Patchwork [v4] KVM: PPC: vfio kvm device: support spapr tce

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Submitter Alexey Kardashevskiy
Date Nov. 25, 2013, 8:49 a.m.
Message ID <1385369342-24423-1-git-send-email-aik@ozlabs.ru>
Download mbox | patch
Permalink /patch/293855/
State New
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Comments

Alexey Kardashevskiy - Nov. 25, 2013, 8:49 a.m.
In addition to the external VFIO user API, a VFIO KVM device
has been introduced recently.

sPAPR TCE IOMMU is para-virtualized and the guest does map/unmap
via hypercalls which take a logical bus id (LIOBN) as a target IOMMU
identifier. LIOBNs are made up and linked to IOMMU groups by the user
space. In order to accelerate IOMMU operations in the KVM, we need
to tell KVM the information about LIOBN-to-group mapping.

For that, a new KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN parameter
is added. It accepts a pair of a VFIO group fd and LIOBN.

This also adds a new kvm_vfio_find_group_by_liobn() function which
receives kvm struct, LIOBN and a callback. As it increases the IOMMU
group use counter, the KVMr is required to pass a callback which
called when the VFIO group is about to be removed VFIO-KVM tracking so
the KVM is able to call iommu_group_put() to release the IOMMU group.

The KVM uses kvm_vfio_find_group_by_liobn() once per KVM run and caches
the result in kvm_arch. iommu_group_put() for all groups will be called
when KVM finishes (in the SPAPR TCE in KVM enablement patch).

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v4:
* fixed few bugs
* changed kvm_vfio_find_group_by_liobn() to return informative errors

v3:
* total rework
* added a release callback into kvm_vfio_find_group_by_liobn so now
the user of the API can get a notification if the group is about to
disappear
---
 Documentation/virtual/kvm/devices/vfio.txt |  19 ++++-
 arch/powerpc/kvm/Kconfig                   |   1 +
 arch/powerpc/kvm/Makefile                  |   3 +
 include/linux/kvm_host.h                   |  18 +++++
 include/uapi/linux/kvm.h                   |   7 ++
 virt/kvm/vfio.c                            | 116 ++++++++++++++++++++++++++++-
 6 files changed, 161 insertions(+), 3 deletions(-)
Alex Williamson - Nov. 27, 2013, 8:43 p.m.
On Mon, 2013-11-25 at 19:49 +1100, Alexey Kardashevskiy wrote:
> In addition to the external VFIO user API, a VFIO KVM device
> has been introduced recently.
> 
> sPAPR TCE IOMMU is para-virtualized and the guest does map/unmap
> via hypercalls which take a logical bus id (LIOBN) as a target IOMMU
> identifier. LIOBNs are made up and linked to IOMMU groups by the user
> space. In order to accelerate IOMMU operations in the KVM, we need
> to tell KVM the information about LIOBN-to-group mapping.
> 
> For that, a new KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN parameter
> is added. It accepts a pair of a VFIO group fd and LIOBN.
> 
> This also adds a new kvm_vfio_find_group_by_liobn() function which
> receives kvm struct, LIOBN and a callback. As it increases the IOMMU
> group use counter, the KVMr is required to pass a callback which
> called when the VFIO group is about to be removed VFIO-KVM tracking so
> the KVM is able to call iommu_group_put() to release the IOMMU group.
> 
> The KVM uses kvm_vfio_find_group_by_liobn() once per KVM run and caches
> the result in kvm_arch. iommu_group_put() for all groups will be called
> when KVM finishes (in the SPAPR TCE in KVM enablement patch).
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> Changes:
> v4:
> * fixed few bugs
> * changed kvm_vfio_find_group_by_liobn() to return informative errors
> 
> v3:
> * total rework
> * added a release callback into kvm_vfio_find_group_by_liobn so now
> the user of the API can get a notification if the group is about to
> disappear
> ---
>  Documentation/virtual/kvm/devices/vfio.txt |  19 ++++-
>  arch/powerpc/kvm/Kconfig                   |   1 +
>  arch/powerpc/kvm/Makefile                  |   3 +
>  include/linux/kvm_host.h                   |  18 +++++
>  include/uapi/linux/kvm.h                   |   7 ++
>  virt/kvm/vfio.c                            | 116 ++++++++++++++++++++++++++++-
>  6 files changed, 161 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
> index ef51740..7ecb3b2 100644
> --- a/Documentation/virtual/kvm/devices/vfio.txt
> +++ b/Documentation/virtual/kvm/devices/vfio.txt
> @@ -16,7 +16,22 @@ Groups:
>  
>  KVM_DEV_VFIO_GROUP attributes:
>    KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
> +	kvm_device_attr.addr points to an int32_t file descriptor
> +	for the VFIO group.
> +
>    KVM_DEV_VFIO_GROUP_DEL: Remove a VFIO group from VFIO-KVM device tracking
> +	kvm_device_attr.addr points to an int32_t file descriptor
> +	for the VFIO group.
> +
> +  KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN: sets a liobn for a VFIO group
> +	kvm_device_attr.addr points to a struct:
> +		struct kvm_vfio_spapr_tce_liobn {
> +			__u32	argsz;
> +			__u32	fd;

