[3.16.y-ckt stable] Patch "iommu/vt-d: Fix passthrough mode with translation-disabled devices" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    iommu/vt-d: Fix passthrough mode with translation-disabled devices

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt14.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 42d0b06312f9888f88d6caf35f842fe599fa2e4a Mon Sep 17 00:00:00 2001
From: David Woodhouse <David.Woodhouse at intel.com>
Date: Mon, 11 May 2015 14:59:20 +0100
Subject: iommu/vt-d: Fix passthrough mode with translation-disabled devices

commit 4ed6a540fab8ea4388c1703b73ecfed68a2009d1 upstream.

When we use 'intel_iommu=igfx_off' to disable translation for the
graphics, and when we discover that the BIOS has misconfigured the DMAR
setup for I/OAT, we use a special DUMMY_DEVICE_DOMAIN_INFO value in
dev->archdata.iommu to indicate that translation is disabled.

With passthrough mode, we were attempting to dereference that as a
normal pointer to a struct device_domain_info when setting up an
identity mapping for the affected device.

This fixes the problem by making device_to_iommu() explicitly check for
the special value and indicate that no IOMMU was found to handle the
devices in question.

Signed-off-by: David Woodhouse <David.Woodhouse at intel.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/iommu/intel-iommu.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index afbde3730b11..baffab3948d7 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -666,6 +666,11 @@ static void domain_update_iommu_cap(struct dmar_domain *domain)
 	domain_update_iommu_superpage(domain);
 }

+static int iommu_dummy(struct device *dev)
+{
+	return dev->archdata.iommu == DUMMY_DEVICE_DOMAIN_INFO;
+}
+
 static struct intel_iommu *device_to_iommu(struct device *dev, u8 *bus, u8 *devfn)
 {
 	struct dmar_drhd_unit *drhd = NULL;
@@ -675,6 +680,9 @@ static struct intel_iommu *device_to_iommu(struct device *dev, u8 *bus, u8 *devf
 	u16 segment;
 	int i;

+	if (iommu_dummy(dev))
+		return NULL;
+
 	if (dev_is_pci(dev)) {
 		pdev = to_pci_dev(dev);
 		segment = pci_domain_nr(pdev->bus);
@@ -2965,11 +2973,6 @@ static inline struct dmar_domain *get_valid_domain_for_dev(struct device *dev)
 	return __get_valid_domain_for_dev(dev);
 }

-static int iommu_dummy(struct device *dev)
-{
-	return dev->archdata.iommu == DUMMY_DEVICE_DOMAIN_INFO;
-}
-
 /* Check if the dev needs to go through non-identity map and unmap process.*/
 static int iommu_no_mapping(struct device *dev)
 {