intel-iommu: Fix oops with intel_iommu=igfx_off

The hotplug notifier will call find_domain() to see if the device in
question has been assigned an IOMMU domain. However, this should never
be called for devices with a "dummy" domain, such as graphics devices
when intel_iommu=igfx_off is set and the corresponding IOMMU isn't even
initialised. If you do that, it'll oops as it dereferences the (-1)
pointer.

The notifier function should check iommu_no_mapping() for the
device before doing anything else.

Cc: stable@kernel.org
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 83cabdc118db..e3e84cac0e98 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -3247,6 +3247,9 @@ static int device_notifier(struct notifier_block *nb,
         struct pci_dev *pdev = to_pci_dev(dev);
         struct dmar_domain *domain;
 
+        if (iommu_no_mapping(dev))
+                return 0;
+
         domain = find_domain(pdev);
         if (!domain)
                 return 0;