linux-kernel - RE: [PATCH v3 01/10] iommufd: Add data structure for Intel VT-d stage-1 domain allocation

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Message-ID: <BN9PR11MB5276D9CBCBBDE2F6DCB4D1998C419@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 24 May 2023 06:59:55 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
CC:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
Subject: RE: [PATCH v3 01/10] iommufd: Add data structure for Intel VT-d
 stage-1 domain allocation

> From: Liu, Yi L <yi.l.liu@...el.com>
> Sent: Thursday, May 11, 2023 10:51 PM
>
> @@ -353,9 +353,64 @@ struct iommu_vfio_ioas {
>  /**
>   * enum iommu_hwpt_type - IOMMU HWPT Type
>   * @IOMMU_HWPT_TYPE_DEFAULT: default
> + * @IOMMU_HWPT_TYPE_VTD_S1: Intel VT-d stage-1 page table
>   */
>  enum iommu_hwpt_type {
>  	IOMMU_HWPT_TYPE_DEFAULT,
> +	IOMMU_HWPT_TYPE_VTD_S1,
> +};
> +
> +/**
> + * enum iommu_hwpt_intel_vtd_flags - Intel VT-d stage-1 page
> + *				     table entry attributes

No need to have both 'intel' and 'vtd' in one name. There won't
be another vtd. 😊

Also since it's for s1, let's be specific on the naming:

enum iommu_hwpt_vtd_s1_flags

> + * @IOMMU_VTD_PGTBL_SRE: Supervisor request
> + * @IOMMU_VTD_PGTBL_EAFE: Extended access enable
> + * @IOMMU_VTD_PGTBL_PCD: Page-level cache disable
> + * @IOMMU_VTD_PGTBL_PWT: Page-level write through
> + * @IOMMU_VTD_PGTBL_EMTE: Extended mem type enable
> + * @IOMMU_VTD_PGTBL_CD: PASID-level cache disable
> + * @IOMMU_VTD_PGTBL_WPE: Write protect enable

similarly above should be IOMMU_VTD_S1_SRE.

PGTBL can be skipped.

> + */
> +enum iommu_hwpt_intel_vtd_flags {
> +	IOMMU_VTD_PGTBL_SRE = 1 << 0,
> +	IOMMU_VTD_PGTBL_EAFE = 1 << 1,
> +	IOMMU_VTD_PGTBL_PCD = 1 << 2,
> +	IOMMU_VTD_PGTBL_PWT = 1 << 3,
> +	IOMMU_VTD_PGTBL_EMTE = 1 << 4,
> +	IOMMU_VTD_PGTBL_CD = 1 << 5,
> +	IOMMU_VTD_PGTBL_WPE = 1 << 6,
> +	IOMMU_VTD_PGTBL_LAST = 1 << 7,
> +};
> +
> +/**
> + * struct iommu_hwpt_intel_vtd - Intel VT-d specific user-managed
> + *                               stage-1 page table info

struct iommu_hwpt_vtd_s1

> + * @flags: Combination of enum iommu_hwpt_intel_vtd_flags
> + * @pgtbl_addr: The base address of the user-managed stage-1 page table.

no need to highlight 'user-managed' in every reference to stage-1

> + * @pat: Page attribute table data to compute effective memory type
> + * @emt: Extended memory type
> + * @addr_width: The address width of the untranslated addresses that are
> + *              subjected to the user-managed stage-1 page table.

"The address width of the stage-1 page table"

> + * @__reserved: Must be 0
> + *
> + * The Intel VT-d specific data for creating hw_pagetable to represent
> + * the user-managed stage-1 page table that is used in nested translation.

"VT-d specific data for creating a stage-1 page table that ..."

> + *
> + * In nested translation, the stage-1 page table locates in the address
> + * space that defined by the corresponding stage-2 page table. Hence the

"locates in the address space of the specified stage-2 page table"

> + * stage-1 page table base address value should not be higher than the
> + * maximum untranslated address of stage-2 page table.

"should not exceed the maximum allowed input address of stage-2"

> + *
> + * The paging level of the stage-1 page table should be compatible with
> + * the hardware iommu. Otherwise, the allocation would be failed.

there is no information about paging level in this structure

> + */
> +struct iommu_hwpt_intel_vtd {
> +	__u64 flags;
> +	__u64 pgtbl_addr;
> +	__u32 pat;
> +	__u32 emt;
> +	__u32 addr_width;
> +	__u32 __reserved;
>  };
> 

I'd prefer to move vendor specific definitions before 'enum iommu_hwpt_type'
so any new added type can be easily correlated between the type enumeration
and following change in the comment of 'struct iommu_hwpt_alloc'

>  /**
> @@ -391,6 +446,8 @@ enum iommu_hwpt_type {
>   * +------------------------------+-------------------------------------+-----------+
>   * | IOMMU_HWPT_TYPE_DEFAULT      |               N/A                   |    IOAS   |
>   * +------------------------------+-------------------------------------+-----------+
> + * | IOMMU_HWPT_TYPE_VTD_S1       |      struct iommu_hwpt_intel_vtd    |
> HWPT   |
> + * +------------------------------+-------------------------------------+-----------+
>   */
>  struct iommu_hwpt_alloc {
>  	__u32 size;
> --
> 2.34.1