linux-kernel - Re: [PATCH v3 1/2] vfio: Fix unbalanced vfio_df

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Message-ID: <20250710114025.513b0af4@DESKTOP-0403QTC.>
Date: Thu, 10 Jul 2025 11:40:25 -0700
From: Jacob Pan <jacob.pan@...ux.microsoft.com>
To: linux-kernel@...r.kernel.org, "iommu@...ts.linux.dev"
 <iommu@...ts.linux.dev>, Alex Williamson <alex.williamson@...hat.com>,
 "Liu, Yi L" <yi.l.liu@...el.com>, "jgg@...dia.com" <jgg@...dia.com>, Jacob
 Pan <jacob.pan@...ux.microsoft.com>
Cc: Zhang Yu <zhangyu1@...rosoft.com>, Easwar Hariharan
 <eahariha@...ux.microsoft.com>, Saurabh Sengar
 <ssengar@...ux.microsoft.com>
Subject: Re: [PATCH v3 1/2] vfio: Fix unbalanced vfio_df_close call in
 no-iommu mode

Hi Alex et al,

Just wondering if there are more comments?

Thanks,

Jacob

On Wed, 18 Jun 2025 16:46:17 -0700
Jacob Pan <jacob.pan@...ux.microsoft.com> wrote:

> 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()") Suggested-by: Alex Williamson
> <alex.williamson@...hat.com> Suggested-by: Jason Gunthorpe
> <jgg@...dia.com> Signed-off-by: Jacob Pan
> <jacob.pan@...ux.microsoft.com> ---
> v3: Apply a concise fix from Alex
> v2: Use a fix from Jason
> ---
>  drivers/vfio/group.c   | 7 +++----
>  drivers/vfio/iommufd.c | 4 ++++
>  2 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> index c321d442f0da..c376a6279de0 100644
> --- a/drivers/vfio/group.c
> +++ b/drivers/vfio/group.c
> @@ -192,11 +192,10 @@ 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);
> diff --git a/drivers/vfio/iommufd.c b/drivers/vfio/iommufd.c
> index c8c3a2d53f86..a38d262c6028 100644
> --- a/drivers/vfio/iommufd.c
> +++ b/drivers/vfio/iommufd.c
> @@ -25,6 +25,10 @@ int vfio_df_iommufd_bind(struct vfio_device_file
> *df) 
>  	lockdep_assert_held(&vdev->dev_set->lock);
>  
> +	/* Returns 0 to permit device opening under noiommu mode */
> +	if (vfio_device_is_noiommu(vdev))
> +		return 0;
> +
>  	return vdev->ops->bind_iommufd(vdev, ictx, &df->devid);
>  }
>