__s32 per the definition below

> +			__u32	liobn;
> +		};
> +		where
> +		@argsz is a struct size;
> +		@fd is a file descriptor for a VFIO group;
> +		@liobn is a logical bus id to be associated with the group.
>  
> -For each, kvm_device_attr.addr points to an int32_t file descriptor
> -for the VFIO group.
> diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
> index 9a50d82..f463958 100644
> --- a/arch/powerpc/kvm/Kconfig
> +++ b/arch/powerpc/kvm/Kconfig
> @@ -60,6 +60,7 @@ config KVM_BOOK3S_64
>  	select KVM_BOOK3S_64_HANDLER
>  	select KVM
>  	select SPAPR_TCE_IOMMU if IOMMU_SUPPORT
> +	select KVM_VFIO
>  	---help---
>  	  Support running unmodified book3s_64 and book3s_32 guest kernels
>  	  in virtual machines on book3s_64 host processors.
> diff --git a/arch/powerpc/kvm/Makefile b/arch/powerpc/kvm/Makefile
> index 6646c95..2438d2e 100644
> --- a/arch/powerpc/kvm/Makefile
> +++ b/arch/powerpc/kvm/Makefile
> @@ -87,6 +87,9 @@ kvm-book3s_64-builtin-objs-$(CONFIG_KVM_BOOK3S_64_HV) := \
>  kvm-book3s_64-objs-$(CONFIG_KVM_XICS) += \
>  	book3s_xics.o
>  
> +kvm-book3s_64-objs-$(CONFIG_KVM_VFIO) += \
> +	$(KVM)/vfio.o \
> +
>  kvm-book3s_64-module-objs := \
>  	$(KVM)/kvm_main.o \
>  	$(KVM)/eventfd.o \
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 88ff96a..1d2ad5e 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1112,5 +1112,23 @@ static inline bool kvm_vcpu_eligible_for_directed_yield(struct kvm_vcpu *vcpu)
>  }
>  
>  #endif /* CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT */
> +
> +typedef void (*kvm_vfio_release_group_callback)(struct kvm *kvm,
> +		unsigned long liobn);

Seems like a bit of namespace pollution that this is named generically
but is specific to spapr/liobn.  Is this ever needed w/o
CONFIG_SPAPR_TCE_IOMMU?

> +#if defined(CONFIG_KVM_VFIO) && defined(CONFIG_SPAPR_TCE_IOMMU)
> +
> +extern struct iommu_group *kvm_vfio_find_group_by_liobn(struct kvm *kvm,
> +		unsigned long liobn, kvm_vfio_release_group_callback cb);
> +
> +#else
> +
> +static inline struct iommu_group *kvm_vfio_find_group_by_liobn(struct kvm *kvm,
> +		unsigned long liobn, ikvm_vfio_release_group_callback cb)
> +{
> +	return NULL;

The real function returns ERR_PTR(-errno) now, this should too.

> +}
> +#endif /* CONFIG_KVM_VFIO && CONFIG_SPAPR_TCE_IOMMU */

Why isn't this

#ifdef CONFIG_SPAPR_TCE_IOMMU
#ifdef CONFIG_KVM_VFIO
extern...
#else
static inline...
#endif
#endif

?

