RE: [PATCH v3 03/14] vfio/type1: Report iommu nesting info to userspace

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

Hi Alex,

> From: Alex Williamson < alex.williamson@redhat.com >
> Sent: Friday, July 3, 2020 2:39 AM
> 
> On Wed, 24 Jun 2020 01:55:16 -0700
> Liu Yi L <yi.l.liu@intel.com> 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 , 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>
> > ---
> >  drivers/vfio/vfio_iommu_type1.c | 73
> +++++++++++++++++++++++++++++++++++++++++
> >  include/uapi/linux/vfio.h       |  9 +++++
> >  2 files changed, 82 insertions(+)
> >
> > diff --git a/drivers/vfio/vfio_iommu_type1.c
> > b/drivers/vfio/vfio_iommu_type1.c index 7accb59..8c143d5 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -72,6 +72,7 @@ struct vfio_iommu {
> >  	uint64_t		pgsize_bitmap;
> >  	bool			v2;
> >  	bool			nesting;
> > +	struct iommu_nesting_info *nesting_info;
> >  	bool			dirty_page_tracking;
> >  	bool			pinned_page_dirty_scope;
> >  };
> 
> Mind the structure packing and alignment, placing a pointer in the middle
> of a
> section of bools is going to create wasteful holes in the data structure.

how about below? Add the @nesting_info and @vmm in the end of this struct.
I've two questions, the first one is how the place the comment of the
@external_domain; second question is do you want me to move the @nesting
field to be near-by with the @nesting_info and @vmm. :) please let me know
your preference.

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 iommu_nesting_info 	*nesting_info;
	struct vfio_mm			*vmm;
};

> > @@ -130,6 +131,9 @@ 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)))
> > +
> >  #define DIRTY_BITMAP_BYTES(n)	(ALIGN(n, BITS_PER_TYPE(u64)) /
> BITS_PER_BYTE)
> >
> >  /*
> > @@ -1959,6 +1963,12 @@ 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 +2039,36 @@ 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);
> > +		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);
> > +			goto out_detach;
> > +		}
> > +		iommu->nesting_info = info;
> > +	}
> > +
> >  	/* Get aperture info */
> >  	iommu_domain_get_attr(domain->domain, DOMAIN_ATTR_GEOMETRY,
> &geo);
> >
> > @@ -2138,6 +2178,7 @@ static int vfio_iommu_type1_attach_group(void
> *iommu_data,
> >  	return 0;
> >
> >  out_detach:
> > +	kfree(iommu->nesting_info);
> 
> This looks prone to a use-after-free.

how about setting iommu->nesting_info to NULL? just as the next comment
from you.

> >  	vfio_iommu_detach_group(domain, group);
> >  out_domain:
> >  	iommu_domain_free(domain->domain);
> > @@ -2338,6 +2379,8 @@ static void vfio_iommu_type1_detach_group(void
> *iommu_data,
> >  					vfio_iommu_unmap_unpin_all(iommu);
> >  				else
> >
> 	vfio_iommu_unmap_unpin_reaccount(iommu);
> > +
> > +				kfree(iommu->nesting_info);
> 
> As does this.  Set to NULL since get_info tests the pointer before trying to
> use it.

got it.

> >  			}
> >  			iommu_domain_free(domain->domain);
> >  			list_del(&domain->next);
> > @@ -2546,6 +2589,30 @@ 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 +2653,12 @@ 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 eca66926..f1f39e1 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -14,6 +14,7 @@
> >
> >  #include <linux/types.h>
> >  #include <linux/ioctl.h>
> > +#include <linux/iommu.h>
> 
> Why?  We're not directly referencing any IOMMU UAPI structures here.

oh, yes. will remove it.

> >
> >  #define VFIO_API_VERSION	0
> >
> > @@ -1039,6 +1040,14 @@ struct vfio_iommu_type1_info_cap_migration {
> >  	__u64	max_dirty_bitmap_size;		/* in bytes */
> >  };
> >
> > +#define VFIO_IOMMU_TYPE1_INFO_CAP_NESTING  3
> > +
> > +struct vfio_iommu_type1_info_cap_nesting {
> > +	struct	vfio_info_cap_header header;
> > +	__u32	flags;
> 
> I think there's an alignment issue here for a uapi.  The header field is
> 8-bytes total
> and info[] should start at an 8-byte alignment to allow data[] within info
> to have
> 8-byte alignment.  This could lead to the structure having a compiler
> dependent
> size and offsets.  We should add a 4-byte reserved field here to resolve.

got it. or how about defining the flags as __u64?

> 
> > +	__u8	info[];
> > +};
> 
> This should have a lot more description around it, a user could not infer
> that info[]
> is including a struct iommu_nesting_info from the information provided here.
> Thanks,

sure. BTW. do you think it is necessary to add a flag to indicate the info[]
is a struct iommu_nesting_info? or as a start, it's not necessary to do it.

Regards,
Yi Liu

> Alex
> 
> > +
> >  #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
> >
> >  /**

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