iommu/vt-d: Allow RMRR on graphics devices too

commit 18436afd upstream.

Commit c875d2c1 ("iommu/vt-d: Exclude devices using RMRRs from IOMMU API
domains") prevents certain options for devices with RMRRs. This even
prevents those devices from getting a 1:1 mapping with 'iommu=pt',
because we don't have the code to handle *preserving* the RMRR regions
when moving the device between domains.

There's already an exclusion for USB devices, because we know the only
reason for RMRRs there is a misguided desire to keep legacy
keyboard/mouse emulation running in some theoretical OS which doesn't
have support for USB in its own right... but which *does* enable the
IOMMU.

Add an exclusion for graphics devices too, so that 'iommu=pt' works
there. We should be able to successfully assign graphics devices to
guests too, as long as the initial handling of stolen memory is
reconfigured appropriately. This has certainly worked in the past.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/iommu/intel-iommu.c

@@ -51,6 +51,7 @@
 #define CONTEXT_SIZE		VTD_PAGE_SIZE
 
 #define IS_GFX_DEVICE(pdev) ((pdev->class >> 16) == PCI_BASE_CLASS_DISPLAY)
+#define IS_USB_DEVICE(pdev) ((pdev->class >> 8) == PCI_CLASS_SERIAL_USB)
 #define IS_ISA_DEVICE(pdev) ((pdev->class >> 8) == PCI_CLASS_BRIDGE_ISA)
 #define IS_AZALIA(pdev) ((pdev)->vendor == 0x8086 && (pdev)->device == 0x3a3e)
 
@@ -2538,6 +2539,10 @@ static bool device_has_rmrr(struct device *dev)
  * In both cases we assume that PCI USB devices with RMRRs have them largely
  * for historical reasons and that the RMRR space is not actively used post
  * boot.  This exclusion may change if vendors begin to abuse it.
+ *
+ * The same exception is made for graphics devices, with the requirement that
+ * any use of the RMRR regions will be torn down before assigning the device
+ * to a guest.
  */
 static bool device_is_rmrr_locked(struct device *dev)
 {
@@ -2547,7 +2552,7 @@ static bool device_is_rmrr_locked(struct device *dev)
 	if (dev_is_pci(dev)) {
 		struct pci_dev *pdev = to_pci_dev(dev);
 
-		if ((pdev->class >> 8) == PCI_CLASS_SERIAL_USB)
+		if (IS_USB_DEVICE(pdev) || IS_GFX_DEVICE(pdev))
 			return false;
 	}