diff --git a/drivers/iommu/iommufd/Makefile b/drivers/iommu/iommufd/Makefile
index ca28a135b967..2fdff04000b3 100644
--- a/drivers/iommu/iommufd/Makefile
+++ b/drivers/iommu/iommufd/Makefile
@@ -5,6 +5,7 @@ iommufd-y := \
 	io_pagetable.o \
 	ioas.o \
 	main.o \
-	pages.o
+	pages.o \
+	vfio_compat.o
 
 obj-$(CONFIG_IOMMUFD) += iommufd.o
diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 40302cc0da36..8fe5f162ccbc 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -18,6 +18,7 @@ struct iommufd_ctx {
 	struct xarray objects;
 
 	u8 account_mode;
+	struct iommufd_ioas *vfio_ioas;
 };
 
 /*
@@ -92,6 +93,9 @@ struct iommufd_ucmd {
 	void *cmd;
 };
 
+int iommufd_vfio_ioctl(struct iommufd_ctx *ictx, unsigned int cmd,
+		       unsigned long arg);
+
 /* Copy the response in ucmd->cmd back to userspace. */
 static inline int iommufd_ucmd_respond(struct iommufd_ucmd *ucmd,
 				       size_t cmd_len)
@@ -222,6 +226,8 @@ int iommufd_ioas_option(struct iommufd_ucmd *ucmd);
 int iommufd_option_rlimit_mode(struct iommu_option *cmd,
 			       struct iommufd_ctx *ictx);
 
+int iommufd_vfio_ioas(struct iommufd_ucmd *ucmd);
+
 /*
  * A HW pagetable is called an iommu_domain inside the kernel. This user object
  * allows directly creating and inspecting the domains. Domains that have kernel
diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 4153f6a20255..5cf69c4d591d 100644
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -133,6 +133,8 @@ bool iommufd_object_destroy_user(struct iommufd_ctx *ictx,
 		return false;
 	}
 	__xa_erase(&ictx->objects, obj->id);
+	if (ictx->vfio_ioas && &ictx->vfio_ioas->obj == obj)
+		ictx->vfio_ioas = NULL;
 	xa_unlock(&ictx->objects);
 	up_write(&obj->destroy_rwsem);
 
@@ -271,27 +273,31 @@ static const struct iommufd_ioctl_op iommufd_ioctl_ops[] = {
 		 length),
 	IOCTL_OP(IOMMU_OPTION, iommufd_option, struct iommu_option,
 		 val64),
+	IOCTL_OP(IOMMU_VFIO_IOAS, iommufd_vfio_ioas, struct iommu_vfio_ioas,
+		 __reserved),
 };
 
 static long iommufd_fops_ioctl(struct file *filp, unsigned int cmd,
 			       unsigned long arg)
 {
+	struct iommufd_ctx *ictx = filp->private_data;
 	const struct iommufd_ioctl_op *op;
 	struct iommufd_ucmd ucmd = {};
 	union ucmd_buffer buf;
 	unsigned int nr;
 	int ret;
 
-	ucmd.ictx = filp->private_data;
+	nr = _IOC_NR(cmd);
+	if (nr < IOMMUFD_CMD_BASE ||
+	    (nr - IOMMUFD_CMD_BASE) >= ARRAY_SIZE(iommufd_ioctl_ops))
+		return iommufd_vfio_ioctl(ictx, cmd, arg);
+
+	ucmd.ictx = ictx;
 	ucmd.ubuffer = (void __user *)arg;
