[PATCH V4 03/10] iommufd: Allow binding to a noiommu device

Jacob Pan
2026-04-14T21:14:17Z

From: Jason Gunthorpe <jgg@nvidia.com>

Allow iommufd to bind devices without an IOMMU (noiommu mode) by creating
a dummy IOMMU group for such devices and skipping hwpt operations.

This enables noiommu devices to operate through the same iommufd API as IOMMU-
capable devices.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Jacob Pan <jacob.pan@linux.microsoft.com>

---
v4:
- handle partially initialized idev w/o igroup (Sashiko)
v3:
- handle new error cases iommufd_device_bind. (Mostafa)
---
drivers/iommu/iommufd/device.c | 132 +++++++++++++++++++++++----------
1 file changed, 93 insertions(+), 39 deletions(-)

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index 2f30ea069f66..0283ac39be55 100644
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -23,6 +23,11 @@ struct iommufd_attach {
struct xarray device_array;
};

+static bool is_vfio_noiommu(struct iommufd_device *idev)
+{
+ return !device_iommu_mapped(idev->dev) || !idev->dev->iommu;
+}
+
static void iommufd_group_release(struct kref *kref)
{
struct iommufd_group *igroup =
@@ -30,9 +35,11 @@ static void iommufd_group_release(struct kref *kref)

WARN_ON(!xa_empty(&igroup->pasid_attach));

- xa_cmpxchg(&igroup->ictx->groups, iommu_group_id(igroup->group), igroup,
- NULL, GFP_KERNEL);
- iommu_group_put(igroup->group);
+ if (igroup->group) {
+ xa_cmpxchg(&igroup->ictx->groups, iommu_group_id(igroup->group),
+ igroup, NULL, GFP_KERNEL);
+ iommu_group_put(igroup->group);
+ }
mutex_destroy(&igroup->lock);
kfree(igroup);
}
@@ -204,32 +211,19 @@ void iommufd_device_destroy(struct iommufd_object *obj)
struct iommufd_device *idev =
container_of(obj, struct iommufd_device, obj);

- iommu_device_release_dma_owner(idev->dev);
+ if (!idev->igroup)
+ return;
+ if (!is_vfio_noiommu(idev))
+ iommu_device_release_dma_owner(idev->dev);
iommufd_put_group(idev->igroup);
if (!iommufd_selftest_is_mock_dev(idev->dev))
iommufd_ctx_put(idev->ictx);
}

-/**
- * iommufd_device_bind - Bind a physical device to an iommu fd
- * @ictx: iommufd file descriptor
- * @dev: Pointer to a physical device struct
- * @id: Output ID number to return to userspace for this device
- *
- * A successful bind establishes an ownership over the device and returns
- * struct iommufd_device pointer, otherwise returns error pointer.
- *
- * A driver using this API must set driver_managed_dma and must not touch
- * the device until this routine succeeds and establishes ownership.
- *
- * Binding a PCI device places the entire RID under iommufd control.
- *
- * The caller must undo this with iommufd_device_unbind()
- */
-struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx,
- struct device *dev, u32 *id)
+static int iommufd_bind_iommu(struct iommufd_device *idev)
{
- struct iommufd_device *idev;
+ struct iommufd_ctx *ictx = idev->ictx;
+ struct device *dev = idev->dev;
struct iommufd_group *igroup;
int rc;

@@ -238,11 +232,11 @@ struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx,
* to restore cache coherency.
*/
if (!device_iommu_capable(dev, IOMMU_CAP_CACHE_COHERENCY))
- return ERR_PTR(-EINVAL);
+ return -EINVAL;

- igroup = iommufd_get_group(ictx, dev);
+ igroup = iommufd_get_group(idev->ictx, dev);
if (IS_ERR(igroup))
- return ERR_CAST(igroup);
+ return PTR_ERR(igroup);

/*
* For historical compat with VFIO the insecure interrupt path is
@@ -268,21 +262,69 @@ struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx,
if (rc)
goto out_group_put;

