linux-kernel - Re: [PATCH 1/2] iommu: Report domain nesting info for arm-smmu-v3

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Message-ID: <28c0204d-2a5e-4eb9-d869-9dbd6edab55a@redhat.com>
Date:   Fri, 12 Feb 2021 19:13:22 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Vivek Gautam <vivek.gautam@....com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org,
        virtualization@...ts.linux-foundation.org
Cc:     joro@...tes.org, will.deacon@....com, mst@...hat.com,
        robin.murphy@....com, jean-philippe@...aro.org,
        alex.williamson@...hat.com, kevin.tian@...el.com,
        jacob.jun.pan@...ux.intel.com, yi.l.liu@...el.com,
        Lorenzo.Pieralisi@....com, shameerali.kolothum.thodi@...wei.com
Subject: Re: [PATCH 1/2] iommu: Report domain nesting info for arm-smmu-v3

Hi Vivek,
On 2/12/21 11:58 AM, Vivek Gautam wrote:
> Add a vendor specific structure for domain nesting info for
> arm smmu-v3, and necessary info fields required to populate
> stage1 page tables.
> 
> Signed-off-by: Vivek Gautam <vivek.gautam@....com>
> ---
>  include/uapi/linux/iommu.h | 31 +++++++++++++++++++++++++------
>  1 file changed, 25 insertions(+), 6 deletions(-)
> 
> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> index 4d3d988fa353..5f059bcf7720 100644
> --- a/include/uapi/linux/iommu.h
> +++ b/include/uapi/linux/iommu.h
> @@ -323,7 +323,8 @@ struct iommu_gpasid_bind_data {
>  #define IOMMU_GPASID_BIND_VERSION_1	1
>  	__u32 version;
>  #define IOMMU_PASID_FORMAT_INTEL_VTD	1
> -#define IOMMU_PASID_FORMAT_LAST		2
> +#define IOMMU_PASID_FORMAT_ARM_SMMU_V3	2
> +#define IOMMU_PASID_FORMAT_LAST		3
>  	__u32 format;
>  	__u32 addr_width;
>  #define IOMMU_SVA_GPASID_VAL	(1 << 0) /* guest PASID valid */
> @@ -409,6 +410,21 @@ struct iommu_nesting_info_vtd {
>  	__u64	ecap_reg;
>  };
>  
> +/*
> + * struct iommu_nesting_info_arm_smmuv3 - Arm SMMU-v3 nesting info.
> + */
> +struct iommu_nesting_info_arm_smmuv3 {
> +	__u32	flags;
> +	__u16	asid_bits;
> +
> +	/* Arm LPAE page table format as per kernel */
> +#define ARM_PGTBL_32_LPAE_S1		(0x0)
> +#define ARM_PGTBL_64_LPAE_S1		(0x2)
Shouldn't it be a bitfield instead as both can be supported (the actual
driver only supports 64b table format though). Does it match matches
IDR0.TTF?
> +	__u8	pgtbl_fmt;
So I understand this API is supposed to allow VFIO to expose those info
early enough to the userspace to help configuring the viommu and avoid
errors later on. I wonder how far we want to go on this path. What about
those other caps that impact the STE/CD validity. There may be others...

SMMU_IDR0.CD2L (support of 2 stage CD)
SMMU_IDR0.TTENDIAN (endianness)
SMMU_IDR0.HTTU (if 0 forbids HA/HD setting in the CD)
SMMU_IDR3.STT (impacts T0SZ)

Thanks

Eric

> +
> +	__u8	padding[9];
> +};
> +
>  /*
>   * struct iommu_nesting_info - Information for nesting-capable IOMMU.
>   *			       userspace should check it before using
> @@ -445,11 +461,13 @@ struct iommu_nesting_info_vtd {
>   * +---------------+------------------------------------------------------+
>   *
>   * data struct types defined for @format:
> - * +================================+=====================================+
> - * | @format                        | data struct                         |
> - * +================================+=====================================+
> - * | IOMMU_PASID_FORMAT_INTEL_VTD   | struct iommu_nesting_info_vtd       |
> - * +--------------------------------+-------------------------------------+
> + * +================================+======================================+
> + * | @format                        | data struct                          |
> + * +================================+======================================+
> + * | IOMMU_PASID_FORMAT_INTEL_VTD   | struct iommu_nesting_info_vtd        |
> + * +---------------+-------------------------------------------------------+
> + * | IOMMU_PASID_FORMAT_ARM_SMMU_V3 | struct iommu_nesting_info_arm_smmuv3 |
> + * +--------------------------------+--------------------------------------+
>   *
>   */
>  struct iommu_nesting_info {
> @@ -466,6 +484,7 @@ struct iommu_nesting_info {
>  	/* Vendor specific data */
>  	union {
>  		struct iommu_nesting_info_vtd vtd;
> +		struct iommu_nesting_info_arm_smmuv3 smmuv3;
>  	} vendor;
>  };
>  
>