linux-kernel - [PATCH 4.0 039/105] iommu/vt-d: Fix passthrough mode with translation-disabled devices

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Date:	Fri, 19 Jun 2015 13:35:29 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, David Woodhouse <David.Woodhouse@...el.com>
Subject: [PATCH 4.0 039/105] iommu/vt-d: Fix passthrough mode with translation-disabled devices

4.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Woodhouse <David.Woodhouse@...el.com>

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@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/iommu/intel-iommu.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -673,6 +673,11 @@ static void domain_update_iommu_cap(stru
 	domain->iommu_superpage = domain_update_iommu_superpage(NULL);
 }
 
+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;
@@ -682,6 +687,9 @@ static struct intel_iommu *device_to_iom
 	u16 segment = 0;
 	int i;
 
+	if (iommu_dummy(dev))
+		return NULL;
+
 	if (dev_is_pci(dev)) {
 		pdev = to_pci_dev(dev);
 		segment = pci_domain_nr(pdev->bus);
@@ -2974,11 +2982,6 @@ static inline struct dmar_domain *get_va
 	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)
 {


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