RE: [PATCH v4 04/15] vfio/type1: Report iommu nesting info to userspace

["Liu, Yi L" <yi.l.liu@intel.com>]

Hi Eric,

> From: Auger Eric < eric.auger@redhat.com >
> Sent: Monday, July 6, 2020 9:45 PM
> 
> Hi Yi,
> 
> On 7/6/20 3:10 PM, Liu, Yi L wrote:
> > Hi Eric,
> >
> >> From: Auger Eric <eric.auger@redhat.com>
> >> Sent: Monday, July 6, 2020 6:37 PM
> >>
> >> Yi,
> >>
> >> On 7/4/20 1:26 PM, Liu Yi L wrote:
> >>> This patch exports iommu nesting capability info to user space through
> >>> VFIO. User space is expected to check this info for supported uAPIs (e.g.
> >>> PASID alloc/free, bind page table, and cache invalidation) and the vendor
> >>> specific format information for first level/stage page table that will be
> >>> bound to.
> >>>
> >>> The nesting info is available only after the nesting iommu type is set
> >>> for a container. Current implementation imposes one limitation - one
> >>> nesting container should include at most one group. The philosophy of
> >>> vfio container is having all groups/devices within the container share
> >>> the same IOMMU context. When vSVA is enabled, one IOMMU context could
> >>> include one 2nd-level address space and multiple 1st-level address spaces.
> >>> While the 2nd-leve address space is reasonably sharable by multiple groups
> >> level
> >
> > oh, yes.
> >
> >>> , blindly sharing 1st-level address spaces across all groups within the
> >>> container might instead break the guest expectation. In the future sub/
> >>> super container concept might be introduced to allow partial address space
> >>> sharing within an IOMMU context. But for now let's go with this restriction
> >>> by requiring singleton container for using nesting iommu features. Below
> >>> link has the related discussion about this decision.
> >>>
> >>> https://lkml.org/lkml/2020/5/15/1028
> >>>
> >>> 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>
> >>> ---
> >>> v3 -> v4:
> >>> *) address comments against v3.
> >>>
> >>> v1 -> v2:
> >>> *) added in v2
> >>> ---
> >>>
> >>>  drivers/vfio/vfio_iommu_type1.c | 105
> >> +++++++++++++++++++++++++++++++++++-----
> >>>  include/uapi/linux/vfio.h       |  16 ++++++
> >>>  2 files changed, 109 insertions(+), 12 deletions(-)
> >>>
> >>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> >>> index 7accb59..80623b8 100644
> >>> --- a/drivers/vfio/vfio_iommu_type1.c
> >>> +++ b/drivers/vfio/vfio_iommu_type1.c
> >>> @@ -62,18 +62,20 @@ MODULE_PARM_DESC(dma_entry_limit,
> >>>  		 "Maximum number of user DMA mappings per container (65535).");
> >>>
> >>>  struct vfio_iommu {
> >>> -	struct list_head	domain_list;
> >>> -	struct list_head	iova_list;
> >>> -	struct vfio_domain	*external_domain; /* domain for external user */
> >>> -	struct mutex		lock;
> >>> -	struct rb_root		dma_list;
> >>> -	struct blocking_notifier_head notifier;
> >>> -	unsigned int		dma_avail;
> >>> -	uint64_t		pgsize_bitmap;
> >>> -	bool			v2;
> >>> -	bool			nesting;
> >>> -	bool			dirty_page_tracking;
> >>> -	bool			pinned_page_dirty_scope;
> >>> +	struct list_head		domain_list;
> >>> +	struct list_head		iova_list;
> >>> +	struct vfio_domain		*external_domain; /* domain for
> >>> +							     external user */
> >> nit: put the comment before the field?
> >
> > do you mean below?
> >
> > +	/* domain for external user */
> > +	struct vfio_domain		*external_domain;
> yes that's what I meant

got you. :-)

