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

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Message-Id: <20250618234618.1910456-1-jacob.pan@linux.microsoft.com>
Date: Wed, 18 Jun 2025 16:46:17 -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: [PATCH v3 1/2] vfio: Fix unbalanced vfio_df_close call in no-iommu mode

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);
 }
 
-- 
2.34.1