RE: [PATCH v6 04/15] 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, August 21, 2020 3:52 AM
> 
> On Mon, 27 Jul 2020 23:27:33 -0700
> Liu Yi L <yi.l.liu@intel.com> wrote:
> 
> > This patch exports iommu nesting capability info to user space through
> > VFIO. Userspace 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 container set to be NESTED type.
> > Current implementation imposes one limitation - one nesting container
> > should include at most one iommu 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-level 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://lore.kernel.org/kvm/20200515115924.37e6996d@w520.home/
> >
> > This patch also changes the NESTING type container behaviour. Something
> > that would have succeeded before will now fail: Before this series, if
> > user asked for a VFIO_IOMMU_TYPE1_NESTING, it would have succeeded even
> > if the SMMU didn't support stage-2, as the driver would have silently
> > fallen back on stage-1 mappings (which work exactly the same as stage-2
> > only since there was no nesting supported). After the series, we do check
> > for DOMAIN_ATTR_NESTING so if user asks for VFIO_IOMMU_TYPE1_NESTING
> and
> > the SMMU doesn't support stage-2, the ioctl fails. But it should be a good
> > fix and completely harmless. Detail can be found in below link as well.
> >
> > https://lore.kernel.org/kvm/20200717090900.GC4850@myrica/
> >
> > 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>
> > ---
> > v5 -> v6:
> > *) address comments against v5 from Eric Auger.
> > *) don't report nesting cap to userspace if the nesting_info->format is
> >    invalid.
> >
> > v4 -> v5:
> > *) address comments from Eric Auger.
> > *) return struct iommu_nesting_info for
> VFIO_IOMMU_TYPE1_INFO_CAP_NESTING as
> >    cap is much "cheap", if needs extension in future, just define another cap.
> >    https://lore.kernel.org/kvm/20200708132947.5b7ee954@x1.home/
> >
> > v3 -> v4:
> > *) address comments against v3.
> >
> > v1 -> v2:
> > *) added in v2
> > ---
> >  drivers/vfio/vfio_iommu_type1.c | 106
> +++++++++++++++++++++++++++++++++++-----
> >  include/uapi/linux/vfio.h       |  19 +++++++
> >  2 files changed, 113 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index 3bd70ff..18ff0c3 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;
> > +	/* 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 CONTAINER_HAS_DOMAIN(iommu)	(((iommu)->external_domain) || \
> > +					 (!list_empty(&(iommu)->domain_list)))
> > +
> >  #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 && CONTAINER_HAS_DOMAIN(iommu)) {
> > +		mutex_unlock(&iommu->lock);
> > +		return -EINVAL;
> > +	}
> > +
> >  	group = kzalloc(sizeof(*group), GFP_KERNEL);
> >  	domain = kzalloc(sizeof(*domain), GFP_KERNEL);
> >  	if (!group || !domain) {
> > @@ -2029,6 +2047,32 @@ static int vfio_iommu_type1_attach_group(void
> *iommu_data,
> >  	if (ret)
> >  		goto out_domain;
> 
> 
> I think that currently a user can configure a VFIO_TYPE1_NESTING_IOMMU
> IOMMU type with a non-IOMMU backed mdev.  Does that make any sort of
> sense or is this a bug?  Thanks,

I guess we don't support such case as non-IOMMU mdev is attached to the
external domain. It won't come to the part where allocates domain and
sets nesting for the domain.

Regards,
Yi Liu

> Alex
> 
> >
> > +	/* Nesting cap info is available only after attaching */
> > +	if (iommu->nesting) {
> > +		struct iommu_nesting_info tmp = { .argsz = 0, };
> > +
> > +		/* 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;
> > +
> > +		iommu->nesting_info = kzalloc(tmp.argsz, GFP_KERNEL);
> > +		if (!iommu->nesting_info) {
> > +			ret = -ENOMEM;
> > +			goto out_detach;
> > +		}
> > +
> > +		/* Now get the nesting info */
> > +		iommu->nesting_info->argsz = tmp.argsz;
> > +		ret = iommu_domain_get_attr(domain->domain,
> > +					    DOMAIN_ATTR_NESTING,
> > +					    iommu->nesting_info);
> > +		if (ret)
> > +			goto out_detach;
> > +	}
> > +
> >  	/* Get aperture info */
> >  	iommu_domain_get_attr(domain->domain, DOMAIN_ATTR_GEOMETRY,
> &geo);
> >
> > @@ -2138,6 +2182,7 @@ 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 +2383,8 @@ 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 +2593,39 @@ 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_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;
> > +
> > +	/* when nesting_info is null, no need go further */
> > +	if (!iommu->nesting_info)
> > +		return 0;
> > +
> > +	/* when @format of nesting_info is 0, fail the call */
> > +	if (iommu->nesting_info->format == 0)
> > +		return -ENOENT;
> > +
> > +	size = offsetof(struct vfio_iommu_type1_info_cap_nesting, info) +
> > +	       iommu->nesting_info->argsz;
> > +
> > +	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->argsz);
> > +
> > +	return 0;
> > +}
> > +
> >  static int vfio_iommu_type1_get_info(struct vfio_iommu *iommu,
> >  				     unsigned long arg)
> >  {
> > @@ -2581,6 +2661,8 @@ static int vfio_iommu_type1_get_info(struct
> vfio_iommu *iommu,
> >  	if (!ret)
> >  		ret = vfio_iommu_iova_build_caps(iommu, &caps);
> >
> > +	ret = vfio_iommu_add_nesting_cap(iommu, &caps);
> > +
> >  	mutex_unlock(&iommu->lock);
> >
> >  	if (ret)
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index 9204705..0cf3d6d 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>
> >
> >  #define VFIO_API_VERSION	0
> >
> > @@ -1039,6 +1040,24 @@ struct vfio_iommu_type1_info_cap_migration {
> >  	__u64	max_dirty_bitmap_size;		/* in bytes */
> >  };
> >
> > +/*
> > + * The nesting capability allows to report the related capability
> > + * and info for nesting iommu type.
> > + *
> > + * The structures below define version 1 of this capability.
> > + *
> > + * Userspace selected VFIO_TYPE1_NESTING_IOMMU type should check
> > + * this capability to get supported features.
> > + *
> > + * @info: the nesting info provided by IOMMU driver.
> > + */
> > +#define VFIO_IOMMU_TYPE1_INFO_CAP_NESTING  3
> > +
> > +struct vfio_iommu_type1_info_cap_nesting {
> > +	struct	vfio_info_cap_header header;
> > +	struct iommu_nesting_info info;
> > +};
> > +
> >  #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
> >
> >  /**

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