> >
> >>> +	struct mutex			lock;
> >>> +	struct rb_root			dma_list;
> >>> +	struct blocking_notifier_head	notifier;
> >>> +	unsigned int			dma_avail;
> >>> +	uint64_t			pgsize_bitmap;
> >>> +	bool				v2;
> >>> +	bool				nesting;
> >>> +	bool				dirty_page_tracking;
> >>> +	bool				pinned_page_dirty_scope;
> >>> +	struct iommu_nesting_info	*nesting_info;
> >>>  };
> >>>
> >>>  struct vfio_domain {
> >>> @@ -130,6 +132,9 @@ struct vfio_regions {
> >>>  #define IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)	\
> >>>  					(!list_empty(&iommu->domain_list))
> >>>
> >>> +#define IS_DOMAIN_IN_CONTAINER(iommu)	((iommu-
> >external_domain) || \
> >>> +					 (!list_empty(&iommu->domain_list)))
> >> rename into something like CONTAINER_HAS_DOMAIN()?
> >
> > got it.
> >
> >>> +
> >>>  #define DIRTY_BITMAP_BYTES(n)	(ALIGN(n, BITS_PER_TYPE(u64)) /
> >> BITS_PER_BYTE)
> >>>
> >>>  /*
> >>> @@ -1929,6 +1934,13 @@ static void vfio_iommu_iova_insert_copy(struct
> >> vfio_iommu *iommu,
> >>>
> >>>  	list_splice_tail(iova_copy, iova);
> >>>  }
> >>> +
> >>> +static void vfio_iommu_release_nesting_info(struct vfio_iommu *iommu)
> >>> +{
> >>> +	kfree(iommu->nesting_info);
> >>> +	iommu->nesting_info = NULL;
> >>> +}
> >>> +
> >>>  static int vfio_iommu_type1_attach_group(void *iommu_data,
> >>>  					 struct iommu_group *iommu_group)
> >>>  {
> >>> @@ -1959,6 +1971,12 @@ static int vfio_iommu_type1_attach_group(void
> >> *iommu_data,
> >>>  		}
> >>>  	}
> >>>
> >>> +	/* Nesting type container can include only one group */
> >>> +	if (iommu->nesting && IS_DOMAIN_IN_CONTAINER(iommu)) {
> >>> +		mutex_unlock(&iommu->lock);
> >>> +		return -EINVAL;
> >>> +	}
> >>> +
> >>>  	group = kzalloc(sizeof(*group), GFP_KERNEL);
> >>>  	domain = kzalloc(sizeof(*domain), GFP_KERNEL);
> >>>  	if (!group || !domain) {
> >>> @@ -2029,6 +2047,36 @@ static int vfio_iommu_type1_attach_group(void
> >> *iommu_data,
> >>>  	if (ret)
> >>>  		goto out_domain;
> >>>
> >>> +	/* Nesting cap info is available only after attaching */
> >>> +	if (iommu->nesting) {
> >>> +		struct iommu_nesting_info tmp;
> >>> +		struct iommu_nesting_info *info;
> >>> +
> >>> +		/* First get the size of vendor specific nesting info */
> >>> +		ret = iommu_domain_get_attr(domain->domain,
> >>> +					    DOMAIN_ATTR_NESTING,
> >>> +					    &tmp);
> >>> +		if (ret)
> >>> +			goto out_detach;
> >>> +
> >>> +		info = kzalloc(tmp.size, GFP_KERNEL);
> >> nit: you may directly use iommu->nesting_info
> >
> > got you.
> >
> >>> +		if (!info) {
> >>> +			ret = -ENOMEM;
> >>> +			goto out_detach;
> >>> +		}
> >>> +
> >>> +		/* Now get the nesting info */
> >>> +		info->size = tmp.size;
> >>> +		ret = iommu_domain_get_attr(domain->domain,
> >>> +					    DOMAIN_ATTR_NESTING,
> >>> +					    info);
> >>> +		if (ret) {
> >>> +			kfree(info);
> >> ... and set it back to NULL here if it fails
> >
> > and maybe no need to free it here as vfio_iommu_release_nesting_info()
> > will free the nesting_info.
> >
> >>> +			goto out_detach;
> >>> +		}
> >>> +		iommu->nesting_info = info;
> >>> +	}
> >>> +
> >>>  	/* Get aperture info */
> >>>  	iommu_domain_get_attr(domain->domain, DOMAIN_ATTR_GEOMETRY,
> >> &geo);
> >>>
> >>> @@ -2138,6 +2186,7 @@ static int vfio_iommu_type1_attach_group(void
> >> *iommu_data,
> >>>  	return 0;
> >>>
> >>>  out_detach:
> >>> +	vfio_iommu_release_nesting_info(iommu);
> >>>  	vfio_iommu_detach_group(domain, group);
> >>>  out_domain:
> >>>  	iommu_domain_free(domain->domain);
> >>> @@ -2338,6 +2387,8 @@ static void vfio_iommu_type1_detach_group(void
> >> *iommu_data,
> >>>  					vfio_iommu_unmap_unpin_all(iommu);
> >>>  				else
> >>>
> >> 	vfio_iommu_unmap_unpin_reaccount(iommu);
> >>> +
> >>> +				vfio_iommu_release_nesting_info(iommu);
> >>>  			}
> >>>  			iommu_domain_free(domain->domain);
> >>>  			list_del(&domain->next);
> >>> @@ -2546,6 +2597,30 @@ static int vfio_iommu_migration_build_caps(struct
> >> vfio_iommu *iommu,
> >>>  	return vfio_info_add_capability(caps, &cap_mig.header, sizeof(cap_mig));
> >>>  }
> >>>
> >>> +static int vfio_iommu_info_add_nesting_cap(struct vfio_iommu *iommu,
> >>> +					   struct vfio_info_cap *caps)
> >>> +{
> >>> +	struct vfio_info_cap_header *header;
> >>> +	struct vfio_iommu_type1_info_cap_nesting *nesting_cap;
> >>> +	size_t size;
> >>> +
> >>> +	size = sizeof(*nesting_cap) + iommu->nesting_info->size;
> >>> +
> >>> +	header = vfio_info_cap_add(caps, size,
> >>> +				   VFIO_IOMMU_TYPE1_INFO_CAP_NESTING, 1);
> >>> +	if (IS_ERR(header))
> >>> +		return PTR_ERR(header);
> >>> +
> >>> +	nesting_cap = container_of(header,
> >>> +				   struct vfio_iommu_type1_info_cap_nesting,
> >>> +				   header);
> >>> +
> >>> +	memcpy(&nesting_cap->info, iommu->nesting_info,
> >>> +	       iommu->nesting_info->size);
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>>  static int vfio_iommu_type1_get_info(struct vfio_iommu *iommu,
> >>>  				     unsigned long arg)
> >>>  {
> >>> @@ -2586,6 +2661,12 @@ static int vfio_iommu_type1_get_info(struct
> >> vfio_iommu *iommu,
> >>>  	if (ret)
> >>>  		return ret;
> >>>
> >>> +	if (iommu->nesting_info) {
> >>> +		ret = vfio_iommu_info_add_nesting_cap(iommu, &caps);
> >>> +		if (ret)
> >>> +			return ret;
> >>> +	}
> >>> +
> >>>  	if (caps.size) {
> >>>  		info.flags |= VFIO_IOMMU_INFO_CAPS;
> >>>
> >>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> >>> index 9204705..3e3de9c 100644
> >>> --- a/include/uapi/linux/vfio.h
> >>> +++ b/include/uapi/linux/vfio.h
> >>> @@ -1039,6 +1039,22 @@ struct vfio_iommu_type1_info_cap_migration {
> >>>  	__u64	max_dirty_bitmap_size;		/* in bytes */
> >>>  };
> >>>
> >>> +#define VFIO_IOMMU_TYPE1_INFO_CAP_NESTING  3
> >>
> >> You may improve the documentation by taking examples from the above caps.
> >
> > yes, it is. I somehow broke the style. how about below?
> >
> >
> >
> > /*
> >  * The nesting capability allows to report the related capability
> >  * and info for nesting iommu type.
> >  *
> >  * The structures below define version 1 of this capability.
> >  *
> >  * User space should check this cap for setup nesting iommu type.
> before setting up stage 1 information? The wording above sounds a bit
> confusing to me as it can be interpreted as before choosing
> VFIO_TYPE1_NESTING_IOMMU.
> 