 	ret = get_user(ucmd.user_size, (u32 __user *)ucmd.ubuffer);
 	if (ret)
 		return ret;
 
-	nr = _IOC_NR(cmd);
-	if (nr < IOMMUFD_CMD_BASE ||
-	    (nr - IOMMUFD_CMD_BASE) >= ARRAY_SIZE(iommufd_ioctl_ops))
-		return -ENOIOCTLCMD;
 	op = &iommufd_ioctl_ops[nr - IOMMUFD_CMD_BASE];
 	if (op->ioctl_num != cmd)
 		return -ENOIOCTLCMD;
diff --git a/drivers/iommu/iommufd/vfio_compat.c b/drivers/iommu/iommufd/vfio_compat.c
new file mode 100644
index 000000000000..3ceca0e8311c
--- /dev/null
+++ b/drivers/iommu/iommufd/vfio_compat.c
@@ -0,0 +1,472 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2021-2022, NVIDIA CORPORATION & AFFILIATES
+ */
+#include <linux/file.h>
+#include <linux/interval_tree.h>
+#include <linux/iommu.h>
+#include <linux/iommufd.h>
+#include <linux/slab.h>
+#include <linux/vfio.h>
+#include <uapi/linux/vfio.h>
+#include <uapi/linux/iommufd.h>
+
+#include "iommufd_private.h"
+
+static struct iommufd_ioas *get_compat_ioas(struct iommufd_ctx *ictx)
+{
+	struct iommufd_ioas *ioas = ERR_PTR(-ENODEV);
+
+	xa_lock(&ictx->objects);
+	if (!ictx->vfio_ioas || !iommufd_lock_obj(&ictx->vfio_ioas->obj))
+		goto out_unlock;
+	ioas = ictx->vfio_ioas;
+out_unlock:
+	xa_unlock(&ictx->objects);
+	return ioas;
+}
+
+/**
+ * iommufd_vfio_compat_ioas_id - Return the IOAS ID that vfio should use
+ * @ictx: Context to operate on
+ * @out_ioas_id: The ioas_id the caller should use
+ *
+ * The compatibility IOAS is the IOAS that the vfio compatibility ioctls operate
+ * on since they do not have an IOAS ID input in their ABI. Only attaching a
+ * group should cause a default creation of the internal ioas, this returns the
+ * existing ioas if it has already been assigned somehow.
+ */
+int iommufd_vfio_compat_ioas_id(struct iommufd_ctx *ictx, u32 *out_ioas_id)
+{
+	struct iommufd_ioas *ioas = NULL;
+	struct iommufd_ioas *out_ioas;
+
+	ioas = iommufd_ioas_alloc(ictx);
+	if (IS_ERR(ioas))
+		return PTR_ERR(ioas);
+
+	xa_lock(&ictx->objects);
+	if (ictx->vfio_ioas && iommufd_lock_obj(&ictx->vfio_ioas->obj))
+		out_ioas = ictx->vfio_ioas;
+	else {
+		out_ioas = ioas;
+		ictx->vfio_ioas = ioas;
+	}
+	xa_unlock(&ictx->objects);
+
+	*out_ioas_id = out_ioas->obj.id;
+	if (out_ioas != ioas) {
+		iommufd_put_object(&out_ioas->obj);
+		iommufd_object_abort(ictx, &ioas->obj);
+		return 0;
+	}
+	/*
+	 * An automatically created compat IOAS is treated as a userspace
+	 * created object. Userspace can learn the ID via IOMMU_VFIO_IOAS_GET,
+	 * and if not manually destroyed it will be destroyed automatically
+	 * at iommufd release.