> +
>  #endif
>  
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 7c1a349..51d5464 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -847,6 +847,13 @@ struct kvm_device_attr {
>  #define  KVM_DEV_VFIO_GROUP			1
>  #define   KVM_DEV_VFIO_GROUP_ADD			1
>  #define   KVM_DEV_VFIO_GROUP_DEL			2
> +#define   KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN	3
> +
> +struct kvm_vfio_spapr_tce_liobn {
> +	__u32	argsz;
> +	__s32	fd;
> +	__u32	liobn;
> +};
>  
>  /*
>   * ioctls for VM fds
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index ca4260e..ddc945d 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -22,6 +22,12 @@
>  struct kvm_vfio_group {
>  	struct list_head node;
>  	struct vfio_group *vfio_group;
> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> +	struct {
> +		unsigned long liobn;
> +		kvm_vfio_release_group_callback cb;
> +	} spapr_tce;
> +#endif
>  };
>  
>  struct kvm_vfio {
> @@ -59,6 +65,51 @@ static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
>  	symbol_put(vfio_group_put_external_user);
>  }
>  
> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> +struct iommu_group *kvm_vfio_find_group_by_liobn(struct kvm *kvm,
> +		unsigned long liobn, kvm_vfio_release_group_callback cb)
> +{
> +	struct kvm_vfio_group *kvg;
> +	int group_id;
> +	struct iommu_group *grp;
> +	struct kvm_vfio *kv = NULL;
> +	struct kvm_device *tmp;
> +
> +	if (!cb)
> +		return ERR_PTR(-EINVAL);
> +
> +	/* Find a VFIO KVM device */
> +	list_for_each_entry(tmp, &kvm->devices, vm_node) {
> +		if (tmp->ops != &kvm_vfio_ops)
> +			continue;
> +
> +		kv = tmp->private;
> +		break;
> +	}
> +
> +	if (!kv)
> +		return ERR_PTR(-EIO);
> +

I'm getting tired of noting that this ignores kv->lock...

> +	/* Find a group */
> +	list_for_each_entry(kvg, &kv->group_list, node) {
> +		if (kvg->spapr_tce.liobn != liobn)
> +			continue;
> +
> +		if (kvg->spapr_tce.cb)
> +			return ERR_PTR(-EBUSY);
> +
> +		kvg->spapr_tce.cb = cb;
> +		group_id = vfio_external_user_iommu_id(kvg->vfio_group);
> +		grp = iommu_group_get_by_id(group_id);
> +
> +		return grp;
> +	}
> +
> +	return ERR_PTR(-ENODEV);
> +}
> +EXPORT_SYMBOL_GPL(kvm_vfio_find_group_by_liobn);
> +#endif
> +
>  /*
>   * Groups can use the same or different IOMMU domains.  If the same then
>   * adding a new group may change the coherency of groups we've previously
> @@ -140,7 +191,9 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>  
>  		list_add_tail(&kvg->node, &kv->group_list);
>  		kvg->vfio_group = vfio_group;
> -
> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> +		kvg->spapr_tce.liobn = -1;
> +#endif
>  		mutex_unlock(&kv->lock);
>  
>  		kvm_vfio_update_coherency(dev);
> @@ -170,6 +223,11 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>  				continue;
>  
>  			list_del(&kvg->node);
> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> +			if (kvg->spapr_tce.cb)
> +				kvg->spapr_tce.cb(dev->kvm,
> +						kvg->spapr_tce.liobn);
> +#endif
>  			kvm_vfio_group_put_external_user(kvg->vfio_group);
>  			kfree(kvg);
>  			ret = 0;
> @@ -183,6 +241,59 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>  		kvm_vfio_update_coherency(dev);
>  
>  		return ret;
> +
> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> +	case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN: {
> +		struct kvm_vfio_spapr_tce_liobn param;
> +		unsigned long minsz;
> +		struct kvm_vfio *kv = dev->private;
> +		struct vfio_group *vfio_group;
> +		struct kvm_vfio_group *kvg;
> +		struct fd f;
> +
> +		minsz = offsetofend(struct kvm_vfio_spapr_tce_liobn, liobn);
> +
> +		if (copy_from_user(&param, (void __user *)arg, minsz))
> +			return -EFAULT;
> +
> +		if (param.argsz < minsz)
> +			return -EINVAL;
> +
> +		f = fdget(param.fd);
> +		if (!f.file)
> +			return -EBADF;
> +
> +		vfio_group = kvm_vfio_group_get_external_user(f.file);
> +		fdput(f);
> +
> +		if (IS_ERR(vfio_group))
> +			return PTR_ERR(vfio_group);
> +
> +		ret = -ENOENT;
> +
> +		mutex_lock(&kv->lock);
> +
> +		list_for_each_entry(kvg, &kv->group_list, node) {
> +			if (kvg->vfio_group != vfio_group)
> +				continue;
> +
> +			if (kvg->spapr_tce.liobn != -1) {
> +				ret = -EBUSY;
> +				break;
> +			}
> +
> +			kvg->spapr_tce.liobn = param.liobn;
> +			ret = 0;
> +			break;
> +		}
> +
> +		mutex_unlock(&kv->lock);
> +
> +		kvm_vfio_group_put_external_user(vfio_group);
> +
> +		return ret;
> +	}
> +#endif /* CONFIG_SPAPR_TCE_IOMMU */
>  	}
>  
>  	return -ENXIO;
> @@ -207,6 +318,9 @@ static int kvm_vfio_has_attr(struct kvm_device *dev,
>  		switch (attr->attr) {
>  		case KVM_DEV_VFIO_GROUP_ADD:
>  		case KVM_DEV_VFIO_GROUP_DEL:
> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> +		case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN:
> +#endif
>  			return 0;
>  		}
>  



