Re: [PATCH v6 02/15] iommu: Report domain nesting info

Auger Eric
2020-08-13T12:53:03Z

Yi,
On 7/28/20 8:27 AM, Liu Yi L wrote:
> IOMMUs that support nesting translation needs report the capability info
s/needs/need to
> to userspace. It gives information about requirements the userspace needs
> to implement plus other features characterizing the physical implementation.
>
> This patch reports nesting info by DOMAIN_ATTR_NESTING. Caller can get
> nesting info after setting DOMAIN_ATTR_NESTING. For VFIO, it is after
> selecting VFIO_TYPE1_NESTING_IOMMU.
This is not what this patch does ;-) It 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,
one a 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>
> ---
> 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 | 74 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 74 insertions(+)
>
> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> index 7c8e075..5e4745a 100644
> --- a/include/uapi/linux/iommu.h
> +++ b/include/uapi/linux/iommu.h
> @@ -332,4 +332,78 @@ struct iommu_gpasid_bind_data {
> } vendor;
> };
>
> +/*
> + * 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.
> + * @data: vendor specific cap info. 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 TBD API. |
s/TBD/IOMMU
> + * +---------------+------------------------------------------------------+
> + * | BIND_PGTBL | IOMMU vendor driver sets it to mandate userspace |
> + * | | bind the first level/stage page table to associated |
s/bind/to bind
> + * | | 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 |

> + * | | explicitly invalidate the IOMMU cache through IOMMU |
to explicitly
> + * | | UAPI according to vendor-specific requirement when |
> + * | | changing the 1st level/stage page table. |
> + * +---------------+------------------------------------------------------+
> + *
> + * @data[] types defined for @format:
> + * +================================+=====================================+
> + * | @format | @data[] |
> + * +================================+=====================================+
> + * | 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;
> + __u32 padding;
> + __u8 data[];
> +};
As opposed to other IOMMU UAPI structs there is no union member at the
end. Also this struct is not documented in [PATCH v7 1/7] docs: IOMMU
user API. Shouldn't we align.

You may also consider to move this patch in Jacob's series for
consistency, thoughts?

> +
> +/*
> + * 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;
> + __u32 padding;
> + __u64 cap_reg;
> + __u64 ecap_reg;
> +};
> +
> #endif /* _UAPI_IOMMU_H */
>

Thanks

Eric