RE: [PATCH v2 02/15] iommu: Report domain nesting info

[Liu, Yi L]

Hi Alex,

> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Sent: Friday, June 12, 2020 3:30 AM
> 
> On Thu, 11 Jun 2020 05:15:21 -0700
> Liu Yi L <yi.l.liu@xxxxxxxxx> wrote:
> 
> > IOMMUs that support nesting translation needs report the capability
> > info to userspace, e.g. the format of first level/stage paging structures.
> >
> > 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>
> > ---
> > @Jean, Eric: as nesting was introduced for ARM, but looks like no
> > actual user of it. right? So I'm wondering if we can reuse
> > DOMAIN_ATTR_NESTING to retrieve nesting info? how about your opinions?
> >
> >  include/linux/iommu.h      |  1 +
> >  include/uapi/linux/iommu.h | 34 ++++++++++++++++++++++++++++++++++
> >  2 files changed, 35 insertions(+)
> >
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h index
> > 78a26ae..f6e4b49 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -126,6 +126,7 @@ enum iommu_attr {
> >  	DOMAIN_ATTR_FSL_PAMUV1,
> >  	DOMAIN_ATTR_NESTING,	/* two stages of translation */
> >  	DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
> > +	DOMAIN_ATTR_NESTING_INFO,
> >  	DOMAIN_ATTR_MAX,
> >  };
> >
> > diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> > index 303f148..02eac73 100644
> > --- a/include/uapi/linux/iommu.h
> > +++ b/include/uapi/linux/iommu.h
> > @@ -332,4 +332,38 @@ struct iommu_gpasid_bind_data {
> >  	};
> >  };
> >
> > +struct iommu_nesting_info {
> > +	__u32	size;
> > +	__u32	format;
> > +	__u32	features;
> > +#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	flags;
> > +	__u8	data[];
> > +};
> > +
> > +/*
> > + * @flags:	VT-d specific flags. Currently reserved for future
> > + *		extension.
> > + * @addr_width:	The output addr width of first level/stage translation
> > + * @pasid_bits:	Maximum supported PASID bits, 0 represents no PASID
> > + *		support.
> > + * @cap_reg:	Describe basic capabilities as defined in VT-d capability
> > + *		register.
> > + * @cap_mask:	Mark valid capability bits in @cap_reg.
> > + * @ecap_reg:	Describe the extended capabilities as defined in VT-d
> > + *		extended capability register.
> > + * @ecap_mask:	Mark the valid capability bits in @ecap_reg.
> 
> Please explain this a little further, why do we need to tell userspace about
> cap/ecap register bits that aren't valid through this interface?
> Thanks,

we only want to tell userspace about the bits marked in the cap/ecap_mask.
cap/ecap_mask is kind of white-list of the cap/ecap register. userspace should
only care about the bits in the white-list, for other bits, it should ignore.

Regards,
Yi Liu

> Alex
> 
> 
> > + */
> > +struct iommu_nesting_info_vtd {
> > +	__u32	flags;
> > +	__u16	addr_width;
> > +	__u16	pasid_bits;
> > +	__u64	cap_reg;
> > +	__u64	cap_mask;
> > +	__u64	ecap_reg;
> > +	__u64	ecap_mask;
> > +};
> > +
> >  #endif /* _UAPI_IOMMU_H */