From: Ben Hutchings <ben@decadent.org.uk>
Date: Wed, 21 Aug 2019 00:05:30 +0100
Subject: intel-iommu: Add option to exclude integrated GPU only
Bug-Debian: https://bugs.debian.org/935270
Bug-Kali: https://bugs.kali.org/view.php?id=5644

There is still laptop firmware that touches the integrated GPU behind
the operating system's back, and doesn't say so in the RMRR table.
Enabling the IOMMU for all devices causes breakage, but turning it off
for all graphics devices seems like a major weakness.

Add an option, intel_iommu=intgpu_off, to exclude only integrated GPUs
from remapping.  This is a narrower exclusion than igfx_off: it only
affects Intel devices on the root bus.  Devices attached through an
external port (Thunderbolt or ExpressCard) won't be on the root bus.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 Documentation/admin-guide/kernel-parameters.txt |  2 ++
 drivers/iommu/intel/iommu.c                     | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2174,6 +2174,8 @@
 			bypassed by not enabling DMAR with this option. In
 			this case, gfx device will use physical address for
 			DMA.
+		intgpu_off [Default Off]
+			Bypass the DMAR unit for an integrated GPU only.
 		strict [Default Off]
 			Deprecated, equivalent to iommu.strict=1.
 		sp_off [Default Off]
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -35,6 +35,9 @@
 #define CONTEXT_SIZE		VTD_PAGE_SIZE
 
 #define IS_GFX_DEVICE(pdev) ((pdev->class >> 16) == PCI_BASE_CLASS_DISPLAY)
+#define IS_INTGPU_DEVICE(pdev) (IS_GFX_DEVICE(pdev) &&		\
+				(pdev)->vendor == 0x8086 &&	\
+				pci_is_root_bus((pdev)->bus))
 #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)
@@ -221,12 +224,14 @@ int intel_iommu_sm = IS_ENABLED(CONFIG_I
 int intel_iommu_enabled = 0;
 EXPORT_SYMBOL_GPL(intel_iommu_enabled);
 
+static int dmar_map_intgpu = 1;
 static int intel_iommu_superpage = 1;
 static int iommu_identity_mapping;
 static int iommu_skip_te_disable;
 static int disable_igfx_iommu;
 
 #define IDENTMAP_AZALIA		4
+#define IDENTMAP_INTGPU		8
 
 const struct iommu_ops intel_iommu_ops;
 static const struct iommu_dirty_ops intel_dirty_ops;
@@ -266,6 +271,9 @@ static int __init intel_iommu_setup(char
 		} else if (!strncmp(str, "igfx_off", 8)) {
 			disable_igfx_iommu = 1;
 			pr_info("Disable GFX device mapping\n");
+		} else if (!strncmp(str, "intgpu_off", 10)) {
+			dmar_map_intgpu = 0;
+			pr_info("Disable integrated GPU device mapping\n");
 		} else if (!strncmp(str, "forcedac", 8)) {
 			pr_warn("intel_iommu=forcedac deprecated; use iommu.forcedac instead\n");
 			iommu_dma_forcedac = true;
@@ -2401,6 +2409,9 @@ static int device_def_domain_type(struct
 
 		if ((iommu_identity_mapping & IDENTMAP_AZALIA) && IS_AZALIA(pdev))
 			return IOMMU_DOMAIN_IDENTITY;
+
+		if ((iommu_identity_mapping & IDENTMAP_INTGPU) && IS_INTGPU_DEVICE(pdev))
+			return IOMMU_DOMAIN_IDENTITY;
 	}
 
 	return 0;
@@ -2701,6 +2712,9 @@ static int __init init_dmars(void)
 		iommu_set_root_entry(iommu);
 	}
 
+	if (!dmar_map_intgpu)
+		iommu_identity_mapping |= IDENTMAP_INTGPU;
+
 	check_tylersburg_isoch();
 
 	ret = si_domain_init(hw_pass_through);
