linux-kernel - Re: [RFC 17/20] iommu/iommufd: Report iova range to userspace

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Message-ID: <YUtCYZI3oQcwKrUh@myrica>
Date:   Wed, 22 Sep 2021 15:49:05 +0100
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Liu Yi L <yi.l.liu@...el.com>
Cc:     alex.williamson@...hat.com, jgg@...dia.com, hch@....de,
        jasowang@...hat.com, joro@...tes.org, kevin.tian@...el.com,
        parav@...lanox.com, lkml@...ux.net, pbonzini@...hat.com,
        lushenming@...wei.com, eric.auger@...hat.com, corbet@....net,
        ashok.raj@...el.com, yi.l.liu@...ux.intel.com,
        jun.j.tian@...el.com, hao.wu@...el.com, dave.jiang@...el.com,
        jacob.jun.pan@...ux.intel.com, kwankhede@...dia.com,
        robin.murphy@....com, kvm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
        linux-kernel@...r.kernel.org, baolu.lu@...ux.intel.com,
        david@...son.dropbear.id.au, nicolinc@...dia.com
Subject: Re: [RFC 17/20] iommu/iommufd: Report iova range to userspace

On Sun, Sep 19, 2021 at 02:38:45PM +0800, Liu Yi L wrote:
> [HACK. will fix in v2]
> 
> IOVA range is critical info for userspace to manage DMA for an I/O address
> space. This patch reports the valid iova range info of a given device.
> 
> Due to aforementioned hack, this info comes from the hacked vfio type1
> driver. To follow the same format in vfio, we also introduce a cap chain
> format in IOMMU_DEVICE_GET_INFO to carry the iova range info.
[...]
> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> index 49731be71213..f408ad3c8ade 100644
> --- a/include/uapi/linux/iommu.h
> +++ b/include/uapi/linux/iommu.h
> @@ -68,6 +68,7 @@
>   *		   +---------------+------------+
>   *		   ...
>   * @addr_width:    the address width of supported I/O address spaces.
> + * @cap_offset:	   Offset within info struct of first cap
>   *
>   * Availability: after device is bound to iommufd
>   */
> @@ -77,9 +78,11 @@ struct iommu_device_info {
>  #define IOMMU_DEVICE_INFO_ENFORCE_SNOOP	(1 << 0) /* IOMMU enforced snoop */
>  #define IOMMU_DEVICE_INFO_PGSIZES	(1 << 1) /* supported page sizes */
>  #define IOMMU_DEVICE_INFO_ADDR_WIDTH	(1 << 2) /* addr_wdith field valid */
> +#define IOMMU_DEVICE_INFO_CAPS		(1 << 3) /* info supports cap chain */
>  	__u64	dev_cookie;
>  	__u64   pgsize_bitmap;
>  	__u32	addr_width;
> +	__u32   cap_offset;

We can also add vendor-specific page table and PASID table properties as
capabilities, otherwise we'll need giant unions in the iommu_device_info
struct. That made me wonder whether pgsize and addr_width should also be
separate capabilities for consistency, but this way might be good enough.
There won't be many more generic capabilities. I have "output address
width" and "PASID width", the rest is specific to Arm and SMMU table
formats.

Thanks,
Jean

>  };
>  
>  #define IOMMU_DEVICE_GET_INFO	_IO(IOMMU_TYPE, IOMMU_BASE + 1)
> -- 
> 2.25.1
>