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 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;

> > +	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.
 *
 * @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