+	 */
+	iommufd_object_finalize(ictx, &ioas->obj);
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_vfio_compat_ioas_id, IOMMUFD_VFIO);
+
+int iommufd_vfio_ioas(struct iommufd_ucmd *ucmd)
+{
+	struct iommu_vfio_ioas *cmd = ucmd->cmd;
+	struct iommufd_ioas *ioas;
+
+	if (cmd->__reserved)
+		return -EOPNOTSUPP;
+	switch (cmd->op) {
+	case IOMMU_VFIO_IOAS_GET:
+		ioas = get_compat_ioas(ucmd->ictx);
+		if (IS_ERR(ioas))
+			return PTR_ERR(ioas);
+		cmd->ioas_id = ioas->obj.id;
+		iommufd_put_object(&ioas->obj);
+		return iommufd_ucmd_respond(ucmd, sizeof(*cmd));
+
+	case IOMMU_VFIO_IOAS_SET:
+		ioas = iommufd_get_ioas(ucmd, cmd->ioas_id);
+		if (IS_ERR(ioas))
+			return PTR_ERR(ioas);
+		xa_lock(&ucmd->ictx->objects);
+		ucmd->ictx->vfio_ioas = ioas;
+		xa_unlock(&ucmd->ictx->objects);
+		iommufd_put_object(&ioas->obj);
+		return 0;
+
+	case IOMMU_VFIO_IOAS_CLEAR:
+		xa_lock(&ucmd->ictx->objects);
+		ucmd->ictx->vfio_ioas = NULL;
+		xa_unlock(&ucmd->ictx->objects);
+		return 0;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static int iommufd_vfio_map_dma(struct iommufd_ctx *ictx, unsigned int cmd,
+				void __user *arg)
+{
+	u32 supported_flags = VFIO_DMA_MAP_FLAG_READ | VFIO_DMA_MAP_FLAG_WRITE;
+	size_t minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
+	struct vfio_iommu_type1_dma_map map;
+	int iommu_prot = IOMMU_CACHE;
+	struct iommufd_ioas *ioas;
+	unsigned long iova;
+	int rc;
+
+	if (copy_from_user(&map, arg, minsz))
+		return -EFAULT;
+
+	if (map.argsz < minsz || map.flags & ~supported_flags)
+		return -EINVAL;
+
+	if (map.flags & VFIO_DMA_MAP_FLAG_READ)
+		iommu_prot |= IOMMU_READ;
+	if (map.flags & VFIO_DMA_MAP_FLAG_WRITE)
+		iommu_prot |= IOMMU_WRITE;
+
+	ioas = get_compat_ioas(ictx);
+	if (IS_ERR(ioas))
+		return PTR_ERR(ioas);
+
+	/*
+	 * Maps created through the legacy interface always use VFIO compatible
+	 * rlimit accounting. If the user wishes to use the faster user based
+	 * rlimit accounting then they must use the new interface.
+	 */
+	iova = map.iova;
+	rc = iopt_map_user_pages(ictx, &ioas->iopt, &iova, u64_to_user_ptr(map.vaddr),
+				 map.size, iommu_prot, 0);
+	iommufd_put_object(&ioas->obj);
+	return rc;
+}
+
+static int iommufd_vfio_unmap_dma(struct iommufd_ctx *ictx, unsigned int cmd,
+				  void __user *arg)
+{
+	size_t minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size);
+	/*
+	 * VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP is obsoleted by the new
+	 * dirty tracking direction:
+	 *  https://lore.kernel.org/kvm/20220731125503.142683-1-yishaih@nvidia.com/
+	 *  https://lore.kernel.org/kvm/20220428210933.3583-1-joao.m.martins@oracle.com/
+	 */
+	u32 supported_flags = VFIO_DMA_UNMAP_FLAG_ALL;
+	struct vfio_iommu_type1_dma_unmap unmap;
+	unsigned long unmapped = 0;
+	struct iommufd_ioas *ioas;
+	int rc;
+
+	if (copy_from_user(&unmap, arg, minsz))
+		return -EFAULT;
+
+	if (unmap.argsz < minsz || unmap.flags & ~supported_flags)
+		return -EINVAL;
+
+	ioas = get_compat_ioas(ictx);
+	if (IS_ERR(ioas))
+		return PTR_ERR(ioas);
+
+	if (unmap.flags & VFIO_DMA_UNMAP_FLAG_ALL) {
+		if (unmap.iova != 0 || unmap.size != 0) {
+			rc = -EINVAL;
+			goto err_put;
+		}
+		rc = iopt_unmap_all(&ioas->iopt, &unmapped);
+	} else {
+		if (READ_ONCE(ioas->iopt.disable_large_pages)) {
+			/*
+			 * Create cuts at the start and last of the requested
+			 * range. If the start IOVA is 0 then it doesn't need to
+			 * be cut.