+ /* igroup refcount moves into iommufd_device */
+ idev->igroup = igroup;
+ return 0;
+
+out_group_put:
+ iommufd_put_group(igroup);
+ return rc;
+}
+
+/**
+ * iommufd_device_bind - Bind a physical device to an iommu fd
+ * @ictx: iommufd file descriptor
+ * @dev: Pointer to a physical device struct
+ * @id: Output ID number to return to userspace for this device
+ *
+ * A successful bind establishes an ownership over the device and returns
+ * struct iommufd_device pointer, otherwise returns error pointer.
+ *
+ * A driver using this API must set driver_managed_dma and must not touch
+ * the device until this routine succeeds and establishes ownership.
+ *
+ * Binding a PCI device places the entire RID under iommufd control.
+ *
+ * The caller must undo this with iommufd_device_unbind()
+ */
+struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx,
+ struct device *dev, u32 *id)
+{
+ struct iommufd_device *idev;
+ int rc;
+
idev = iommufd_object_alloc(ictx, idev, IOMMUFD_OBJ_DEVICE);
- if (IS_ERR(idev)) {
- rc = PTR_ERR(idev);
- goto out_release_owner;
- }
+ if (IS_ERR(idev))
+ return idev;
+
idev->ictx = ictx;
- if (!iommufd_selftest_is_mock_dev(dev))
- iommufd_ctx_get(ictx);
idev->dev = dev;
idev->enforce_cache_coherency =
device_iommu_capable(dev, IOMMU_CAP_ENFORCE_CACHE_COHERENCY);
+
+ if (!is_vfio_noiommu(idev)) {
+ rc = iommufd_bind_iommu(idev);
+ if (rc)
+ goto err_out;
+ } else {
+ struct iommufd_group *igroup;
+
+ /*
+ * Create a dummy igroup, lots of stuff expects ths igroup to be
+ * present, but a NULL igroup->group is OK
+ */
+ igroup = iommufd_alloc_group(ictx, NULL);
+ if (IS_ERR(igroup)) {
+ rc = PTR_ERR(igroup);
+ goto err_out;
+ }
+ idev->igroup = igroup;
+ }
+
+ if (!iommufd_selftest_is_mock_dev(dev))
+ iommufd_ctx_get(ictx);
/* The calling driver is a user until iommufd_device_unbind() */
refcount_inc(&idev->obj.users);
- /* igroup refcount moves into iommufd_device */
- idev->igroup = igroup;

/*
* If the caller fails after this success it must call
@@ -294,11 +336,14 @@ struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx,
*id = idev->obj.id;
return idev;

-out_release_owner:
- iommu_device_release_dma_owner(dev);
-out_group_put:
- iommufd_put_group(igroup);
+err_out:
+ /*
+ * Be careful that iommufd_device_destroy() can handle partial
+ * initialization.
+ */
+ iommufd_object_abort_and_destroy(ictx, &idev->obj);
return ERR_PTR(rc);
+
}
EXPORT_SYMBOL_NS_GPL(iommufd_device_bind, "IOMMUFD");

@@ -512,6 +557,9 @@ static int iommufd_hwpt_attach_device(struct iommufd_hw_pagetable *hwpt,
struct iommufd_attach_handle *handle;
int rc;

+ if (is_vfio_noiommu(idev))
+ return 0;
+
if (!iommufd_hwpt_compatible_device(hwpt, idev))
return -EINVAL;

@@ -559,6 +607,9 @@ static void iommufd_hwpt_detach_device(struct iommufd_hw_pagetable *hwpt,
{
struct iommufd_attach_handle *handle;

+ if (is_vfio_noiommu(idev))
+ return;
+
handle = iommufd_device_get_attach_handle(idev, pasid);
if (pasid == IOMMU_NO_PASID)
iommu_detach_group_handle(hwpt->domain, idev->igroup->group);
@@ -577,6 +628,9 @@ static int iommufd_hwpt_replace_device(struct iommufd_device *idev,
struct iommufd_attach_handle *handle, *old_handle;
int rc;

+ if (is_vfio_noiommu(idev))
+ return 0;
+
if (!iommufd_hwpt_compatible_device(hwpt, idev))
return -EINVAL;

@@ -652,7 +706,7 @@ int iommufd_hw_pagetable_attach(struct iommufd_hw_pagetable *hwpt,
goto err_release_devid;
}

- if (attach_resv) {
+ if (attach_resv && !is_vfio_noiommu(idev)) {
rc = iommufd_device_attach_reserved_iova(idev, hwpt_paging);
if (rc)
goto err_release_devid;
--
2.34.1