Re: [PATCH v2 2/2] vfio: Fix unbalanced vfio_df_close call in no-iommu mode

[Alex Williamson <alex.williamson@redhat.com>]

On Tue,  3 Jun 2025 08:23:43 -0700
Jacob Pan <jacob.pan@linux.microsoft.com> wrote:

> From: Jason Gunthorpe <jgg@nvidia.com>
> 
> For devices with no-iommu enabled in IOMMUFD VFIO compat mode, the group
> open path skips vfio_df_open(), leaving open_count at 0. This causes a
> warning in vfio_assert_device_open(device) when vfio_df_close() is called
> during group close.
> 
> The correct behavior is to skip only the IOMMUFD bind in the device open
> path for no-iommu devices. Commit 6086efe73498 omitted vfio_df_open(),
> which was too broad. This patch restores the previous behavior, ensuring
> the vfio_df_open is called in the group open path.
> 
> Fixes: 6086efe73498 ("vfio-iommufd: Move noiommu compat validation out of vfio_iommufd_bind()")
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Tested-by: Jacob Pan <jacob.pan@linux.microsoft.com>
> Signed-off-by: Jacob Pan <jacob.pan@linux.microsoft.com>
> ---
> v2: Use a fix from Jason
> ---
>  drivers/vfio/group.c     | 10 +++++-----
>  drivers/vfio/iommufd.c   |  3 ---
>  drivers/vfio/vfio_main.c | 26 ++++++++++++++++----------
>  3 files changed, 21 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> index c321d442f0da..8f5fe8a392de 100644
> --- a/drivers/vfio/group.c
> +++ b/drivers/vfio/group.c
> @@ -192,18 +192,18 @@ static int vfio_df_group_open(struct vfio_device_file *df)
>  		 * implies they expected translation to exist
>  		 */
>  		if (!capable(CAP_SYS_RAWIO) ||
> -		    vfio_iommufd_device_has_compat_ioas(device, df->iommufd))
> +		    vfio_iommufd_device_has_compat_ioas(device, df->iommufd)) {
>  			ret = -EPERM;
> -		else
> -			ret = 0;
> -		goto out_put_kvm;
> +			goto out_put_kvm;
> +		}
>  	}
>  
>  	ret = vfio_df_open(df);
>  	if (ret)
>  		goto out_put_kvm;
>  
> -	if (df->iommufd && device->open_count == 1) {
> +	if (df->iommufd && device->open_count == 1 &&
> +	    !vfio_device_is_noiommu(device)) {

Why do we need this?

int vfio_iommufd_compat_attach_ioas(struct vfio_device *vdev,
                                    struct iommufd_ctx *ictx)
{
        u32 ioas_id;
        int ret;

        lockdep_assert_held(&vdev->dev_set->lock);

        /* compat noiommu does not need to do ioas attach */
        if (vfio_device_is_noiommu(vdev))
                return 0;


>  		ret = vfio_iommufd_compat_attach_ioas(device, df->iommufd);
>  		if (ret)
>  			goto out_close_device;
> diff --git a/drivers/vfio/iommufd.c b/drivers/vfio/iommufd.c
> index c8c3a2d53f86..26c9c3068c77 100644
> --- a/drivers/vfio/iommufd.c
> +++ b/drivers/vfio/iommufd.c
> @@ -54,9 +54,6 @@ void vfio_df_iommufd_unbind(struct vfio_device_file *df)
>  
>  	lockdep_assert_held(&vdev->dev_set->lock);
>  
> -	if (vfio_device_is_noiommu(vdev))
> -		return;
> -

Why not keep this and add similar to vfio_df_iommufd_bind()?  It seems
cleaner to me.  Thanks,

Alex

>  	if (vdev->ops->unbind_iommufd)
>  		vdev->ops->unbind_iommufd(vdev);
>  }
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 5046cae05222..ac2dbd4e5d04 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -506,17 +506,19 @@ static int vfio_df_device_first_open(struct vfio_device_file *df)
>  {
>  	struct vfio_device *device = df->device;
>  	struct iommufd_ctx *iommufd = df->iommufd;
> -	int ret;
> +	int ret = 0;
>  
>  	lockdep_assert_held(&device->dev_set->lock);
>  
>  	if (!try_module_get(device->dev->driver->owner))
>  		return -ENODEV;
>  
> -	if (iommufd)
> -		ret = vfio_df_iommufd_bind(df);
> -	else
> +	if (iommufd) {
> +		if (!vfio_device_is_noiommu(device))
> +			ret = vfio_df_iommufd_bind(df);
> +	} else {
>  		ret = vfio_device_group_use_iommu(device);
> +	}
>  	if (ret)
>  		goto err_module_put;
>  
> @@ -528,10 +530,12 @@ static int vfio_df_device_first_open(struct vfio_device_file *df)
>  	return 0;
>  
>  err_unuse_iommu:
> -	if (iommufd)
> -		vfio_df_iommufd_unbind(df);
> -	else
> +	if (iommufd) {
> +		if (!vfio_device_is_noiommu(device))
> +			vfio_df_iommufd_unbind(df);
> +	} else {
>  		vfio_device_group_unuse_iommu(device);
> +	}
>  err_module_put:
>  	module_put(device->dev->driver->owner);
>  	return ret;
> @@ -546,10 +550,12 @@ static void vfio_df_device_last_close(struct vfio_device_file *df)
>  
>  	if (device->ops->close_device)
>  		device->ops->close_device(device);
> -	if (iommufd)
> -		vfio_df_iommufd_unbind(df);
> -	else
> +	if (iommufd) {
> +		if (!vfio_device_is_noiommu(device))
> +			vfio_df_iommufd_unbind(df);
> +	} else {
>  		vfio_device_group_unuse_iommu(device);
> +	}
>  	module_put(device->dev->driver->owner);
>  }
>