+			 */
+			unsigned long iovas[] = { unmap.iova + unmap.size - 1,
+						  unmap.iova - 1 };
+
+			rc = iopt_cut_iova(&ioas->iopt, iovas,
+					   unmap.iova ? 2 : 1);
+			if (rc)
+				goto err_put;
+		}
+		rc = iopt_unmap_iova(&ioas->iopt, unmap.iova, unmap.size,
+				     &unmapped);
+	}
+	unmap.size = unmapped;
+	if (copy_to_user(arg, &unmap, minsz))
+		rc = -EFAULT;
+
+err_put:
+	iommufd_put_object(&ioas->obj);
+	return rc;
+}
+
+static int iommufd_vfio_cc_iommu(struct iommufd_ctx *ictx)
+{
+	struct iommufd_hw_pagetable *hwpt;
+	struct iommufd_ioas *ioas;
+	int rc = 1;
+
+	ioas = get_compat_ioas(ictx);
+	if (IS_ERR(ioas))
+		return PTR_ERR(ioas);
+
+	mutex_lock(&ioas->mutex);
+	list_for_each_entry(hwpt, &ioas->hwpt_list, hwpt_item) {
+		if (!hwpt->enforce_cache_coherency) {
+			rc = 0;
+			break;
+		}
+	}
+	mutex_unlock(&ioas->mutex);
+
+	iommufd_put_object(&ioas->obj);
+	return rc;
+}
+
+static int iommufd_vfio_check_extension(struct iommufd_ctx *ictx,
+					unsigned long type)
+{
+	switch (type) {
+	case VFIO_TYPE1_IOMMU:
+	case VFIO_TYPE1v2_IOMMU:
+	case VFIO_UNMAP_ALL:
+		return 1;
+
+	case VFIO_DMA_CC_IOMMU:
+		return iommufd_vfio_cc_iommu(ictx);
+
+	/*
+	 * This is obsolete, and to be removed from VFIO. It was an incomplete
+	 * idea that got merged.
+	 * https://lore.kernel.org/kvm/0-v1-0093c9b0e345+19-vfio_no_nesting_jgg@nvidia.com/
+	 */
+	case VFIO_TYPE1_NESTING_IOMMU:
+		return 0;
+
+	/*
+	 * VFIO_DMA_MAP_FLAG_VADDR
+	 * https://lore.kernel.org/kvm/1611939252-7240-1-git-send-email-steven.sistare@oracle.com/
+	 * https://lore.kernel.org/all/Yz777bJZjTyLrHEQ@nvidia.com/
+	 *
+	 * It is hard to see how this could be implemented safely.
+	 */
+	case VFIO_UPDATE_VADDR:
+	default:
+		return 0;
+	}
+}
+
+static int iommufd_vfio_set_iommu(struct iommufd_ctx *ictx, unsigned long type)
+{
+	struct iommufd_ioas *ioas = NULL;
+	int rc = 0;
+
+	if (type != VFIO_TYPE1_IOMMU && type != VFIO_TYPE1v2_IOMMU)
+		return -EINVAL;
+
+	/* VFIO fails the set_iommu if there is no group */
+	ioas = get_compat_ioas(ictx);
+	if (IS_ERR(ioas))
+		return PTR_ERR(ioas);
+
+	/*
+	 * The difference between TYPE1 and TYPE1v2 is the ability to unmap in
+	 * the middle of mapped ranges. This is complicated by huge page support
+	 * which creates single large IOPTEs that cannot be split by the iommu
+	 * driver. TYPE1 is very old at this point and likely nothing uses it,
+	 * however it is simple enough to emulate by simply disabling the
+	 * problematic large IOPTEs. Then we can safely unmap within any range.
