Patch "iommu/vt-d: Allow RMRR on graphics devices too" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
iommu-vt-d-allow-rmrr-on-graphics-devices-too.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: David Woodhouse <[email protected]>
Date: Wed, 25 Mar 2015 15:05:47 +0000
Subject: iommu/vt-d: Allow RMRR on graphics devices too

From: David Woodhouse <[email protected]>

commit 18436afdc11a00ac881990b454cfb2eae81d6003 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.

---
 drivers/iommu/intel-iommu.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

@@ -50,6 +50,7 @@
 #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)
 

@@ -2554,6 +2555,10 @@ static bool device_has_rmrr(struct devic
  * 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)
 {

@@ -2563,7 +2568,7 @@ static bool device_is_rmrr_locked(struct
 	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;
 	}
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/iommu-vt-d-fix-passthrough-mode-with-translation-disabled-devices.patch queue-4.0/iommu-vt-d-allow-rmrr-on-graphics-devices-too.patch
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