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From: "Tian, Kevin" <kevin.tian@intel.com>
To: Nicolin Chen <nicolinc@nvidia.com>, "will@kernel.org" <will@kernel.org>,
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Subject: RE: [PATCH RFCv1 12/14] iommufd: Add IOMMUFD_OBJ_VQUEUE and
 IOMMUFD_CMD_VQUEUE_ALLOC
Thread-Topic: [PATCH RFCv1 12/14] iommufd: Add IOMMUFD_OBJ_VQUEUE and
 IOMMUFD_CMD_VQUEUE_ALLOC
Thread-Index: AQHajVVtTIyOrzFsYEOvw2C4tndA2rGkop0Q
Date: Thu, 23 May 2024 07:05:28 +0000
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References: <cover.1712978212.git.nicolinc@nvidia.com>
 <b0ee53af3f59602834e67ddf86c748ca304da175.1712978213.git.nicolinc@nvidia.com>
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> From: Nicolin Chen <nicolinc@nvidia.com>
> Sent: Saturday, April 13, 2024 11:47 AM
> +
> +/**
> + * struct iommu_vqueue_tegra241_cmdqv - NVIDIA Tegra241's Virtual
> Command Queue
> + *                                      for its CMDQV Extension for ARM =
SMMUv3
> + *                                      (IOMMU_VQUEUE_DATA_TEGRA241_CMDQ=
V)
> + * @vcmdq_id: logical ID of a virtual command queue in the VIOMMU
> instance
> + * @vcmdq_log2size: (1 << @vcmdq_log2size) will be the size of the vcmdq
> + * @vcmdq_base: guest physical address (IPA) to the vcmdq base address
> + */
> +struct iommu_vqueue_tegra241_cmdqv {
> +	__u32 vcmdq_id;
> +	__u32 vcmdq_log2size;
> +	__aligned_u64 vcmdq_base;
> +};

Is there restriction that log2size cannot exceed 12?

According to patch14:

+	q_base =3D arm_smmu_domain_ipa_to_pa(vintf->s2_domain, arg.vcmdq_base);
+	vcmdq->cmdq.q.q_base  =3D q_base & VCMDQ_ADDR;
+	vcmdq->cmdq.q.q_base |=3D	arg.vcmdq_log2size;

It only converts the IPA to HPA for the starting page, assuming
continuous host pages backing a guest cmd queue including
multiple pages. but what guarantees it?