+	 */
+	if (type == VFIO_TYPE1_IOMMU)
+		rc = iopt_disable_large_pages(&ioas->iopt);
+	iommufd_put_object(&ioas->obj);
+	return rc;
+}
+
+static unsigned long iommufd_get_pagesizes(struct iommufd_ioas *ioas)
+{
+	struct io_pagetable *iopt = &ioas->iopt;
+	unsigned long pgsize_bitmap = ULONG_MAX;
+	struct iommu_domain *domain;
+	unsigned long index;
+
+	down_read(&iopt->domains_rwsem);
+	xa_for_each(&iopt->domains, index, domain)
+		pgsize_bitmap &= domain->pgsize_bitmap;
+
+	/* See vfio_update_pgsize_bitmap() */
+	if (pgsize_bitmap & ~PAGE_MASK) {
+		pgsize_bitmap &= PAGE_MASK;
+		pgsize_bitmap |= PAGE_SIZE;
+	}
+	pgsize_bitmap = max(pgsize_bitmap, ioas->iopt.iova_alignment);
+	up_read(&iopt->domains_rwsem);
+	return pgsize_bitmap;
+}
+
+static int iommufd_fill_cap_iova(struct iommufd_ioas *ioas,
+				 struct vfio_info_cap_header __user *cur,
+				 size_t avail)
+{
+	struct vfio_iommu_type1_info_cap_iova_range __user *ucap_iovas =
+		container_of(cur,
+			     struct vfio_iommu_type1_info_cap_iova_range __user,
+			     header);
+	struct vfio_iommu_type1_info_cap_iova_range cap_iovas = {
+		.header = {
+			.id = VFIO_IOMMU_TYPE1_INFO_CAP_IOVA_RANGE,
+			.version = 1,
+		},
+	};
+	struct interval_tree_span_iter span;
+
+	interval_tree_for_each_span(&span, &ioas->iopt.reserved_itree, 0,
+				    ULONG_MAX) {
+		struct vfio_iova_range range;
+
+		if (!span.is_hole)
+			continue;
+		range.start = span.start_hole;
+		range.end = span.last_hole;
+		if (avail >= struct_size(&cap_iovas, iova_ranges,
+					 cap_iovas.nr_iovas + 1) &&
+		    copy_to_user(&ucap_iovas->iova_ranges[cap_iovas.nr_iovas],
+				 &range, sizeof(range)))
+			return -EFAULT;
+		cap_iovas.nr_iovas++;
+	}
+	if (avail >= struct_size(&cap_iovas, iova_ranges, cap_iovas.nr_iovas) &&
+	    copy_to_user(ucap_iovas, &cap_iovas, sizeof(cap_iovas)))
+		return -EFAULT;
+	return struct_size(&cap_iovas, iova_ranges, cap_iovas.nr_iovas);
+}
+
+static int iommufd_fill_cap_dma_avail(struct iommufd_ioas *ioas,
+				      struct vfio_info_cap_header __user *cur,
+				      size_t avail)
+{
+	struct vfio_iommu_type1_info_dma_avail cap_dma = {
+		.header = {
+			.id = VFIO_IOMMU_TYPE1_INFO_DMA_AVAIL,
+			.version = 1,
+		},
+		/*
+		 * iommufd's limit is based on the cgroup's memory limit.
+		 * Normally vfio would return U16_MAX here, and provide a module
+		 * parameter to adjust it. Since S390 qemu userspace actually
+		 * pays attention and needs a value bigger than U16_MAX return
+		 * U32_MAX.
