From: Jason Gunthorpe <jgg@nvidia.com>
Date: Mon, 4 Jul 2022 22:10:50 -0300
Subject: vfio: Move IOMMU_CAP_CACHE_COHERENCY test to after we know we have a
 group
Git-commit: afe4e376ac5d568367b447ca90c12858d0935b86
Patch-mainline: v5.19-rc7
References: bsc#1205701

The test isn't going to work if a group doesn't exist. Normally this isn't
a problem since VFIO isn't going to create a device if there is no group,
but the special CONFIG_VFIO_NOIOMMU behavior allows bypassing this
prevention. The new cap test effectively forces a group and breaks this
config option.

Move the cap test to vfio_group_find_or_alloc() which is the earliest time
we know we have a group available and thus are not running in noiommu mode.

Fixes: e8ae0e140c05 ("vfio: Require that devices support DMA cache coherence")
Reported-by: Xiang Chen <chenxiang66@hisilicon.com>
Tested-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/0-v1-e8934b490f36+f4-vfio_cap_fix_jgg@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 drivers/vfio/vfio.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 61e71c1154be..e60b06f2ac22 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -549,6 +549,16 @@ static struct vfio_group *vfio_group_find_or_alloc(struct device *dev)
 	if (!iommu_group)
 		return ERR_PTR(-EINVAL);
 
+	/*
+	 * VFIO always sets IOMMU_CACHE because we offer no way for userspace to
+	 * restore cache coherency. It has to be checked here because it is only
+	 * valid for cases where we are using iommu groups.
+	 */
+	if (!iommu_capable(dev->bus, IOMMU_CAP_CACHE_COHERENCY)) {
+		iommu_group_put(iommu_group);
+		return ERR_PTR(-EINVAL);
+	}
+
 	group = vfio_group_get_from_iommu(iommu_group);
 	if (!group)
 		group = vfio_create_group(iommu_group, VFIO_IOMMU);
@@ -601,13 +611,6 @@ static int __vfio_register_dev(struct vfio_device *device,
 
 int vfio_register_group_dev(struct vfio_device *device)
 {
-	/*
-	 * VFIO always sets IOMMU_CACHE because we offer no way for userspace to
-	 * restore cache coherency.
-	 */
-	if (!iommu_capable(device->dev->bus, IOMMU_CAP_CACHE_COHERENCY))
-		return -EINVAL;
-
 	return __vfio_register_dev(device,
 		vfio_group_find_or_alloc(device->dev));
 }