[PATCH v6 24/25] iommu/tegra241-cmdqv: Add user-space use support

[Nicolin Chen]

On Sat, Jun 14, 2025 at 12:14:49AM -0700, Nicolin Chen wrote:

I made some small changes:

>  /**
>   * struct tegra241_vintf - Virtual Interface
> + * @vsmmu: Embedded arm_vsmmu structure
>   * @idx: Global index in the CMDQV
>   * @enabled: Enable status
>   * @hyp_own: Owned by hypervisor (in-kernel)
>   * @cmdqv: Parent CMDQV pointer
>   * @lvcmdqs: List of logical VCMDQ pointers

Added:
+ * @lvcmdq_mutex: Lock to serialize user-allocated lvcmdq

for the following change:

> @@ -154,19 +172,41 @@ struct tegra241_vintf {
>  
>  	struct tegra241_cmdqv *cmdqv;
>  	struct tegra241_vcmdq **lvcmdqs;
> +	struct mutex lvcmdq_mutex; /* user space race */
[...]

> +static void
> +tegra241_vintf_destroy_lvcmdq_user(struct iommufd_hw_queue *hw_queue)
> +{
> +	struct tegra241_vcmdq *vcmdq = hw_queue_to_vcmdq(hw_queue);
> +
> +	tegra241_vcmdq_hw_deinit(vcmdq);
> +	tegra241_vcmdq_unmap_lvcmdq(vcmdq);
> +	tegra241_vintf_free_lvcmdq(vcmdq->vintf, vcmdq->lidx);
> +	if (vcmdq->prev)
> +		iommufd_hw_queue_undepend(vcmdq, vcmdq->prev, core);

Added mutex to pair with tegra241_vintf_alloc_lvcmdq_user():

mutex_lock(&vcmdq->vintf->lvcmdq_mutex);
...
mutex_unlock(&vcmdq->vintf->lvcmdq_mutex);

> +	/*
> +	 * Initialize the user-owned VINTF without a LVCMDQ, because it has to
> +	 * wait for the allocation of a user-owned LVCMDQ, for security reason.
> +	 * It is different than the kernel-owned VINTF0, which had pre-assigned
> +	 * and pre-allocated global VCMDQs that would be mapped to the LVCMDQs
> +	 * by the tegra241_vintf_hw_init() call.
> +	 */
> +	ret = tegra241_vintf_hw_init(vintf, false);

Revised a bit:
+	/*                                                                                                                                                                              
+	 * Initialize the user-owned VINTF without a LVCMDQ, as it cannot pre-                                                                                                          
+	 * allocate a LVCMDQ until user space wants one, for security reasons.                                                                                                          
[...]

Thanks
Nicolin