oh, yep. this cap is available only for nesting type iommu. a.ka.
VFIO_TYPE1_NESTING_IOMMU is selected.

> You also need to document it returns the capability only after a group
> is attached - which looks strange by the way -.

I think this should be aligned with VFIO_IOMMU_GET_INFO usage.
GET_INFO is meaningful after VFIO_SET_IOMMU, which includes
group attaching.

Regards,
Yi Liu

> Thanks
> 
> Eric
> >  *
> >  * @info:	the nesting info provided by IOMMU driver. Today
> >  *		it is expected to be a struct iommu_nesting_info
> >  *		data.
> > #define VFIO_IOMMU_TYPE1_INFO_CAP_NESTING  3
> >
> > struct vfio_iommu_type1_info_cap_nesting {
> > 	...
> > };
> >
> >>> +
> >>> +/*
> >>> + * Reporting nesting info to user space.
> >>> + *
> >>> + * @info:	the nesting info provided by IOMMU driver. Today
> >>> + *		it is expected to be a struct iommu_nesting_info
> >>> + *		data.
> >> Is it expected to change?
> >
> > honestly, I'm not quite sure on it. I did considered to embed
> > struct iommu_nesting_info here instead of using info[]. but I
> > hesitated as using info[] may leave more flexibility on this
> > struct. how about your opinion? perhaps it's fine to embed the
> > struct iommu_nesting_info here as long as VFIO is setup nesting
> > based on IOMMU UAPI.
> >
> >>> + */
> >>> +struct vfio_iommu_type1_info_cap_nesting {
> >>> +	struct	vfio_info_cap_header header;
> >>> +	__u32	flags;
> >> You may document flags.
> >
> > sure. it's reserved for future.
> >
> > Regards,
> > Yi Liu
> >
> >>> +	__u32	padding;
> >>> +	__u8	info[];
> >>> +};
> >>> +
> >>>  #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
> >>>
> >>>  /**
> >>>
> >> Thanks
> >>
> >> Eric
> >