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

[Auger Eric <eric.auger@redhat.com>]

Hi Yi,

On 8/14/20 9:15 AM, Liu, Yi L wrote:
> Hi Eric,
> 
>> From: Auger Eric <eric.auger@redhat.com>
>> Sent: Thursday, August 13, 2020 8:53 PM
>>
>> 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.
> 
> got it. let me apply your suggestion. thanks. :-)
> 
>>>
>>> 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
> 
> got it.
> 
>>> + * +---------------+------------------------------------------------------+
>>> + * | BIND_PGTBL    |  IOMMU vendor driver sets it to mandate userspace    |
>>> + * |               |  bind the first level/stage page table to associated |
>> s/bind/to bind
> 
> got it.
> 
>>> + * |               |  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
> 
> I see.
> 
>>> + * |               |  U
>>> API 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.
> 
> nice catch. do you think it would be better to adding a union and
> put the struct iommu_nesting_info_vtd in it?
Yes I think so. At least it would be consistent with the rest of the API
and with the guidelines.
> 
>> 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?
> 
> this was talked one time between Jacob and me. It was put in this
> series as the major user of nesting_info is in this series. e.g.
> vfio checks the SYSWIDE_PASID. but I'm open to merge it with Jacob's
> series if it would make the merge easier.
Yep I think it would make sense to move in Jacob's series to have a
general understanding of the uapi

Thanks

Eric
> 
> Thanks,
> Yi Liu
> 
>>> +
>>> +/*
>>> + * 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
>>
>