +		if (fwspec->ops != ops)
> +			return -EINVAL;
> +		return 0;
> +	}
> +
> +	if (!fwspec->ops) {
> +		ops = iommu_ops_from_fwnode(iommu_fwnode);
> +		if (!ops)
> +			return driver_deferred_probe_check_state(dev);
> +		fwspec->ops = ops;
> +	}
> +
> +	of_node_get(to_of_node(iommu_fwnode));
> +	fwspec->iommu_fwnode = iommu_fwnode;
> +	return 0;
> +}
> +
> +struct iommu_fwspec *iommu_fwspec_alloc(void)
> +{
> +	struct iommu_fwspec *fwspec;
> +
> +	fwspec = kzalloc(sizeof(*fwspec), GFP_KERNEL);
> +	if (!fwspec)
> +		return ERR_PTR(-ENOMEM);
> +	return fwspec;
> +}
> +
> +void iommu_fwspec_dealloc(struct iommu_fwspec *fwspec)
> +{
> +	if (!fwspec)
> +		return;
> +
> +	if (fwspec->iommu_fwnode)
> +		fwnode_handle_put(fwspec->iommu_fwnode);
> +	kfree(fwspec);
> +}
> +
>  int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
>  		      const struct iommu_ops *ops)
>  {
>  	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> +	int ret;
>  
>  	if (fwspec)
>  		return ops == fwspec->ops ? 0 : -EINVAL;
> @@ -2931,29 +2980,22 @@ int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
>  	if (!dev_iommu_get(dev))
>  		return -ENOMEM;
>  
> -	fwspec = kzalloc(sizeof(*fwspec), GFP_KERNEL);
> -	if (!fwspec)
> -		return -ENOMEM;
> +	fwspec = iommu_fwspec_alloc();
> +	if (IS_ERR(fwspec))
> +		return PTR_ERR(fwspec);
>  
> -	of_node_get(to_of_node(iommu_fwnode));
> -	fwspec->iommu_fwnode = iommu_fwnode;
>  	fwspec->ops = ops;
> +	ret = iommu_fwspec_assign_iommu(fwspec, dev, iommu_fwnode);
> +	if (ret) {
> +		iommu_fwspec_dealloc(fwspec);
> +		return ret;
> +	}
> +
>  	dev_iommu_fwspec_set(dev, fwspec);
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(iommu_fwspec_init);
>  
> -void iommu_fwspec_free(struct device *dev)
> -{
> -	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> -
> -	if (fwspec) {
> -		fwnode_handle_put(fwspec->iommu_fwnode);
> -		kfree(fwspec);
> -		dev_iommu_fwspec_set(dev, NULL);
> -	}
> -}
> -EXPORT_SYMBOL_GPL(iommu_fwspec_free);
>  
>  int iommu_fwspec_add_ids(struct device *dev, u32 *ids, int num_ids)
>  {
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index e98a4ca8f536b7..c7c68cb59aa4dc 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -813,9 +813,18 @@ struct iommu_sva {
>  	struct iommu_domain		*domain;
>  };
>  
> +struct iommu_fwspec *iommu_fwspec_alloc(void);
> +void iommu_fwspec_dealloc(struct iommu_fwspec *fwspec);
> +
>  int iommu_fwspec_init(struct device *dev, struct fwnode_handle *iommu_fwnode,
>  		      const struct iommu_ops *ops);
> -void iommu_fwspec_free(struct device *dev);
> +static inline void iommu_fwspec_free(struct device *dev)
> +{
> +	if (!dev->iommu)
> +		return;
> +	iommu_fwspec_dealloc(dev->iommu->fwspec);
> +	dev->iommu->fwspec = NULL;
> +}
>  int iommu_fwspec_add_ids(struct device *dev, u32 *ids, int num_ids);
>  const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode);
>  

- Hector