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

[Liu, Yi L]

Hi Eric,

> From: Auger Eric <eric.auger@xxxxxxxxxx>
> 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@xxxxxxxxx>
> > CC: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > Cc: Eric Auger <eric.auger@xxxxxxxxxx>
> > Cc: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > Cc: Joerg Roedel <joro@xxxxxxxxxx>
> > Cc: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > ---
> > 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?

> 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.

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
>