+		 */
+		.avail = U32_MAX,
+	};
+
+	if (avail >= sizeof(cap_dma) &&
+	    copy_to_user(cur, &cap_dma, sizeof(cap_dma)))
+		return -EFAULT;
+	return sizeof(cap_dma);
+}
+
+static int iommufd_vfio_iommu_get_info(struct iommufd_ctx *ictx,
+				       void __user *arg)
+{
+	typedef int (*fill_cap_fn)(struct iommufd_ioas *ioas,
+				   struct vfio_info_cap_header __user *cur,
+				   size_t avail);
+	static const fill_cap_fn fill_fns[] = {
+		iommufd_fill_cap_dma_avail,
+		iommufd_fill_cap_iova,
+	};
+	size_t minsz = offsetofend(struct vfio_iommu_type1_info, iova_pgsizes);
+	struct vfio_info_cap_header __user *last_cap = NULL;
+	struct vfio_iommu_type1_info info;
+	struct iommufd_ioas *ioas;
+	size_t total_cap_size;
+	int rc;
+	int i;
+
+	if (copy_from_user(&info, arg, minsz))
+		return -EFAULT;
+
+	if (info.argsz < minsz)
+		return -EINVAL;
+	minsz = min_t(size_t, info.argsz, sizeof(info));
+
+	ioas = get_compat_ioas(ictx);
+	if (IS_ERR(ioas))
+		return PTR_ERR(ioas);
+
+	info.flags = VFIO_IOMMU_INFO_PGSIZES;
+	info.iova_pgsizes = iommufd_get_pagesizes(ioas);
+	info.cap_offset = 0;
+
+	down_read(&ioas->iopt.iova_rwsem);
+	total_cap_size = sizeof(info);
+	for (i = 0; i != ARRAY_SIZE(fill_fns); i++) {
+		int cap_size;
+
+		if (info.argsz > total_cap_size)
+			cap_size = fill_fns[i](ioas, arg + total_cap_size,
+					       info.argsz - total_cap_size);
+		else
+			cap_size = fill_fns[i](ioas, NULL, 0);
+		if (cap_size < 0) {
+			rc = cap_size;
+			goto out_put;
+		}
+		if (last_cap && info.argsz >= total_cap_size &&
+		    put_user(total_cap_size, &last_cap->next)) {
+			rc = -EFAULT;
+			goto out_put;
+		}
+		last_cap = arg + total_cap_size;
+		total_cap_size += cap_size;
+	}
+
+	/*
+	 * If the user did not provide enough space then only some caps are
+	 * returned and the argsz will be updated to the correct amount to get
+	 * all caps.
+	 */
+	if (info.argsz >= total_cap_size)
+		info.cap_offset = sizeof(info);
+	info.argsz = total_cap_size;
+	info.flags |= VFIO_IOMMU_INFO_CAPS;
+	if (copy_to_user(arg, &info, minsz)) {
+		rc = -EFAULT;
+		goto out_put;
+	}
+	rc = 0;
+
+out_put:
+	up_read(&ioas->iopt.iova_rwsem);
+	iommufd_put_object(&ioas->obj);
+	return rc;
+}
+
+int iommufd_vfio_ioctl(struct iommufd_ctx *ictx, unsigned int cmd,
+		       unsigned long arg)
+{
+	void __user *uarg = (void __user *)arg;
+
+	switch (cmd) {
+	case VFIO_GET_API_VERSION:
+		return VFIO_API_VERSION;
+	case VFIO_SET_IOMMU:
+		return iommufd_vfio_set_iommu(ictx, arg);
+	case VFIO_CHECK_EXTENSION:
+		return iommufd_vfio_check_extension(ictx, arg);
+	case VFIO_IOMMU_GET_INFO:
+		return iommufd_vfio_iommu_get_info(ictx, uarg);
+	case VFIO_IOMMU_MAP_DMA:
+		return iommufd_vfio_map_dma(ictx, cmd, uarg);
+	case VFIO_IOMMU_UNMAP_DMA:
