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

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Message-ID: <aF2WoRtkhCMw4Nut@Asurada-Nvidia>
Date: Thu, 26 Jun 2025 11:51:13 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: <jgg@...dia.com>, <kevin.tian@...el.com>, <corbet@....net>,
	<will@...nel.org>
CC: <bagasdotme@...il.com>, <robin.murphy@....com>, <joro@...tes.org>,
	<thierry.reding@...il.com>, <vdumpa@...dia.com>, <jonathanh@...dia.com>,
	<shuah@...nel.org>, <jsnitsel@...hat.com>, <nathan@...nel.org>,
	<peterz@...radead.org>, <yi.l.liu@...el.com>, <mshavit@...gle.com>,
	<praan@...gle.com>, <zhangzekun11@...wei.com>, <iommu@...ts.linux.dev>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-tegra@...r.kernel.org>,
	<linux-kselftest@...r.kernel.org>, <patches@...ts.linux.dev>,
	<mochs@...dia.com>, <alok.a.tiwari@...cle.com>, <vasant.hegde@....com>,
	<dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>
Subject: Re: [PATCH v6 24/25] iommu/tegra241-cmdqv: Add user-space use support

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