Re: [PATCH V2 03/11] iommufd: Allow binding to a noiommu device

[Mostafa Saleh <smostafa@google.com>]

On Thu, Mar 12, 2026 at 08:56:29AM -0700, Jacob Pan wrote:
> 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>
> ---
>  drivers/iommu/iommufd/device.c | 113 ++++++++++++++++++++++-----------
>  1 file changed, 76 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> index 54d73016468f..c38d3efa3d6f 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;

Do this need to check for CONFIG_VFIO_NOIOMMU and maybe the module
param enable_unsafe_noiommu_mode similar to the legacy implemenation?

> +}
> +
>  static void iommufd_group_release(struct kref *kref)
>  {
>  	struct iommufd_group *igroup =
> @@ -205,32 +210,17 @@ 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 (!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;
>  
> @@ -239,11 +229,11 @@ 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
> @@ -269,21 +259,66 @@ 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);

The next code introduces new error cases, do that need to be cleaned in
that case by calling iommufd_object_abort_and_destroy()?

Thanks,
Mostafa

> -	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)
> +			return ERR_PTR(rc);
> +	} 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))
> +			return ERR_CAST(igroup);
> +		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
> @@ -295,11 +330,6 @@ 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);
> -	return ERR_PTR(rc);
>  }
>  EXPORT_SYMBOL_NS_GPL(iommufd_device_bind, "IOMMUFD");
>  
> @@ -513,6 +543,9 @@ 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;
>  
> @@ -560,6 +593,9 @@ 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);
> @@ -578,6 +614,9 @@ 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;
>  
> @@ -653,7 +692,7 @@ 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
>