Re: [PATCH v7 01/16] iommu: Report domain nesting info

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 10 Sep 2020 03:45:18 -0700
Liu Yi L <yi.l.liu@intel.com> wrote:

> IOMMUs that support nesting translation needs report the capability info
> to userspace. It gives information about requirements the userspace needs
> to implement plus other features characterizing the physical implementation.
> 
> This patch introduces a new IOMMU UAPI struct that gives information about
> the nesting capabilities and features. This struct is supposed to be returned
> by iommu_domain_get_attr() with DOMAIN_ATTR_NESTING attribute parameter, with
> one domain whose type has been set to DOMAIN_ATTR_NESTING.
> 
> Cc: Kevin Tian <kevin.tian@intel.com>
> CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
> v6 -> v7:
> *) rephrase the commit message, replace the @data[] field in struct
>    iommu_nesting_info with union per comments from Eric Auger.
> 
> v5 -> v6:
> *) rephrase the feature notes per comments from Eric Auger.
> *) rename @size of struct iommu_nesting_info to @argsz.
> 
> v4 -> v5:
> *) address comments from Eric Auger.
> 
> v3 -> v4:
> *) split the SMMU driver changes to be a separate patch
> *) move the @addr_width and @pasid_bits from vendor specific
>    part to generic part.
> *) tweak the description for the @features field of struct
>    iommu_nesting_info.
> *) add description on the @data[] field of struct iommu_nesting_info
> 
> v2 -> v3:
> *) remvoe cap/ecap_mask in iommu_nesting_info.
> *) reuse DOMAIN_ATTR_NESTING to get nesting info.
> *) return an empty iommu_nesting_info for SMMU drivers per Jean'
>    suggestion.
> ---
>  include/uapi/linux/iommu.h | 76 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 76 insertions(+)
> 
> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> index 1ebc23d..ff987e4 100644
> --- a/include/uapi/linux/iommu.h
> +++ b/include/uapi/linux/iommu.h
> @@ -341,4 +341,80 @@ struct iommu_gpasid_bind_data {
>  	} vendor;
>  };
>  
> +/*
> + * struct iommu_nesting_info_vtd - Intel VT-d specific nesting info.
> + *
> + * @flags:	VT-d specific flags. Currently reserved for future
> + *		extension. must be set to 0.
> + * @cap_reg:	Describe basic capabilities as defined in VT-d capability
> + *		register.
> + * @ecap_reg:	Describe the extended capabilities as defined in VT-d
> + *		extended capability register.
> + */
> +struct iommu_nesting_info_vtd {
> +	__u32	flags;
> +	__u64	cap_reg;
> +	__u64	ecap_reg;
> +};


The vendor union has 8-byte alignment, so flags here will be 8-byte
aligned, followed by a compiler dependent gap before the 8-byte fields.
We should fill that gap with padding to make it deterministic for
userspace.  Thanks,

Alex

> +
> +/*
> + * struct iommu_nesting_info - Information for nesting-capable IOMMU.
> + *			       userspace should check it before using
> + *			       nesting capability.
> + *
> + * @argsz:	size of the whole structure.
> + * @flags:	currently reserved for future extension. must set to 0.
> + * @format:	PASID table entry format, the same definition as struct
> + *		iommu_gpasid_bind_data @format.
> + * @features:	supported nesting features.
> + * @addr_width:	The output addr width of first level/stage translation
> + * @pasid_bits:	Maximum supported PASID bits, 0 represents no PASID
> + *		support.
> + * @vendor:	vendor specific data, structure type can be deduced from
> + *		@format field.
> + *
> + * +===============+======================================================+
> + * | feature       |  Notes                                               |
> + * +===============+======================================================+
> + * | SYSWIDE_PASID |  IOMMU vendor driver sets it to mandate userspace    |
> + * |               |  to allocate PASID from kernel. All PASID allocation |
> + * |               |  free must be mediated through the IOMMU UAPI.       |
> + * +---------------+------------------------------------------------------+
> + * | BIND_PGTBL    |  IOMMU vendor driver sets it to mandate userspace to |
> + * |               |  bind the first level/stage page table to associated |
> + * |               |  PASID (either the one specified in bind request or  |
> + * |               |  the default PASID of iommu domain), through IOMMU   |
> + * |               |  UAPI.                                               |
> + * +---------------+------------------------------------------------------+
> + * | CACHE_INVLD   |  IOMMU vendor driver sets it to mandate userspace to |
> + * |               |  explicitly invalidate the IOMMU cache through IOMMU |
> + * |               |  UAPI according to vendor-specific requirement when  |
> + * |               |  changing the 1st level/stage page table.            |
> + * +---------------+------------------------------------------------------+
> + *
> + * data struct types defined for @format:
> + * +================================+=====================================+
> + * | @format                        | data struct                         |
> + * +================================+=====================================+
> + * | IOMMU_PASID_FORMAT_INTEL_VTD   | struct iommu_nesting_info_vtd       |
> + * +--------------------------------+-------------------------------------+
> + *
> + */
> +struct iommu_nesting_info {
> +	__u32	argsz;
> +	__u32	flags;
> +	__u32	format;
> +#define IOMMU_NESTING_FEAT_SYSWIDE_PASID	(1 << 0)
> +#define IOMMU_NESTING_FEAT_BIND_PGTBL		(1 << 1)
> +#define IOMMU_NESTING_FEAT_CACHE_INVLD		(1 << 2)
> +	__u32	features;
> +	__u16	addr_width;
> +	__u16	pasid_bits;
> +	__u8	padding[12];
> +	/* Vendor specific data */
> +	union {
> +		struct iommu_nesting_info_vtd vtd;
> +	} vendor;
> +};
> +
>  #endif /* _UAPI_IOMMU_H */

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