Re: [PATCH RFC v5 2/6] iommu/arm-smmu-v3: Allocate streams individually

[Nicolin Chen]

On Tue, Oct 06, 2026 at 08:19:08PM +0800, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@xxxxxxx>
> 
> Change master->streams from an embedded array of struct arm_smmu_stream
> to an array of pointers, with each stream individually allocated.
> 
> Prepare for shared-SID support where multiple masters will point to the
> same stream object. With embedded structs, sharing requires duplicating
> stream state and manually keeping fields like ste_installed in sync.
> With individually allocated streams, a sharing master can simply point to
> the existing stream.
> 
> The sort comparator is updated to dereference the pointer indirection.
> 
> No functional change.
> 
> Suggested-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Link: https://lore.kernel.org/linux-iommu/arG6hmng3NddGEHm@xxxxxxxxxx/
> Assisted-by: LLM
> Signed-off-by: Peng Fan <peng.fan@xxxxxxx>

Reviewed-by: Nicolin Chen <nicolinc@xxxxxxxxxx>

> diff --git a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
> index 6644075c1431e..bc62a3d5a63f9 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
> @@ -1257,7 +1257,7 @@ static int tegra241_vintf_init_vsid(struct iommufd_vdevice *vdev)
>  	struct arm_smmu_master *master = dev_iommu_priv_get(dev);
>  	struct tegra241_vintf *vintf = viommu_to_vintf(vdev->viommu);
>  	struct tegra241_vintf_sid *vsid = vdev_to_vsid(vdev);
> -	struct arm_smmu_stream *stream = &master->streams[0];
> +	struct arm_smmu_stream *stream = master->streams[0];

Sashiko raised a concern of an out-of-bounds pointer dereference.

Though it's practically not possible, probably it would be safer
to move this behind the check:

	if (master->num_streams != 1)
		return -EOPNOTSUPP;

Nicolin