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Patch

diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
index ef51740..7ecb3b2 100644
--- a/Documentation/virtual/kvm/devices/vfio.txt
+++ b/Documentation/virtual/kvm/devices/vfio.txt
@@ -16,7 +16,22 @@  Groups:
 
 KVM_DEV_VFIO_GROUP attributes:
   KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
+	kvm_device_attr.addr points to an int32_t file descriptor
+	for the VFIO group.
+
   KVM_DEV_VFIO_GROUP_DEL: Remove a VFIO group from VFIO-KVM device tracking
+	kvm_device_attr.addr points to an int32_t file descriptor
+	for the VFIO group.
+
+  KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN: sets a liobn for a VFIO group
+	kvm_device_attr.addr points to a struct:
+		struct kvm_vfio_spapr_tce_liobn {
+			__u32	argsz;
+			__u32	fd;
+			__u32	liobn;
+		};
+		where
+		@argsz is a struct size;
+		@fd is a file descriptor for a VFIO group;
+		@liobn is a logical bus id to be associated with the group.
 
-For each, kvm_device_attr.addr points to an int32_t file descriptor
-for the VFIO group.
diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
index 9a50d82..f463958 100644
--- a/arch/powerpc/kvm/Kconfig
+++ b/arch/powerpc/kvm/Kconfig
@@ -60,6 +60,7 @@  config KVM_BOOK3S_64
 	select KVM_BOOK3S_64_HANDLER
 	select KVM
 	select SPAPR_TCE_IOMMU if IOMMU_SUPPORT
+	select KVM_VFIO
 	---help---
 	  Support running unmodified book3s_64 and book3s_32 guest kernels
 	  in virtual machines on book3s_64 host processors.
diff --git a/arch/powerpc/kvm/Makefile b/arch/powerpc/kvm/Makefile
index 6646c95..2438d2e 100644
--- a/arch/powerpc/kvm/Makefile
+++ b/arch/powerpc/kvm/Makefile
@@ -87,6 +87,9 @@  kvm-book3s_64-builtin-objs-$(CONFIG_KVM_BOOK3S_64_HV) := \
 kvm-book3s_64-objs-$(CONFIG_KVM_XICS) += \
 	book3s_xics.o
 
+kvm-book3s_64-objs-$(CONFIG_KVM_VFIO) += \
+	$(KVM)/vfio.o \
+
 kvm-book3s_64-module-objs := \
 	$(KVM)/kvm_main.o \
 	$(KVM)/eventfd.o \
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 88ff96a..1d2ad5e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1112,5 +1112,23 @@  static inline bool kvm_vcpu_eligible_for_directed_yield(struct kvm_vcpu *vcpu)
 }
 
 #endif /* CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT */
+
+typedef void (*kvm_vfio_release_group_callback)(struct kvm *kvm,
+		unsigned long liobn);
+
+#if defined(CONFIG_KVM_VFIO) && defined(CONFIG_SPAPR_TCE_IOMMU)
+
+extern struct iommu_group *kvm_vfio_find_group_by_liobn(struct kvm *kvm,
+		unsigned long liobn, kvm_vfio_release_group_callback cb);
+
+#else
+
+static inline struct iommu_group *kvm_vfio_find_group_by_liobn(struct kvm *kvm,
+		unsigned long liobn, ikvm_vfio_release_group_callback cb)
+{
+	return NULL;
+}
+#endif /* CONFIG_KVM_VFIO && CONFIG_SPAPR_TCE_IOMMU */
+
 #endif
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 7c1a349..51d5464 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -847,6 +847,13 @@  struct kvm_device_attr {
 #define  KVM_DEV_VFIO_GROUP			1
 #define   KVM_DEV_VFIO_GROUP_ADD			1
 #define   KVM_DEV_VFIO_GROUP_DEL			2
+#define   KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN	3
+
+struct kvm_vfio_spapr_tce_liobn {
+	__u32	argsz;
+	__s32	fd;
+	__u32	liobn;
+};
 
