vfio: Move IOMMU_CAP_CACHE_COHERENCY test to after we know we have a group

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>

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 61e71c1154be673e9c40989958ff0c6a86600161..e60b06f2ac22393ae4f3deaf02e680d506368eab 100644 (file)
--- 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));
 }