Re: [PATCH 4/8] iommu/msm: Look up masters per IOMMU instance

[Dmitry Baryshkov]

On Tue, Apr 21, 2026 at 11:45:10AM +0200, Alexandre MINETTE via B4 Relay wrote:
> From: Alexandre MINETTE <contact@xxxxxxxxxxx>
> 
> MSM IOMMU stores context descriptors on each IOMMU instance. Looking up
> the descriptor through dev_iommu_priv_get() is not sufficient because a
> device can reference multiple IOMMU provider nodes.
> 
> Look up the master from the target IOMMU ctx_list instead, and use the
> same helper when probing and attaching devices. This avoids dereferencing
> a NULL master when an IOMMU already has context entries for another
> device, and keeps separate context descriptors for separate IOMMU
> instances.
> 
> This is required to boot APQ8064 boards using multiple IOMMU contexts.

Which cores / devices? Could you please add a (trimmed) backtrace? Also
a Fixes tag would be nice.

> 
> Signed-off-by: Alexandre MINETTE <contact@xxxxxxxxxxx>
> ---
>  drivers/iommu/msm_iommu.c | 28 ++++++++++++++++------------
>  1 file changed, 16 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/iommu/msm_iommu.c b/drivers/iommu/msm_iommu.c
> index 0ad5ff431d5b..9c03878d0d2c 100644
> --- a/drivers/iommu/msm_iommu.c
> +++ b/drivers/iommu/msm_iommu.c
> @@ -357,17 +357,25 @@ static int msm_iommu_domain_config(struct msm_priv *priv)
>  	return 0;
>  }
>  
> +static struct msm_iommu_ctx_dev *find_iommu_master(struct msm_iommu_dev *iommu,
> +						   struct device *dev)
> +{
> +	struct msm_iommu_ctx_dev *master;
> +
> +	list_for_each_entry(master, &iommu->ctx_list, list)
> +		if (master->of_node == dev->of_node)
> +			return master;
> +
> +	return NULL;
> +}
> +
>  /* Must be called under msm_iommu_lock */
>  static struct msm_iommu_dev *find_iommu_for_dev(struct device *dev)
>  {
>  	struct msm_iommu_dev *iommu, *ret = NULL;
> -	struct msm_iommu_ctx_dev *master;
>  
>  	list_for_each_entry(iommu, &qcom_iommu_devices, dev_node) {
> -		master = list_first_entry(&iommu->ctx_list,
> -					  struct msm_iommu_ctx_dev,
> -					  list);
> -		if (master->of_node == dev->of_node) {
> +		if (find_iommu_master(iommu, dev)) {
>  			ret = iommu;
>  			break;
>  		}
> @@ -405,10 +413,7 @@ static int msm_iommu_attach_dev(struct iommu_domain *domain, struct device *dev,
>  
>  	spin_lock_irqsave(&msm_iommu_lock, flags);
>  	list_for_each_entry(iommu, &qcom_iommu_devices, dev_node) {
> -		master = list_first_entry(&iommu->ctx_list,
> -					  struct msm_iommu_ctx_dev,
> -					  list);
> -		if (master->of_node == dev->of_node) {
> +		if (find_iommu_master(iommu, dev)) {
>  			ret = __enable_clocks(iommu);
>  			if (ret)
>  				goto fail;
> @@ -601,10 +606,10 @@ static int insert_iommu_master(struct device *dev,
>  				struct msm_iommu_dev **iommu,
>  				const struct of_phandle_args *spec)
>  {
> -	struct msm_iommu_ctx_dev *master = dev_iommu_priv_get(dev);
> +	struct msm_iommu_ctx_dev *master = find_iommu_master(*iommu, dev);
>  	int sid;
>  
> -	if (list_empty(&(*iommu)->ctx_list)) {
> +	if (!master) {
>  		master = kzalloc_obj(*master, GFP_ATOMIC);
>  		if (!master) {
>  			dev_err(dev, "Failed to allocate iommu_master\n");
> @@ -612,7 +617,6 @@ static int insert_iommu_master(struct device *dev,
>  		}
>  		master->of_node = dev->of_node;
>  		list_add(&master->list, &(*iommu)->ctx_list);
> -		dev_iommu_priv_set(dev, master);
>  	}
>  
>  	for (sid = 0; sid < master->num_mids; sid++)
> 
> -- 
> 2.43.0
> 
> 

-- 
With best wishes
Dmitry