 /*
  * ioctls for VM fds
diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
index ca4260e..ddc945d 100644
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -22,6 +22,12 @@ 
 struct kvm_vfio_group {
 	struct list_head node;
 	struct vfio_group *vfio_group;
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+	struct {
+		unsigned long liobn;
+		kvm_vfio_release_group_callback cb;
+	} spapr_tce;
+#endif
 };
 
 struct kvm_vfio {
@@ -59,6 +65,51 @@  static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
 	symbol_put(vfio_group_put_external_user);
 }
 
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+struct iommu_group *kvm_vfio_find_group_by_liobn(struct kvm *kvm,
+		unsigned long liobn, kvm_vfio_release_group_callback cb)
+{
+	struct kvm_vfio_group *kvg;
+	int group_id;
+	struct iommu_group *grp;
+	struct kvm_vfio *kv = NULL;
+	struct kvm_device *tmp;
+
+	if (!cb)
+		return ERR_PTR(-EINVAL);
+
+	/* Find a VFIO KVM device */
+	list_for_each_entry(tmp, &kvm->devices, vm_node) {
+		if (tmp->ops != &kvm_vfio_ops)
+			continue;
+
+		kv = tmp->private;
+		break;
+	}
+
+	if (!kv)
+		return ERR_PTR(-EIO);
+
+	/* Find a group */
+	list_for_each_entry(kvg, &kv->group_list, node) {
+		if (kvg->spapr_tce.liobn != liobn)
+			continue;
+
+		if (kvg->spapr_tce.cb)
+			return ERR_PTR(-EBUSY);
+
+		kvg->spapr_tce.cb = cb;
+		group_id = vfio_external_user_iommu_id(kvg->vfio_group);
+		grp = iommu_group_get_by_id(group_id);
+
+		return grp;
+	}
+
+	return ERR_PTR(-ENODEV);
+}
+EXPORT_SYMBOL_GPL(kvm_vfio_find_group_by_liobn);
+#endif
+
 /*
  * Groups can use the same or different IOMMU domains.  If the same then
  * adding a new group may change the coherency of groups we've previously
@@ -140,7 +191,9 @@  static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
 
 		list_add_tail(&kvg->node, &kv->group_list);
 		kvg->vfio_group = vfio_group;
-
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+		kvg->spapr_tce.liobn = -1;
+#endif
 		mutex_unlock(&kv->lock);
 
 		kvm_vfio_update_coherency(dev);
@@ -170,6 +223,11 @@  static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
 				continue;
 
 			list_del(&kvg->node);
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+			if (kvg->spapr_tce.cb)
+				kvg->spapr_tce.cb(dev->kvm,
+						kvg->spapr_tce.liobn);
+#endif
 			kvm_vfio_group_put_external_user(kvg->vfio_group);
 			kfree(kvg);
 			ret = 0;
@@ -183,6 +241,59 @@  static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
 		kvm_vfio_update_coherency(dev);
 
 		return ret;
+
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+	case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN: {
+		struct kvm_vfio_spapr_tce_liobn param;
+		unsigned long minsz;
+		struct kvm_vfio *kv = dev->private;
+		struct vfio_group *vfio_group;
+		struct kvm_vfio_group *kvg;
+		struct fd f;
+
+		minsz = offsetofend(struct kvm_vfio_spapr_tce_liobn, liobn);
+
+		if (copy_from_user(&param, (void __user *)arg, minsz))
+			return -EFAULT;
+
+		if (param.argsz < minsz)
+			return -EINVAL;
+
+		f = fdget(param.fd);
+		if (!f.file)
+			return -EBADF;
+
+		vfio_group = kvm_vfio_group_get_external_user(f.file);
+		fdput(f);
+
+		if (IS_ERR(vfio_group))
+			return PTR_ERR(vfio_group);
+
+		ret = -ENOENT;
+
+		mutex_lock(&kv->lock);
+
+		list_for_each_entry(kvg, &kv->group_list, node) {
+			if (kvg->vfio_group != vfio_group)
+				continue;
+
+			if (kvg->spapr_tce.liobn != -1) {
+				ret = -EBUSY;
+				break;
+			}
+
+			kvg->spapr_tce.liobn = param.liobn;
+			ret = 0;
+			break;
+		}
+
+		mutex_unlock(&kv->lock);
+
+		kvm_vfio_group_put_external_user(vfio_group);
+
+		return ret;
+	}
+#endif /* CONFIG_SPAPR_TCE_IOMMU */
 	}
 
 	return -ENXIO;
@@ -207,6 +318,9 @@  static int kvm_vfio_has_attr(struct kvm_device *dev,
 		switch (attr->attr) {
 		case KVM_DEV_VFIO_GROUP_ADD:
 		case KVM_DEV_VFIO_GROUP_DEL:
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+		case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN:
+#endif
 			return 0;
 		}