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

[Liu, Yi L]

Hi Jean,

> From: Jean-Philippe Brucker < jean-philippe@xxxxxxxxxx>
> Sent: Wednesday, June 17, 2020 10:39 PM
> 
> [+ Will and Robin]
> 
> Hi Yi,
> 
> On Thu, Jun 11, 2020 at 05:15:21AM -0700, Liu Yi L 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?
> 
> Sure, I think we could rework the getters for DOMAIN_ATTR_NESTING since they
> aren't used, but we do need to keep the setters as is.
> 
> Before attaching a domain, VFIO sets DOMAIN_ATTR_NESTING if userspace
> requested a VFIO_TYPE1_NESTING_IOMMU container. This is necessary for the
> SMMU driver to know how to attach later, but at that point we don't know whether
> the SMMU does support nesting (since the domain isn't attached to any endpoint).
> During attach, the SMMU driver adapts to the SMMU's capabilities, and may well
> fallback to one stage if the SMMU doesn't support nesting.

got you. so even VFIO sets DOMAIN_ATTR_NESTING successfully, it doesn't mean
the nesting will be used. yeah, it's a little bit different with VT-d side. intel iommu
driver will fail ATT_NESTING setting if it found not all iommu units in the system
are nesting capable.

> VFIO should check after attaching that the nesting attribute held, by calling
> iommu_domain_get_attr(NESTING). At the moment it does not, and since your
> 03/15 patch does that with additional info, I agree with reusing
> DOMAIN_ATTR_NESTING instead of adding DOMAIN_ATTR_NESTING_INFO.
>
> However it requires changing the get_attr(NESTING) implementations in both SMMU
> drivers as a precursor of this series, to avoid breaking
> VFIO_TYPE1_NESTING_IOMMU on Arm. Since we haven't yet defined the
> nesting_info structs for SMMUv2 and v3, I suppose we could return an empty struct
> iommu_nesting_info for now?

got you. I think it works. So far, I didn't see any getter for ATTR_NESTING, once
SMMU drivers return empty struct iommu_nesting_info, VFIO won't fail. will
do it when switching to reuse ATTR_NESTING for getting nesting info.

> >
> >  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;
> 
> What goes into format? And flags? This structure needs some documentation.

format will be the same with the definition of @format in iommu_gpasid_bind_data.
flags is reserved for future extension. will add description in next version. :-)

struct iommu_gpasid_bind_data {
        __u32 argsz;
#define IOMMU_GPASID_BIND_VERSION_1     1
        __u32 version;
#define IOMMU_PASID_FORMAT_INTEL_VTD    1
        __u32 format;
#define IOMMU_SVA_GPASID_VAL    (1 << 0) /* guest PASID valid */
        __u64 flags;
        __u64 gpgd;
        __u64 hpasid;
        __u64 gpasid;
        __u32 addr_width;
        __u8  padding[12];
        /* Vendor specific data */
        union {
                struct iommu_gpasid_bind_data_vtd vtd;
        } vendor;
};

Regards,
Yi Liu

> Thanks,
> Jean
> 
> > +	__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.
> > + */
> > +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 */
> > --
> > 2.7.4
> >