PCI: Treat "external-facing" devices themselves as internal

"External-facing" devices are internal devices that expose PCIe hierarchies
such as Thunderbolt outside the platform [1].  Previously these internal
devices were marked as "untrusted" the same as devices downstream from
them.

Use the ACPI or DT information to identify external-facing devices, but
only mark the devices *downstream* from them as "untrusted" [2].  The
external-facing device itself is no longer marked as untrusted.

[1] https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#identifying-externally-exposed-pcie-root-ports
[2] https://lore.kernel.org/linux-pci/20200610230906.GA1528594@bjorn-Precision-5520/
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Rajat Jain <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>

Author: Rajat Jain

drivers/iommu/intel/iommu.c

@@ -4730,20 +4730,20 @@ const struct attribute_group *intel_iommu_groups[] = {
 	NULL,
 };
 
-static inline bool has_untrusted_dev(void)
+static inline bool has_external_pci(void)
 {
 	struct pci_dev *pdev = NULL;
 
 	for_each_pci_dev(pdev)
-		if (pdev->untrusted)
+		if (pdev->external_facing)
 			return true;
 
 	return false;
 }
 
 static int __init platform_optin_force_iommu(void)
 {
-	if (!dmar_platform_optin() || no_platform_optin || !has_untrusted_dev())
+	if (!dmar_platform_optin() || no_platform_optin || !has_external_pci())
 		return 0;
 
 	if (no_iommu || dmar_disabled)

drivers/pci/of.c

@@ -42,7 +42,7 @@ void pci_set_bus_of_node(struct pci_bus *bus)
 	} else {
 		node = of_node_get(bus->self->dev.of_node);
 		if (node && of_property_read_bool(node, "external-facing"))
-			bus->self->untrusted = true;
+			bus->self->external_facing = true;
 	}
 
 	bus->dev.of_node = node;

drivers/pci/pci-acpi.c

@@ -1213,7 +1213,7 @@ static void pci_acpi_optimize_delay(struct pci_dev *pdev,
 	ACPI_FREE(obj);
 }
 
-static void pci_acpi_set_untrusted(struct pci_dev *dev)
+static void pci_acpi_set_external_facing(struct pci_dev *dev)
 {
 	u8 val;
 
@@ -1224,11 +1224,10 @@ static void pci_acpi_set_untrusted(struct pci_dev *dev)
 
 	/*
 	 * These root ports expose PCIe (including DMA) outside of the
-	 * system so make sure we treat them and everything behind as
-	 * untrusted.
+	 * system.  Everything downstream from them is external.
 	 */
 	if (val)
-		dev->untrusted = 1;
+		dev->external_facing = 1;
 }
 
 static void pci_acpi_setup(struct device *dev)
@@ -1240,7 +1239,7 @@ static void pci_acpi_setup(struct device *dev)
 		return;
 
 	pci_acpi_optimize_delay(pci_dev, adev->handle);
-	pci_acpi_set_untrusted(pci_dev);
+	pci_acpi_set_external_facing(pci_dev);
 	pci_acpi_add_edr_notifier(pci_dev);
 
 	pci_acpi_add_pm_notifier(adev, pci_dev);

drivers/pci/probe.c

@@ -1552,7 +1552,7 @@ static void set_pcie_untrusted(struct pci_dev *dev)
 	 * untrusted as well.
 	 */
 	parent = pci_upstream_bridge(dev);
-	if (parent && parent->untrusted)
+	if (parent && (parent->untrusted || parent->external_facing))
 		dev->untrusted = true;
 }
 

include/linux/pci.h

@@ -432,6 +432,12 @@ struct pci_dev {
 	 * mappings to make sure they cannot access arbitrary memory.
 	 */
 	unsigned int	untrusted:1;
+	/*
+	 * Info from the platform, e.g., ACPI or device tree, may mark a
+	 * device as "external-facing".  An external-facing device is
+	 * itself internal but devices downstream from it are external.
+	 */
+	unsigned int	external_facing:1;
 	unsigned int	broken_intx_masking:1;	/* INTx masking can't be used */
 	unsigned int	io_window_1k:1;		/* Intel bridge 1K I/O windows */
 	unsigned int	irq_managed:1;