diff --git a/Documentation/ABI/testing/sysfs-bus-thunderbolt b/Documentation/ABI/testing/sysfs-bus-thunderbolt
index 151584a1f950..b21fba14689b 100644
--- a/Documentation/ABI/testing/sysfs-bus-thunderbolt
+++ b/Documentation/ABI/testing/sysfs-bus-thunderbolt
@@ -21,6 +21,15 @@ Description:	Holds a comma separated list of device unique_ids that
 		If a device is authorized automatically during boot its
 		boot attribute is set to 1.
 
+What: /sys/bus/thunderbolt/devices/.../domainX/iommu_dma_protection
+Date:		Mar 2019
+KernelVersion:	4.21
+Contact:	thunderbolt-software@lists.01.org
+Description:	This attribute tells whether the system uses IOMMU
+		for DMA protection. Value of 1 means IOMMU is used 0 means
+		it is not (DMA protection is solely based on Thunderbolt
+		security levels).
+
 What: /sys/bus/thunderbolt/devices/.../domainX/security
 Date:		Sep 2017
 KernelVersion:	4.13
diff --git a/Documentation/admin-guide/thunderbolt.rst b/Documentation/admin-guide/thunderbolt.rst
index 35fccba6a9a6..ccac2596a49f 100644
--- a/Documentation/admin-guide/thunderbolt.rst
+++ b/Documentation/admin-guide/thunderbolt.rst
@@ -133,6 +133,29 @@ If the user still wants to connect the device they can either approve
 the device without a key or write a new key and write 1 to the
 ``authorized`` file to get the new key stored on the device NVM.
 
+DMA protection utilizing IOMMU
+------------------------------
+Recent systems shipping with Windows 10 version 1803 or later may support a
+feature called `Kernel DMA Protection for Thunderbolt 3`_.  This means that
+Thunderbolt security is handled by an IOMMU so connected devices cannot
+access memory regions outside of what is allocated for them by drivers.
+When Linux is running on such system it automatically enables IOMMU if not
+enabled by the user already. These systems can be identified by reading
+``1`` from ``/sys/bus/thunderbolt/devices/domainX/iommu_dma_protection``
+attribute.
+
+The driver does not do anything special in this case but because DMA
+protection is handled by the IOMMU, security levels (if set) are
+redundant. For this reason some systems ship with security level set to
+``none``. Other systems have security level set to ``user`` in order to
+support downgrade to older Windows, so users who want to automatically
+authorize devices when IOMMU DMA protection is enabled can use the
+following ``udev`` rule::
+
+  ACTION=="add", SUBSYSTEM=="thunderbolt", ATTRS{iommu_dma_protection}=="1", ATTR{authorized}=="0", ATTR{authorized}="1"
+
+.. _Kernel DMA Protection for Thunderbolt 3: https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt
+
 Upgrading NVM on Thunderbolt device or host
 -------------------------------------------
 Since most of the functionality is handled in firmware running on a
diff --git a/drivers/thunderbolt/domain.c b/drivers/thunderbolt/domain.c
index 93e562f18d40..7416bdbd8576 100644
--- a/drivers/thunderbolt/domain.c
+++ b/drivers/thunderbolt/domain.c
@@ -7,7 +7,9 @@
  */
 
 #include <linux/device.h>
+#include <linux/dmar.h>
 #include <linux/idr.h>
+#include <linux/iommu.h>
 #include <linux/module.h>
 #include <linux/pm_runtime.h>
 #include <linux/slab.h>
@@ -236,6 +238,20 @@ static ssize_t boot_acl_store(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RW(boot_acl);
 
+static ssize_t iommu_dma_protection_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	/*
+	 * Kernel DMA protection is a feature where Thunderbolt security is
+	 * handled natively using IOMMU. It is enabled when IOMMU is
+	 * enabled and ACPI DMAR table has DMAR_PLATFORM_OPT_IN set.
+	 */
+	return sprintf(buf, "%d\n",
+		       iommu_present(&pci_bus_type) && dmar_platform_optin());
+}
+static DEVICE_ATTR_RO(iommu_dma_protection);
+
 static ssize_t security_show(struct device *dev, struct device_attribute *attr,
 			     char *buf)
 {
@@ -251,6 +267,7 @@ static DEVICE_ATTR_RO(security);
 
 static struct attribute *domain_attrs[] = {
 	&dev_attr_boot_acl.attr,
+	&dev_attr_iommu_dma_protection.attr,
 	&dev_attr_security.attr,
 	NULL,
 };
