linux-kernel - Re: [PATCH 08/12] iommufd/device: Report supported hwpt

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Date:   Fri, 10 Mar 2023 11:30:04 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Yi Liu <yi.l.liu@...el.com>, joro@...tes.org,
        alex.williamson@...hat.com, jgg@...dia.com, kevin.tian@...el.com,
        robin.murphy@....com
Cc:     baolu.lu@...ux.intel.com, cohuck@...hat.com, eric.auger@...hat.com,
        nicolinc@...dia.com, kvm@...r.kernel.org, mjrosato@...ux.ibm.com,
        chao.p.peng@...ux.intel.com, yi.y.sun@...ux.intel.com,
        peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 08/12] iommufd/device: Report supported hwpt_types

On 3/9/23 4:09 PM, Yi Liu wrote:
> This provides a way for userspace to probe the supported hwpt data
> types by kernel. Currently, kernel only supports IOMMU_HWPT_TYPE_DEFAULT,
> new types would be added per vendor drivers' extension.
> 
> Userspace that wants to allocate hw_pagetable with user data should check
> this. While for the allocation without user data, no need for it. It is
> supported by default.
> 
> Co-developed-by: Nicolin Chen <nicolinc@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> Signed-off-by: Yi Liu <yi.l.liu@...el.com>
> ---
>   drivers/iommu/iommufd/device.c          |  1 +
>   drivers/iommu/iommufd/hw_pagetable.c    | 18 +++++++++++++++---
>   drivers/iommu/iommufd/iommufd_private.h |  2 ++
>   drivers/iommu/iommufd/main.c            |  2 +-
>   include/uapi/linux/iommufd.h            |  8 ++++++++
>   5 files changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> index 19cd6df46c6a..0328071dcac1 100644
> --- a/drivers/iommu/iommufd/device.c
> +++ b/drivers/iommu/iommufd/device.c
> @@ -322,6 +322,7 @@ int iommufd_device_get_hw_info(struct iommufd_ucmd *ucmd)
>   
>   	cmd->out_data_type = ops->driver_type;
>   	cmd->data_len = length;
> +	cmd->out_hwpt_type_bitmap = iommufd_hwpt_type_bitmaps[ops->driver_type];
>   
>   	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
>   
> diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
> index 67facca98de1..160712256c64 100644
> --- a/drivers/iommu/iommufd/hw_pagetable.c
> +++ b/drivers/iommu/iommufd/hw_pagetable.c
> @@ -173,6 +173,14 @@ static const size_t iommufd_hwpt_alloc_data_size[] = {
>   	[IOMMU_HWPT_TYPE_DEFAULT] = 0,
>   };
>   
> +/*
> + * bitmaps of supported hwpt types of by underlying iommu, indexed
> + * by ops->driver_type which is one of enum iommu_hw_info_type.
> + */
> +const u64 iommufd_hwpt_type_bitmaps[] =  {
> +	[IOMMU_HW_INFO_TYPE_DEFAULT] = BIT_ULL(IOMMU_HWPT_TYPE_DEFAULT),
> +};

I am a bit confused here. Why do you need this array? What I read is
that you want to convert ops->driver_type to a bit position in
cmd->out_hwpt_type_bitmap.

Am I getting it right?

If so, why not just
	cmd->out_hwpt_type_bitmap = BIT_ULL(ops->driver_type);

?	

Best regards,
baolu