intel_txt: Force IOMMU on for Intel TXT launch

The tboot module will DMA protect all of memory in order to ensure the that
kernel will be able to initialize without compromise (from DMA).  Consequently,
the kernel must enable Intel Virtualization Technology for Directed I/O
(VT-d or Intel IOMMU) in order to replace this broad protection with the
appropriate page-granular protection.  Otherwise DMA devices will be unable
to read or write from memory and the kernel will eventually panic.

Because runtime IOMMU support is configurable by command line options, this
patch will force it to be enabled regardless of the options specified, and will
log a message if it was required to force it on.

 dmar.c        |    7 +++++++
 intel-iommu.c |   17 +++++++++++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

Signed-off-by: Joseph Cihula <joseph.cihula@intel.com>
Signed-off-by: Shane Wang <shane.wang@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index ebc9b8dca881..2dc72a6d7412 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -38,6 +38,7 @@
 #include <linux/intel-iommu.h>
 #include <linux/sysdev.h>
 #include <asm/cacheflush.h>
+#include <asm/tboot.h>
 #include <asm/iommu.h>
 #include "pci.h"
 
@@ -3183,12 +3184,22 @@ static int __init init_iommu_sysfs(void)
 int __init intel_iommu_init(void)
 {
 	int ret = 0;
+	int force_on = 0;
 
-	if (dmar_table_init())
+	/* VT-d is required for a TXT/tboot launch, so enforce that */
+	force_on = tboot_force_iommu();
+
+	if (dmar_table_init()) {
+		if (force_on)
+			panic("tboot: Failed to initialize DMAR table\n");
 		return 	-ENODEV;
+	}
 
-	if (dmar_dev_scope_init())
+	if (dmar_dev_scope_init()) {
+		if (force_on)
+			panic("tboot: Failed to initialize DMAR device scope\n");
 		return 	-ENODEV;
+	}
 
 	/*
 	 * Check the need for DMA-remapping initialization now.
@@ -3204,6 +3215,8 @@ int __init intel_iommu_init(void)
 
 	ret = init_dmars();
 	if (ret) {
+		if (force_on)
+			panic("tboot: Failed to initialize DMARs\n");
 		printk(KERN_ERR "IOMMU: dmar init failed\n");
 		put_iova_domain(&reserved_iova_list);
 		iommu_exit_mempool();