+		return iommufd_vfio_unmap_dma(ictx, cmd, uarg);
+	case VFIO_IOMMU_DIRTY_PAGES:
+	default:
+		return -ENOIOCTLCMD;
+	}
+	return -ENOIOCTLCMD;
+}
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index 46c481a26d79..84af9a239769 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -54,6 +54,7 @@ void iommufd_access_unpin_pages(struct iommufd_access *access,
 				unsigned long iova, unsigned long length);
 int iommufd_access_rw(struct iommufd_access *access, unsigned long iova,
 		      void *data, size_t len, unsigned int flags);
+int iommufd_vfio_compat_ioas_id(struct iommufd_ctx *ictx, u32 *out_ioas_id);
 #else /* !CONFIG_IOMMUFD */
 static inline struct iommufd_ctx *iommufd_ctx_from_file(struct file *file)
 {
@@ -84,5 +85,11 @@ static inline int iommufd_access_rw(struct iommufd_access *access, unsigned long
 {
 	return -EOPNOTSUPP;
 }
+
+static inline int iommufd_vfio_compat_ioas_id(struct iommufd_ctx *ictx,
+					      u32 *out_ioas_id)
+{
+	return -EOPNOTSUPP;
+}
 #endif /* CONFIG_IOMMUFD */
 #endif
diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
index 30cc5c5e2b34..98ebba80cfa1 100644
--- a/include/uapi/linux/iommufd.h
+++ b/include/uapi/linux/iommufd.h
@@ -44,6 +44,7 @@ enum {
 	IOMMUFD_CMD_IOAS_MAP,
 	IOMMUFD_CMD_IOAS_UNMAP,
 	IOMMUFD_CMD_OPTION,
+	IOMMUFD_CMD_VFIO_IOAS,
 };
 
 /**
@@ -308,4 +309,39 @@ struct iommu_option {
 	__aligned_u64 val64;
 };
 #define IOMMU_OPTION _IO(IOMMUFD_TYPE, IOMMUFD_CMD_OPTION)
+
+/**
+ * enum iommufd_vfio_ioas_op - IOMMU_VFIO_IOAS_* ioctls
+ * @IOMMU_VFIO_IOAS_GET: Get the current compatibility IOAS
+ * @IOMMU_VFIO_IOAS_SET: Change the current compatibility IOAS
+ * @IOMMU_VFIO_IOAS_CLEAR: Disable VFIO compatibility
+ */
+enum iommufd_vfio_ioas_op {
+	IOMMU_VFIO_IOAS_GET = 0,
+	IOMMU_VFIO_IOAS_SET = 1,
+	IOMMU_VFIO_IOAS_CLEAR = 2,
+};
+
+/**
+ * struct iommu_vfio_ioas - ioctl(IOMMU_VFIO_IOAS)
+ * @size: sizeof(struct iommu_vfio_ioas)
+ * @ioas_id: For IOMMU_VFIO_IOAS_SET the input IOAS ID to set
+ *           For IOMMU_VFIO_IOAS_GET will output the IOAS ID
+ * @op: One of enum iommufd_vfio_ioas_op
+ * @__reserved: Must be 0
+ *
+ * The VFIO compatibility support uses a single ioas because VFIO APIs do not
+ * support the ID field. Set or Get the IOAS that VFIO compatibility will use.
+ * When VFIO_GROUP_SET_CONTAINER is used on an iommufd it will get the
+ * compatibility ioas, either by taking what is already set, or auto creating
+ * one. From then on VFIO will continue to use that ioas and is not effected by
+ * this ioctl. SET or CLEAR does not destroy any auto-created IOAS.
+ */
+struct iommu_vfio_ioas {
+	__u32 size;
+	__u32 ioas_id;
+	__u16 op;
+	__u16 __reserved;
+};
+#define IOMMU_VFIO_IOAS _IO(IOMMUFD_TYPE, IOMMUFD_CMD_VFIO_IOAS)
 #endif