Re: [PATCH v7 11/12] iommu: Consolidate per-device fault data management

[Jason Gunthorpe]

On Wed, Nov 15, 2023 at 11:02:25AM +0800, Lu Baolu wrote:

> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index d19031c1b0e6..c17d5979d70d 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -597,6 +597,8 @@ struct iommu_device {
>  /**
>   * struct iommu_fault_param - per-device IOMMU fault data
>   * @lock: protect pending faults list
> + * @users: user counter to manage the lifetime of the data, this field
> + *         is protected by dev->iommu->lock.
>   * @dev: the device that owns this param
>   * @queue: IOPF queue
>   * @queue_list: index into queue->devices
> @@ -606,6 +608,7 @@ struct iommu_device {
>   */
>  struct iommu_fault_param {
>  	struct mutex lock;
> +	int users;

Use refcount_t for the debugging features

>  	struct device *dev;
>  	struct iopf_queue *queue;

But why do we need this to be refcounted? iopf_queue_remove_device()
is always called before we get to release? This struct isn't very big
so I'd just leave it allocated and free it during release?

> @@ -72,23 +115,14 @@ static int iommu_handle_iopf(struct iommu_fault *fault, struct device *dev)
>  	struct iopf_group *group;
>  	struct iopf_fault *iopf, *next;
>  	struct iommu_domain *domain = NULL;
> -	struct iommu_fault_param *iopf_param;
> -	struct dev_iommu *param = dev->iommu;
> +	struct iommu_fault_param *iopf_param = dev->iommu->fault_param;
>  
> -	lockdep_assert_held(&param->lock);
> +	lockdep_assert_held(&iopf_param->lock);

This patch seems like it is doing a few things, can the locking
changes be kept in their own patch?

Jason